Anthracnose Fruit and Root Necrosis of Strawberry Are Caused by a Dominant Species Within the Species Complex in the United States.

Strawberry anthracnose fruit rot and root necrosis, caused by , are primary limiting factors in fruit production fields in the United States. Recent research focusing on the phenotypic and genetic characteristics of this species has shed light on the diversity of the species complex. In this study, we performed multilocus sequence analysis of four genetic loci to characterize 217 isolates collected over a 23-year period from symptomatic plant tissues of strawberry from six different states. The results revealed two spp. ( and ), with 97.7% of the isolate collection (212 of 217) belonging to as a dominant clonal linage, regardless of the isolation source. No correlation between species groups and geographical origins of the isolates was observed. Further sequence comparison between historical and contemporary isolates showed the same populations being widely distributed throughout the strawberry nurseries and production fields in the United States and Canada. Subsequently, a subset of 12 isolates representing different quinone-outside inhibitor fungicide resistance profiles from root or fruit tissue of strawberry was selected for comparison of pathogenicity on strawberry. In this test, isolates of different resistance groups or different isolation sources exhibited a similar degree of aggressiveness and caused indistinguishable symptoms on strawberry crowns ( = 0.9555 and 0.7873, respectively) and fruit ( = 0.1638 and 0.1141, respectively), although a significant difference among individual isolates was observed in detached-fruit assays ( = 0.0123). Separate pathogenicity tests using isolates of the two species revealed being more aggressive than in infecting strawberry roots and crowns ( = 0.0073). Therefore, given the occurrence and pathogenicity of , this species is likely the sole cause responsible for strawberry anthracnose in the United States.