INITIAL INFECTION PROCESSES BY COLLETOTRICHUM-GLOEOSPORIOIDES ON AVOCADO FRUIT

Infection of avocado fruit by Colletotrichum gloeospioroides was studied using light and transmission electron microscopy. In unripe fruit C gloeosporoides produced an appressorium and an infection peg which ceased growth in the cuticle. In field-inoculated avocado fruit sampled up to 4 d after inoculation, most infection pegs had penetrated the fruit 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 the subcuticular region of the fruit peel within 48 h of inoculation. There was no further development of these infection pegs until the climacteric rise in respiration when fruit produced amounts of CO2 in excess of 50 ml CO2 kg-1 h-1. When the fungus resumed growth, infection pegs enlarged either within the walls or within the lumen of epidermal cells. Subsequent intracellular and intercellular development of the fungus resulted in the rapid degradation of cell wall and membrane structural integrity, although cells were not killed in advance of invasion during these early stages of colonization.