| dc.description.abstract | Common beans (Phaseolus vulgaris) are widely grown throughout the world and provide
valuable protein, vitamins and other nutrients. If the challenges related to its production
are resolved, food security can be guaranteed for the growing population. Disease-causing
pathogens are a major constraint in bean production. Curtobacterium flaccumfaciens pv.
flaccumfaciens causes bacterial wilt of common bean disease. This pathogen causes high
economic losses due to seedling death, yield loss and seed discoloration. Copper
fungicides can reduce secondary spread but are expensive, harmful to the environment
and lead to resistance of the pathogen. Bacterial control agents are effective and
environmentally friendly alternatives to chemicals, as they provide protection throughout
the crop period and are specific to plant diseases. However, less has been done in
managing bacterial wilt using bacterial bio-controls. The objectives of this study were; to
isolate wilt-causing pathogen in dry beans, to isolate bacterial antagonists against the
pathogen from the rhizosphere of P. vulgaris and to control the pathogen in vitro and in
vivo using the recovered bacterial bio-controls. The study was done in an experimental
bean field located in Kimbimbi, Kirinyaga County. From infected leaves and seeds of
bean plants, Curtobacterium species were isolated and characterized morphologically,
biochemically, molecularly and by pathogenicity tests. Biological control agents were
identified in the soil samples obtained from the rhizospheres of bean plants and screened
against Curtobacterium flaccumfaciens using soft agar overlay assay. Primer pair 8F and
1492R were used for amplification of the 16S rRNA gene and sequencing. Analysis of the
16S rRNA gene was conducted to identify the Cff isolates and bacterial antagonists. Both
a foliar spray and a seed treatment were used to apply bio-controls. A completely
randomized design was employed for the experiment. Data on disease incidence and
disease severity were analyzed using analysis of variance at a 95% confidence level.
Phylogenetic analysis was done using the neighbor-joining method and phylogenetic tree
constructed with MEGA software. Eleven Curtobacterium spp. were identified. Nine
bacterial control agents showed antagonistic activities against Cff. A partial 16S rRNA
gene sequence of these isolates identified species belonging to the genera Bacillus,
Paenibacillus and Pseudomonas. Seed treatment coupled with foliar application of the
antagonistic bacteria significantly reduced disease incidence and disease severity ranging
from 16-29% and 4-10% respectively, compared to the control. Pseudomonas fluorescens
was most successful in controlling the Cff pathogen with an efficacy of 81%, while B.
cereus and P. polymyxa reduced the disease development by 79% and 68%, respectively.
The use of rhizobacterial species provides a safe, effective and sustainable alternative to
control bacterial wilt in the common bean. Herein, the rhizobacteria P. fluorescens, B.
cereus and P. polymyxa species seed treatment coupled with foliar application
significantly reduced the disease incidence and disease severity of bean bacterial wilt. The
study recommends further research on distribution of bacterial wilt of common bean
disease in bean-producing regions of Kenya and to determine if the isolated bacterial
control agents are effective against other plant diseases | en_US |
