Population dynamics of Colletotrichum gloeosporioides on different parts of an avocado (Persea Americana) tree

Abstract

Colletotrichum gloeosporioides in different parts of a single avocado tree, and its debris under the tree, was enumerated at monthly intervals, during a period of two years. A positive correlation between quiescent infections-QI on flowers and rainfall (RF), and a negative correlation of QI on twigs and RF were observed. The positive correlation between RF and QI on leaves was significant only when RF was pre-lagged by 3 months, and the level of significance increased progressively when RF was pre-lagged upto 6 months. Disease symptoms were never observed on the vegetative parts of the tree and flowers, but a high number of QI was observed on twigs and leaves. This is probably how C. gloeosporioides survives between fruiting seasons. The different relationships between QI on each part of the tree and RF, demonstrate how this pathogen may have adopted itself to survive on the tree. Therefore the results suggest that once the C. gloeosporioides propagules find their way to a tree, the pathogen remains there throughout its life time causing anthracnose on fruits. There was a significant drop in the density of QI of C. gloeosporioides on larger, mature fruits compared to that of smaller, immature fruits. Throughout this study, the free-living viable fungal propagule counts of debris under the tree varied from 101 to 103 CFU/g while those of washings of leaves, twigs and flowers varied from 0 to 102 CFU/g.