INITIAL INFECTION PROCESSES BY COLLETOTRICHUM-GLOEOSPORIOIDES ON AVOCADO FRUIT

Infection of avocado fruit by Colletotrichum gloeospioroides was studi ed using light and transmission electron microscopy. In unripe fruit C gloeosporoides produced an appressorium and an infection peg which ce ased growth in the cuticle. In field-inoculated avocado fruit sampled up to 4 d after inoculation, most infection pegs had penetrated the fr uit cuticle to a depth of less than 1.5 mum. In fruit inoculated after harvest, however, the majority of infection pegs had grown down to th e subcuticular region of the fruit peel within 48 h of inoculation. Th ere was no further development of these infection pegs until the clima cteric rise in respiration when fruit produced amounts of CO2 in exces s of 50 ml CO2 kg-1 h-1. When the fungus resumed growth, infection peg s enlarged either within the walls or within the lumen of epidermal ce lls. Subsequent intracellular and intercellular development of the fun gus resulted in the rapid degradation of cell wall and membrane struct ural integrity, although cells were not killed in advance of invasion during these early stages of colonization.