Characterizing members of the Cladosporium cladosporioides species complex as fruit rot pathogens of red raspberries in the mid-Atlantic and co-occurrence with Drosophila suzukii (spotted wing drosophila)

摘要

Fruit rot, primarily caused by Botrytis cinerea, is a major driver of pre- and post-harvest yield losses in fall red raspberries in the Mid-Atlantic. Recent observations indicate that Cladosporium fruit rot may also reduce yields. In a two-year survey of two Maryland farms, 1-30% of fall-bearing red raspberry fruit exhibited Cladosporium fruit rot (CFR) symptoms pre-harvest and symptoms developed post-harvest in 16% of fruit harvested when under-ripe and 51% of fruit harvested red ripe. Cladosporium cladosporioides and C. pseudocladosporioides were identified based on BLAST analysis of TEF-1 alpha and actin gene regions, but determinations against voucher specimen sequences were not always congruent with phylogenetic analyses; sequences from many isolates matched C. anthropophilum voucher sequences still labeled as C. cladosporioides. Isolates of all three species caused fruit rot on non-wounded drupes (33-66%) and incidence increased when drupes were wounded (50-100%) (P<0.05). In the field, 21-33% of CFR-affected fruit were infested with D. suzukii larvae; Cladosporium propagules were recovered from frass of 25-71% of larvae and determined to be C. cladosporioides or C. pseudocladosporioides, conspecific with fruit-derived isolates. Further, frass-derived isolates of both species initiated rot, with similar incidence to raspberry-derived isolates (P>0.05). This first description of Cladosporium fruit rot of red raspberry in the Mid-Atlantic provides an expansive perspective on CFR pre- and post-harvest biology as well as pathogen diversity. Several lines of evidence point to linkages between CFR and D. suzukii epidemiology which require further exploration.