Seedling Blight Research Articles

First Report of Trichoderma parareesei Causing Seedling Blight on Eggplant in China.

Eggplant (Solanum melongena L.) is an economically important vegetable crop in subtropics and tropics. In March 2021, a serious disease on eggplant seedlings about 20 days after transplanting was found in Rong'an County (25°28' N; 109°53' E), Guangxi, China, with an incidence of diseased plants of 35%. The initial symptom was water-soaked spots on the leaves, followed by irregular black-brown spots that gradually expanded outward, causing leaf necrosis and defoliation. Even parts of eggplant seedlings died after lesions extended to the stem and the surface of the diseased tissues was covered with white to blue mold. Four diseased eggplants were randomly collected from different fields. Small pieces of the symptomatic tissues were surface sterilized and incubated on potato dextrose agar (PDA) at 28°C for 4 days. A total of 12 strains with similar morphological characteristics were isolated, and four representative strains (FW-01 to FW-04) were characterized. The colony was initially white, changing to yellow-green after 7 days. Phialides were lageniform or ampulliform, 2.9 to 9.75 μm × 1.36 to 4.3 μm (n=50). Conidia were green, ellipsoidal to oblong, smooth, 2.1 to 3.3 μm × 1.6 to 2.33 μm (n=50). Chlamydospores were not observed on PDA. These morphological characteristics are consistent with the description of the genus Trichoderma (Samuels et al. 2012). To confirm the identification, from mycelia of the four isolates and DNA was extracted using the Fungal Genomic DNA Extraction Kit (Bioer Technology [Hangzhou] Co., Ltd.). Three gene regions (ITS, tef1 and rpb2) were amplified (Sadfi-Zouaoui et al. 2009; Atanasova et al. 2010) and sequenced (GenBank Accessions: OL677389 to OL677392 for ITS, OL743178 to OL743181 for tef1 and OL743182 to OL743185 for rpb2). ITS sequences shared 100% identity with sequences of T. reesei (MW514156) and T. parareesei (HM466668), and tef1 and rpb2 sequences showed more than 99% similarity with sequences of T. parareesei (KM263190 and HM182962). The phylogenetic tree of the concatenated sequences showed that four isolates were clustered with T. parareesei. Therefore, the isolates were identified as T. parareesei. To satisfy Koch's postulates, the pathogenicity of four strains was tested on healthy eggplant seedlings planted in a sterile potting mix. Eggplants at four leaves stage were inoculated using conidial suspensions (with a concentration of 1 × 106 conidia/ml), with two leaves of each eggplant inoculated with each isolate and the test repeated three times. The control eggplants leaves were inoculated with sterile water. All plants were placed in a greenhouse at 22 ± 3°C and 85% relative humidity, with a photoperiod of 12 h. The water-soaked spots appeared 48 h after inoculation. All inoculated leaves showed symptoms 3 days post-inoculation. The diseased leaves became brittle and abcissed, while the control leaves remained symptomless. Only T. parareesei was successfully re-isolated from the lesions. Atanasova et al. (2010) found that T. parareesei inhibited the growth of Lepidium sativum seedlings under in vitro conditions (Atanasova et al. 2010). To our knowledge, this is the first report of T. parareesei causing eggplant seedling blight in China. The pathogen can cause substantial economic losses in eggplant production. Therefore, the identification of the pathogen is of great significance for the diagnosis and control of the disease. The results of this study deepen the understanding of the pathogenicity of Trichoderma.

Phytic acid is a new substitutable plant-derived antifungal agent for the seedling blight of Pinus sylvestris var. mongolica caused by Fusarium oxysporum

Phytic acid (PA) is a new substitutable plant-derived antifungal agent; however, few reports have been published regarding its antifungal effects on pathogenic fungi. The present study explored the in vitro antifungal activity of PA against four phytopathogenic fungi and found that PA was the most effective at inhibiting the growth of Fusarium oxysporum. This study aimed to investigate the in vivo and in vitro antifungal activities of PA against the seedling blight of Pinus sylvestris var. mongolica caused by F. oxysporum and to determine its possible mechanism of action. The results showed that PA inhibited spore germination and mycelial growth of F. oxysporum in a concentration-dependent manner and exhibited strong inhibition when its concentration exceeded 1000 mg/L. It mainly destroyed the integrity of the cell membrane, increasing its cell membrane permeability, causing the cell contents to spill out, and impairing fungal growth. In addition, the leakage of intercellular electrolytes and soluble proteins indicated that PA used at its EC20 and EC50 increased the membrane permeability of F. oxysporum. The increase in malondialdehyde and hydrogen peroxide content confirmed that PA treatment at its EC20 and EC50 damaged the cell membrane of the pathogen. Scanning electron microscopy revealed that PA affected the morphology of mycelia, causing them to shrivel, distort, and break. Furthermore, PA significantly reduced the activities of the antioxidant-related enzymes superoxide dismutase and catalase, as well as that of the pathogenicity-related enzymes polygalacturonase, pectin lyase, and endoglucanase (EG) in F. oxysporum (P < 0.05). In particular, EG enzyme activity was maximally inhibited in F. oxysporum treated with PA at its EC50. Moreover, PA significantly inhibited the incidence of disease, and growth indices in Pinus sylvestris var. mongolica seedling blight was determined. In summary, PA has a substantial inhibitory effect on F. oxysporum. Therefore, PA could serve as a new substitutable plant-derived antifungal agent for the seedling blight of P. sylvestris var. mongolica caused by F. oxysporum.

Silver nanoparticles affect wheat (Triticum aestivum L.) germination, seedling blight and yield.

The aim of the study was to evaluate the effect of two types of negatively charged quasi-spherical silver nanoparticles (AgNPs) at concentrations of 10, 20 and 30mgL-1 and silver ions at a concentration of 30mgL-1 on the growth, selected physiological aspects and yielding of wheat (Triticum aestivum L.) cv. Tybalt, and on plant resistance to seedling blight. Seed germination, α-amylase activity in seeds, morphology and infestation of seedlings by pathogens were assessed in a hydroponic treatment. Growth rate, PSII efficiency, heading and yield of the same plants were then analysed in pot culture. Results showed that the AgNPs and silver ions had a negative effect on roots, but reduced seedling blight and improved leaf area compared to the control. In addition, the AgNPs reduced with sodium borohydride in the presence of trisodium citrate at concentrations of 10 and 20mgL-1 stimulated germination, α-amylase activity and shoot length, which was not observed in the case of silver ions and the AgNPs reduced with sodium hypophosphite in the presence of sodium hexametaphosphate. In a pot experiment, the AgNPs improved plant growth, PSII efficiency, accelerated heading and increased yield-related parameters compared with the control. Results revealed the interaction strength in the following order: TCSB-AgNPs>SHSH-AgNPs>silver ions. TCSB-AgNPs in the lowest concentration had the most favourable effect, indicating their great potential for use in improving wheat cultivation.

Pest categorisation of Stenocarpella maydis.

The EFSA Plant Health Panelperformed a pest categorisation of Stenocarpella maydis, a clearly defined fungus causing seedling blight, stalk and ear rot in maize, its only confirmed main host. The pathogen occurs in many countries of North, Central and South America, Africa, Asia and Oceania where maize is grown commercially. It is present in the EU with restricted distribution (Czech Republic and Spain). Stenocarpella maydis is not included in Commission Implementing Regulation (EU) 2019/2072. Plants for planting (maize seeds) is the main pathway of entry and spread in the EU. Host availability and climate are favourable for the establishment of the pathogen in maize-growing areas of the EU. The pathogen has a direct impact on yield and quality of maize production. Phytosanitary measures are available to mitigate further introduction and spread of the pathogen into the EU. The Panelconcludes that S. maydis satisfies all the criteria to be regarded as a potential Union quarantine pest.

Identification and distribution of fungal pathogens associated with seedling blight of rice in the southern United States

AbstractSurveys were conducted in the five southern rice‐producing states of Arkansas, Louisiana, Mississippi, Missouri and Texas in the United States during the 2018 and 2019 cropping seasons to determine the distribution and pathogenicity of fungal pathogens associated with seedling blight in rice. A total of 349 pathogenic fungal isolates were collected and identified as belonging to four genera: Rhizoctonia solani, Fusarium spp., Sclerotium rolfsii and Marasmius graminum based on morphological characteristics, molecular analysis and Koch's postulates. R. solani (252 out of 349 pathogenic isolates) was the most prevalent fungus isolated from diseased samples. Of the 252 pathogenic R. solani isolates, 245 were further classified as anastomosis group 11 (AG‐11) and 7 as AG‐4. Isolates of R. solani AG‐4 and M. graminum were the most aggressive, with the highest stand loss (63% to 100%) and median disease rating (DR; 5.0), followed by isolates of R. solani AG‐11 (stand loss = 4% to 100% and DR = 0.6 to 5.0), Fusarium spp. (stand loss = 26% to 48% and DR = 2.0 to 5.0) and S. rolfsii (stand loss = 33% to 48% and DR = 2.0 to 3.0) in causing seedling blight in rice. R. solani (62% to 83% of total pathogenic isolates) and Fusarium spp. (10% to 24% of total pathogenic isolates) were predominant in all the five states surveyed. S. rolfsii and M. graminum were present only in Louisiana and Texas. The results of this first systematic survey of rice seedling diseases in the southern United States will help develop effective fungicide seed treatment strategies for control of stand loss caused by seedling blight, one of the major factors limiting rice production.

Silicon Reduces the Severity of Fusarium Infection on Young Wheat Parts In Vitro

Background: Although silicon (Si) has been referred as an essential element for controlling destructive diseases of wheat, available data are limited about enhancing adult wheat resistance against Fusarium causing head blight. Also, no reports seem to exist on the use of Si to reduce Fusarium seedling blight (FSB) on young wheat parts in vitro. Under in vitro conditions, Fusarium infection happened at the seedling stage cannot be called Fusarium head blight, because it is not a “head” disease, instead it could be called “FSB”. Objective and Methods: This research aimed to elucidate the bio-efficacy of soluble Si at 1.7 mM to increase wheat resistance to FSB measured by latent period (LP) of detached leaf inoculation, area under disease progress curve (AUDPC) of Petri-dish inoculation and coleoptile length reduction (CLR) of a coleoptile infection detected in vitro. Si treatments were applied to six bread and durum wheat cultivars of contrasting susceptibility to disease infected with four Fusarium species displaying a diverse pathogenicity. Results: Differences were observed on wheat detached leaves and seedlings in the resistance of Si-Fusarium-inoculated treatments relative to fungal-inoculated-controls, showing the beneficial role played by this element in decreasing head blight disease symptoms on young plant parts under in vitro conditions. In all wheat cultivars infected with different Fusarium species, the application of Si did increase host resistance measured in vitro; 1.7 mM Si resulted in significantly higher LP and lesser AUDPC and CLR compared with controls. More importantly, Si at 1.7 mM increased host resistance of susceptible to moderately susceptible cultivars measured by LP, AUDPC and CLR to the same level of resistance exhibited by a wheat cultivar high in quantitative resistance without Si. Conclusion: This is the first report presenting the utility of three distinct in vitro bio-assays to investigate the effect of Si in the wheat- FSB pathosystem. The application of silicon to complement host resistance to head blight appears to be an effective strategy for disease management in wheat.

Characterisation of Pythium aristosporum Oomycete-A Novel Pathogen Causing Rice Seedling Blight in China.

Rice seedling blight is a globally occurring seedling disease caused by multiple pathogens. It is currently the most common disease affecting rice production in northeast China; hence, determining the causal agents, including its biological characteristics, host range, and fungicide efficacy is vital for its effective management. The present study obtained 45 pathogenic isolates from diseased rice seedlings in Suihua, Heilongjiang Province, China. Of these, five pathogens were identified based on their morphology and molecular identification, while 10 oomycete isolates were identified as Pythium aristosporum—the first to be reported in rice seedling blight. Its optimum growth conditions include a temperature of 25 °C, pH 6, and photoperiod of 24 h. Except for soybean (Glycine max (L.) Merr.), black soybean (Glycine max var.), and cucumber (Cucumis sativus L.), P. aristosporum can potentially infect and cause seedling blight on other hosts, such as wheat (Triticum aestivum L.), maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), alfalfa (Medicago sativa L.), oats (Avena sativa L.), and white clover (Trifolium repens L.). Its isolates were found to be highly sensitive to metalaxyl + propamocarb (EC50 = 0.0138 μg/mL) with 84.1% efficacy at 313 μg/mL. These results can serve as the basis for controlling P. aristosporum.

First Report of Maize Seedling Blight Caused by Fusarium pseudograminearum in China.

Maize (Zea mays L.) is one of the most important food and feed crops in China, with a cultivation area of more than 40 million hectares (http://www.fao.org/faostat/en/#data/QC). In July 2021, a serious maize seeding blight occurred in Changjia Town, Gaoqing Country, Zibo City, Shandong Province, China, and the disease incidence was up to 50% in some fields. The root system of infected plants displayed poor development. The primary roots were brown and rotted. The leaves at the base of the plants were drying up, then the whole plant withered. To determine the cause agent of the disease, symptomatic roots of diseased seedlings were collected and surface-sterilized (70% ethanol for 30 s and 3% sodium hypochlorite (NaClO) for 90 s), subsequently rinsed three times with sterile distilled water, placed on potato dextrose agar (PDA), then incubated at 25°C for 2 days. Two cultures with similar morphological characteristics were purified through single-spore isolation technique and identified by morphology and molecular methods as Fusarium pseudograminearum O'Donnell & T. Aoki 1999. Plentiful macroconidia formed in 5-day-old carboxymethyl cellulose (CMC) cultures; microconidia were absent. Macroconidia were thick-walled and curved, usually 3- to 5- septa, 31.6 ± 0.6 μm × 4.8 ± 0.1 μm (n = 50). Colony pigmentation on PDA was pink to red, with white to pink aerial mycelia on PDA cultures was abundant and filled the petri dishes. For molecular identification, the rDNA internal transcribed spacer (ITS) gene and translation elongation factor 1 alpha (TEF-1α) gene of two isolates (SAIA41B and SAIA41C) were amplified with ITS1/ITS4 (White et al., 1990) and EF-1/EF-2 (O'Donnell et al., 1998), respectively. Blastn analysis of both the ITS sequence (accession numbers OM108101 and OM108102) and TEF-1α sequence (accession numbers OM142205 and OM142206) revealed 100% (481/481 bp for ITS and 637/637 bp for TEF-1α) sequence identity with the sequences of F. pseudograminearum reported in GenBank (MW699613 for ITS and JN862232 for TEF-1α). The molecular identification was further confirmed by the F. pseudograminearum species-specific PCR primers Fp1-1/Fp1-2 (Aoki and O'Donnell 1999). The expected 523-bp fragments were obtained for isolates SAIA41B and SAIA41C. In the pathogenicity test, healthy germinating maize roots (Zhengdan958) were inoculated with PDA culture blocks of isolate SAIA41C. Plants inoculated only with PDA culture blocks served as controls. Maize plants were put in petri dishes and placed in an incubator with a 12-h photoperiod at 25 oC and 100% relative humidity. Seven days later, roots of the plants inoculated with isolate SAIA41C were poorly developed and became brown necrotic and rotted, which were identical to the symptoms observed in the fields, whereas the roots of control plants were developed normally. The pathogen was re-isolated from the necrotic tissue of the inoculated roots but not from the control plants, and its identity was confirmed by PCR with the primes Fp1-1/Fp1-2 described above, fulfilling Koch's Postulates. To our knowledge, this is the first report of maize seedling blight caused by F. pseudograminearum in China. Our finding indicates the potential spread of F. pseudograminearum on maize, and more attention should be paid to prevention and control of maize seedling blight caused by F. pseudograminearum. The author(s) declare no conflict of interest. Acknowledgements: This research was supported by National Natural Science Foundation of China (No. 32102181), Shandong Provincial Natural Science Foundation (No. ZR2021QC059), Wheat Industry Technology System of Shandong Province (No. SDAIT-01-10), and Agricultural Science and Technology Innovation Project of SAAS (No. CXGC2021A38 and CXGC2021A33).

Evaluation of Pseudomonas and Bacillus Strains as Potential Biocontrol Agents against Fusarium Wilt of Chickpea

Evaluation of Pseudomonas and Bacillus Strains as Potential Biocontrol Agents against Fusarium Wilt of Chickpea

In Search of Resistance Against Fusarium Ear Rot: Ferulic Acid Contents in Maize Pericarp Are Associated With Antifungal Activity and Inhibition of Fumonisin Production.

Fusarium verticillioides is a fungal pathogen of maize that causes seedling blight, stem rot, and Fusarium ear rot. Fungal infestation of maize kernels and ears affects grain quality from the ensuing mycotoxin buildup. Among the mycotoxins produced by F. verticillioides, fumonisins accumulate to high levels in Fusarium-infected maize kernels, fumonisin B1 (FB1) being the most abundant in naturally infected maize. Achieving resistance to Fusarium ear rot has been challenging, as various environmental factors facilitate fungal infection. Among the maize grain components that contribute to resistance to F. verticillioides infection, the pericarp is the first barrier faced by the fungus and thus plays a key role. Phenolic acids are major constituents of maize pericarp, of which ferulic acid (FA) is the predominant molecular species. In this work, we explored the relationship between FA levels, fungal infection, and FB1 production in 51 maize genotypes and whether the antioxidant activity of FA might play a role. We confirmed that FA is a major component of the seed pericarp, whose levels as bound FA varied between 4.5 and 26.3 mg/g across maize genotypes. We selected two pools of five maize varieties, with contrasting FA contents: low FA (LFA; 6.14 ± 0.40 mg/g) and high FA (HFA; 15.49 ± 1.31 mg/g). In vitro, HFA extracts inhibited fungal growth with effects comparable to FA concentrations in the 0.25–0.50 mM range. We also established a kernel assay to study F. verticillioides colonization and FB1 production in the LFA and HFA genotypes. Fungal colonization was significantly lower in HFA genotypes relative to LFA genotypes, based on ergosterol levels. Moreover, FB1 production was also inhibited in the HFA genotypes. Importantly, the antioxidant activity of maize pericarp extracts was associated with FA contents, with HFA extracts exhibiting a greater antioxidant activity than LFA extracts. Overall, our results highlight the role of FA and its antioxidant activity on resistance to Fusarium ear rot and provide the basis of a phenotypic trait that can be deployed for breeding selection.

First Report of Microdochium nivale and M. majus Causing Brown Foot Rot of Wheat in China.

Microdochium nivale and M. majus not only cause seedling blight of wheat (Triticum aestivum L.) in cold dry soils, but also cause foot rot and ear blight of wheat under favorable conditions (Haigh et al. 2009). In May 2017, 2019, and 2020, a serious foot rot of wheat with an incidence of 92%, 45%, and 51% was observed in the field in Xiangcheng County (33.43° N, 114.84° E), Tanghe County (32.43° N, 112.66° E), and Linzhou City (36.13° N, 113.75° E), Henan Province, respectively. The serious brown lesions of the lower leaf sheaths is visible. The pathogens were isolated from brown leaf sheaths on potato dextrose agar (PDA) after being surface-sterilized (70% EtOH for 30 s followed by 3% NaClO for 1.5 min) and rinsed three times in sterile distilled water. After 5 d, mycelia were transferred to fresh PDA, and nine representative isolates (G17ZK2-1, G17ZK2-2, G17ZK2-3, g19TH10-4, g19TH10-5, g19TH10-6, G20LZ1-6, G20LZ1-7, and G20LZ1-8) were further purified by hyphal tipping. Species were identified based on morphological characteristics, and sequence analysis of partial sequences of the translation elongation factor-1α (TEF), the RNA polymerase II subunit (RPB2) gene and β-tubulin gene (Abdelhalim et al. 2020). Among the nine isolates, six isolates belonged to M. majus, three isolates belonged to M. nivale. Sequences of six isolates M. majus and three isolates M. nivale were deposited in GenBank with accession numbers MW428296-MW428298, MZ734119-MZ734121and MZ734139-MZ734141(TEF), MW384889, MW428291, MW428292, MZ734203-MZ734205 and MZ734161-MZ734163(RPB2), MW428293-MW428295, MZ501004-MZ501006 and MZ501024-MZ501026 (β-tubulin). For all the genes, isolates revealed 98-100% similarity to M. majus and M. nivale accessions, respectively. Microscopy of the six M. majus isolates showed: the conidia were falcate, straight to curved, apex pointed or obtuse to subacute, lacking basal differentiation, with 1 to 6 septa, 3.6 to 5.0 × 15.0 to 30.5 μm (av.= 4.5 × 23.2; n = 60). The three M. nivale isolates showed: the conidia were hyaline, 1 to 3 septa, 2.4 to 4.4 × 11.9 to 26.0 μm (av.= 3.5 × 14.7; n = 60). Perithecia of M. majus are dark brown, globose, and 95.2 to 190.5 × 95.2 to 228.6 μm (av.= 144.4 ×152.5; n = 30). Asci are clavate, and 6.8 to 11.0 ×68.2 to 77.3 μm (av.= 8.6×72.0; n = 30), contain eight ascospores. Mature ascospores are ellipsoidal, and 3.8 to 4.9 ×11.5 to 19.2 μm (av.= 4.0 ×15.2; n = 30), with 1 to 3 septa. These morphological characteristics were consistent with previous descriptions of these two species (Glynn et al. 2005). For pathogenicity tests, mycelia of M. nivale and M. majus was prepared using the modified procedure of Zhang et al. (2015). Two-week-old healthy wheat seedlings (cv. Aikang 58) were inoculated using 1 mL of prepared mycelia to one seedling, which was sprayied on soil. Control seedlings were inoculated with 1 mL distilled water containing 0.2% gelatin. After 10 days under 15/10℃, 16h/8h, all the inoculated plants had developed brown spots; while control plants remained healthy. The pathogens were reisolated from inoculated plants and identified as M. nivale and M. majus based on morphological characteristics and molecular methods described above. Although there are reports of M. majus associated with brown foot rot of wheat in Anhui Province and M. nivale associated with seedling blight of oat in Gansu Province (Chen et al. 2021; Tai et al. 2019). To our knowledge, this is the first report of brown foot rot of wheat caused by M. nivale and M. majus in China.

Cover crop selection affects maize susceptibility to the fungal pathogen Fusarium verticillioides

In this study, we show the impact of cover crop legacy in soil towards susceptibility of next generation maize to the fungal pathogen Fusarium verticillioides. The use of different plant species as cover crops in organic cropping systems has been shown to provide several ecosystem services. The direct benefits of using leguminous cover crops such as pea or mycorrhizal species such as cereal rye or oats for soil fertility and cash crop yield are well known. However, the impacts of different cover crop species on subsequent cash crop pest suppression is rarely accounted for in agricultural management. Legacy of cover crop species are of importance considering recent findings that plants promoting arbuscular mycorrhizal communities, such as cereal rye and oats as cover crops, can provide increased benefits to successive maize crops against insect pests. In this study, we test whether such benefits might also include resistance against pathogens. We examined progression of rot lesions in ear, stalk and seedling blight by Fusarium verticillioides in maize plants that were grown in soil with a cover crop monoculture history of either winter pea, triticale or radish. This study shows for the first time that soil legacy of mycorrhizal monocot triticale as a cover crop renders maize plants more susceptible to ear rot and seedling blight by Fusarium verticillioides as compared to a soil legacy of radish. This suggests that although soil legacy of radish may be detrimental to management of insects, it is effective in suppressing progression of Fusarium verticillioides in maize. This work demonstrates the significance of cover crop selection to manage fungal pathogens such as Fusarium verticillioides, it further suggests trade-offs in plant resistance to various pests’ taxa at the cover crop species level.

Cyclo(l-proline-l-serine) Dipeptide Suppresses Seed Borne Fungal Pathogens of Rice: Altered Cellular Membrane Integrity of Fungal Hyphae and Seed Quality Benefits.

Five proline-containing diketopiperazines (Pro-DKPs) produced by antagonistic microorganisms as secondary metabolites were selected and synthesized under laboratory conditions. Out of five synthesized Pro-DKPs, cyclo(l-Pro-l-Ser) (DKP-6) revealed the best inhibition of fungal pathogens (Fusarium verticillioides and Fusarium fujikuroi) of rice under in vitro conditions with effective doses lower than standard fungicide carbendazim. DKP-6 induced stress on the fungal cell membrane integrity, which was revealed by calcofluor white and propidium iodide assays, endorsed by ultra-microscopic details and soluble protein leakage assays. In vivo seed treatment of infested rice seeds with DKP-6 at 2000 μg/mL for 10 h of seed treatment inflicted best reduction in seed rot and seedling blight with respect to control and carbendazim. Significant enhancement in seedling quality parameters were also observed. The work presented the strong influence of cyclo(l-Pro-l-Ser) as a mycocidal seed treatment agent better than synthetic toxic fungicides for rice.

Isolation, Characterization and Draft Genome Analysis of Bacteriophages Infecting Acidovorax citrulli.

Bacterial fruit blotch and seedling blight, caused by Acidovorax citrulli, is one of the most destructive diseases of melon and watermelon in many countries. Pathogen-free seed and cultural practices are major pillars of the disease control. However, use of bacteriophages as natural biocontrol agents might also contribute to the disease management. Therefore, we isolated 12 bacteriophages specific to A. citrulli, from phyllosphere and rhizosphere of diseased watermelon plants. The phage strains were characterized based on their host range, plaque and virion morphology, thermal inactivation point, adsorption rate, one step growth curve, restriction fragment length polymorphism (RFLP), and genomic analysis. Transmission electron microscopy of three phage strains indicated that they belong to the order Caudovirales, family Siphoviridae. All phages lysed 30 out of 32 tested A. citrulli strains isolated in Serbia, and did not lyse other less related bacterial species. They produced clear plaques, 2 mm in diameter, on bacterial lawns of different A. citrulli strains after 24 h of incubation. The thermal inactivation point was 66 or 67°C. They were stable at pH 5–9, but were sensitive to chloroform and inactivated in either 5 or 10 min exposure to ultraviolet (UV) light. RFLP analysis using EcoRI, BsmI and BamHI enzymes did not show genetic differences among the tested phages. Adsorption rate and one step growth curve were determined for the Acidovorax phage ACF1. Draft genome sequence of the ACF1 phage was 59.377 bp in size, with guanine-cytosine (GC) content 64.5%, including 89 open reading frames. This phage shared a very high genomic identity with Acidovorax phage ACPWH, isolated in South Korea. Evaluation of systemic nature of ACF1 strain showed that it can be absorbed by roots and translocated to upper parts of watermelon plants where it survived up to 10 days.

5-n-alkylresorcinol-based metabolic response of rice to the interaction with Burkholderia glumae: a chemical characterization of the temporal and spatial variations depending on environmental conditions

ABSTRACT Burkholderia glumae is a relevant worldwide pathogen of rice. B. glumae unfavorably affects the throughput of rice crops provoking seedling death and blight panicles. Different intrinsic and extrinsic factors influence the interaction, the host physiological response and its metabolic performance, e.g. biosynthesis of protecting metabolites such as 5-n-alkylresorcinols (AR). However, the metabolic responses of rice interacting with B. glumae and involving different factors are still unraveled. Thus, AR variations in two Colombian rice genotypes, grown in two climatically different locations and inoculated independently with two B. glumae strains were evaluated through total AR content and LC-MS-based characterization. AR accumulated in rice plants at different levels depending on genotypes, plant parts and phenological stages. Rice genotypes were affected by pathogen inoculation, promoting AR variations. Such pathogen-mediated influence was also affected by the test factors. This AR-based rice response against B. glumae constitutes a contribution to understand better this biotic interaction.

Investigation and Genome-Wide Association Analysis of Fusarium Seedling Blight Resistance in Chinese Elite Wheat Lines

Fusarium seedling blight (FSB) is an important disease of wheat occurring as part of the Fusarium disease complex consisting also of Fusarium head blight (FHB). 240 Chinese elite cultivars and lines were evaluated in greenhouse experiments for FSB resistance and genotyped using the wheat 90 K single nucleotide polymorphism arrays. Among them, 23 accessions had an average lesion length of less than 0.6 cm, exhibiting potential for breeding for FSB resistance in wheat. Jingfumai 1 and Yangmai 11 had a relatively high resistance to both FSB and FHB simultaneously. Six relatively stable quantitative trait loci (QTLs) were detected on chromosome arms 1DL, 3AS, 3BL, 6BL, 7AL, and Un using the mixed linear model approach, interpreting 4.83–7.53% of phenotypic variation. There was a negative correlation between the average FSB lesion length and the BLUE FHB index with a low coefficient, and resistance to both diseases appeared to be conferred by different QTLs across the same population. Four KASP markers were detected on 1DL, 3AS, 3BL, and 6BL in QTLs to facilitate marker-assisted selection. Combined with transcriptome data analysis, eight defense-related genes were considered as candidates for mapping QTLs. The resistant elite germplasm, mapped QTLs, and KASP markers developed in this study are useful resources for enhancing Fusarium seedling blight in wheat breeding.

Novel Genetic Dysregulations and Oxidative Damage in Fusarium graminearum Induced by Plant Defense Eliciting Psychrophilic Bacillus atrophaeus TS1.

This study elaborates inter-kingdom signaling mechanisms, presenting a sustainable and eco-friendly approach to combat biotic as well as abiotic stress in wheat. Fusarium graminearum is a devastating pathogen causing head and seedling blight in wheat, leading to huge yield and economic losses. Psychrophilic Bacillus atrophaeus strain TS1 was found as a potential biocontrol agent for suppression of F. graminearum under low temperature by carrying out extensive biochemical and molecular studies in comparison with a temperate biocontrol model strain Bacillus amyloliquefaciens FZB42 at 15 and 25 °C. TS1 was able to produce hydrolytic extracellular enzymes as well as antimicrobial lipopeptides, i.e., surfactin, bacillomycin, and fengycin, efficiently at low temperatures. The Bacillus strain-induced oxidative cellular damage, ultrastructural deformities, and novel genetic dysregulations in the fungal pathogen as the bacterial treatment at low temperature were able to downregulate the expression of newly predicted novel fungal genes potentially belonging to necrosis inducing protein families (fgHCE and fgNPP1). The wheat pot experiments conducted at 15 and 25 °C revealed the potential of TS1 to elicit sudden induction of plant defense, namely, H2O2 and callose enhanced activity of plant defense-related enzymes and induced over-expression of defense-related genes which accumulatively lead to the suppression of F. graminearum and decreased diseased leaf area.

Protein Elicitor EsxA Induces Resistance to Seedling Blight and PR Genes Differential Transcription in Rice

Protein elicitors can induce plant systemic resistance to pathogens. In an earlier study, we cloned an EsxA gene from the plant growth-promoting rhizobacterium Paenibacillus terrae NK3-4 and expressed it in Pichia pastoris. In addition to being important for the pathogenicity of animal pathogens, EsxA can also induce an immune response in animals. While, we found the exogenously expressed EsxA has the activity of elicitor, which can trigger hypersensitive response and reactive oxygen species burst in leaves as well as enhanced rice plant growth. The effects of EsxA on seedling blight (Fusarium oxysporum) resistance and gene transcription, including pathogenesis-related (PR) genes in rice were evaluated. The germination rate was 95.0% for seeds treated with EsxA and then inoculated with F. oxysporum, which was 2.8-times higher than that of F. oxysporum-infected control seeds that were not treated with EsxA (Con). The buds and roots of EsxA-treated seedlings were 2.4- and 15.9-times longer than those of Con seedlings. The plants and roots of seedlings dipped in an EsxA solution and then inoculated with F. oxysporum were longer than those of the Con seedlings. Theplant length, number of total roots, and number of white roots were respectively 23.2%, 1.74-times, and 7.42-times greater for the seedlings sprayed with EsxA and then inoculated with F. oxysporum than for the Con seedlings. The EsxA induction efficiency (spray treatment) on seedling blight resistance was 60.9%. The transcriptome analysis revealed 1137 and 239 rice genes with EsxA-induced up-regulated and down-regulated transcription levels, respectively. At 48 h after the EsxA treatment, the transcription of 611 and 160 genes was up-regulated and down-regulated, respectively, compared with the transcription levels for the untreated control at the same time-point. Many disease resistance-related PR genes had up-regulated transcription levels. The qPCR data were consistent with the transcriptome sequencing results. EsxA triggered rice ISR to seedling blight and gene differential transcription, including the up-regulated transcription of rice PR genes. These findings may be relevant for the use of EsxA as a protein elicitor to control plant diseases.

Influence of Fusarium spp. Inoculation Dose Simulating Pathogen Pressure on Grain Production Parameters of Zea mays L.

Several fungi species from genus Fusarium can infect maize crop and cause seedling blight, root rot, stalk rot, cob and ear rot. Maize yield and grain quality are negatively affected by the disease, while mycotoxins accumulating in grains represent a serious threat to human and animal health. In this research two maize hybrids were subject to artificial infection in field with Fusarium spp. suspension at three incremental dose levels simulating increasing pathogen pressure. Results indicated that earlier maturing hybrid (‘Turda 248’ – FAO 300 maturity group) following artificial infection displayed lower infection index of ears (up to 15.33%) while the later-maturing hybrid (‘Turda 332’ – FAO 380 maturity group) displayed higher infection levels of up to 30.87%. Uninoculated controls presented infection index of ears below 2% for both hybrids. For the hybrid ‘Turda 248’ the highest pathogen pressure (inoculation dose 12 mL/ear) caused 23.10% yield decrease relative to control, while same dose for the hybrid ‘Turda 332’ caused 21.20% yield decrease relative to control. Once with increased inoculation dose the grain quality parameters displayed changes. The observed trend was an increasing protein content and decreasing starch content once with increased pathogen pressure. Identification of resistant genotypes and study of the climatic factors that undergo disease development remain important research approaches for efficient control of the pathogen populations in agroecosystems.

Bio-efficacy of seed priming with fungicides against major soil borne diseases of maize : Efficacy of seed priming with fungicides against soil borne diseases of maize

Field experiments were conducted during kharif 2017 and rabi 2017-18 to evaluate the bio-efficacy of fungicides (Carbendazim 25% + Mancozeb 50% WS, Carbendazim 50 WP, Mancozeb 75 WP and Carboxin 37.5% + Thiram 37.5% WS) against the seed rot and seedling blight of maize at Research Farm, Zonal Agricultural Research Station, Jhabua (MP). All the fungicides were found significantly effective against the seed rot and seedling blight compared to control. The maximum seed germination (86.98 and 86.32% in kharif and rabi, respectively), shoot length (32.76 and 38.30 cm in kharif and rabi, respectively), root length (4.79 and 5.12 cm in kharif and rabi, respectively) and seedling vigour index (3254.8 in kharif and 3748.0 in rabi) were recorded on Carbendazim 25% + Mancozeb 50% WS @ 35 g/kg seeds (T3) followed by Carbendazim 25% + Mancozeb 50% WS @ 3.0 g/kg seeds (T2). While the lowest values of these parameters were in control. Similarly, lowest % disease incidences of seed rot (9.08 and 8.0% in respective seasons) and seedling blight (5.81 and 4.11%) was recorded with Carbendazim 25% + Mancozeb 50% WS @ 35 g/kg seeds followed by Carbendazim 25% + Mancozeb 50% WS @ 30 g/kg seeds. Yield attributes, yields and economics of maize also significantly influenced by various fungicides. Significantly higher grain yield of 2795 kg/ha and stover yield of 3860 kg/ha was recorded in Carbendazim 25% + Mancozeb 50% WS @ 35 g/kg seeds and which was on par with Carbendazim 25% + Mancozeb 50% WS @ 30 g/kg seeds. Maximum gross returns of Rs. 47914, net returns of Rs. 36615 and B:C ratio of 2.60 were also recorded with the seed priming with Carbendazim 25% + Mancozeb 50% WS @ 35 g/kg seeds.