http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Characterization of Sclerotinia minor populations in Texas
Agriculture is a crucial component of the economy of Texas with millions of pounds of peanuts, cotton, wheat, and corn produced annually. However, Texas agricultural crops are not exempt from pathogens, especially Sclerotinia minor Jagger, which was introduced into Texas approximately 25 years ago. A dramatic increase in S. minor disease incidence in the High Plains of Texas during 2004 provided the basis for this study of the pathogen populations in Texas. To characterize the S. minor populations in Texas, aggressiveness and fungicide sensitivity assays were conducted to assess phenotypic characteristics as well as the use of five microsatellite markers to genotypically characterize the pathogen. A large diversity among the populations was found for the phenotypic characteristics; however, there was no evidence that a genotypically unique, highly aggressive, and fungicide resistant "super pathogen" had been introduced or evolved. The populations of S. minor in Texas were moderately aggressive (26.15% of infected tissue), but there were also isolates found that have the inability to infect peanuts (less than 3% of infected tissue) as well as highly aggressive pathogens with theAll fungicides tested were effective in limiting the growth of the pathogen; however, there were significant differences in the effectiveness of the fungicides. Thiophanate-methyl and dichloran were the least effective fungicides in inhibiting the growth of S. minor while boscalid, iprodione, and fluazinam were the best. Fluazinam exerted the most lasting suppressive effect on pathogen. A positive correlation between aggressiveness and fungicide sensitivity to fluazinam and boscalid was found; therefore, no ecological tradeoff was found when increasing these two phenotypic characteristics. Whereas extensive genotypic diversity (50 unique genotypes) was found in Texas, the predominate pathogen was a clone. Genotype TX1 was a clone that accounted for more than 48% of genotypes in Texas populations, identified in all of the sampled counties. The index of association demonstrated that there was a lack of gene flow occurring in the S. minor populations, therefore confirming that the pathogen reproduced primarily through mycelogenic germination. ability to infect more an 55% of the leaflet surface. All fungicides tested were effective in limiting the growth of the pathogen; however, there were significant differences in the effectiveness of the fungicides. Thiophanate-methyl and dichloran were the least effective fungicides in inhibiting the growth of S. minor while boscalid, iprodione, and fluazinam were the best. Fluazinam exerted the most lasting suppressive effect on pathogen. A positive correlation between aggressiveness and fungicide sensitivity to fluazinam and boscalid was found; therefore, no ecological tradeoff was found when increasing these two phenotypic characteristics. Whereas extensive genotypic diversity (50 unique genotypes) was found in Texas, the predominate pathogen was a clone. Genotype TX1 was a clone that accounted for more than 48% of genotypes in Texas populations, identified in all of the sampled counties. The index of association demonstrated that there was a lack of gene flow occurring in the S. minor populations, therefore confirming that the pathogen reproduced primarily through mycelogenic germination.
Title from author supplied metadata (automated record created 2010-03-12 12:08:51).
Master of Science Texas A&M University 2006 http://hdl.handle.net/1969.1/ETD-TAMU-1843