Abstract:
The typical dry bean, Phaseolus vulgaris, is the essential food legume for direct human
consumption. They play a significant role in food security and nutrition. Despite their nutritional
importance, its production growth rates have declined in Kenya due to diseases, insect pests,
plant nutritional deficiencies, and drought. Therefore, this study's main objective was to
determine whether there are differences in bean varieties' tolerance to whitefly transmitted viral
diseases. The study had a survey and laboratory phases. The survey covered wetter midlands of
Central Kitui County, where fifty-two farms were repeatedly covered in two bean production
sites in two years (2017-2018), in Kyangwinya West Ward and Kitui East Ward. A questionnaire
was administered to collect data on bean production acreage, type of cropping system, pest and
diseases, pesticide, and fertilizer use by farmers on bean production. Each farms’ location was
marked using the global positioning system (GPS) device. Rainfall data of the production period
was secured from Kenya Agricultural and Livestock Sub-Centre of Ithookwe, centrally placed at
2 Kilometres west of Kitui Town. The Whitefly specimens were collected from the named
regions and the specimen preserved in 70% ethanol. Bean disease lesions were noted following
the procedure of observation of the bean leaves for disease symptoms. Viral symptoms were
recorded based on the data from observation. Fungal identification was done using pathogens on
Potato Dextrose Agar (PDA) combined with a drug (streptomycin and neomycin) while bacteria
were differentiated through selective media YDC (yeast extract-dextrose-CaCo3). The fungi were
grouped using spore characters on PDA, while bacteria were grouped depending on their color
on YDC. Bean production acreage and yield levels were subjected to analysis of variance. The
highest density of B. tabaci was observed in Kyangwithya-West ward at close to 2 whiteflies per
field plot of 1m2. After laboratory analysis, disease incidence among the varieties showed that
improved varieties had a higher incidence of fungal, bacterial, and viral diseases than the local
cultivars. Mwezi-Moja had the least disease incidence of 1%, while Rosecoco, B1, and Nyayo,
with ≥ 5% of fungal diseases, identified as Altenaria and Phoma species as common ones on the
dead lesions. The bacterial diseases found on the leaves were Pseudomonas spp, grouped in the
fungal lesions. The local cultivar with the least incidence was Wairimu indicating 1% fungal
disease occurrence, mainly being Altenaria species. The local variety bearing the highest viral
disease was Mwitemia at 3%, of Bean Golden Yellow Mosaic Virus (BGYMV). However, the
varieties had a less than 10% incidence of both fungal and viral diseases. There is a need to
develop bean genotypes through seed breeding, which are ecologically adaptive to the waterstressed environment to increase food security.
