SURVIVAL OF COLLETOTRICHUM-LINDEMUTHIANUM IN BEAN DEBRIS IN NEW-YORK-STATE

Colletotrichum lindemuthianum, the causal agent of bean anthracnose, overwintered 4 mo in bean (Phaseolus vulgaris) debris placed 0, 10, and 20 cm deep in soil on 14 November 1988. A bean plant assay was developed for the detection of low inoculum levels in overwintered debris. The fungus could not be isolated from infested debris on agar medium in April 1989 but could be detected using the host plant assay. The fungus was no longer detectable 22 mo after placement at any depth. Additional field trials were conducted at three locations over a 3-yr period. C. lindemuthianum was recovered from naturally infested bean debris after exposure to winter conditions for 3 mo (December through February). The inoculum concentration in overwintered bean debris at the three locations was sufficient to initiate disease on bean plants the following growing season. The relationship between inoculum density and disease severity in the bean plant assay was determined. Disease severity on inoculated leaves increased as inoculum density increased. The relationship can be used as a guideline for estimating the inoculum density in overwintered debris.