Anthracnose symptoms in onions (Allium cepa L.) and celery (Apium graveolens) were observed for the first time in Michigan during the 2010 growing season. Disease symptoms were found in 37 onion and 50 celery fields during the period of 2010 through 2012. Based on colony morphology, conidial characteristics, internal transcriber spacer (ITS) and glutamine synthetase (GS) sequences and species−specific molecular markers, the causal agents were identified as Colletotrichum coccodes(on onions) and Colletotrichum acutatum (on celery). These new diseases were named onion leaf and neck anthracnose and celery leaf curl and petiole anthracnose. A total of 901 C. coccodesand 549 C. acutatum isolates were recovered from symptomatic onion and celery tissue respectively. A subsample isolates of C. coccodes (N=110) and C. acutatum (N=113) were included in population genetics studies. Four Inter−Simple Sequence Repeat (ISSR) markers banding patterns differed by Colletotrichum spp. isolated from onion and celery, and controls (C. gloeosporoides and C. dematium). Within the C. coccodes isolates the banding patterns were identical, while 4% polymorphism was observed among C. acutatum isolates. A total of 2,300 and 2,423 transcripts contained Simple Sequence Repeat (SSR) motif suitable for primer design for C. coccodes and C. acutatum respectively. Out of the primers tested, 64 and 89% amplified the expected fragment size on C. coccodes and C. acutatum DNA, respectively. No polymorphisms were observed in the SSR primers tested on C. coccodes isolates, while 12% of the primers tested in C. acutatum showed polymorphic loci.Isolates of C. coccodes and C. acutatum from onion and celery were tested for their pathogenicity and virulence. When ripe cherry tomato (Solanum lycopersicum L.) fruit were inoculated with 824 C. coccodes isolates from onion, differences in virulence were identified based on the field where they originated. When 81 C. acutatum isolates were used to inoculate ‘Green Bay’ celery seedlings, differences among isolates were found, but differences were not found among collection year, field, or county. A combination of extended high RH period (≥24h) and high temperatures (≥25°C) resulted in >20% disease severity on ‘Infinity’ onion seedlings. On celery, leaf curl and petiole lesions occurred at all temperatures (15 − 30°C) and leaf wetness duration (0 − 96h) tested. Incidence was highest when inoculated plants were subjected to an extended period of leaf wetness (96h) or at 30°C. When 16 onion cultivars were evaluated for their susceptibility to C. coccodes, disease was significantly lower in ‘Hendrix’ and higher in ‘Highlander’ and ‘Candy’. Fungicides in the strobilurin, multi−site and demethylation inhibitors groups limited disease in onion and celery. Efficacious fungicides resulted in higher marketable celery yields when compared with the untreated inoculated control. Adequate management of onion leaf and neck anthracnose and celery leaf curl and petiole anthracnose should include crop rotation, pathogen free seed, greenhouse and field sanitation, cultivar selection, and alternation of preventative efficacious fungicides to limit infection, symptom development and yield loses caused by these pathogens in onion and celery crops in Michigan.
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