Effect Of Cropping Systems On The Occurrence Of Fungal And Bacterial Diseases Of Legumes In Western Kenya

Bacterial and fungal diseases of legumes are a major constraint in legume production in western
Kenya and persistently curtail optimal yields and quality of food legumes. This study aimed at
determining the occurrence of fungal and bacterial diseases of these legumes and the
contribution of seed quality to their occurrence, in diverse agro-ecological zones of western
Kenya. The study was carried out during the short rains season (months of October, November
and December) of 2013 in seven Counties with diverse agro-ecological zones. A total of 635
farms were sampled in the study covering both participating and non- participating farmers in the
legume up-scaling projects in the area. A semi-structured questionnaire together with visual
observations were used to obtain information on legume production practices, distribution,
incidence and severity of common diseases of food legumes grown. Bean seed samples as well
as plant tissues were collected from farmers for laboratory analysis. Geographical information
system coordinates and elevation of each farm sampled were taken for the purpose of generating
legume disease distribution and intensity maps. The collected seed samples were analyzed for
purity, germination, bacterial and fungal contamination as outlined in International Seed Testing
Association. Most of the legume farmers were small scale and allocated less than 0.1 Ha of land
for legume production. Majority of the farmers intercropped legumes with other crops and
planted local (landraces) legume varieties. There were 13 different bean varieties grown, with
Rose coco and KK8 accounting for 23% and 22%, respectively. The most commonly grown
legumes were common bean, cowpeas and groundnuts. The major diseases affecting all the
legumes were common bacterial blight and root rots. Fungal and bacterial disease prevalence
significantly (P ≤ 0.05) varied in the different regions and agro-ecological zones (AEZ). There
was however, no significant (P ≤ 0.05) difference in disease intensity among farmers
participating and those not participating in the legume up scaling projects in the different
regions. Most bean samples had the recommended percentage germination of 95% but low
percentage purity of 74.1%. Of the germinated seedlings, 7% showed infection and most samples
contained 12% of discoloured and shriveled seeds. Fungi isolated from the seeds were Fusarium
solani and Colletotrichum lindemuthianum while Xanthomonas campestris pv phaseoli and
Pseudomonas savastanoi pv phaseolicola were the main bacterial pathogens with infection
levels of as high as 2000-3000 CFU/seed. There was significant (P ≤ 0.05) variation in the
frequency of fungal and bacterial pathogens populations among regions. The results of this study
showed that there was a high prevalence of fungal and bacterial diseases of legumes due to
cropping practices. Farm-saved bean seeds contained a high level of bacterial blight pathogen
inocula due to continuous recycling of seed from previous cropping seasons. There is therefore,
need to accurately monitor legume diseases and create awareness among farmers on use of
disease-free seeds and application of appropriate agronomic practices to reduce the effects of
seed-borne diseases.

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