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Chilli is an important commercial crop affected by many pathogens causing pre-emergence and post- emergence damping-off, die-back and wilt to an extent of 62 per cent in seedling stage. Survey was conducted in North-Eastern Karnataka to assess the incidence and severity of seedling diseases of chilli and the results revealed that the maximum incidence was noticed in Ballari district with 32.07 per cent and during the survey the major diseases such as damping-off caused by Fusarium oxysporum and die-back caused by Colletotrichum capsici were noticed. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of the location of the pathogen inoculum on damage caused by Globisporangium (syn. Pythium) ultimum, Fusarium culmorum and Rhizoctonia solani in pot tests with maize. For this purpose, pathogen inoculum was added to potting substrate, and the resulting mix was used to fill the whole pot volume, the upper half, or the lower half of pots. The remaining volume was filled with non-inoculated substrate. In a second experimental approach, maize seeds were germinated in non-inoculated potting substrate and the seedlings were transferred to inoculated substrate. The seeds were untreated, treated with the chemical thiram, or treated with a bacterial or a fungal biocontrol agent. With each of the pathogens, the damage to the developing maize seedlings was the strongest when the seeds germinated in the inoculated potting substrate. When only the roots were in contact with the inoculum, there was limited damage by R. solani and F. culmorum, and no damage by G. ultimum. This implies that in experiments with artificial inoculation, the seeds should always be in immediate contact with the inoculum if a strong pathogenic effect is desired. Conversely, seed treatments must, in the first place, be able to protect the spermosphere, while the requirement to protect the roots at a distance from the seed seems to depend on the pathogen. [ABSTRACT FROM AUTHOR]

Aims: To isolate and characterize fungi associated with diseased soybean seedlings in Midwestern soybean production fields and to determine the influence of environmental and edaphic factors on their incidence. Methods and Results: Seedlings were collected from fields with seedling disease history in 2012 and 2013 for fungal isolation. Environmental and edaphic data associated with each field was collected. 3036 fungal isolates were obtained and assigned to 76 species. The most abundant genera recovered were Fusarium (73%) and Trichoderma (11.2%). Other genera included Mortierella, Clonostachys, Rhizoctonia, Alternaria, Mucor, Phoma, Macrophomina and Phomopsis. Most recovered species are known soybean pathogens. However, non‐pathogenic organisms were also isolated. Crop history, soil density, water source, precipitation and temperature were the main factors influencing the abundance of fungal species. Conclusion: Key fungal species associated with soybean seedling diseases occurring in several US production regions were characterized. This work also identified major environment and edaphic factors affecting the abundance and occurrence of these species. Significance and Impact of the Study: The identification and characterization of the main pathogens associated with seedling diseases across major soybean‐producing areas could help manage those pathogens, and devise more effective and sustainable practices to reduce the damage they cause. [ABSTRACT FROM AUTHOR]

Black root rot disease of cotton seedlings caused by Thielavioposis basicola was first reported in New South Wales (NSW), Australia in 1990. In 2018, T. basicola was reclassified into a new genus Berkeleyomyces, accommodating two closely related species: B. basicola and B. rouxiae. However, species status of cotton-T. basicola in NSW remains unsolved. Ninety-five isolates recovered from black root rot diseased cotton seedlings sampled across NSW in 2017/18 season was subjected to morphological, multigene sequencing (ITS, MCM7, RPB2), and pathogenicity assessments for their species identification. Berkeleyomyces rouxiae was accurately identified as the causal agent of black root rot of cotton. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of the location of the pathogen inoculum on damage caused by Globisporangium (syn. Pythium) ultimum, Fusarium culmorum and Rhizoctonia solani in pot tests with maize. For this purpose, pathogen inoculum was added to potting substrate, and the resulting mix was used to fill the whole pot volume, the upper half, or the lower half of pots. The remaining volume was filled with non-inoculated substrate. In a second experimental approach, maize seeds were germinated in non-inoculated potting substrate and the seedlings were transferred to inoculated substrate. The seeds were untreated, treated with the chemical thiram, or treated with a bacterial or a fungal biocontrol agent. With each of the pathogens, the damage to the developing maize seedlings was the strongest when the seeds germinated in the inoculated potting substrate. When only the roots were in contact with the inoculum, there was limited damage by R. solani and F. culmorum, and no damage by G. ultimum. This implies that in experiments with artificial inoculation, the seeds should always be in immediate contact with the inoculum if a strong pathogenic effect is desired. Conversely, seed treatments must, in the first place, be able to protect the spermosphere, while the requirement to protect the roots at a distance from the seed seems to depend on the pathogen.

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Pythium isolates from diseased and dead bait plants of maize and cress grown in compost or various soils (maize fields, parkland under deciduous trees, grassland) were characterised and tested for pathogenicity to maize (Zea mays L.). In pot tests performed under controlled conditions, pathogenicity of the isolates to maize was apparent by reduction of root and shoot growth, whereas damping-off of maize seedlings was less frequent. Contrarily, pea seedlings were killed by pathogenic Pythium isolates. Pythium isolates from diseased maize seedlings and pathogenic strains from other gramineous plants (P. phragmitis, P. aff.phragmitis, P. catenulatum) were not necessarily more virulent to maize compared to isolates originating from dicotyledonous plants (cress). The most virulent isolates originated from compost and caused a reduction of maize shoot growth of up to 60%. Phylogenetic analysis revealed that they were very closely related to P. ultimum var. ultimum and P. arrhenomanes, respectively. Isolates originating from maize fields, grassland and parkland under deciduous trees, a reference culture of P. arrhenomanes and strains of P. phragmitis, P. aff. phragmitis and P. catenulatum with known pathogenicity on reed were non-pathogenic on maize. Isolates from compost, and from maize fields generally had a higher temperature optimum for mycelial growth (30 °C) and a faster growth rate (1.5–2.0 mm h−1) compared to the isolates from parkland under deciduous trees and grassland soil (20–25 °C, ~1.0 mm h−1), respectively. This study indicates a potential impact of pathogenic Pythium on maize plants even in the absence of visible symptoms. [ABSTRACT FROM AUTHOR]

Cotton is a billion-dollar crop in Australia, especially in the regional areas of New South Wales (NSW) and Queensland. Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (Fov) is of an important disease on cotton globally and in Australia. The Australian cotton industry is currently adopting highly resistant cultivars to Fov. Therefore, it is expected that Fusarium wilt pressure will be minimal on the cotton crop. However, we recovered a total of 186 putative Fusarium isolates from cotton seedlings exhibiting atypical symptoms of either Fusarium damping-off or Fusarium wilt sampled across NSW during the 2017/18 and 2018/19 seasons. On a basis of sequence analysis of the translation elongation factor 1-alpha (TEF1), eight Fusarium species were identified that being Fusarium oxysporum and F. equiseti species complex, F. falciforme, F. nygamai, F. brachygibbosum, F. acuminatum, F. chlamydosporum, and F. redolens. Of these, F. oxysporum species complex (FOSC) accounted for over 80% of the total number of isolates recovered. The predominant number of isolates (78.5%) were clustered with non-Australian Fov races 1–8. The remaining 21.5% of the FOSC isolates in our study was clustered with the Australian Fov biotypes, a unique phylogenetic group within the FOSC. Our study is the first TEF1-based assessment of Fusarium diversity associated with collar rot diseased cotton seedlings sampled across NSW, Australia. [ABSTRACT FROM AUTHOR]

Buckwheat is a rapidly growing cover crop with the potential to improve soil quality and health. In this study, the impact of buckwheat plant material (BPM) as a soil amendment on seedling emergence and suppression of damping-off and root rot of radish (Rhizoctonia solani) and cucumber (Pythium ultimum) was investigated in pot assays. Fresh BPM grown in a greenhouse potting mix for 4 weeks was chopped in small 1-2 cm long pieces and incorporated into field soil containing 0-10% of R. solani or P. ultimum inoculum produced on sterilized rye seed. The infested soil was then incubated for 0-8 weeks prior to planting radish or cucumber seed. The effects of BPM on plant growth and disease development were determined 2 weeks after planting. There was no disease protection if radish and cucumber seeds were planted within 1-2 weeks after soil incorporation of BPM. Disease protection was evident when planting was delayed for 3 weeks after BPM amendment to soil. BPM soil amendment provided protection of radish plants from Rhizoctonia damping-off and protection of cucumber plants from Pythium damping-off and root rot. BPM amendments had no effect on promoting plant growth but slightly increased soil pH. In amended soil receiving 4% and 10% of BPM planted with radish or cucumber seeds 0, 3 and 8 weeks later, total populations of indigenous fungi were 0.66-2.01 log units higher and bacteria were 0.53-0.92 log units higher compared with the populations in the non-amended soils. Buckwheat soil amendment offers a potential option to improve plant and soil health. [ABSTRACT FROM AUTHOR]

Cotton is an economically important crop worldwide that suffers severe losses due to a wide range of fungal/bacterial pathogens and nematodes. Given its susceptibility to various pathogens, it is important to obtain a broad-spectrum resistance in cotton. Resistance to several fungal and bacterial diseases has been obtained by overexpressing the Non-expressor of Pathogenesis-Related genes-1 ( NPR1) in various plant species with apparently minimal or no pleiotropic effects. We examined the efficacy of this approach in cotton by constitutive expression of the Arabidopsis ( Arabidopsis thaliana) NPR1 gene. The results show that NPR1-expressing lines exhibited significant resistance to Verticillium dahliae isolate TS2, Fusarium oxysporum f. sp . vasinfectum, Rhizoctonia solani, and Alternaria alternata. Interestingly, the transformants also showed significant resistance to reniform nematodes. Analysis of defense-related, biochemical and molecular responses suggest that when challenged with pathogens or certain systemic acquired resistance-inducing chemicals, the transgenic lines respond to a greater degree compared to the wild-type plants. Importantly, the basal activities of the defense-related genes and enzymes in uninduced transformants were no different than those in their non-transgenic counterparts. The results provide additional evidence supporting the role of NPR1 as an important part of the plant defense system and suggest a means to achieve broad-spectrum resistance to pathogens via genetic engineering. [ABSTRACT FROM AUTHOR]

The biocontrol efficacy of Bacillus amyloliquefaciens FS6 against seedling diseases and gray mold of ginseng ( Panax ginseng ), as well as application techniques, were evaluated in a series of field trials. FS6 fermentation broth showed a strong antagonistic effect against the ginseng fungal pathogens, and the inhibition rates on mycelial growth and spore germination were 84 to 88% and 71 to 72%, respectively. Field evaluation showed that combination of seed and soil treatments exhibited better protection than that of individual treatment alone. FS6 wettable powder soil treatment in combination with thiamethoxam plus metalaxyl-M plus fludioxonil for seed coating performed the best, with >83% overall control efficacy for seedling diseases. FS6 had a long-acting effect of >78% control efficacy on ginseng gray mold at 30 days after the last application, almost 2.5- and 2-fold better than that of B . amyloliquefaciens B7900 wettable powder and cyprodinil, respectively. In addition, FS6 reduced the diversity and relative abundance of fungi and affected the fungi and bacterial composition in the rhizosphere soil of ginseng. Therefore, FS6 can be used to effectively control seedling diseases and gray mold in ginseng.

During August and September 2020, symptoms of leaf chlorosis, stunting, and wilting were observed on indoor hemp plants (Cannabis sativa L. cv. 'Wedding Cake') in a commercial indoor facility located in Coolidge, Arizona. Plants were grown in soilless coconut coir growing medium (Worm Factory COIR250G10), watered with 1.5 to 2.1 liters every 24 h through drip irrigation, and supplemented with 18 h of lighting. About 35% of plants displayed symptoms as described above and many symptomatic plants collapsed. To identify the causal agent, crown and root tissues from four symptomatic plants were harvested and rinsed with tap water. Tissue fragments (approx. 2 to 4 mm in size) were excised from the margins of the stem and root lesions, surface sterilized in 0.6% sodium hypochlorite for 1 min, rinsed well in sterile distilled water, blotted dry, and plated on potato dextrose agar (PDA) and on oomycete-selective clarified V8 media containing pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP). Plates were incubated at room temperature (21-24 oC). Five isolates resembling Pythium were transferred after 3 days and maintained on clarified V8 media. Morphological characteristics were observed on grass blade cultures (Waterhouse 1967). Grass blades were placed on CV8 inoculated with the isolate. After a 1-day incubation at 25°C, the colonized blades were transferred to 8 ml of soil water extract in a Petri dish. Ten sporangia and oogonia were selected randomly and their diameters were measured under the microscope. Sporangia were mostly filamentous, undifferentiated or inflated lobulate, ranging from 7 to 17 µm in diameter. Knob-like appressoria were observed on branching clusters. Bulbous-like antheridia were formed on branched stalk with 1-8 antheridia per oogonium. Globose oogonia were terminal or intercalary and ranged from 21 to 33 µm in diameter. Globose oospores were mostly aplerotic and ranged from 15 to 21 μm in diameter. Based on these morphological characteristics, isolates were tentatively identified as Pythium myriotylum (Watanabe, 2002). Genomic DNA was extracted from mycelial mats of two isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and two identical nucleotide sequences were obtained and deposited under accession number MW380925. A BLASTn search revealed ≥ 98% query coverage and 100% match with sequences HQ237488.1, KY019264.1, and KM434129, which were isolates of P. myriotylum from palm, tobacco, and ginger, respectively. To fulfill Koch's postulates, pathogenicity tests were conducted with 2 isolates using plants of 'Wedding Cake' grown in 12 1.9-liter pots filled with a steam-disinfested potting mix (Sungro Professional Growing Mix). Pots were placed in a plastic container and watered to flooding three times a week. Plants were maintained in a greenhouse with 18 h/10 h day/night supplemental light cycle (15-28 oC). Plants were fertilized weekly with Peters Professional fertilizer at 1mg/ml. Four plants were inoculated with each isolate at three weeks after seed sowing by placing two 5-mm mycelial plugs from active growing 4 days-old cultures on PDA media adjacent to the main root mass at an approximately 3 cm depth. Four plants were inoculated with blank PDA plugs as controls. Symptoms of leaf chlorosis, crown rot and wilting were observed after four weeks while control plants remained symptomless. P. myriotylum was re-isolated from necrotic roots of inoculated plants after surface-sterilization, but not from control plants. The pathogenicity test was repeated once. While P. myriotylum often occurs in warmer regions and has a wide host range of >100 host plant species including numerous economically important crops (Wang et al., 2003), there are only two reports of this pathogen on indoor hemp plants in a greenhouse in Connecticut (McGehee et al., 2019) and in Canada (Punja et al., 2019). This is the first report of P. myriotylum causing root and crown rot of indoor hemp in Arizona. A more careful water management in soilless growth medium to reduce periods of saturation would minimize the risk of Pythium root rot in indoor hemp production.

Sudden death syndrome (SDS) caused by Fusarium virguliforme is among the most important diseases affecting soybean in the United States. The use of biological control agents (BCAs) such as Trichoderma spp. can be a valuable resource to suppress F. virguliforme populations. Therefore, this research focused on screening possible BCAs against F. virguliforme and evaluating mycoparasitism and the induction of systemic resistance as mechanisms underlying the antagonistic activity of selected BCAs against F. virguliforme. In total, 47 potential BCAs, including 41 Trichoderma isolates and 6 Mortierella isolates, were screened in a dual-plate assay. The most effective isolates belonged to the Trichoderma harzianum species and were able to inhibit F. virguliforme radial growth by up to 92%. Selected Trichoderma isolates were tested in the greenhouse and in a microplot study. They reduced root rot caused by F. virguliforme when the plants were coinoculated with the pathogen and the BCA. The tested BCA's ability to reduce F. virguliforme growth may be related to several mechanisms of action, including mycoparasitism and induction of defense-related genes in plants, as revealed by monitoring the expression of defense-related genes in soybean. Our results highlight the potential of native Trichoderma isolates to inhibit F. virguliforme growth and reduce SDS severity, providing the basis for future implementation of biological control in soybean production. More efforts are needed to implement the use of these approaches in production fields, and to deepen the current knowledge on the biology of these highly antagonistic isolates.

Corn and soybean have been rotated for decades in the north central regions of the United States, but it is unknown how the use of long-term rotation affects the population of soilborne fungi pathogenic to both crops. Pythium populations were obtained from 73 commercial corn-soybean rotation fields in Iowa from 1993 to 1995. A total of 163 Pythium isolates were obtained from soil, diseased soybean seedlings, or diseased corn seedlings, and these isolates were pooled into six populations according to the source of samples. The isolates were evaluated for their aggressiveness on corn and soybean for each population. Regardless of the source of sampling, each population had many Pythium isolates that were highly aggressive on both crops. Seventy-one percent of the isolates from soil were pathogenic, and 29% were highly aggressive on both crops. Three populations of Pythium isolates were obtained from diseased soybean seedlings. Eighty-five percent of those isolates were pathogenic, and 49 to 64% were highly aggressive on corn and soybean. Of the isolates obtained from diseased corn seedlings, 87% were pathogenic and 43% were highly aggressive on corn and soybean. For each Pythium population, aggressiveness on soybean and corn (measured by disease index) were highly correlated. Further, 23 P. ultimum isolates were identified from diseased soybean seedlings and tested for pathogenicity on corn and soybean. Disease index of the isolates varied, but the correlation between disease indices on the two crops was significant (r = 0.75, P < 0.001). The study suggests that long-term corn-soybean rotation fields contain many Pythium isolates that are highly aggressive on seedlings of both crops.