Yam Tuber rot: identification and Control of Pathogens in Storage
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Date
2011-07-14
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Abstract
This work was done to improve farmers’ indigenous white yam storage practices. Farmers from four yam-producing communities were interviewed by the use of questionnaires to ascertain farmers’ knowledge on field and post-harvest diseases of yam. The interviewed farmers ranked pests and diseases next to credit facilities which were regarded as number one constraint. Sixty five percent (65%) of farmers interviewed considered yam tuber rot disease as a major disease in the communities. Hundred percent (100%) of the interviewed farmers who stored their yams indicated that they experienced rots during post-harvest storage of tubers. Estimated losses given by the farmers ranged between 60% and 100%.
Rotten white yam tuber samples were collected from farms in three communities. Nine fungal organisms were isolated by direct tissue plating on PDA medium. These were: Fusarium oxysporum, Aspergillus flavus, Aspergillus niger, Penicillium spp., Botryodiplodia theobromae, Trichoderma viride, Rhizopus spp., Pestalotia guepini and Alternaria solani. Each of these isolates caused rot lesions when inoculated into healthy test yam tubers. Koch’s postulate was completed with each isolate through re-isolation. B. theobromae, A.. niger, Rhizopus spp. and A. solani were the most frequently isolated fungi species from the rotten yam tuber samples, with frequency of isolations in the order of 30.07%, 16.08%, 16.08% and 12.59%, respectively.
Extracts (60% Concentration, w/v) of Ginger rhizome, Black pepper seed and Cassia alata leaves were tested against the growth of B. theobromae and F. oxysporum. Percent inhibition of radial growth of fungal organisms due to the botanical extract was used to represent activity of the product. The ginger extracts inhibited the growth of B. theobromae and F. oxysporium 72 hours in incubation by 64.64% and 86.36%, respectively. For black pepper extract, the growth inhibitions for the two fungi were 81.23% and 100%, whilst those of Cassia leaf extract were 66.85% and 56.82%. The extracts of ginger and seed extract of black pepper were active in inhibiting growth of the two test fungi. Cassia alata leaf extract was least effective.
Efficacy of two chemical fungicides, Shavit F71.5 WP and Metalaxyl Mancozeb WP, in controlling yam tuber rot was also investigated. Two white yam cultivars, ‘dente’ and ‘pona’, were used in the experiments. Shavit F71.5 WP reduced the occurrence of yam tuber rot disease by 71% and 70% during storage of ‘dente’ and ‘pona’, respectively. Metalaxyl Mancozeb reduced rot of yam tubers by 46% and 60% in ‘dente’ and ‘pona’, respectively. The two chemical fungicides were effective in controlling rot diseases of yam during storage. However, Shavit WP was relatively better than Metalaxyl Mancozeb.
Description
A thesis submitted to the School of Graduate Studies of the Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the Award of a degree in MSc. Crop Protection (Plant Pathology), February 2011