The role of the spore matrix on spore behaviour of Colletotrichum musae

The effect of the spore matrix on spore survival and germination was studied in 7 isolates of C.musae. It was concluded that the matrix from spores collected fresh from infected bananas and those collected from 10-12d old cultures contains germination inhibitors. The inhibitors appear to be produced simultaneously with the matrix and continue to be produced for 4-5 generations in culture although in some isolates their continued activity in culture may diminish. Inhibitory activity, however, is dependent on the age of the spore matrix within each generation rather than on the number of generations in culture. Germination rates of freshly collected spores at concentrations of 107 to 108 spores/ml in aqueous suspensions were low. Removal of the spore matrix by washing, or its dilution by 10 to 10,000 times in water, substantially increased germination. By resuspending the spores in 25% to 75% spore supernatant containing the matrix, however, germination was once again inhibited. The germination rates of spores over 100 days old, however, were depressed by washing. Similarly, the rate of disease induction by spores over 70 to 100 days old was also decreased by washing, and restored by resuspension in the matrix. In attempting to determine how the presence of the spore matrix affected spore behaviour a number of observations were made. It was noted that prior to germtube emergence, conidia suspended in water swelled by 7.7% to 12.3% of their initial volume in 2-2.5 hours. This was not affected by the presence or absence of the matrix. It was found that low germination rates under crowded conditions (1.5 X 106-107 conidia/ml) were not affected by the supply of either oxygen or air. On the contrary, prolonged aeration depressed germination further, especially in washed spores. Exposure of pre-germinated spores to ultraviolet light for 3h to 4h caused a significant reduction in the germination of washed, matrix-free spores compared to that in unwashed, matrix-enveloped spores. It was also found that the pigmentation of spores and matrix increased with age and that older spores were less affected by U.V light than were freshly produced spores. It was also found that the survival of conidia at below freezing (-4C), normal (18C) and high temperature (37C) was best when the matrix was intact. It was discovered that the capacity for germination of stored somewhat dehydrated spores was damaged by suspending them immediately in water. A period of from 24 to 48h under conditions of high RH was required to rehydrate them, after which suspending them in water caused no damage and considerably higher germination rates were obtained than in the absence of rehydration. Spore response to rehydration was greater in unwashed than in washed spores. It is concluded that the spore matrix serves a critically important role in the ecology of this fungus, and probably other Colletotrichum species, in regulating spore metabolism during dormancy and germination and in protecting spores from desiccation, U.V. radiation and adverse temperatures or sudden wetting