Distribution and fungicide sensitivity of fungal pathogens causing anthracnose-like lesions on tomatoes grown in Ohio

The primary causal agents of anthracnose-like fruit rots in Ohio and their potential resistance to fungicides commonly used to control these fungal pathogens were determined. Nineteen tomato production fields throughout the state were sampled in 2002 and 2003 for fruit with anthracnose-like lesions. Fungi were isolated from these samples, classified using restriction fragment length polymorphism analysis, and identified by internal transcribed spacer sequence analysis. Some of the fungi isolated may represent secondary invaders of preexisting wounds or lesions. Colletotrichum spp. were most abundant in our collection, representing 136 of the 187 isolates. In addition, there were 23 Alternaria, 12 Fusarium, 12 Phomopsis, and 4 Mucor isolates. Colletotrichum, Alternaria, and Fusarium spp. were found throughout the major tomato production areas in the state. In a laboratory investigation, a subset of the Colletotrichum, Alternoria, and Fusarium isolates caused symptoms similar to early development of anthracnose on wounded tomato fruit. In vitro inhibition assays indicated that most Colletotrichum isolates were sensitive to labeled rates of azoxystrobin, chlorothalonil, and mancozeb. However, some Alternaria isolates were less sensitive to azoxystrobin and chlorothalonil than the Colletotrichum isolates. In addition, most Fusarium isolates were also more insensitive to azoxystrobin and mancozeb, and most Phomopsis isolates were not inhibited by azoxystrobin at the levels tested. The patterns of insensitivity to azoxystrobin and chlorothalonil were also observed in situ with excised fruit. Because the fungicides tested are not currently labeled for control of tomato diseases caused by Fusarium or Phomopsis, these results indicate that some pathogen species that can cause anthracnose-like symptoms may not be entirely sensitive to fungicides commonly used in tomato production.