Small but significant genetic differentiation among populations ofPhyllachora maydisin the midwestern United States revealed by microsatellite (SSR) markers

Abstract

AbstractPhyllachora maydisMaubl, the causal pathogen of tar spot of corn (Zea maysL.), has emerged recently in the United States and Canada. Studies related to its genetic diversity and population structure are limited and are necessary to improve our understanding of this pathogen’s biology, ecology, epidemiology, and evolutionary potential within this region. This study developed and used 13 microsatellites (SSR markers) to assess the genetic population structure, diversity, gene flow and reproductive mode of 181P. maydissamples across five states in the Midwest U.S. The polymorphic information content (PIC) of loci ranged from 0.32 to 0.72 per locus, indicating their high utility for assessing the dynamics ofP. maydispopulations. Analysis of molecular variance (AMOVA) detected a significantly low, but statistically significant genetic differentiation (FST= 0.15) among populations, where 85% of the variance resided within populations.P. maydispopulations were highly diverse (He = 0.55), with moderate gene flow (Nm = 2.80), and showed evidence of sexual recombination (r̄d;p = > 0.001). Structure analysis showed the samples were not geographically structured but rather grouped into two genetic clusters (k =2) of severe genetic admixture suggesting possible long-distance dispersal of aerial spores or infected corn materials among the five Midwest states. Both principal coordinate analysis (PCoA) and discriminate analysis of principal component (DAPC) supported the STRUCTURE analysis of the two clusters. These 13 highly polymorphic molecular markers could be used for future investigations of this pathogen’s population dynamics within the U.S., and possibly populations outside.