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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1843 |
| Date | 02 June 2009 |
| Creators | Henry, Merribeth Annette |
| Contributors | Kenerley, Charles M. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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