Pythium spp. cause seed decay, damping-off, and root rot in soybean and corn; however, their diversity and importance as pathogens in Minnesota are unknown. Our objectives were to identify the Pythium spp. present in Minnesota soybean fields, determine their aggressiveness on corn and soybean, and investigate their sensitivity to seed treatment fungicides. For identification, sequences obtained using internal transcribed space ITS4 and ITS1 primers were compared with reference sequences in the National Center for Biotechnology Information database. Seedling and soil samples yielded over 30 oomycete species. Aggressiveness was determined using two methods; a seed assay, which also examined temperature effects on aggressiveness, and a seedling assay. Of 21 species evaluated, seven Pythium spp. were pathogenic on both soybean and corn, reducing root growth by 20% or more while two Pythium and one Phytopythium spp. were pathogenic only on soybean. Aggressiveness of many isolates increased as temperature increased from 15°C to 25°C. The sensitivity of 10 pathogenic species to azoxystrobin, ethaboxam, mefenoxam, pyraclostrobin, or trifloxystrobin was tested. EC50 values for mefenoxam and ethaboxam were 10-2 of those to strobilurin fungicides. Pythium spp. in Minnesota are diverse and a significant cause of seedling disease on soybean and corn. Most Pythium spp. isolated in this study were more sensitive to mefenoxam and ethaboxam than to strobilurin fungicides.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-02-16-0196-RE

Pythium, Phytophthora, and Phytopythium spp. Associated with Soybean in Minnesota, Their Relative Aggressiveness on Soybean and Corn, and Their Sensitivity to Seed Treatment Fungicides.

Fusarium head blight (FHB) is a major fungal disease that contributes to severe economic losses for wheat and barley production in Canada and other parts of the world. Rapid developments in molecul...

Building on a foundation: advances in epidemiology, resistance breeding, and forecasting research for reducing the impact of fusarium head blight in wheat and barley

Fusarium spp. associated with fusarium head blight (FHB) on cereals in Ontario was monitored in this study. Nine species were recovered from 24 300 putatively infected kernels collected from 486 af...

Prevalence of Fusarium species causing head blight of spring wheat, barley and oat in Ontario during 2001–2017

Species composition, toxigenic potential and aggressiveness of Fusarium isolates causing Head Blight of barley in Uruguay.

Root rot diseases remain a major global threat to the productivity of agricultural crops. They are usually caused by more than one type of pathogen and are thus often referred to as a root rot complex. Fungal and oomycete species are the predominant participants in the complex, while bacteria and viruses are also known to cause root rot. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to counter root rot, however, resistance is often quantitative in nature. Several genetics studies in various crops have identified the quantitative trait loci associated with resistance. With access to whole genome sequences, the identity of the genes within the reported loci is becoming available. Several of the identified genes have been implicated in pathogen responses. However, it is becoming apparent that at the molecular level, each pathogen engages a unique set of proteins to either infest the host successfully or be defeated or contained in attempting so. In this review, a comprehensive summary of the genes and the potential mechanisms underlying resistance or susceptibility against the most investigated root rots of important agricultural crops is presented.

https://www.preprints.org/manuscript/202012.0681/v1/download

Understanding Root Rot Disease in Agricultural Crops

The pathogenicity of eight Fusarium species causing fusarium head blight (FHB) in barley was studied under controlled conditions. Six barley genotypes varying in resistance to FHB were artificially inoculated with six isolates each of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. poae and F. sporotrichioides 10-14 d after heading. Symptoms of FHB were rated as disease severity using a 0-9 scale, 4, 7, 14, 21 and 28 d after inoculation, and as percentage of infected spikelets (IS) after 21 d. All species tested caused head blight symptoms on the barley genotypes, but only F. crookwellense, F. culmorum and F. graminearum resulted in severe disease development (> 65% IS) and were considered highly pathogenic. Fusarium avenaceum had 48% IS, which was significantly lower than those of the three highly pathogenic species and was moderately pathogenic. The remaining species had < 15% IS and were weakly pathogenic. There were significant differences (P < 0.05) in aggressiveness among isolates within species and in susceptibility among barley genotypes, suggesting that screening for resistance to FHB requires the use of aggressive isolates or a mixture of several isolates. This is the first report showing that F. crookwellense is highly pathogenic and F. avenaceum is moderately pathogenic on barley.

/pdf/pathogenicity-of-fusarium-species-causing-head-blight-in-3qnr2k69mj.pdf

Pathogenicity of Fusarium species causing head blight in barley

Collections containing microbes (often referred to as “culture collections”) and collections of seeds or clonal materials for higher plants (often referred to as “germplasm collections”) can provide abundant resources for plant pathologists, breeders, geneticists, and other plant science professionals. However, many such professionals (including graduate students, postdoctoral fellows, and technical staff) lack adequate guidance on locating, obtaining, and processing such materials. Regulatory procedures and considerations of biological security, ambiguities regarding intellectual property rights, lack of knowledge about collection databases, and other hurdles dissuade many professionals from effectively exploiting collection resources. The Collections and Germplasm Committee of the American Phytopathological Society, together with colleagues from international collections and the World Federation of Culture Collections, has assembled this guide summarizing the benefits and utilization of living collections for plant pathology. We show how to locate major and minor collections, obtain biological materials, and comply with regulatory and shipping requirements. We briefly discuss the relevance of intellectual property rights, the problem of endangered collections (especially those with invaluable and irreplaceable materials), and make specific recommendations for the support of living collections. Prior reviews of culture collections originated from diverse perspectives. Examples from an extensive literature are quality control and preservation (27,41, 47,54,68), taxonomy and research (13,26), organizations, legislation, and regulation (77), relevance to plant pathology and other disciplines (51,52,73), and genomics (50,68). Capsule histories of several culture collections, plus extensive lists of associated databases, are available (50). Public seed banks have been subjected to similar review. The USDA-Agricultural Research Service National Plant Germplasm System (NPGS) was the subject of detailed reporting, covering history (66,83), management (16), quality control and preservation (10,65,82), structure (1,16,86), personnel (86), information technology (53,67), conserved species (38,66), collecting of germplasm (58,84), and examples of associated research (86). For Canada, the locations and holdings of seed banks and clonal repositories were reviewed, and instructions were provided for online viewing and ordering of holdings (8). Earlier, multifaceted reviews (7,9) gave a worldwide perspective on plant germplasm. The fiscal health of collections has been the subject of repeated reviews (or perhaps more accurately, laments) and news items (2,11,73). Although we firmly acknowledge the importance of nonliving collections (museums and herbaria), we have chosen to restrict our discussion to collections of living materials. Readers wishing to learn more about herbaria and other nonliving collections are referred to other sources (37,46,87). Here, we concentrate on collections containing organisms that can be maintained in refrigerated conditions (as with many seeds or clonal stocks of higher plants) or grown in culture and then lyophilized or kept in cryogenic storage at ultra-low temperatures (as with many microorganisms). Some obligate parasites or symbionts are also kept in collections (e.g., plant viruses, vesicular-arbuscular mycorrhizal fungi and rusts), either in cryogenic storage or by maintaining them on their plant hosts.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-91-5-0476

Plant Germplasm Centers and Microbial Culture Collections: A User's Guide to Key Genetic Resources for Plant Pathology.

Pythium species cause seed rot (SR) and damping-off (DO) in soybean worldwide. In a previous study, a number of Pythium species were isolated from infected soybean plants across Ontario and Quebec, but their comparative pathogenicities to soybean were not examined. In the present research, 24 isolates from eight Pythium spp. were evaluated for their pathogenicity in causing soybean SR and DO in a greenhouse environment. The effect of temperature on the ability of these isolates to cause SR was also studied. There were significant differences among the eight Pythium spp. for both SR and DO. When tested at 25°C, Pythium ultimum was the most pathogenic species, causing 97.0% SR and 46.4% DO, on average, in the two soybean cultivars used. Pythium aphanidermatum was the second most pathogenic species, resulting in 88.5% SR and 41.8% DO. The two species resulted in significantly greater SR and DO than the other six species tested and were considered highly pathogenic. Of the two cultivars used in these trials, ‘Beechwood’ was significantly more susceptible than ‘Nattawa’ to both SR and DO. Temperature had a significant influence on SR caused by Pythium spp. At all four temperatures tested (4°C, 12°C, 20°C and 28°C), P. ultimum was highly pathogenic, while P. arrenomanes, P. coloratum and P. dissotocum were the least pathogenic. The interactions between temperature and Pythium spp. were more pronounced for P. aphanidermatum, which showed an increased percentage of SR with an increase in temperature, and for P. irregulare, P. macrosporum and P. sylvaticum, which showed a decreased percentage of SR with an increase in temperature.

/pdf/pathogenicity-of-pythium-species-causing-seed-rot-and-12x3o6jdai.pdf

Pathogenicity of Pythium species causing seed rot and damping-off in soybean under controlled conditions

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Pathogenicity of Fusarium species causing head blight in barley

Plant Germplasm Centers and Microbial Culture Collections: A User's Guide to Key Genetic Resources for Plant Pathology.

Pathogenicity of Pythium species causing seed rot and damping-off in soybean under controlled conditions