Non-inoculated Control Plants Research Articles

First Report of Root Rot onkiwifruitsCaused byAthelia rolfsiiin Hefei, China.

Kiwifruits (Actinidia ssp.), known as "King of vitamin C", have been wildly cultivated. In August 2020, about 15% of A. deliciosa (cv. Xuxiang) and A. macrosperma (rootstock) plants displayed symptoms typical of root rot at a farm in Hefei (117°25'E, 31°86'N), Anhui Province of China (Fig.1 a-b). Symptoms first appeared at the root and stem junction which were covered by cottony white mycelium during warm and humid summer. Then, the infected tissues were rotted, and subsequently the whole plant withered. Tan to brown sclerotia were observed on the basal stem epidermis and soil surface surrounding the stem (Fig.1 c-d). Infected plant tissues and sclerotia were collected for isolating the fungal pathogen. The samples were surface sterilized in 70% alcohol for 30 s, followed by 2% sodium hypochlorite for 3 min, washed five times with sterile double-distilled water (ddH2O), dried, placed on potato dextrose agar, and incubated at 25 °C in the dark. In total, twelve fungal isolates were obtained. The mycelia of all the isolates were white with a fluffy appearance (Fig.1 e). Sclerotia formed after 7 days were initially white (Fig.1 f) and gradually turned to dark brown (Fig.1 g) measuring 0.67 to 2.03 mm in diameter (mean = 1.367 ± 0.16 mm;n= 30). Hyphae were hyaline, septate. Some cells possessed multiple nuclei (Fig.1 h) and clamp connections (Fig.1 i). No spores were observed. For species-level identification, ITS1/ITS4 and EF1-983F/EF1-2218R primers were used to amplify the internal transcribed spacer regions (ITS) and translation elongation factor-1 alpha regions (TEF-1α), respectively (White et al. 1990; Rehner & Buckley 2005). Based on ITS and TEF-1α sequence analyses, all 12 isolates were categorized into two groups, group one including isolates NC-1 and NC-6~10 and group two containing NC-2~5 and NC-11~12. The length of ITS sequences for NC-1 (MW311079) was 684bp and 99% to 100% similar to Athelia rolfsii (MN610007.1, MN258360.1). Similarly, ITS sequences for NC-2 (MW311080) were 99% to 100% similar to A. rolfsii (MH858139.1; MN872304.1). Also, TEF-1α sequences of NC-1 (MW322687) and NC-2 (MW322688) were 96% to 99% similar to sequences of A. rolfsii (MN702794.1, GU187681.1, MN702789.1). Based on morphology and phylogenetic analyses (Fig.1 j&k), the isolates NC-1 and NC-2 were identified as Athelia rolfsii (anamorph Sclerotium rolfsii) (Mordue. 1974; Punja. 1985). To fulfill Koch's postulates, ten sclerotia of NC-1 were incorporated into the soil near stems of healthy Xuxiang plants (Fig.2 a). Similar treatments were also used for plants of A. macrosperma or A. arguta (Fig.2 g&m). Each control group had the same number of plants (n=3) for inoculating with ddH2O. The plants were kept in an incubator with a relative humidity of 80% and temperature of 28°C with 16/8 hours light/dark photoperiod. After twenty days, the pathogen-inoculated plants developed similar symptoms of root rot observed in the field (Fig.2 b-d, h-j, n-o). Similarly, four days after inoculation with sclerotia, leaves developed water-soaked lesions (Fig.2 e, k&p). No significant difference in pathogenicity was observed between NC-1 and NC-2. Non-inoculated control plants remained disease-free (Fig.2 f, l&q). The pathogenicity experiments were repeated three times. The pathogen was re-isolated from infected tissues and sclerotia, and isolates were confirmed as A. rolfsii by the ITS sequences. A. rolfsii has been reported to cause root rot in kiwifruit in the USA (Raabe. 1988). To our knowledge, this is the first report A. rolfsiicausing root rot on kiwifruits in China.

First report of Diaporthe ueckerae causing stem canker on soybean (Glycine max L.) in Colombia.

In October 2018, soybean plants displaying elongated black to reddish-brown lesions on stems were observed in a field planted to the cv. BRS Serena in the locality of Puerto López (Meta, Colombia), with 20% incidence of diseased plants. Symptomatic stems were collected from five plants, and small pieces (∼5 mm2) were surface sterilized, plated on potato dextrose agar (PDA) and incubated for 2 weeks at 25°C in darkness. Three fungal isolates with similar morphology were obtained, i.e., by subculturing single hyphal tips, and their colonies on PDA were grayish-white, fluffy, with aerial mycelium, dark colored substrate mycelium, and produced circular black stroma. Pycnidia were globose, black, occurred as clusters, embedded in tissue, erumpent at maturity, with an elongated neck, and often had yellowish conidial cirrus extruding from the ostiole. Alpha conidia were observed for all isolates after 30 days growth on sterile soybean stem pieces (5 cm) on water agar, under 25ºC and 12 h light/12h darkness photoperiod. Alpha conidia (n = 50) measured 6.0 - 7.0 µm (6.4 ± 0.4 µm) × 2.0 - 3.0 µm (2.5± 0.4 µm), were aseptate, hyaline, smooth, ellipsoidal, often biguttulate, with subtruncate base. Beta conidia were not observed. Observed morphological characteristics of these isolates were similar to those reported in Diaporthe spp. by Udayanga et al. (2015). DNA from each fungal isolate was used to sequence the internal transcribed spacer region (ITS), and the translation elongation factor 1-α (TEF1) gene, using the primer pairs ITS5/ITS4 (White et al. 1990) and EF1-728F/EF1- 986R (Carbone & Kohn, 1999), respectively. Results from an NCBI-BLASTn, revealed that the ITS sequences of the three isolates (GenBank accessions MW566593 to MW566595) had 98% (581/584 bp) identity with D. miriciae strain BRIP 54736j (NR_147535.1), whereas the TEF1 sequences (GenBank accessions MW597410 to MW597412) had 97 to 100% (330-339/339 bp) identity with D. ueckerae strain FAU656 (KJ590747). The species Diaporthe miriciae R.G. Shivas, S.M. Thomps. & Y.P. Tan, and Diaporthe ueckerae Udayanga & Castl. are synonymous, with the latter taking the nomenclature priority (Gao et al. 2016). According to a multilocus phylogenetic analysis, by maximum likelihood, the three isolates clustered together in a clade with reference type strains of D. ueckerae (Udayanga et al. 2015). Soybean plants cv. BRS Serena (growth stages V3 to V4) were used to verify the pathogenicity of each isolate using a toothpick inoculation method (Mena et al. 2020). A single toothpick colonized by D. ueckerae was inserted directly into the stem of each plant (10 plants per isolate) approximately 1 cm below the first trifoliate node. Noncolonized sterile toothpicks, inserted in 10 soybean plants served as the non-inoculated control. Plants were arbitrarily distributed inside a glasshouse, and incubated at high relative humidity (>90% HR). After 15 days, inoculated plants showed elongated reddish-brown necrosis at the inoculated sites, that were similar to symptoms observed in the field. Non-inoculated control plants were asymptomatic. Fungal cultures recovered from symptomatic stems were morphologically identical to the original isolates. This is the first report of soybean stem canker caused by D. ueckerae in Colombia. Due to the economic importance of this disease elsewhere (Backman et al. 1985; Mena et al. 2020), further research on disease management strategies to mitigate potential crop losses is warranted.

First Report of Spot Blotch Caused by Bipolaris sorokiniana on Winter Rye in Kentucky.

The Kentucky distilling industry ranks as one of the state's largest industries and continues to expand. In 2017, the Kentucky distilling industry was responsible for approximately $235 million in state and local tax revenues (Coomes and Kornstein, 2019). Rye (Secale cereale L.) grains are a vital component for production of some distilled spirits. Although winter rye is produced on relatively few hectares in Kentucky currently, a recent initiative has supported expanding production to help meet the growing demand of local distilleries. University of Kentucky winter rye research field trials were visited in Caldwell and Logan Counties, KY in May 2018, and in Fayette County, KY in May 2019. Leaves were collected that had dark brown, oval to irregular-shaped lesions with definite margins and yellow halos. Symptoms were present on approximately 50% to 80% of the flag leaves, with severity ranging from 5% to 30% of the flag leaf area affected. Leaves were surface-disinfested by soaking in a 2% NaOCl solution for 1 min and rinsed twice in sterilized water and then placed in a humidity chamber (plastic bag with moist paper towels) at room temperature (approximately 24°C) to induce fungal sporulation. Seventeen single-spore isolates were obtained and stored at -80°C in 15% glycerol solution. Isolates were grown on potato dextrose agar under 12 h cycles of white light/darkness for 5 days. Colonies were gray to black. Conidia that formed were mostly straight or slightly curved, dark olivaceous brown, 3-7 septate, and 41.0-90.4 × 15.2-29.3 µm. Based on the symptoms observed on the collected leaves and these morphological characteristics similar to those described by Chang and Hwang (2000) and Manamgoda et al. (2014), the fungus was tentatively identified as Bipolaris sorokiniana (Sorokin) Shoemaker. The sequence of internal transcribed spacer regions (ITS) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were used to identify three isolates (18Bs004, 18Bs111 and 19Bs064) using primer ITS1/ITS4 (White et al. 1990) and GPD1/GPD2 (Berbee et al. 1999), respectively. The sequences were deposited in GenBank with accession numbers MT457817, MT457818 and MZ066635 for ITS sequences and MZ073644 to MZ073646 for GAPDH sequences. BLAST searches with ITS and GAPDH sequences matched 100% identity (344/344 bp and 515/515 bp for ITS and GAPDH sequences, respectively) to B. sorokiniana (GenBank accession No. MT254731 and MH844813, respectively). To prove pathogenicity, a conidial suspension (1 × 105 conidia/ml) was used to inoculate 15-day-old cultivar 'Serafino' winter rye plants in the greenhouse. Leaves of 8 plants were inoculated with 50 ml of the conidial suspension using a spray bottle. Plants were covered with a transparent plastic bag for 48 h, and symptoms were observed 10 days after inoculation. Leaf lesions, similar to those described above, were present on all inoculated plants, but no symptoms were observed on non-inoculated control plants. Bipolaris sorokiniana was reisolated from symptomatic leaves and the identity of the pathogen was confirmed based on the morphology previously described. To our knowledge, this is the first report of spot blotch caused by B. sorokiniana on winter rye in Kentucky, but B. sorokiniana has been reported on rye in the neighboring state of Virginia (Roane 2009). Kentucky produces approximately 150,000 and 4,000 ha of winter wheat (Triticum aestivum) and winter barley (Hordeum vulgare) annually, respectively, which are both known hosts of B. sorokiniana (Kumar et al. 2002). An isolate of B. sorokiniana from rye was reported by Ghazvini and Tekauz (2007) to be less virulent on barley differential lines. Further research is needed to better understand spot blotch distribution, susceptibility in winter rye cultivars, and potential yield and quality loss implications in winter rye production and end use. It is unknown how susceptible various winter rye cultivars grown in Kentucky are to spot blotch.

First report of root rot of Polygonatum odoratum caused by Fusarium acuminatum in China.

Polygonatum odoratum (Mill.) Druce is used in traditional Chinese medicine and also consumed as a vegetable. In July of 2020, a root rot was observed on P. odoratum in a commercial field located in Benxi city (41º23'32" N, 124º04'27" E), Liaoning province of China. About 35% diseased plants in the field exhibited poor vigor, were stunted, and had yellow or brown leaves. Affected plants wilted and died. Roots of the plants were poorly developed, had brown lesions, and later rotted. To determine the causal agent, symptomatic roots with typical lesions were cut into small pieces, surface sterilized in 2% sodium hypochlorite (NaOCl) for 3 min, rinsed three times in sterile water, and plated onto PDA medium. After 5 days of incubation at 26°C, whitish-pink to red colonies growing from the root samples were observed and transferred to carnation leaf agar (CLA). Ten single conidia isolates obtained from the colonies on CLA were incubated at 26°C for 10 days. Abundant macroconidia were formed in sporodochia on CLA. Macroconidia were falcate, slender, distinctively curved in the bottom half of the apical cell, had 3 to 5 septa, and 33.1 - 46.3 × 5.0 - 7.2 μm (n=50). Chlamydospores formed in chains or single, measuring 13.8 to 14.5 μm in diameter. Microconidia were not observed on CLA. Morphologically, the isolates were identified as Fusarium acuminatum (Leslie and Summerell, 2006). To confirm the species identity, the partial translation elongation factor 1 alpha (TEF1-α) gene and rDNA internal transcribed spacer (ITS) region of isolate YZ5-2 were amplified and sequenced (O'Donnell et al. 2015; White et al.1990). BLASTn analysis of both TEF sequence (MW423623) and ITS sequence (MW423626), revealed 100% (696/692 bp) and 99.64% (563/602 bp) sequence identity with F. acuminatum LC546967 and MF509746, respectively. Pathogenicity tests were carried out in the greenhouse. A conidial suspension (2 × 106 conidia per ml) of the isolate YZ5-2 was prepared from 7-day-old cultures grown in potato dextrose broth (PDB) o n a shaker (140 rpm) at 26±1°C. Five 12-liter pots were filled with sterilized field soil and each pot was drenched with 300ml of conidial suspension. Five control pots with sterilized field soil and 300 ml PDB were also included. Roots of 20 healthy P. odoratum plants were surface disinfected in 2% NaOCl for 3 min, and rinsed with sterilized water. Prior to planting, 2-3 pinholes (1.5× 1.0 mm) were made using a toothpick on the root surface of each plant, and they were then planted in each pot (2 plants per pot). All ten pots were maintained in a greenhouse at 22-26°C for 40 days. Plants grown in the pots inoculated with the conidial suspension were stunted, had yellowed leaves and were wilted. The roots of the affected plants were rotted. Disease symptoms were similar to those observed in field. Non-inoculated control plants had no symptoms. F. acuminatum was reisolated from inoculated plants and was identical to the original isolate. The experiment was repeated twice with similar results. To our knowledge, this is the first report of root rot of P. odoratum caused by F. acuminatum in China. The disease has since been observed on P. odoratum in fields in Liaoyang and Qingyuan city in Liaoning Province of China, and it has become an important threat to P. odoratum production in China.

Improved chromium tolerance of Medicago sativa by plant growth-promoting rhizobacteria (PGPR)

BackgroundSoil pollution by heavy metals increases the bioavailability of metals like hexavalent chromium (Cr (VI)), subsequently limiting plant growth and reducing the efficiency of phytoremediation. Plant growth-promoting rhizobacteria (PGPR) have substantial potential to enhance plant growth as well as plant tolerance to metal stress. The aim of this research was to investigate Cr (VI) phytoremediation enhancement by PGPR. ResultsThe results showed that the 27 rhizobacterial isolates studied were confirmed as Cr (VI)-resistant PGPR, by using classical biochemical tests (phosphate solubilization, nitrogen fixation, indole acetic acid, exopolysaccharides, hydrogen cyanide, siderophores, ammonia, cellulase, pectinase, and chitinase production) and showed variable levels of Cr (VI) resistance (300–600 mg/L). The best four selected Cr (VI)-resistant PGPR (NT15, NT19, NT20, and NT27) retained most of the PGP traits in the presence of 100–200 mg/L concentrations of Cr (VI). The inoculation of Medicago sativa with any of these four isolates improved the shoot and root dry weight. The NT27 isolate identified using 16S rDNA gene sequence analyses as a strain of Pseudomonas sp. was most effective in terms of plant growth promotion and stress level decrease. It increased shoot and root dry weights of M. sativa by 97.6 and 95.4%, respectively, in the presence of Cr (VI) when compared to non-inoculated control plants. It also greatly increased chlorophyll content and decreased the levels of stress markers, malondialdehyde, hydrogen peroxide, and proline. The results of the effect of Pseudomonas sp. on Cr content and bioaccumulation factor (BAF) of the shoots and roots of M. sativa plants showed the increase of plant biomass concomitantly with the increase of Cr root concentration in inoculated plants. This would lead to a higher potential of Cr (VI) phytostabilization. ConclusionsThis study demonstrates that the association M. sativa-Pseudomonas sp. may be an efficient biological system for the bioremediation of Cr (VI)-contaminated soils.

First report of fruit blight caused by Alternaria alternata on sesame in Northeast China.

Sesame (Sesamum indicum L.) is an important oilseed crop in China and it is also used in food and health products. In August of 2019, a blight sesame fruit was observed in a field of Liaoyang city, Liaoning province of China. Initial disease symptoms consisted of brown or dark brown spots on fruit. With time, lesions coalesced and the whole fruit turned dark brown or black. Most of the diseased fruit had thin and small, deformed, necrotic, hardened cracked epidermal lesions. Lesions were also produced on stem and petioles leading to leaf abscission. The disease results in premature fruit death, and in turn, considerable yield losses. To determine the causal agent, symptomatic fruit with developing lesions were collected, and surface sterilized in 2% NaClO for 3 min, rinsed three times in distilled water, and plated onto PDA medium. After incubation at 25°C for 5 days, a dark olivaceous fungus with abundant, branched, brown to black, and septate hyphae was consistently isolated. Twenty single spores were separated with an inoculation needle under stereomicroscope. The conidia were in chains, brown, obclavate, ovoid or ellipsoid, with 1-6 transverse septa and 0-4 longitudinal or oblique septa 12.5 to 45 × 6.5 to 14.5 μm in size. Conidiophores were septate, light brown to olive brown, measuring 22-60 μm × 2-4 μm. The morphological characteristics of the 20 isolates all matched the description of Alternaria alternata (Simmons, 2007). The internal transcribed spacer (ITS) region of rDNA of 15 isolates was amplified using primers ITS1/ITS4 (White et al. 1990) and EF1-728F/EF1-986R (Carbone et al. 1999) and sequenced. Identical sequences were obtained and the sequence of the isolate ZMHG12 was submitted to GenBank (Accession no. MW418181 and MW700316). BLAST analysis of the sequences of the isolates of ZMHG12 showed 100% to A. alternata (KP739875 and LC132712). In pathogenicity tests, a conidial suspension (2.5 × 105 conidia per ml) was prepared from 7 days-old cultures of isolate ZMHG12 grown on PDA at 25°C. Fruit of 10 two-month-old potted sesame plants (Variety "Liaozhi 8") were sprayed with the conidia suspension until runoff. Another 10 plants sprayed with distilled water to served as non-inoculated controls. All plants were maintained for 48 h in a humid chamber with a temperature of 25°C to 26°C, and then moved to a greenhouse. Ten days after inoculation, all fruit of inoculated plants exhibited symptoms similar to those observed in the field and non-inoculated control plants remained symptomless. The experiment was repeated twice with similar results. A. alternata has been reported as a pathogen caused leaf blight disease of sesame in Pakistan (Nayyar et al. 2017). To our knowledge, this is the first report of A.alternata causing fruit blight of sesame in China. To date, we have observed the disease on sesames in fields of Fuxin, Chaoyang and Tieling city in Liaoning Province, and Tongliao city in Inner Mongolia of China, and it has become an important disease in sesame production of China. References : Simmons E. G. 2007. Alternaria: An identification manual. CBS Fungal Biodiversity Center, Utrecht, Netherlands. White T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego. Carbone I., et al. 1999. Mycologia, 91: 553-556. Nayyar, B. G., et al. 2017. Plant Pathology Journal, 33 (6): 543-553.

Consortia of Plant-Growth-Promoting Rhizobacteria Isolated from Halophytes Improve Response of Eight Crops to Soil Salinization and Climate Change Conditions

Soil salinization is an environmental problem that adversely affects plant growth and crop productivity worldwide. As an alternative to the conventional approach of breeding salt-tolerant plant cultivars, we explored the use of plant-growth-promoting rhizobacteria (PGPR) from halophytic plants to enhance crop growth under saline conditions. Here, we report the effect of five PGPR consortia from halophytes on the growth of eight (alfalfa, flax, maize, millet, rice, strawberry, sunflower, and wheat) of the crops most commonly produced on salinized soils worldwide. To test the efficiency of halotolerant consortia, we designed a complex environmental matrix simulating future climate-change scenarios, including increased CO2 levels and temperature. Overall, biofertilizers enhanced growth of most crops with respect to non-inoculated control plants under different CO2 concentrations (400/700 ppm), temperatures (25/+4 °C), and salinity conditions (0 and 85 mM NaCl). Biofertilizers counteracted the detrimental effect of salinity on crop growth. Specifically, strawberry and rice showed the greatest positive additive response to inoculation in the presence of salt; above-ground biomasses were 35% and 3% greater, respectively, than their respective control grown without salt. Furthermore, depending on the interaction of environmental factors (salinity × CO2 × temperature) analyzed, the results varied—influencing the most effective biofertilizer determined for each crop now, or in the future. Our findings highlight the importance of conducting studies that consider stress interaction for realistic assessments of the potential of biofertilizers in a climate-changed world.

First Report of Alternaria japonica, a causal agent of black spot, on kale in South Carolina, United States.

In January 2020, charcoal gray, dull lesions were observed on leaves of organic kale (Brassica oleracea var. acephala) cv. Darkibor in two fields in Lexington County, South Carolina, the county with the most acres of leafy brassicas in the state. Leaf spots, also visible on the leaf underside, covered <5% of the leaf area. No spores were present. Portions of leaf spots from eight leaves, four per field, were cultured on one-quarter-strength potato dextrose agar (PDA/4). Eleven isolates of Alternaria spp. were recovered. Isolates ALT12 and UL3 were cultured in A. solani medium and DNA was extracted (Maiero et al. 1991). The internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (tef1), RNA polymerase second largest subunit (rpb2), and Alternaria major allergen (Alt a 1) genes were amplified with the primer pairs V9G/ITS4, EF1-728F/EF1-986R, RPB2-5F2/FRPB2-7cR, and Alt-for/Alt-rev, respectively, and sequenced (Woudenberg et al. 2014). Sequences for isolates ALT12 and UL3, collected from different leaves in the same field, were identical to each other and to isolate AC97 (ITS accession number: LC440597; tef1: LC482018; rpb2: LC476803; Alt a 1: LC481628) of A. japonica Yoshii (Nishikawa and Nakashima 2020). ITS, tef1, repb2, and Alta a 1 sequences for each isolate were deposited in GenBank under the accessions MW374952, MW389653, MW389655, and MW389657 for ALT12 and MW374951, MW389652, MW389654, and MW389656 for UL3, respectively. Conidia of A. japonica (20 of ALT12, 10 of UL3) produced by 7-day-old cultures on Spezieller Nährstoffarmer Agar measured 62.1 ± 11.4 x 18.8 ± 2.2 μm (standard deviation). Median numbers of transverse and longitudinal septae were 6 (4 to 8) and 2 (1 to 3), respectively. Conidia formed singly or in chains of two. Cells were constricted around the transverse septae (Nishikawa and Nakashima 2020; Woudenburg et al. 2014). Chlamydospores were present in cultures of ALT12. ALT12 was pathogenic on kale cv. Darkibor and Winterbor inoculated in a greenhouse following procedures of Al-Lami et al. (2019). Four replicate pots with two plants each were used; plants were 6, 9, and 5 weeks old in trials 1, 2, and 3, respectively. The oldest three leaves of each plant were spray inoculated with a suspension of 5 x 105 conidia/ml; noninoculated control plants were sprayed with water. All plants were kept for 48 h at 100% RH, then moved to a bench in a greenhouse held at 21/16°C day/night temperatures. The second and third oldest leaves were rated 13 days after inoculation. Small gray or black spots developed on inoculated leaves and petioles in all trials, and on one noninoculated leaf in trial one. Disease incidence on inoculated leaves (73.1%) was greater than on noninoculated leaves (0.05%) (P<0.0001). Cultivars did not differ in susceptibility (P=0.12). Portions of lesions on inoculated leaves and portions of noninoculated leaves were cultured onto PDA/4 amended with antibiotics (Keinath 2013). A. japonica was reisolated from 46 of 50 inoculated leaf blades; 22 of 28 inoculated petioles; and 1 of 8, 0 of 8, and 0 of 7 noninoculated leaves in the three trials, respectively. Growers in South Carolina consider black spot, or Alternaria leaf spot, the most important fungal disease on organic kale. The presence of a second causal agent in addition to A. brassicae may increase disease occurrence. A. japonica previously was reported on arugula in California (Tidwell et al. 2014). This is the first report of A. japonica in the eastern United States.

Root endophytic fungus Serendipita indica modulates barley leaf blade proteome by increasing the abundance of photosynthetic proteins in response to salinity.

The present study aimed at analysing the proteome pattern of the leaf blade of barley (Hordeum vulgare L.) in Serendipita indica-colonised plants to decipher the molecular mechanism of S. indica-mediated salt stress. This work is aligned with our previous research on barley leaf sheath to study proteomic pattern variability in leaf blade and sheath of barley plant in response to salinity and S. indica inoculation. The experiment was conducted using a completely randomised factorial design with four replications and two treatments: salinity (0 and 300mmoll-1 NaCl) and fungus (noninoculated and S. indica-inoculated). The leaf blades of the salt-treated S. indica-colonised and noninoculated plants were harvested after 2weeks of salt treatment for the physiological and proteomic analyses. After exposure to 300mmoll-1 NaCl, shoot dry matter production in noninoculated control plants decreased 84% which was about twofold higher than inoculated plants with S. indica. However, the accumulation of sodium in the shoot of S. indica-inoculated plants was significantly lower than the control plants. Analysis of the proteome profile revealed a high number of significantly up-regulated proteins involved in photosynthesis (26 out of 42 identified proteins). The results demonstrated how the enhanced plant growth and salt stress resistance induced by S. indica was positively associated with the up-regulation of several proteins involved in photosynthesis and carbohydrate metabolism. In fact, S. indica improved photosynthesis in order to reach the best possible performance of the host plant under salt stress. Current research provides new insight into the mechanism applied by S. indica in reducing the negative impacts of salt stress in barley at physiological and molecular levels.

Evaluating nematode resistance of grapevine rootstocks based on Xiphinema index reproduction rates in a fast screening assay

By feeding on grapevine roots, the ectoparasite Xiphinema index transmits grapevine fanleaf virus (GFLV), causing fanleaf degeneration in the plant. Therefore, rootstock breeding programs are considered a key to resistance to both threats. Previous screening depends on long-lasting inoculation experiments and mainly focuses on evaluating gall formation on the parasitized roots to identify potential resistance in grapevines. Since the roots of grapevine rootstocks resistant to X. index and even those of susceptible cultivars showed no reliable gall formation after parasitism, and further, root thickening was regularly found on non-inoculated control plants, nematode reproduction rates were used to validate rootstock phenotypes regarding susceptibility or resistance to X. index. For our approach, a glass vial assay was performed, and 35 days after inoculation the nematode population was determined by counting juveniles after the extraction. Reproduction rates were high on susceptible rootstock cultivars and decreased the more resistant a cultivar is considered. Besides focusing solely on root gall formation, the nematode reproduction rate should be included as a reliable indicator for resistance screening. The described assay setup enables the evaluation of resistance levels by fast screening to select promising rootstock candidates.

A fresh weight-based method for evaluating soybean resistance to red crown rot.

Soybean red crown rot (RCR) caused by Calonectria ilicicola is a serious soil-borne disease affecting soybean production and quality. The current visual necrosis-based method for the measurement of RCR severity is prone to subjectivity as well as time consuming and laborious as it requires digging out and washing the roots to remove adhering soil prior to the visual scoring. Using cultivar Enrei, we show that, upon C. ilicicola infection, relative fresh weights (RFW; fresh weights relative to non-inoculated control plants) showed a significant negative correlation with visual RCR severity in apical shoot (trifoliate and above, R2 = 0.96), shoot (unifoliate and above, R2 = 0.82) and roots (R2 = 0.89). Furthermore, apical shoot RFW efficiently correlated with varying levels of C. ilicicola resistance in two test sets containing 37 soybean cultivars and three wild soybean accessions, exhibiting a significant correlation with visual severity (R2 = 0.72 and 0.79, p < 0.01). Taken together, our results suggest that RFW can serve as an index of soybean RCR severity, providing a simple, rapid, consistent, and cost-effective method for evaluating C. ilicicola resistance in soybeans.

Bio-protective effect of a root-nodulating Rhizobium etli strain in common bean (Phaseolus vulgaris) against Meloidogyne incognita and Radopholus similis in an in vitro autotrophic tripartite culture system

Summary The bio-protective effect of a root-nodulating strain (CNPAF 512) of the nitrogen-fixing rhizobium, Rhizobium etli, against both a sedentary (Meloidogyne incognita) and a migratory (Radopholus similis) endoparasitic nematode in common bean (Phaseolus vulgaris) was examined using an in vitro autotrophic tripartite culture system. Two in vitro assays were carried out with each of the nematode species. Each assay consisted of two treatments: the plants were either inoculated with the rhizobial strain or remained non-inoculated (control plants). To examine the effect of either pre- or simultaneous inoculation of the rhizobial strain on the reproduction of M. incognita and R. similis, one assay was carried out in which the nematodes were inoculated 3 weeks after rhizobial inoculation while another assay was carried out in which the nematodes were inoculated simultaneously with the rihizobial strain. Both pre-inoculation and simultaneous inoculation with R. etli CNPAF 512 significantly suppressed the reproduction of both M. incognita and R. similis.

First report of seedling blight of maize caused by Fusarium asiaticum in Northeast China.

Maize [Zea mays L.] is animportantfood and feed crops in northeast of China. In 2019, maize seedling blight with an incidence of up to 25% was found at the field in Fushun city of Liaoning Province. Typical symptoms of seedlings were yellow, thin, wilt and die. The leaves gradually became yellow from the base of the plant to the top. Root system was poorly developed. The primary roots were usually discolored and rotted. And faintly pink or puce-coloured mould was found on seeds of the rotted seedings. Symptomatic roots of diseased seedling were collected and surface-disinfested with 70% ethanol for 1 min and then in 2% NaClO for 3 min, rinsed with sterilized water three times, cut into small pieces and placed on potato dextrose agar (PDA) medium for 5 days at 25 °C. Colonies on PDA were pink to dark red with fluffy aerial mycelium and red to aubergine pigmentation with the age. The causal agent was transferred to carnation leaf agar (CLA) medium and incubated at 25°C under a 12-h light-dark cycle. 12 Pure cultures were obtained from single conidia with an inoculation needle under stereomicroscope. The harvested macroconidia were hyaline, falcate with single foot cells, 3-5 septate and 28.2- 43.5 μm × 3.7 - 4.9 μm. Chlamydospores were globose to subglobose (5 to 13.5 μm). No microconidia were found. The perithecia were black, ostiolate subglobose. Asci were hyaline, clavate, measuring 58.1- 83.9 µm × 7.7- 11.9 µm and contained eight ascospores. Morphological characters of the pathogen agreed well with descriptions of Fusarium asiaticum (O'Donnell et al.2004; Leslie and Summerell 2006). To confirm the identity, partial translation elongation factor 1 alpha (TEF1-a) gene and rDNA internal transcribed spacer (ITS) region of isolate MSBL-4 were amplified and sequenced (O'Donnell et al. 2015; White et al.1990). BLASTn analysis of both TEF sequence (MT330257) and ITS sequence (MT322117), revealed 100% sequence identity with F. asiaticum KT380116 and KX527878, respectively. The isolate MSBL-4 was NIV chemotype as determined by Tri13F/DON, Tri13NIV/R (Chandler et al, 2003) assays. Pathogenicity studies were conducted on maize hybrid "Liaodan 565". Inoculum of F. asiaticum was prepared from the culture of MSBL-4 incubate in 2% mung beans juice on a shaker (150 rpm) at 25°C for 48 hours. The five liter pots (10 pots) were filled with sterilized field soil and five of them were mixed with conidial suspension (300mL in each pot) at 2 × 105 conidia per ml. Ten kernels per pot were surface disinfected in 2% sodium hypochlorite for 5 min, rinsed with sterilized water and planted. Five pots were inoculated and another uninoculated five pots served as controls. The pots were maintained in a greenhouse at 22-26°C for 40 days. Leaves of the plants in inoculated pots were yellowing and the roots became discolored or necrotic rot at 4 weeks after seedling emergence. All characteristics of the disease were similar to those observed in field. Non-inoculated control plants had no symptoms. Fusarium asiaticum was reisolated from inoculated plants and was identical to the original isolate. The experiment was repeated once with similar results. To our knowledge, this is the first report of seedling blight caused by F. asiaticum on maize in northeast China, and it has posed a threat to maize production of China.

First report of Fusarium lacertarum causing Fusarium Head Blight on sorghum in North Carolina.

In August 2018, sorghum plants (Sorghum bicolor (L.) Moench) from research field plots in Wake County, North Carolina were observed with head blight symptoms including panicles with red lesions, visible mycelium, and necrosis. At the time of collection, all plants in research plots displayed symptoms of Fusarium head blight and panicles averaged 33% area affected by symptoms and signs. From these affected plants, samples (n = 5) were collected for further identification. Symptomatic grains were surface sterilized for one minute in 0.825% sodium hypochlorite solution and rinsed for one minute in sterile, deionized water. After drying on sterile paper towels, grains were plated onto water agar. Resulting fungal hyphal tips were then transferred to antibiotic-amended potato dextrose agar (PDA) and incubated at 25oC. Cultures were incubated for 3 to 5 days. Isolates had abundant white hyphae accompanied with peach-colored pigment production. Macroconidia with 5-6 septations were 23.47 ± 7.74 µm long and 3.47 ± 0.66 µm wide with foot-shaped basal cells, tapering to hooked apical cells. Chlamydospores were present in chains but microconidia were not present. Morphological species recognition (MSR) criteria tentatively identified the isolate as Fusarium lacertarum Subrahm., in the Fusarium incarnatum-equiseti species complex (FIESC) using characteristics described by Leslie and Summerell 2006. Molecular characterization using translation elongation factor 1α (TEF-1 α, primers EF1 and EF2 from O'Donnell et al. 1998), β tubulin (TUB2, primers T1 and T22 from O'Donnell and Cigelnik 1997), and ribosomal protein subunit II (RPB2, primers 5F2 and 11AR from Cerón-Bustamante et al. 2018) was conducted to confirm morphological identification. DNA from the hyphae of pure cultures was extracted using the DNeasy PowerSoil DNA extraction kit according to manufacturer's guidelines. DNA amplification conditions followed the protocols for each primer set (O'Donnell et al. 1998; O'Donnell and Cigelnik 1997; Cerón-Bustamante et al. 2018). BLASTn analysis of TEF-1α (Isolate Accession MT149915, 573bp) alignment had 99.8% identity to F. lacertarum (NCBI accession: JF740828), TUB2 (Isolate Accession MT149914, 1,183bp) alignment had 99.3% identity to F. equiseti (NCBI accession: KJ396338), and RPB2 (Isolate Accession MT184173, 1,538bp) concatenated sequences had 95.3% identity to F. lacertarum (NCBI accession: MH582185). The TUB2 region most closely aligns to F. equiseti, which is likely due to an absence of TUB2 sequences labeled for F. lacertarum in the NCBI database. Pathogenicity was confirmed by spray-inoculating Southern Harvest 80G4 sorghum panicles (n = 9) at anthesis with four ml of conidial suspension (3.3×104 conidia/ml). Control plants (n = 9) were sprayed with sterile water. Plastic bags were placed around panicles for 24 hours to ensure moist conditions during the infection period. Plants were maintained in a greenhouse under a 12-hour light cycle and fertilized bi-weekly with 20-20-20 fertilizer. Symptoms were observed on inoculated panicles after 14 days, and the F. lacertarum isolate was recovered from inoculated plants and confirmed using methods described above. Fusarium spp. were not re-isolated from non-inoculated control plants. Members of FIESC are known to contribute to the Fusarium Head Blight disease complex and may be capable of producing mycotoxins associated with infections (Lincy et al. 2011; Marin et al. 2012; Moretti 2017); however, mycotoxin characterization in F. lacertarum has not been characterized. To our knowledge, this is the first report of F. lacertarum causing disease to sorghum in North Carolina and the United States. Fusarium lacertarum may cause impactful losses to sorghum producers due to direct yield and quality losses by the pathogen as well as the potential for mycotoxins to impact trade.

Diversity analysis of ACC deaminase producing bacteria associated with rhizosphere of coconut tree (Cocos nucifera L.) grown in Lakshadweep islands of India and their ability to promote plant growth under saline conditions

ACC deaminase producing Plant growth promoting rhizobacteria (PGPR) offers a great promise for ameliorating the negative impacts of salinity stress manifested on plants. In this context, 28 rhizospheric bacteria associated with ACC deaminase potential (198−1069 nmol α-ketobutyrate mg protein−1 h−1) were isolated from 5 different islands of Lakshadweep, union territory, India- Agatti, Kavaratti, Bangaram, Kadmat, and Thinnakara islands using DF-minimal medium. The diversity of cultivable ACC deaminase producing bacteria was analysed by PCR-RFLP (Restriction Fragment Length Polymorphism) method using three endonucleases AluI, MspI and HaeIII which led to the grouping of these isolates into six clusters at 80 % similarity index. Subsequently, isolates were functionally characterized for various PGP traits such that indole-3-acetic acid (IAA) production (∼10−80 μg mL−1); 16 isolates had phosphate solubilizing potential ranging from ∼19 to 88 P mg L−1 ; siderophore and ammonia production abilities were observed in 5 and 24 isolates, respectively while two strains tolerated up to 8% NaCl. Phylogenetic analysis of 16S rRNA gene sequences of representative strain from each cluster revealed that twenty-eight ACC deaminase producing PGPR belong to eight distinct genera: Pseudomonas, Bacillus, Azospirillum, Azotobacter, Escherichia, Paenibacillus, Burkholderia, and Klebsiella. Two isolates, CO1 (Pseudomonas putida) and CO8 (Bacillus paramycoides) were evaluated for plant growth promoting effects on French bean (Phaseolus vulgaris) under salinity (100 mM NaCl) stress. Both the selected isolates in consortium form significantly increased the root length, shoot length, root fresh and dry weight, shoot fresh and dry weight of French bean seedlings exposed to salinity stress, compared to non-inoculated control plants. The co-inoculation with selected strains CO1 and CO8 has significantly improved chlorophyll concentration, relative water content, membrane stability index, gas exchange parameters including net photosynthesis rate (PN), stomatal conductance (gs), transpiration rate (E) and water use efficiency of French bean plants by ∼100 %, ∼85 %, ∼40 %, ∼198 %, ∼80 %, ∼70 % and ∼75 %, respectively under saline conditions in comparison with non-inoculated plants. Moreover, the consortium treated French bean plants showed lower levels of stress-induced ethylene by 38 %, electrolyte leakage and Malondialdehyde (MDA) content by ∼15 % under salt stress compared to non-inoculated ones. This study unveiled the potential of halotolerant strains, Pseudomonas putida and Bacillus paramycoides as French bean biofertilizers in mitigating the adverse effects of salinity in plant growth in sustainable agriculture.

A Comparative Transcriptome Analysis, Conserved Regulatory Elements and Associated Transcription Factors Related to Accumulation of Fusariotoxins in Grain of Rye (Secale cereale L.) Hybrids.

Detoxification of fusariotoxin is a type V Fusarium head blight (FHB) resistance and is considered a component of type II resistance, which is related to the spread of infection within spikes. Understanding this type of resistance is vital for FHB resistance, but to date, nothing is known about candidate genes that confer this resistance in rye due to scarce genomic resources. In this study, we generated a transcriptomic resource. The molecular response was mined through a comprehensive transcriptomic analysis of two rye hybrids differing in the build-up of fusariotoxin contents in grain upon pathogen infection. Gene mining identified candidate genes and pathways contributing to the detoxification of fusariotoxins in rye. Moreover, we found cis regulatory elements in the promoters of identified genes and linked them to transcription factors. In the fusariotoxin analysis, we found that grain from the Nordic seed rye hybrid “Helltop” accumulated 4 times higher concentrations of deoxynivalenol (DON), 9 times higher nivalenol (NIV), and 28 times higher of zearalenone (ZEN) than that of the hybrid “DH372” after artificial inoculation under field conditions. In the transcriptome analysis, we identified 6675 and 5151 differentially expressed genes (DEGs) in DH372 and Helltop, respectively, compared to non-inoculated control plants. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEGs were associated with glycolysis and the mechanistic target of rapamycin (mTOR) signaling pathway in Helltop, whereas carbon fixation in photosynthesis organisms were represented in DH372. The gene ontology (GO) enrichment and gene set enrichment analysis (GSEA) of DEGs lead to identification of the metabolic and biosynthetic processes of peptides and amides in DH372, whereas photosynthesis, negative regulation of catalytic activity, and protein-chromophore linkage were the significant pathways in Helltop. In the process of gene mining, we found four genes that were known to be involved in FHB resistance in wheat and that were differentially expressed after infection only in DH372 but not in Helltop. Based on our results, we assume that DH372 employed a specific response to pathogen infection that led to detoxification of fusariotoxin and prevented their accumulation in grain. Our results indicate that DH372 might resist the accumulation of fusariotoxin through activation of the glycolysis and drug metabolism via cytochrome P450. The identified genes in DH372 might be regulated by the WRKY family transcription factors as associated cis regulatory elements found in the in silico analysis. The results of this study will help rye breeders to develop strategies against type V FHB.

Inoculation of drought-stressed wheat plant (Triticum aestivum L.) with single and combined inoculants of Arbuscular mycorrhizal fungi

The current study aimed to compare between inoculation of wheat plant with a single and combinations of several species of Arbuscular mycorrhizal fungi (AMF), and promoting its growth under water stress conditions. In a greenhouse experiment, the effect of three AMF species on wheat plant growth was studied using single-inoculations with Glomus monosporum, G. mosseae and Gigaspora gigantean, and mixtures of various AMF species. Moreover, inoculation of wheat plant with pair of AM fungi composed mainly of; SN (G. monosporum and Gigaspora gigantean) and AA (G, monosporum and Glomus mosseae) were investigated. Current findings indicate that inoculation with AMF belonging to different families was more effective in improving plant growth than AMF from the same genus and with mono-inoculation. Results showed that plant height inoculated with SN and AA increased by 27.30% and 24.95; respectively, while inoculation with Gigaspora gigantean (GG), G. mosseae (GS) and G. monosporum (GM) increased by 16.01%, 14.6% and 6.83%, respectively. Number of spikes/plant, spike length, number of spikelet/spike, 1000-grain weight and grain yield/plant of wheat plants inoculated with AMF increased significantly, compared with the non-inoculated control plants under water stress. In addition, current results demonstrated that inoculation with SN had relatively higher impact on promoting the growth of wheat plants followed by AA and GG, suggesting that inoculation with AMF consisting of different species may have a better effect than single inoculations. Furthermore, it is observed also that SN; which are combination from different genera have better effect on wheat plant growth, compared to that of AA from the same genus but of different species.

First Report of Root and Crown Rot of American Ginseng Caused by Pythium spinosum in China.

American ginseng (Panax quinquefolius) is a perennial herb whose dried roots are used for health care products, medicine, and food in China (Yuan et al. 2010). Shandong Province is the main area growing American ginseng and contributes more than 50% of the production in China. Wendeng city, located in the east of Shandong Peninsula, is the primary production area of American ginseng in Shandong Province since it has four distinct seasons, sufficient light, loose soil (pH 5.5～7.0), and with thus a similar geographical environment and climate conditions to the American ginseng production area of the United States and Canada. In March 2016, 2-year old American ginseng plants that were planted directly into the ground in the greenhouses in Wendeng city, contained up to 6-10% stunted plants. Water-soaked lesions were observed on the crowns and the tips of fine roots. The leaves of the infected plants became scalded, dark green starting at the top of the plants and gradually move downward. Moreover, the leaves and petioles gradually curled withered and drooped, and the whole plant collapsed. Tissue samples, 10 mm in size, were excised from the water-soaked roots and crowns of diseased plants, rinsed under running water for 24 hours, dipped in a 0.2% calcium hypochlorite solution for 10 minutes, placed on sterile filter paper to dry and then placed on V8 medium (200 mL V8 Campbell Soup, 15 g agar, 0.2 g CaCO3, and 1 L distilled water) and incubated in the dark at 28 °C for 5 days. Five Pythium-like isolates which were arachnoid-cottony on cornmeal agar were isolated and they all produced hyphal swellings, oogonia, antheridia and oospores. Oospores were globose, smooth and plerotic, with some being aplerotic. The dimensions of hyphal swellings, oogonia and oospores respectively ranged from 9.0 to 21.3 (average 14.1) µm, 12.9 to 22.5 (average 18.2) µm, and 12.5 to 20.5 (average 16.7) µm. Finger-like projections were uniformly distributed on the walls of the oogonia and the antheridia were curved rods. The five Pythium-like isolates were identified as P. spinosum based on morphological characteristics (van der Plaats-Niterink, 1981). Genomic DNA was extracted from the isolates of the Pythium sp. using a DNA extraction kit (OMEGA, U.S.A.). The cytochrome c oxidase subunit I (COI) gene and internal transcribed spacer (ITS) region rDNA were amplified and sequenced using primers FM55/FM52R (Long et al. 2012) and ITS1/ITS4, respectively (White et al.1990). The five COI sequences were aligned and were identical for all five isolates, as well as the five ITS sequences. BLASTn analysis of the 538-bp COI sequence (accession no. MT822775) resulted in a 99% identity with that of the P. spinosum strain CBS122663 (accession no. HQ708832.1), and the 916-bp ITS sequence (accession no. MN847595) showed 100% identity with Genbank accession number AB217665 belonging to P. spinosum. Koch's postulates were confirmed. Corn kernels that had been soaked in water for 24 hours in water, autoclaved for 2 hours at 121˚C and allowed to cool were inoculated with agar plugs of P. spinosum grown on corn meal agar medium (CMA) for 10 days. The inoculated corn kernels were incubated at 28 ℃ for 13～15 days, until the corn kernels were covered with white hypha of P. spinosum. Ten healthy approximately 2-years old American ginseng plants growing in Wengdeng greenhouses were transplanted into a sterilized potting soil that was artificially infested with the corn inoculum (3 g inoculum per 100 g loam mixture). Inoculated and non-inoculated control plants were maintained in a greenhouse with a roof covered with sunshade net at 28 °C and 100% relative humidity. The experiment was repeated once. Four days after inoculation (DAI), the crown of inoculated plants developed water-soaked symptoms similar to those observed in field. No symptoms developed on the control plants. By 7 DAI, the inoculated fine roots and crowns showed water-soaked lesions identical to those observed in field, whereas control plants remained symptomless. The re-isolated isolate of P. spinosum was identical morphologically and by DNA sequence analysis to the original isolate. To our knowledge, this is the first report of root rot on American ginseng caused by P. spinosum in China and worldwide. Identification of the pathogen will assist in devising strategies to protect this important medicine plant from the pathogen, and to prevent yield losses.

First Report of Powdery Mildew on Physocarpus opulifolius Caused by Podosphaera physocarpi in Tennessee.

Eastern ninebark (Physocarpus opulifolius (L.) Maxim.) is a popular native perennial plant used in landscapes because of its colorful foliage and spring flower display. Powdery mildew symptoms were observed on container-grown eastern ninebark 'Mindia' Coppertina® plants in a commercial nursery in DeKalb County, TN in May 2016. The disease severity was nearly 40% and the disease incidence was nearly 60% of 1,000 plants. Affected plants displayed witches'-brooms with cream to white colored, thickened shoots with stunted, curly leaves as well as patches of white powdery fungal growth on the surface of young and old leaves, inflorescences, infructescences and stems (Figures 1 and 2). Microscopic observation revealed masses of conidia and mycelium covering symptomatic tissues. Conidiophore foot cells measured 19.2 to 66.7 μm (mean = 38.3 μm) × 5.4 to 15.1 μm (mean = 9.7 μm) (n = 30). Conidia were ovoid and measured 11.4 to 28.5 μm (mean = 20.9 μm) (n = 30) in length and 8.2 to 14.8 μm (mean = 11.7 μm) (n = 30) in width. Conidiophores produced two to six conidia in chains. Fibrosin bodies were observed after treating conidia with a 3% KOH solution. Chasmothecia were numerous, 60.0 to 85.0 μm (mean = 74.2 μm) (n = 30) in size and contained one ascus [60.0 to 82.0 × 52.0 to 69.0 μm; mean = 73.4 × 59.4 μm (n = 30)] with 8 ascospores [25.2 to 28.0 × 14.8 to 16.0 μm; mean = 26.5 × 15.5 μm (n = 30)]. To confirm pathogen identity, total DNA was extracted directly from plant tissue with the UltraClean Microbial DNA Isolation Kit (MO BIO Laboratories, Inc., Carlsbad, CA) following the manufacturer's instructions. The ITS region of the ribosomal DNA was amplified by PCR using primer pair ITS1 and ITS4 (White et al. 1990). The sequence (GenBank acc. no. MT605142) of the amplicon had 100% coverage and 100% identity to that of Podosphaera physocarpi (U. Braun) U. Braun (= Podosphaera aphanis var. physocarpi (U. Braun) U. Braun & S. Takam.) (GenBank acc. no. MT106654). Pathogenicity was confirmed three times by inoculating leaf surfaces of five eastern ninebark 'Mindia' Coppertina® plants by tapping fungal spores from infected eastern ninebark leaves onto the surfaces of healthy leaves. Inoculated plants were maintained in a greenhouse (21 to 23°C) using drip irrigation system until symptoms developed. Five non-inoculated control plants were maintained in the same greenhouse. After two weeks, typical symptoms of powdery mildew developed on the inoculated plants and microscopic examination revealed the same pathogen morphology as the original isolate. All non-inoculated control plants remained disease-free. To our knowledge, this is the first report of powdery mildew caused by P. physocarpi on P. opulifolius in Tennessee. Powdery mildew is known to be a disease problem on eastern ninebark grown in its native range in landscape plantings. Lubell et al. (2011) reported varying levels of powdery mildew resistance among eastern ninebark cultivars. Timely application of fungicides with no phytotoxic effect will be necessary to manage this disease on susceptible eastern ninebark cultivars in affected nurseries.

Effect of symbiosis with arbuscular mycorrhizal fungi on salt stress tolerance in GF677 (peach×almond) rootstock

Genus Prunus is of great importance for cultivation, mainly because its main species provide fruits and seeds, valuable ornamental qualities and timber. However, stone fruit trees and almonds, major cultivars of genus Prunus, are sensitive to salt stress. Such sensitivity causes losses in stone fruit and almond production (ca. 50% of regular yield at high salinity grounds). Having in mind that symbiosis with arbuscular mycorrhiza fungi (AMF) may improve plant tolerance to salt stress and that symbiosis effect should be tested in case-by-case approach, we tested salt stress response of AMF inoculated GF677 rootstock (Prunus dulcis × Prunus persica hybrid) in this study. Adding to that, we tested GF677 symbiosis with two AMF species R. intraradices and F. mosseae. Results showed that under salinity stress AMF inoculated GF677 plants displayed improved physiological parameters (chlorophyll, soluble sugars and proline content) and increased antioxidant enzymes activity in comparison to non-inoculated control plants. Comparison of two AMF species beneficial effects on tested parameters revealed that for total chlorophyll content inoculation with F. mosseae has prevailed, while for total soluble sugars and proline content R. intraradices has prevailed. Finally, GF677 in symbiosis with F. mosseae was selected for molecular studies of salinity response. Since many of plants’ genes involved in simultaneous response to salt stress and AMF colonization remained unidentified so far, we performed bioinformatics analysis of freely online available data to find differentially expressed genes common to these two responses. Upon GO classification and networking analysis of genes identified as common to both responses, we selected two most prominent ones (UDPGT73C6 and CYP707A3) and tested their expression profile in leaves and roots of F. mosseae inoculated GF677 rootstocks under salt stress. Even though specific roles of UDPGT73C6 and CYP707A3 are uncharacterized in Prunus tree species, results suggested their involvement in response to salt stress and AMF inoculation of GF677 plants, which is in concordance with a scarce knowledge on their roles in other plant species. Based on this study finding we may conclude that symbiosis of GF677 rootstocks with AMF increases plants tolerance to salinity stress, which should be considered in other Prunus tree species as well.