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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT

Location: Fruit and Nut Research

Title: Genetic diversity and population structure of Fusicladium effusum on pecan in the U.S.A.

Authors
item Bock, Clive
item Wood, Bruce
item Stevenson, Katherine -
item Arias De Ares, Renee

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 17, 2014
Publication Date: January 17, 2014
Citation: Bock, C.H., Wood, B.W., Stevenson, K.L., Arias De Ares, R.S. 2014. Genetic diversity and population structure of Fusicladium effusum on pecan in the U.S.A.. Plant Disease. 98:916-923.

Interpretive Summary: Fusicladium effusum causes pecan scab, which is the most destructive disease of pecan in the U.S.A. The disease is known to be spread through asexually produced conidia in rain splash and wind. The fungus is pathogenically diverse, yet there is no information on its genetic diversity or population genetics. Molecular markers were used to investigate the genetic diversity and population structure on a hierarchical sample of 194 isolates collected from 11 orchard locations from Florida to Texas. Genetic variation was high throughout the region, with all but 9 of genotypes being unique. Genetic diversity was similar in all populations. An analysis of molecular variance found that the majority of the genetic variability (82.6%) occurred at the scale of the individual tree and only relatively small amounts among populations in trees from an orchard (5.0%) or within groups (12.5%). These results suggested that there is little population differentiation in F. effusum in the southeastern U.S.A. The genetic diversity and the scale over which the diversity is distributed is evidence that F. effusum undergoes regular recombination despite no known sexual stage.

Technical Abstract: Fusicladium effusum causes pecan scab, which is the most destructive disease of pecan in the U.S.A. The disease is known to be spread through asexually produced conidia in rain splash and wind. The fungus has demonstrated pathogenic diversity, yet there is no information on its genetic diversity or population genetics. Universally Primed-PCR (UP-PCR) was used to investigate the genetic diversity and population structure on a hierarchical sample of 194 isolates collected from 11 orchard locations from Florida to Texas, consisting of 3 to 4 isolates from each of 5 to 6 trees at each location. Genetic variation was high throughout the region, with all but 9 of the multilocus haplotypes being unique. Nei’s average gene diversity ranged from 0.083 for a population from Mississippi to 0.160 for a population from Kansas. An analysis of molecular variance of the hierarchically sampled populations found that the majority of the genetic variability (82.6%) occurred at the scale of the individual tree and only relatively small amounts among populations in trees from an orchard (5.0%) or within groups (i.e., orchard location populations) (12.5%). These results suggested that there is little population differentiation in F. effusum in the southeastern U.S.A., although fpt values of genetic distance for pairwise comparisons indicated that some populations could be differentiated. There was evidence of linkage disequilibrium in some populations, and the common occurrence of asexual reproduction in F. effusum could lead to measurable linkage disequilibrium under certain circumstances. However, the genetic diversity, and the scale over which the diversity is distributed is evidence that F. effusum undergoes regular recombination despite no known sexual stage.

Last Modified: 8/29/2014
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