Morphological and ecological features as differentiation criteria for Colletotrichum species

Abstract

Colletotrichum acutatum and Colletotrichum gloeosporioides are important post harvest apple fruit pathogens in temperate regions. Seven Colletotrichum isolates obtained from apple fruits with anthracnose symptoms, and two reference isolates C. gloeosporioides AVO 37 4B (avocado, Israel) and C. acutatum TUT 137 A (strawberry, Israel) were investigated. Pathogenicity of all nine isolates was demonstrated on wound-inoculated apple fruits by fulfilling Koch's postulates. Investigated morphological characteristics involved shape, colour and margin of the colony, as well as conidial shape. Observed ecological parameters were growth and sporulation of isolates after 4, 7 and 11 days of incubation at temperatures of 15, 20, 23, 25, 27, 30, 32 and 35°C and after 10 days of incubation under conditions of day light regime and dark. The isolates were identified by PCR using species-specific primers. The data regarding growth were processed by factorial and one way ANOVA using software Statistica 10. All seven isolates obtained from apple fruits and reference C. acutatum isolate formed velvety, gray colonies with slightly wavy margin, and one celled fusiform conidia on PDA medium. Mycelium of the reference isolate C. gloeosporioides AVO 37 4B was snow-white and conidia were cylindrical. Maximum mycelial growth rate for isolates obtained from apple fruits was at temperature of 23°C, for reference isolate C. acutatum at 27°C and for C. gloeosporioides at 23-27°C. Temperature of 35°C proved to be restrictive for C. acutatum isolates. Isolate C. gloeosporioides had the fastest growth rate compared to all other isolates. Using PCR with species-specific primers all eight isolates were identified as C. acutatum (fragments sized 490 bp were amplified), and one as C. gloeosporioides (fragments sized 450 bp were amplified). The results suggest that differentiation between the two Colletotrichum species based on several morphological and ecological parameters is possible.