The effect of climatic factors on colletotrichum-gloeosporioides, causal agent of mango anthracnose, in the philippines

The epidemiology of the anthracnose pathogen of mango, Colletotrichum gloeosporioides, was studied over two growing seasons in the Philippines. This pathogen spreads within tree canopies as water-borne conidia during rainfall, and causes symptoms on young flush leaves, flowers and fruit. Infection studies with leaves and fruit incubated at different temperatures and humidities led to the derivation of a logistic regression model of the percentage of conidia forming appressoria. This model was compared with a similarly derived model from work in Australia; it appeared that the Philippine isolates of C. gloeosporioides were adapted to the higher mean temperatures of the Philippines. Conidia were observed to germinate and form appressoria at relative humidities (RH) between 95 and 100%, even though free surface moisture was only visible at 100% RH. This model was used retrospectively to estimate infection levels in two field trials which had been established to compare pre- and post-harvest practices in the control of the disease. Using this information to plan applications of a curative fungicide might have resulted in four fewer sprays in the first trial and one less in the second, compared with the standard protective spray programme employed

Effect of humidity and temperature on conidial germination and appressorium development of two Philippine isolates of the mango anthracnose pathogen Colletotrichum gloeosporioides

A comparison of rates of germination and appressorium formation by an isolate of Colletotrichum gloeosporioides on mango leaves, fruit surfaces and cellophane membranes showed that behaviour was broadly similar on all three substrates. Frequency of appressorium formation was slightly higher on cellophane membranes, and both hyaline and melanized appressoria were formed. Only melanized appressoria were formed on mango surfaces. In vitro experiments on membranes showed comparative differences in physiological behaviour with temperature for two Philippine isolates of C. gloeosporioides. The most stimulatory temperature for production of appressoria differed in isolates I-2 and I-4 (25 and 20 degrees C, respectively). At 30 degrees C more appressoria became melanized than at lower temperatures, but the frequency of formation of penetration pegs was highest at 25 degrees C. Conidia of C. gloeosporioides germinated on cellophane membranes at relative humidities as low as 95%, but the percentage of conidia germinating and forming appressoria increased as the RH approached 100%. Approximately 18% of conidia of C. gloeosporioides I-2 held at 62 and 86% RH for 4 weeks retained viability, and some were capable of forming appressoria when placed at 100% RH. These results have implications for epidemiological models for disease control