Histopathology of Compatible Interactions Involving Biotypes of Colletotrichum gloeosporioides That Cause Anthracnose of Stylosanthes Spp

Abstract

The histopathology of compatible interactions between type A and type B Colletotrichum gloeosporioides and Stylosanthes scabra cv. Fitzroy and Stylosanthes guianensis cv. Endeavour was studied by light microscopy and scanning electron microscopy at various times after inoculation. Quantitative studies of germination and penetration processes with whole leaf mounts showed that the processes were similar for the two diseases but that unmelanized appressoria were produced more rapidly (3 h after inoculation) by the type A fungus on both hosts than by the type B fungus on Endeavour (6 h after inoculation). After 6 h for the type A fungus and 12 h for the type B fungus, the majority of appressoria were melanized. First evidence of penetration on the whole leaf mounts was observed 12 h after inoculation on all three interactions. Percentage penetration of the susceptible Endeavour by the type B fungus was significantly higher than that for the type A fungus on Fitzroy (susceptible) and Endeavour (intermediate). Subcuticular infection hyphae were present in transverse leaf sections of both diseases after 12 h and both intercellular and intracellular fungal invasion were observed after 24 h. Acewuli of the type A hngus had developed on Fitzroy by 96 h, whereas acervuli of the type B fungus had developed on Endeavour by 144 h. Mesophyll cells were particularly susceptible to fungal invasion and rapidly collapsed. Swelling of epidermal cell walls in response to invasion was also observed but this did not confer resistance.