Growth Chamber Assays Research Articles

Host Range Characterization of Phytophthora sansomeana Across Corn, Soybean, Wheat, Winter Cereal Rye, Dry Bean, and Oats and an In Vitro Assessment of Seed Treatment Sensitivity.

Formally described in 2009, Phytophthora sansomeana is a pathogen of increasing interest in native, agricultural, and horticulturally important plant species. The objective of this study was to elucidate the symptomatic and asymptomatic host range of P. sansomeana on six agricultural crop species commonly used in field crop rotations in Michigan. In addition, sensitivity to oomicides commonly used in seed treatments, including oxathiapiprolin, mefenoxam, ethaboxam, and pyraclostrobin, was performed to aid in disease management recommendations. Plant biomass, quantity of P. sansomeana DNA in roots, and reisolations were used to assess pathogenicity and virulence of 18 isolates of P. sansomeana on each plant species using an inoculated seedling growth chamber assay. Isolates displayed varying levels of virulence to the hosts tested. Reisolations were completed for each plant species tested, and varying quantities of P. sansomeana DNA were found within all plant species root samples. Corn, wheat, soybean, dry bean, and winter cereal rye plants were symptomatic hosts with significant reduction observed in the total plant biomass. No significant reduction in total plant biomass was observed in oats, and oat roots harbored the least amount of P. sansomeana DNA. No P. sansomeana isolates were insensitive to the oomicide compounds tested with mean absolute inhibition (EC50) values of fungicide required for 50% growth inhibition values of 7.8 × 10-2 μg/ml for mefenoxam, 1.13 × 10-1 μg/ml for ethaboxam, 2.6 × 10-2 μg/ml for oxathiapiprolin, and 3.04 × 10-1 μg/ml for pyraclostrobin. These results suggest that common crop rotations in Michigan may not be a viable option to reduce soilborne inoculum accumulation and oomicide seed treatments could be considered for early-season management of P. sansomeana.

Isolation, selection, and identification of phytopathogenic fungi with bioherbicide potential for the control of field bindweed (Convolvulus arvensis L.)

AbstractField bindweed (Convolvulus arvensis L.) has been described as one of the most noxious weeds in agricultural soils worldwide. Furthermore, its control by conventional herbicides can promote the emergence of resistant biotypes as well as negatively affect human health and the environment. An ecological alternative for weed management is the use of phytopathogenic fungi. In this study, 68 fungal strains were isolated from C. arvensis leaves exhibiting symptoms of fungal disease. Seven isolates were confirmed as pathogenic to C. arvensis in a detached leaf assay. Filtered cell‐free cultures (FCFC) of these seven isolates were then evaluated. FCFC of TV1 and ET4 showed the best results, inhibiting seedling dry weight by up to 48% in vivo and shoot dry weight up to 35% in growth chamber assays. Phytopathogenic evaluation of both isolates showed disease severity >67%, and an ability to inhibit root dry weight by up to 80%. Inhibitory effects were not observed on chickpea, bean, sorghum, maize, or tomato plants, suggesting pathogenic specificity of TV1 and ET4 to field bindweed. Molecular identification revealed a high similarity of TV1 (100% identity) with Macrophomina phaseolina, and a high similarity of ET4 with Alternaria alternata (99.8% identity). To the best of our knowledge, this is the first report of M. phaseolina showing pathogenicity against field bindweed worldwide, and the first report for A. alternata in Mexico. The results reveal that these fungi and/or their FCFC have the potential to be used as bioherbicidal agents against C. arvensis.

Sensitivity of Clarireedia spp. to benzimidazoles and dimethyl inhibitors fungicides and efficacy of biofungicides on dollar spot of warm season turfgrass.

Dollar spot caused by Clarireedia spp. (formerly Sclerotinia homoeocarpa) is an economically destructive fungal disease of turfgrass that can significantly compromise turf quality, playability, and aesthetic value. Fungicides are frequently used to manage the disease but are costly and potentially unfavorable to the environment. Repeated use of some active ingredients has resulted in reduced efficacy on C. jacksonii causing dollar spot in cool-season turfgrasses in the US. Experiments were conducted to study fungicide sensitivity of Clarireedia spp. as well as to develop alternatives to fungicides against dollar spot on warm-season turfgrass in Georgia. First, 79 isolates of Clarireedia spp. collected across the state were tested on fungicide-amended agar plates for their sensitivity to thiophanate-methyl (benzimidazole) and propiconazole (dimethyl inhibitor). Seventy-seven isolates (97.5%) were sensitive (0.001 to 0.654 μg/mL) and two isolates (2.5%) were found resistant (>1000 μg/mL) to thiophanate-methyl. However, in the case of propiconazole, 27 isolates (34.2%) were sensitive (0.005 to 0.098 μg/mL) while 52 isolates (65.8%) were resistant (0.101 to 3.820 μg/mL). Next, the efficacy of three bio- and six synthetic fungicides and ten different combinations were tested in vitro against C. monteithiana. Seven bio- and synthetic fungicide spray programs comprising Bacillus subtilis QST713 and propiconazole were further tested, either alone or in a tank mix in a reduced rate, on dollar spot infected bermudagrass 'TifTuf' in growth chamber and field environments. These fungicides were selected as they were found to significantly reduce pathogen growth up to 100% on in vitro assays. The most effective spray program in growth chamber assays was 100% B. subtilis QST713 in rotation with 75% B. subtilis QST713 + 25% propiconazole tank mix applied every 14 days. However, the stand-alone application of the biofungicide B. subtilis QST713 every seven days was an effective alternative and equally efficacious as propiconazole, suppressing dollar spot severity and AUDPC up to 75%, while resulting in acceptable turf quality (>7.0) in field experiments. Our study suggests that increased resistance of Clarireedia spp. to benzimidazoles and dimethyl inhibitors warrants continuous surveillance and that biofungicides hold promise to complement synthetic fungicides in an efficacious and environmentally friendly disease management program.

Endophytic Fusarium clavum confers growth and salt tolerance in Cucumis melo

In the present study, we investigated the in-vitro and in-vivo effects of root endophytic fungal species isolated from squirting cucumber Ecballium elaterium on morphological, physiological and biochemical mechanisms of muskmelon (Cucumis melo) in response to salt stress. A total of 23 endophytic fungal isolates belonging to nine different genera were initially screened for their salt tolerance potential in saline medium. Endophytic Fusarium clavum EeR24 exhibited maximum salt tolerance in screening studies and was selected for further studies. Seedlings of C. melo were inoculated with F. clavum EeR24 and one week later were subjected to two salt (100 and 200 mM NaCl) and control (no salt) treatments in a growth chamber and greenhouse experiments. In growth chamber assays, seedlings treated with F. clavum EeR24 exhibited significant increase in growth and biomass under both controlled and saline conditions. Under greenhouse conditions, F. clavum EeR24 significantly improved morphological and physiological traits including plant height, weight, number of leaves, membrane stability, electrical conductivity, photosynthesis, stomatal conductance and transpiration, in C. melo in response to salt stress. Endophyte colonization also led to decreased absorption of Na+ (36–42 %) and Cl- (23–33 %) ions and an improved K+ (35 %) absorption. Under saline conditions, endophyte colonization improved catalase (24–37 %), guaiacol peroxidase (31–42 %) and superoxide dismutase (16–22 %), chlorophyll and phenolic content by 30–64 %, compared to non-colonized plants. Lipid peroxidation activities significantly decreased by 45 % and proline accumulation increased by 18 % in endophyte-colonized compared to non-colonized plants. Histochemical analysis indicated that under saline conditions, endophytic colonization reduced levels of H2O2, superoxide ion production and cell mortality and increased lignin deposition. The endophytic isolate F. clavum EeR24 also exhibited plant growth promoting activities by producing hydrolytic enzymes, IAA, and phosphate solubilization. Furthermore, a study on spatial colonization of the endophyte, using either conventional Petri-plate counts or RFP-tagging, indicated that F. clavum was able to penetrate the root tissues of C. melo. Conclusively, the endophyte F. clavum EeR24 is an effective salt stress reducer and melon growth promotor; hence can be further taken into account for development as an eco-friendly bio-fertilizer to confer salt stress tolerance in melon.

Interaction of Fusarium Wilt Race 4 with Root-Knot Nematode Increases Disease Severity in Cotton.

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum, is a severe disease of cotton (Gossypium spp.). Strains of the wilt pathogen in the United States, such as race 1, require the presence of nematodes such as southern root-knot nematode (Meloidogyne incognita) to cause appreciable disease. The exception is the race 4 strain of the wilt pathogen, which can attack cotton without concomitant infection by plant-parasitic nematodes and was first identified in California in 2001 and in Texas and New Mexico since 2017. The effects of the interaction between M. incognita and race 1 or race 4 on wilt severity and nematode reproduction on two Gossypium hirsutum cultivars, Acala 44 and FM 966, and a G. barbadense cultivar, Pima S-4, were directly compared in growth chamber assays. All three cultivars were susceptible to M. incognita. Suppression of nematode reproduction by the wilt pathogen was detected only for race 4 on all three cultivars on a per plant basis but not on a per gram root tissue basis. The control, M. incognita alone, and race 1 alone treatments caused no symptoms. Inoculation with race 1 and M. incognita caused moderate wilt symptoms in 'Acala 44' and 'FM 966' and mild symptoms in 'Pima S-4'. However, race 4 treatment caused severe wilt in 'Pima S-4' and moderate wilt severity in 'Acala 44' and 'FM 966'. The symptom severity of 'Acala 44' and 'FM 966' further increased in the presence of M. incognita. Thus, race 4 is not only capable of causing wilt in the absence of M. incognita but can also interact with the nematode to further increase disease severity. Though control of wilt caused by race 1 can be achieved mainly through breeding for nematode resistance, it will be imperative to incorporate both southern root-knot nematode and race 4 resistance to effectively control the disease should race 4 expand into southern root-knot nematode-infested fields.

Aluminum phosphate sludge as a phosphorus source for maize production under low soil phosphorus availability.

BackgroundWith increasing food demand as a consequence of the growing world population, there is a corresponding demand for additional sources of phosphorus (P). Alum-phosphate (Al-P) sludge is a by-product of wastewater treatment and can be a good source of P. In this study, the response of maize (Zea mays L.) to Al-P sludge was tested. Maize was chosen as the test crop due to its prevalent use as human and animal food and as a source of biofuel. The objective of the study was to investigate Al-P sludge as a source of P compared to a commercial fertilizer (monoammonium phosphate, MAP).MethodsA growth chamber assay was conducted over four cropping cycles (45 d each). The application rate was 9.7, 19.4, 29.1 and 38.8 mg P kg−1 dry soil. Amendments were applied once at the start of the first cropping cycle. Plants were harvested after each cycle and pots were re-seeded. Dry matter yield (DMY), total P uptake, Al-P uptake, soil total P and Olsen-P concentrations, pH, and EC were measured.ResultsDMY was significantly greater in pots amended with Al-P sludge than in pots treated with MAP. There was a significant rate × cropping cycle interaction effect on DMY with the differences among rates in cycle 1 different from those in cycle 4. Phosphorus uptake depended on cropping cycle, P source and P application rate. With sludge uptake higher than MAP in all cycles, the highest P uptake was observed at the highest application rate except for cycle 2 where this was observed at the rate of 29.1 mg kg−1. For MAP, phosphorus recovery efficiency (PRE) at the highest rate was significantly greater than that at the lowest rate whereas PRE in cycle 1 was significantly higher than that in cycle 4. In the first two cycles, aluminum uptake was negligible in both MAP and Al-P sludge treatments; however, in cycles 3 and 4, there was significantly more Al in maize from sludge amended pots. Our results show that Al-P sludge was as effective as MAP in supplying enough P for biomass yield. We, therefore, conclude that Al-P sludge could be an alternative source of P, especially for growing maize as feedstock for bioenergy.

A Meta-Analysis to Determine the State of Biological Control of Aphanomyces Root Rot.

The increasing incidence and prevalence of the pathogen Aphanomyces euteiches in various pulse-growing regions worldwide necessitates the development of effective management strategies, including biological control agents. Numerous labs have undertaken research examining biological control methods to evaluate aphanomyces root rot suppression in multistep processes that include isolation of inhibitory organisms, lab assays, growth chamber assays, and field trials. Given the emergence of various biocontrol agents and the need to mitigate aphanomyces yield losses, we have undertaken a meta-analysis approach to analyze the effectiveness of biocontrol agents in relation to application method, biocontrol agent richness, biocontrol agent type, the type of study, and reporting system-oriented moderator variables. An effect size, calculated as a natural log response ratio, resulted in a summary weighted mean of −0.411, suggesting the overall effectiveness of biocontrol agents (p < .001). Aphanomyces root rot suppression using biological treatments showed significant heterogeneity for all moderator variables, confirming that the studies do not share a common effect size and the use of a random effect model was appropriate. Across studies, meta-analyses revealed that soil amendments, biocontrol agent application as a seed coating and suspension, bacterial and fungal biocontrol agents, mixed applications, growth chamber and field studies, and qualitative and quantitative reporting systems were all associated with significantly positive outcomes for aphanomyces root rot suppression. Our findings suggest that there is potential promise for biological control of aphanomyces root rot, and more field trials need to be conducted to demonstrate the efficacy level observed under growth chamber conditions. Moreover, we identified a lack of detailed understanding of the mechanism(s) of biological control of aphanomyces root rot as a research priority.

Seed treatment for controlling damping-off caused by Globisporangium irregulare and Globisporangium ultimum var. sporangiiferum in soybean from southern Brazil

Globisporangium irregulare and G. ultimum var. sporangiiferum were recently reported to be associated with soybean damping-off in Brazil. Currently, there is no known information about fungicide seed treatments for soybean. Thus, the objective of this study was to evaluate the efficacy of commercial fungicide-based products to control soybean damping-off caused by G. irregulare and G. ultimum var. sporangiiferum. The experiments were performed with 15 seed treatments (non-treated check, Certeza N, Apron RFC, Maxim, Maxim XL, Maxim Quattro, Maxim Advanced, Vitavax Thiram, Standak Top, Spectro, Verango, Derosal Plus, Carbendazim, Attic and Rancona T) and two soybean cultivars (‘DM57i52’ and ‘NEO530’). In vitro assays were performed to verify the effect of seed treatments on seed germination and seed rot, whereas growth chamber assays were conducted to evaluate the effect of seed treatments on emergence, root rot and seedling dry mass. Products that contain metalaxyl-M were the most effective at controlling damping-off caused by G. irregulare and G. utimum var. sporangiiferum followed by products that contain thiram. Overall, Apron RFC, Maxim Advanced and Maxim Quattro had higher efficacy to reduce damping-off caused by either G. irregulare or G. ultimum var. sporangiiferum therefore, can be recommended for seed treatment of soybean.

Evolutionary Rescue as a Mechanism Allowing a Clonal Grass to Adapt to Novel Climates.

Filing gaps in our understanding of species' abilities to adapt to novel climates is a key challenge for predicting future range shifts and biodiversity loss. Key knowledge gaps are related to the potential for evolutionary rescue in response to climate, especially in long-lived clonally reproducing species. We illustrate a novel approach to assess the potential for evolutionary rescue using a combination of reciprocal transplant experiment in the field to assess performance under a changing climate and independent growth chamber assays to assess growth- and physiology-related plant trait maxima and plasticities of the same clones. We use a clonal grass, Festuca rubra, as a model species. We propagated individual clones and used them in a transplant experiment across broad-scale temperature and precipitation gradients, simulating the projected direction of climate change in the region. Independent information on trait maxima and plasticities of the same clones was obtained by cultivating them in four growth chambers representing climate extremes. Plant survival was affected by interaction between plant traits and climate change, with both trait plasticities and maxima being important for adaptation to novel climates. Key traits include plasticity in extravaginal ramets, aboveground biomass, and osmotic potential. The direction of selection in response to a given climatic change detected in this study mostly contradicted the natural trait clines indicating that short-term selection pressure as identified here does not match long-term selection outcomes. Long-lived clonal species exposed to different climatic changes are subjected to consistent selection pressures on key traits, a necessary condition for adaptation to novel conditions. This points to evolutionary rescue as an important mechanism for dealing with climate change in these species. Our experimental approach may be applied also in other model systems broadening our understanding of evolutionary rescue. Such knowledge cannot be easily deduced from observing the existing field clines.

Infection of cucumber seedling roots by Pseudomonas amygdali pv. lachrymans following artificial substrate inoculation

There are few studies of cucumber roots at the seedling stage infected by Pseudomonas amygdali pv. lachrymans (Pal). We used growth chamber assays to determine the infection of cucumber seedling roots by Pal following artificial substrate inoculation. Symptoms on cucumber roots, leaves, and stems were observed over time. We used real-time fluorescent quantitative PCR (qPCR) to obtain accurate numbers of Pal copies in infected roots, and then statistically assessed the dynamics of Pal copies in roots, stems, and leaves. Results indicated that Pal not only caused root decay, but also damaged the whole plant. Following root infection, the bacteria were transmitted through stems to the leaves. Cucumber seedlings in a moist planting substrate showed lodging, leaf chlorosis and wilt, and rotted roots. This study provides evidence that in moist substrate, Pal can infect cucumber roots and be transmitted throughout the host plant. In addition, the results also provide a foundation for further research on the transmission and proliferation of Pal in cucumber plants under field conditions.

Патогенність ізолятів гриба Gaeumannomyces Tritici (J.Walker) Hern.-Restr. &amp; Crous – збудника офіобольозу та ефективність штамів р. Bacillus проти хвороби

Isolates of Gaeumannomyces spp. obtained from diseased roots of winter wheat showing take-all symptoms were characterized by pathogenicity. All isolates were more pathogenic on wheat and barley than on oat, and were identified as Gaeumannomyces tritici. Most isolates of G. tritici were characterized as middle pathogenic, the pathogenicity of one isolate was higher than those of others, and two isolates showed the lowest pathogenicity. In growth chamber assay, the effect of two Bacillus strains, B. subtilis 16 and B. pumilus 11, on take-all of wheat was studied. Pathogen inoculation was made by isolates of G. tritici of different pathogenicity. It was found that effective biological control depends on take-all severity, which, in turn, co-ordinates with the pathogenicity of fungal isolate. Applying the bacterial cells into the plant growth substrate stimulated the seedling growth when artificial inoculation was performed with a middle pathogenic isolate of G. tritici, and the disease severity was middle. There was no growth promotion by bacterial inoculant at slight disease severity. No stimulating effect was also observed at the high disease severity, where pathogen inoculation was performed with a highly pathogenic isolate of G. tritici.

Beneficial Endophytic Bacterial Populations Associated With Medicinal Plant Thymus vulgaris Alleviate Salt Stress and Confer Resistance to Fusarium oxysporum.

As a result of climate change, salinity has become a major abiotic stress that reduces plant growth and crop productivity worldwide. A variety of endophytic bacteria alleviate salt stress; however, their ecology and biotechnological potential has not been fully realized. To address this gap, a collection of 117 endophytic bacteria were isolated from wild populations of the herb Thymus vulgaris in Sheikh Zuweid and Rafah of North Sinai Province, Egypt, and identified based on their 16S rRNA gene sequences. The endophytes were highly diverse, including 17 genera and 30 species. The number of bacterial species obtained from root tissues was higher (n = 18) compared to stem (n = 14) and leaf (n = 11) tissue. The endophytic bacteria exhibited several plant growth-promoting activities in vitro, including auxin synthesis, diazotrophy, phosphate solubilization, siderophore production, and production of lytic enzymes (i.e., chitinase, cellulase, protease, and lipase). Three endophytes representing Bacillus species associated with T. vulgaris such as EGY05, EGY21, and EGY25 were selected based on their ex-situ activities for growth chamber assays to test for their ability to promote the growth of tomato (Solanum lycopersicum L.) under various NaCl concentrations (50–200 mM). All three strains significantly (P < 0.05) promoted the growth of tomato plants under salt stress, compared to uninoculated controls. In addition, inoculated tomato plants by all tested strains decreased (P < 0.05) the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase). Six strains, representing Bacillus and Enterobacter species EGY01, EGY05, EGY16, EGY21, EGY25, and EGY31 were selected based on in vitro antagonistic activity to F. oxysporum for pot experiments under salt stress. All tested strains reduced the disease severity index (DSI) of tomato plants at all tested salt concentrations. Gas-chromatography/mass-spectrometry analysis of cell-free extracts of B. subtilis (EGY16) showed at least ten compounds were known to have antimicrobial activity, with the major peaks being benzene, 1,3-dimethyl-, p-xylene, dibutyl phthalate, bis (2-ethylhexyl) phthalate, and tetracosane. This study demonstrates that diverse endophytes grow in wild thyme populations and that some are able to alleviate salinity stress and inhibit F. oxysporum pathogenesis, making them promising candidates for biofertilizers and biocontrol agents.

Growth Chamber Assay for Evaluating Resistance to Athelia rolfsii

ABSTRACT Planting resistant cultivars is most sustainable method for managing Athelia rolfsii (= Sclerotium rolfsii), one of the most damaging pathogens of peanut worldwide. However, evaluating germplasm for resistance in the field can be complicated by unfavorable environmental conditions, uneven distribution of sclerotia in soil, and difficulty in growing non-standard peanut genotypes such as wild species. Thus, a growth-chamber assay was used to screen for resistance to A. rolfsii in the laboratory. Thirteen peanut genotypes were used to test the assay: cultivars Georgia-03L, Georgia-12Y, Florida-07, Georgia-07W, Tamrun OL02, FloRun ‘107′, Georgia-06G, and U.S. mini-core accessions CC038 (PI 493581), CC041 (PI 493631), CC068 (PI 493880), CC384 (PI 155107), CC650 (PI 478819), and CC787 (PI 429420). Lesion length, as well as length of visible mycelium, on the main stem and a side stem were recorded at 4, 7, 10, and 13 days after inoculation. In general, patterns of lesion and mycelium growth were similar. The most resistant genotypes, Georgia-03L and CC650, had the smallest lesions and least mycelium growth. However, Georgia-12Y, one of the most resistant cultivars available today, appeared less resistant than Georgia-03L in the assay. Other commercial cultivars were intermediate in lesion and mycelium lengths. The most susceptible entries were CC038, CC041, and CC787. Despite limitations in discriminating among genotypes with intermediate resistance to A. rolfsii, these assays may be useful for pre-screening germplasm to identify physiologically resistant and highly susceptible entries, as well as for screening Arachis species that are difficult to grow in the field.

Establishment of Salsola tragus on aeolian sands: A Southern Colorado Plateau case study

AbstractRussian-thistle (Salsola tragus L.), is a nonnative, C4 photosynthesizing, annual plant that infests disturbed and natural areas in the arid U.S. Southwest. Land managers of natural areas may need to decide whether a S. tragus infestation is potentially harmful and whether it should be actively managed. One factor informing that decision is an understanding of the conditions under which this weed emerges and establishes and how those processes affect where and when infestations occur. We studied S. tragus establishment on aeolian (windblown) sandy soils at Petrified Forest National Park, AZ. Our sites were a previously disturbed sand sheet and a semistabilized sand dune. Measurements in plots on these sites over two growing seasons revealed a similar number of S. tragus seedlings emerging on both sites early in the 2015 growing season. As the season progressed, S. tragus cover (seedling survival and growth) was lower on the sand dune, except for a plot placed entirely on a coppice mound. In 2016, S. tragus seedling emergence and development of cover, measured on plots at both sites, was exceptionally low, as was summer rainfall. A growth chamber assay of seedling emergence from soil and litter samples collected at each site showed emergence was greatest from samples collected where S. tragus litter remained on the soil surface, and otherwise was infrequent. Our study suggests that S. tragus emergence and early establishment are sensitive to low precipitation and that soil-surface microtopography and grass and shrub cover may be determinants of the spatial pattern of infestation on sandy soils. As aeolian sands occur throughout drylands of the U.S. Southwest, deeper understanding of the conditions under which S. tragus seedlings emerge and establish can inform management of this invasive annual in those habitats.

A Novel Root-Knot Nematode Resistance QTL on Chromosome Vu01 in Cowpea.

The root-knot nematode (RKN) species Meloidogyne incognita and M. javanica cause substantial root system damage and suppress yield of susceptible cowpea cultivars. The narrow-based genetic resistance conferred by the Rk gene, present in some commercial cultivars, is not effective against Rk-virulent populations found in several cowpea production areas. The dynamics of virulence within RKN populations require a broadening of the genetic base of resistance in elite cowpea cultivars. As part of this goal, F and F populations from the cross CB46-Null (susceptible) x FN-2-9-04 (resistant) were phenotyped for M. javanica induced root-galling (RG) and egg-mass production (EM) in controlled growth chamber and greenhouse infection assays. In addition, F families of the same cross were phenotyped for RG on field sites infested with Rk-avirulent M. incognita and M. javanica. The response of F to RG and EM indicated that resistance to RKN in FN-2-9-04 is partially dominant, as supported by the degree of dominance in the F and F populations. Two QTL associated with both RG and EM resistance were detected on chromosomes Vu01 and Vu04. The QTL on Vu01 was most effective against aggressive M. javanica, whereas both QTL were effective against avirulent M. incognita. Allelism tests with CB46 x FN-2-9-04 progeny indicated that these parents share the same RKN resistance locus on Vu04, but the strong, broad-based resistance in FN-2-9-04 is conferred by the additive effect of the novel resistance QTL on Vu01. This novel resistance in FN-2-9-04 is an important resource for broadening RKN resistance in elite cowpea cultivars.

Nematophagus fungi increasing phosphorus uptake and promoting plant growth

Some nematophagous fungi control nematodes and are also able to compensate the damage they cause in plant roots. However, the effects of these fungi on plant growth promotion are still underexplored. Here, we evaluated if some nematophagus fungi (Pochonia chlamydosporia and Duddingtonia flagrans) may increase nutrient bioavailability and promote plant growth. A growth chamber assay and a greenhouse study (both without nematodes) were carried out to assess the effects of the fungi on growth and phosphorus uptake by tomato plants. The use of P. chlamydosporia and D. flagrans substantially increased growth and the uptake of nutrients by tomato plants (mainly phosphorus – up to 70% in the best treatments). We conclude that P. chlamydosporia and D. flagrans are potentially useful not just for nematode control but also for promoting plant growth and for increasing nutrient use efficiency.

Synergistic plant–microbe interactions between endophytic bacterial communities and the medicinal plant Glycyrrhiza uralensis F.

Little is known about the composition, diversity, and geographical distribution of bacterial communities associated with medicinal plants in arid lands. To address this, a collection of 116 endophytic bacteria were isolated from wild populations of the herb Glycyrrhiza uralensis Fisch (licorice) in Xinyuan, Gongliu, and Tekesi of Xinjiang Province, China, and identified based on their 16S rRNA gene sequences. The endophytes were highly diverse, including 20 genera and 35 species. The number of distinct bacterial genera obtained from root tissues was higher (n = 14) compared to stem (n = 9) and leaf (n = 6) tissue. Geographically, the diversity of culturable endophytic genera was higher at the Tekesi (n = 14) and Xinyuan (n = 12) sites than the Gongliu site (n = 4), reflecting the extremely low organic carbon content, high salinity, and low nutrient status of Gongliu soils. The endophytic bacteria exhibited a number of plant growth-promoting activities ex situ, including diazotrophy, phosphate and potassium solubilization, siderophore production, auxin synthesis, and production of hydrolytic enzymes. Twelve endophytes were selected based on their ex situ plant growth-promoting activities for growth chamber assays to test for their ability to promote growth of G. uralensis F. and Triticum aestivum (wheat) plants. Several strains belonging to the genera Bacillus (n = 6) and Achromobacter (n = 1) stimulated total biomass production in both G. uralensis and T. aestivum under low-nutrient conditions. This work is the first report on the isolation and characterization of endophytes associated with G. uralensis F. in arid lands. The results demonstrate the broad diversity of endophytes associated with wild licorice and suggest that some Bacillus strains may be promising candidates for biofertilizers to promote enhanced survival and growth of licorice and other valuable crops in arid environments.

Screening Almond Rootstocks for Sources of Resistance to Armillaria Root Disease

Prunus dulcis (almond) is one of the most susceptible horticultural crops to Armillaria root disease. Resistance to Armillaria mellea and Armillaria tabescens, the geographically isolated causal fungi that attack almond and closely related Prunus persica (peach), has been evaluated in studies of almond, peach, and other Prunus rootstocks, but not in one comprehensive study. We evaluated the relative resistance to A. mellea and A. tabescens of six clonally propagated almond and peach rootstocks (Bright’s 5, Empyrean 1, Hansen 536, Krymsk 1, Krymsk 86, and Lovell) in comparison with that of clonally propagated Marianna 2624 rootstock (resistant control) and clonally propagated Nemaguard rootstock (susceptible control). Replicate clones used in the growth chamber assay were micropropagated and rooted in vitro before inoculating the culture medium with Armillaria spp. At 2 months, the most resistant and susceptible rootstocks were Krymsk 86 and Hansen 536, respectively, with 27% vs. 89% mortality. This finding was consistent among two isolates of A. mellea and one isolate of A. tabescens in three replicate experiments. Our finding of low mortality among Krymsk 86, Krymsk 1, and Marianna 2624, which all share Prunus cerasifera (Myrobalan plum) parentage, is consistent with past reports of resistance in the field to A. mellea, but conflicts with reports of susceptibility to A. tabescens. Resistance to A. tabescens of genotypes with Myrobalan plum parentage in our assay may reflect the simplified rooting environment of tissue culture medium, which does not perfectly mimic a field trial, in which biotic and abiotic factors may affect host resistance. Nonetheless, our growth chamber assay may provide a more rapid alternative to identify sources of resistance for breeding and to screen progeny of such crosses.

Biological control of leaf disease of barley with Bacillus strain

A new Bacillus amyloliquefaciens subsp. plantarum strain IMV B-7404 was selected by an in-vitro agar plate assay as a potential biological control agent. The strain strongly inhibited the growth of 12 important plant pathogenic fungi. In growth chamber assays, the severity of spot blotch of barley decreased when culture filtrate was applied on leaves or was introduced into the plant growth medium before fungal inoculation. Apparently, the metabolites of strain IMV B-7404 play a role in disease prevention, which indicates that the strain can stimulate induced systemic resistance (ISR). When the cell suspension was sprayed onto leaves, the disease severity depended on environmental and, probably, some other conditions. We suggest that effective biological control by Bacillus-based products depends on spraying leaves with the cell suspension to co-ordinate with the process of plant infection by the pathogen. The ecological behaviour and biology of both the antagonist and the target pathogen are the key elements in enhancing the efficacy of biocontrol products. It is necessary to know the stage of infection that is most vulnerable. This information needs to be identified individually for each pathosystem and in relation to environmental conditions.

Biological activity of the lipopeptide-producing Bacillus amyloliquefaciens PGPBacCA1 on common bean Phaseolus vulgaris L. pathogens

Bacillus amyloliquefaciens PGPBacCA1 was studied regarding its aptitude to protect common bean seeds from their intrinsic pathogens. Also, the inhibition of different environmental phytopathogenic fungi was tested. Two cultivars of Phaseolus vulgaris L. were evaluated: cv. Nag (black bean) and cv. Alubia (white bean). Aspergillus spp., Penicillium spp. and Fusarium spp. constituted the natural fungal biota of both seeds, whereas white bean and black bean also exhibited Cladosporium spp. and Rhizopus spp., respectively. B. amyloliquefaciens PGPBacCA1 prevented the development of the endophytic fungi of black bean, while only Cladosporium spp. survived in the white variety. Growth chamber assays were carried out and bacilli cells were applied on seeds without affecting neither the vigor nor the germination potential of either type of bean. In addition, B. amyloliquefaciens PGPBacCA1, by dual cultures, was able to inhibit the development of the following phytopathogenic fungi: Sclerotium rolfsii (35%), Sclerotinia sclerotiorum (76.5%), Rhizoctonia solani (73%), Fusarium solani (56.5%), and Penicillium spp. (71.5%). The UV-MALDI TOF MS analysis showed that B. amyloliquefaciens PGPBacCA1 co-produces different homologues of the lipopeptides surfactin, iturin and fengycin in the presence of S. sclerotiorum and F. solani. These compounds were identified as the main responsible for the antagonistic effect. SEM analysis confirmed the antifungal effects of the lipopeptides, which also caused damage to chlamydospores and sclerotia of Fusarium and Sclerotinia, respectively. B. amyloliquefaciens PGPBacCA1 can thus be applied to these bean seeds varieties as a potential bioprotection agent.