Brief Summary of Minutes of Annual Meeting

Accomplishments: Objective 1. Examine commercial and non-commercial biocontrol agents for use as seed treatments, in-furrow treatments or as potting mix amendments. " Cooperative Broccoli Field Trial Project  (Canaday, Keinath, Ownley, Rothrock, Seebold). Canaday - Delays in seed germination were observed with bioactive Monarda herbage incorporated into potting soil, however, differences in growth were not observed at 41 days after seeding. Keinath  After transplantation to field soil, and artificial inoculation with Rhizoctonia solani, Rhizoctonia wirestem was greatest with the Monarda treatment. " Benson  Binucleate Rhizoctonia (BNR) isolates BNR621 and P023, and Trichoderma hamatum isolate 382 induced resistance to the foliar fungal pathogen Botrytis cinerea in geranium. " Canaday  The combination of BioYield (plant growth-promoting rhizobacteria; PGPR) and fungicide treatments with and without application of Actigard (induces systemic acquired resistance in plants) had no effect on the incidence of timber rot (Sclerotinia sclerotiorum) and buckeye rot (Phytophthora nicotianae) affecting four tomato cultivars (Mountain Fresh Plus, Nico, Amelia, Red Defender). " Canaday  The incidence of Tomato Spotted Wilt Virus was greater in Mountain Fresh Plus tomato than in Nico, Amelia, and Red Defender; however, fungal foliar diseases (early blight and Septoria leaf spot) were lowest in Mountain Fresh Plus. " Canaday  The percentage of healthy soybean plants was greatest with a seed treatment combination of the PGPR strain Bacillus subtilis MBI 600 and the fungicides mefenoxam and fludioxinil. " Canaday  The PGPR product BioYield Flowable increased head weight of broccoli cultivars, Arcadia and Packman, but had not effect on Premier Crop. " Keinath - A non-pathogenic (binucleate) Rhizoctonia isolate and BioYield Flowable significantly increased the percentage of healthy broccoli plants and reduced the number of plants with wirestem 30 days after transplanting. " Ownley  Beauveria bassiana 11-98 endophytically colonized tomato and cotton following seed treatment. The extent of colonization was dependent on seed treatment rate and host plant; i.e. the fungus was found in roots, stems and leaves of tomato but primarily in above ground tissues of cotton. " Ownley - New ITS primers were developed for detection of B. bassiana 11-98 DNA within cotton tissues without amplification of ITS sequences in cotton. " Ownley - Application of Beauveria bassiana 11-98 to seedling roots induced systemic resistance in cotton leaves against the bacterial pathogen Xanthomonas axonopodis pv. malvacearum. Objective 2. Examine the effect of cultural practices on soilborne pathogens and plant growth. " Keinath - To maximize biomass production in coastal South Carolina, Cahaba White vetch should be seeded in October or November and incorporated in January or February. " Keinath - Cahaba White vetch reduced the number of wilted seedless watermelon plants in one of two experiments. " Keinath - The plant defense activator Actigard increased the number and weight of seedless watermelons. " Rothrock  The rate of brassica green manures had a greater effect on disease severity of Rhizoctonia in impatiens and petunia, and Meloidogyne incognita in cucumber, than the source of the green manures. " Rothrock  In soils containing varying amounts of sand, infested with Meloidogyne incognita and/ or Thielaviopsis basicola, height of cotton plants was greatly reduced in the sandiest soil with both pathogens present. Thielaviopsis basicola reduced plant growth over all soil textures. " Rothrock - Pythium species were the most important pathogens in stand establishment of rice in cool/wet environmental conditions in field and controlled environmental studies based on stand response to metalaxyl seed treatment. " Westphal  In soybean monoculture no-tillage soil infested with Fusarium solani f. sp. glycines (causes sudden death syndrome; SDS) and soybean cyst nematode (Heterodera glycines), foliar symptoms of SDS were less severe in soil that had not been fumigated than in fumigated plots three years after pathogen infestation, suggesting that microbially-based soil suppressiveness had developed to these pathogens in the non-fumigated soil. " Westphal  Foliar symptoms of SDS in soybean were greater with chisel and moldboard plow tillage than with ridge tillage; yields were also improved with reduced tillage compared to intensive tillage. Objective 3. Examine the genetic diversity of Rhizoctonia solani between natural ecosystems and agricultural ecosystems. " Cubeta  A field population of R. solani anastomosis group 3 (AG-3) consisting of 59 isolates was examined to determine the genetic diversity and evolutionary history of the genetic element M2 dsRNA This genetic element is hypothesized to be associated with altering the expression of metabolic pathways involved in parasitic and saprobic activity of the fungus. Results suggest that differential selective forces of mutation and recombination have contributed to the evolution of the M2 dsRNA genome. The distinct lineages and patterns of evolution inferred with coalescent analyses were unique for the M2 dsRNA genome. " Cubeta - The M2 dsRNA genetic element was detected in representative isolates belonging to three anastomosis groups (AG) of R. solani (AG-1-IA, AG-4, and AG-6; teleomorph = Thanatephorus) and four AG of binucleate Rhizoctonia (AG-A, AG-F, AG-R, and AG-U; teleomorph = Ceratobasidium) using reverse-transcription polymerase chain reaction (PCR). Phylogenetic analysis of M2 dsRNA sequence data resulted in seven inferred haplotypes and there was no unique association with AG to support co-evolution of the M2 dsRNA haplotype within the fungal host. Based on the rooted gene genealogy inferred from coalescent analyses, the ancestral M2 dsRNA haplotype most likely evolved in R. solani AG-1-IA and has recently been acquired by isolates of Ceratobasidium. This is likely the first report of a dsRNA occurring in isolates of binucleate Rhizoctonia and other AG of R. solani. " Cubeta - Horizontal transmission of the 3.57 kb M2 dsRNA between mycelia of somatically incompatible isolates of Rhizoctonia solani AG-3, an economically important pathogen of cultivated plants in the family Solanaceae, was investigated. Nine donor isolates of R. solani AG-3 containing the M2 dsRNA were paired on potato dextrose agar with each of three different recipient isolates where the M2 dsRNA was absent. Reverse-transcription PCR (RT-PCR) was used to detect horizontal transmission of the M2 dsRNA via hyphal anastomosis from donor to recipient isolates by examining hyphal explants taken 3-cm from the hyphal interaction zone. PCR-RFLP genetic-based markers of two nuclear loci and one mitochondrial locus were used to confirm identity and transmission between donor and recipient isolates of R. solani AG-3. The frequency of transmission observed between 72 pairings of the eight donor and three recipient isolates was approximately 4% of the total pairings and differences in the phenotype of the recipient isolates after acquisition of the M2 dsRNA via horizontal transmission were observed. To our knowledge, this represents the first demonstration of transmission of dsRNA between genetically different individuals of R. solani confirmed with nuclear and mitochondrial markers. These results suggest that transmission can occur between somatically incompatible isolates of R. solani AG-3, but that maintenance of the dsRNA in the recipient isolates was not stable following repeated sub-culturing on nutrient medium. " Cubeta - The nuclear intergenic spacer (IGS) and a portion of the mitochondrial large subunit (mtLSU) ribosomal DNA (rDNA) genes from Sclerotinia minor and closely related species were amplified with PCR. The amplified products were sequenced to identify regions of polymorphism to develop oligonucleotide primers for specific amplification of S. minor. One primer (Sm-F) was designed and used with the IGS-12a primer previously developed by Carbone and colleagues for specific amplification of the IGS rDNA region of S. minor. Two additional primers (MtSm-F and MtSm-R) were developed for specific amplification of the mtLSU rDNA region of S. minor. The IGS primers amplified a 260-bp fragment from all isolates of S. minor examined, while the mtLSU primers amplified a 153-bp fragment from all but one isolate of S. minor. Both sets of primers did not amplify DNA of peanut (Arachis hypogaea), Botrytis cinerea, S. homeocarpa, S. sclerotiorum, and S. trifoliorum. The minimum concentration required for amplification of DNA of S. minor with the IGS primers ranged between 50 to 100 pg, while the minimum concentration required for amplification with the mtLSU primers ranged from 1 to 10 ng. DNA of S. minor was detected from asymptomatic and symptomatic leaflets, lateral branches, and pegs of peanut with both sets of primers, but in higher frequency with the IGS primers. Detection of S. minor with the IGS primer set was concordant with results obtained by direct isolation of the fungus from infected peanut tissue. " Rothrock  Rhizoctonia solani from anastomosis groups 4, 7, and 11, and binucleate Rhizoctonia spp. were isolated from cotton seedlings and soil from cotton-producing states participating in the National Cottonseed Treatment Program, suggesting that a diversity of Rhizoctonia isolates is present across the country. Grant Funding Relevant to Objectives " Canaday, C., A. Mengistu, M. Newman, and P. Donald. Screening of Roundup Ready Soybean Varieties and Breeding Lines for Charcoal Rot, SCN and other Yield Limiting Diseases. Amount: $26,000. Sponsor: Tennessee Soybean Promotion Board. Time: 01/01/2007  03/31/2008. " Dick, W. Graduate Fellowships in Soil Microbial Ecology and Environmental Science: Focus on Bioremediation, Biosecurity and Biogeochemical Cycling. Amount: $207,000. Sponsor: CSREES-USDA. Time: 09/01/2005 - 08/31/2008. " Ownley, B., and K. Gwinn. Integration of Beauveria bassiana and Trichoderma harzianum for Control of Soilborne Pathogens in Tomato. Amount: $6,529. Sponsor: IR-4 Biopesticide Research Program. Time: 06/30/2007  06/29/2008.