PREVALENCE AND INCIDENCE OF ANTHRACNOSE OF PAWPAW (Carica papaya), CHARACTERIZATION OF Colletotrichum gloesoporoides AND CONTROL USING PLANT EXTRACTS IN BARINGO AND ELGEYO MARAKWET COUNTIES (KENYA)

KUGUI, SAMUEL KIPROP (2021)
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Thesis

Papaya is the fourth most important fruit crop in Kenya after oranges, mangoes and bananas. It has also become an important export crop particularly in the arid and semiarid lands. Anthracnose caused by Colletotrichum gloeosporioides results in huge economic losses. Therefore information on the epidemiology of the disease and its associated vector as well as control methods are vital in the management of the disease. The aim of the study was to determine the epidemiology of anthracnose in pawpaw, characterize the pathogen and determine the efficacy of plant extracts in controlling the pathogen. Specifically the study determined: the prevalence, incidence and severity of anthracnose in Carica papaya fruits; characterization of Colletotrichum gloeosporoides isolates infecting Carica papaya fruits; evaluated the in-vitro efficacy of plant extracts against isolates of Colletotrichum gloeosporoides; and determine the in-vivo efficacy of plant extracts against Colletotrichum gloeosporoides on anthracnose infected papaya fruits in Baringo and Elgeyo-Marakwet Counties in Kenya. To determine the prevalence, incidences and severity of anthracnose disease, field surveys were conducted in major pawpaw-growing areas of Baringo and Elgeiyo Marakwet Counties from March 2015 to June 2015, during fruiting stage, using the line transect method. A total of 32 farms in 8 areas (4 farms per area), in two counties with pawpaw at fruiting stage were sampled. Characterization of the Colletotrichum gloeosporoides was done at the Kenya Medical Research Institute laboratory using morphological, cultural, pathogenicity and aggressiveness methods. In vitro efficacy test of the plant extracts was done at the University of Eldoret to determine the effectiveness of the plant extracts against the fungi. In vivo tests were done on papaw plants in the field. To determine the efficacy range of the chemical dosages, a logistic regression model was applied. During the study, pawpaw infected with anthracnose disease and those that were not infected were observed. The symptoms of infection were observed on the leaves, initially occurred as small angular, brown to black spots while on the fruits the symptoms were exemplified as tear strain by occurrence of linear necrotic regions. The prevalence of anthracnose in Carica papaya in the farms was 95% in Baringo and upto 83% in Elgeyo-Marakwet County and differed significantly with altitude. The overall incidence of anthracnose infections on fruits was 9.23 ± 1.22% in Baringo County and 4.5 ± 1.1% in Elgeyo Marakwet County resulting in an overall of 7.5 ± 1.0% in the region. The severity of anthracnose disease was found to positively correlate with the incidence. In regions where lower incidences were reported (<8%), there was low severity of the anthracnose disease basically at level 2 followed by level 1. Meanwhile when incidences of anthracnose disease were higher, the severity of the disease increased mainly to levels 4 and 5. The use of Fuerstia africana, Solanum incanum, Carisa edulis, Azadirachta indica and Aloe chiliensis in Baringo and Elgeyo-Marakwet Counties as natural fungicides against pawpaw anthracnose were confirmed by laboratory results from this study. Fuerstia africana plant extracts were the most effective in the bioassay, while Solanum incanum and Aloe chiliensis extracts were the least effective. There were differences in the number of days to healing of Carica papaya infected with anthracnose, with Fuerstia africana extracts taking the shortest time to healing and Carisa edulis extracts taking the longest time. Therefore, the exploitation of one or more of these botanical fungicides for the control of one or more of these pathogens would be biodegrable, cheaper to obtain, environmentally safer and could serve as a good alternative to synthetic fungicides.

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