Location: Southern Horticultural ResearchTitle: Variability of United States isolates of Macrophomina phaseolina based on simple sequence repeats and cross genus transferability to related Botryosphaeraceae) Author
Submitted to: Mycopathologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2010
Publication Date: 3/30/2010
Citation: Baird, R., Mcneil, D., Wadl, P.A., Trigiano, R.N., Allen, T., Shier, T., Wang, X., Rinehart, T.A., Abbas, H.K., Moulton, J.K. 2010. Variability of United States isolates of Macrophomina phaseolina based on simple sequence repeats and cross genus transferability to related Botryosphaeraceae. Mycopathologia. 170(3):169-80. Interpretive Summary: The charcoal rot fungus, Macrophomina phaseolina occurs worldwide and is the most economically important fungal pathogen on a wide host range of plants including agricultural crops such as cotton and soybeans. The pathogen was reported to infect about 500 plant species in more than 100 families. In the United States, annual yield losses for crops such as soybean exceeded more than 1,000 metric tons due to infection with M. phaseolina. Disease severity for the pathogen varies depending upon environmental conditions during each growing season on all susceptible crops. Better understanding of M. phaseolina population diversity within states and regions of the United States (U.S.) will assist breeders in optimization of breeding studies to enable long-term resistance over broader geographical area. Therefore, the objectives of this study were to evaluate the genetic diversity of 109 isolates collected from major geographic regions of continental U.S. and among host plants. Additionally, the cross genus transferability of SSRs to related species was evaluated.
Technical Abstract: Twelve simple sequence repeat (SSRs) loci were used to evaluate genetic diversity of 109 isolates of Macrophomina phaseolina collected from different geographical regions and host species throughout the United States (U.S.). Genetic diversity was assessed using Nei’s minimum genetic distance and the usefulness of each locus was determined by calculating the polymorphism information content (PIC). A total of 98 alleles were detected and of these 31 were unique. Eight of twelve loci were highly informative with PIC values greater than 0.50. The majority of pairwise comparisons of genetic distance were greater than 0.60 indicating moderate to high genetic diversity. Dendrograms based on the genetic dissimilarities were created for the 109 isolates of which 79 were from soybean. Some clustering by host and geography was noted, however, the dendrograms generally grouped isolates independent of host or geography. Additionally, sequencing of the internal transcribed spacer region (ITS) for 10 isolates revealed that all of these isolates were 99% similar. Three SSR loci from M. phaseolina were cross amplified in other genera in the Botryosphaeriaceae. This was the first study genotyping and assessing genetic diversity of isolates collected from a widespread host and geographic range across the US with SSRs. With an additional 34 loci publically available for M. phaseolina, the results indicate that previously developed SSRs from one species can be used in future population, ecological, and genetic studies of M. phaseolina and other genera within the Botryosphaeriaceae.