Survival in Soil of Colletotrichum acutatum and C. gloeosporioides Pathogenic on Strawberry

Abstract

The survival ability in soil of different inocula of strawberry isolates of Colletotrichum gloeosporioides and C. acutatum was studied under laboratory and field conditions. Two isolates of each species used in this study were identified according to morphological characteristics and by molecular techniques. Conidia of all four isolates survived for up to 1 year in autoclaved soil, whereas viability declined rapidly in untreated soils at 22% soil moisture (field capacity), with a 95% reduction in population recorded within 4.0 to 9.8 days. In methyl bromide (MB)-treated field soil at field capacity, a 95% decline in the viability of conidia of the two species was recorded within 8.9 to 12.9 days. At 11% soil moisture content, the time required for a 95% population reduction of the isolates of C. gloeosporioides and C. acutatum conidia was 124.5 and 114.4, and 72.8 and 74.2 days, respectively. C. acutatum was not recovered from naturally infected crowns after burial for 5 months in MB-fumigated and untreated soils at 10- and 20-cm depths under field conditions, but the decline was slower in the MB-fumigated soil. However, recovery of the pathogen from artificially inoculated mummified fruit after 5 months of burial ranged from 15 to 39%. Soil solarization for 4 weeks and MB fumigation treatments eradicated the pathogen from buried, artificially inoculated fruits. Based on this study, the potential contribution of conidia as well as mummified fruits to disease epidemics should be considered.