Role of Infested Seed as Primary Inoculum for Cercospora Leaf Spot in Table Beet.

Abstract

Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is an important determinant of table beet foliar health. Primary inoculum sources include infested crop residues and alternative hosts, but seed-to-seedling transmission has also been reported. We evaluated the localization of C. beticola in table beet seeds and contribution of infested seeds to CLS outbreaks in field studies. In seed dissection experiments, C. beticola was more frequently isolated from the pericarp (95.6%) and operculum (30.4%) compared to the true seed (17.4%). Field trials in Geneva and Freeville had significantly higher CLS incidence, severity, and disease progress in plots established from an infested seed lot than those from a noninfested lot. C. beticola populations collected from infested seeds and field plots were genotyped using 11 microsatellite markers. The population from plants grown from an infested seed lot exhibited high genotypic diversity, mating type equilibrium, and linkage equilibrium, suggesting random mating. Two clonal lineages of C. beticola were identified. Populations from infested seeds and from plants that grew in plots planted with infested seed grouped into cluster 1, while cluster 2 contained populations from plants that grew in plots planted with noninfested seed. The C. beticola population not associated with genotypes from the infested seed in NY was dominated by a few multilocus genotypes and was genetically distinct from the infested seed lot population. Our findings highlight the potential of C.beticola-infested seed as a primary inoculum source.