Strain variation in colletotrichum Gloeosporioides (Penz.) Penz & Sacc.

Abstract

Colletotrichum gloeosporioides (Penz.) Penz. & SAcc. Is observed as a major pathogen infecting a number of crop plants, ornamentals and weeds. Detailed studies on the variability of this pathogen on important vegetables and ornamental plants in different locations of Thiruvananthapuram and Thirissur districts of Kerala were undertaken to distinguish different strains of C. gloeosporioides. Studies on the symptoms and pathogenecity tests of the 69 isolates showed that there were variations in the exoression of symptoms and in initiating symptoms indicating that the isolates were highly variable. Great variability in growth rate, colony characters, degree of sporulation and size of conidia were observed in different isolates. Based on the protein production and enzyme activity three groups of isolates could be distinguished. The isolates varied in their growth under varying temperature and relative humidity. Light intensity had no significant effect on the growth of the pathogen. Among the solid media tested, all the selected isolates exhibited the maximum growth on PDA. Richard’s medium was found to be the best liquid medium for mycelial growth. The degree of sporulation of selected isolates was the highest at 92.9 per cent RH and the lowest at 100 per cent RH. The highest sporulation was observed when exposed for 24 h of continuous light (125 lux) and poor when exposed for 24 h darkness. Basal medium was found to be best for sporulation. The results of host range studies and cross inoculation studies showed that the selected isolates were not host specific even though there were variations among the isolates in the intensity of infection. Inhibition of germination of selected seeds was observed when bioassayed with exotoxin. The purified toxin produced more or less identical symptoms as did by the casual organism. Coon’s medium was found to be the best for production of endotoxin. The maximum production of toxin was observed in 25 day old cultures. Biological groupings of all the 69 isolates studied were done based on the correlation matrix of different characters. Eight different groups of isolates could be distinguished and designated as G1, G2, G3, G4, G5, G6, G7 and G8 strains of C. gloeosporioides.