Efficacy of plant extracts and extracting agents against Colletotrichum gloeosporoides of pawpaw fruits

Abstract

Pawpaw (Carica papaya L.) is a fruit crop of economic importance in Kenya, where small scale farmers are the major producers. One factor limiting pawpaw production is anthracnose disease caused by Colletotrichum gloeosporoides, whose management on farm still remains a major challenge. The objective of this study was to determine the efficacy of plant extracts and extracting agents for controlling anthracnose disease on pawpaw fruits. In vitro spore germination and in-vivo tests were done using extracts from five plants; Aloe chiliensis, Azadiracta indica, Carissa edulis, Fuerstia africana and Solanum incanum; and extracting agents methanol, chloroform and ethanol against the fungus. A logistic regression model was used to estimate the botanicals’ dose response treatment ranges. The efficacy of the crude extracts was greatest when methanol was used for extraction. The highest inhibition was recorded in pawpaw fruits treated with leaf extracts of F. africana. There were significant differences in effects among treatments by methanolic extracts of the five plants on conidial spore germination percentage. Aloe chilensis (Aloe) showed a higher spore germination of 35.7%; while Azadirachta indica (Neem) resulted in the lowest spore germination of 1.2%. There were significant differences in days to healing of C. papaya fruits infected with anthracnose. Pawpaw infected fruits healed fastest (3.5 days) when treated with the methanolic leaf extracts of F. africana; while A. chiliensis ethanolic leaf extracts resulted in the longest healing time of over 7 days. Although these botanical fungicides present high potentials or controlling anthracnose pathogens of pawpaw fruits, their suitability for application within the socio-economic framework of Kenyan small-scale producers still remains a matter for further investigation.