Pathogenic Characterization And Distribution Of Bean Common Mosaic Virus (Bcmv) And Bean Common Mosaic Necrosis Virus (Bcmnv) In Western Kenya

ABSTRACT

Common bean (Phaseolus vulgaris L) is an important food legume crop in Kenya. It is a

major source of protein in human diet. The average yield is 530 kg ha-1 and the country

production is estimated at 529,265 tons. Bean production is declining in Kenya due to

various abiotic and biotic factors. Virus diseases are a major yield reduction factor in

bean production. Among the diseases infecting beans, Bean common mosaic disease

(BCMD) caused by Bean common mosaic virus (BCMV) and Bean common mosaic

necrosis virus (BCMNV) is most widespread. Yield loss due to BCMV and BCMNV

ranging between 6 and 98% in some fields has been reported. Much work has not been

done on the status of BCMV and BCMNV in Kenyan agro ecological zones (AEZs).

This study intended to carry out a diagnostic survey for BCMD in major bean growing

areas of western Kenya and characterize its causal agents BCMV and BCMNV. The

specific objectives were to survey for incidence and severity of BCMD in bean growing

areas of western Kenya, characterize BCMV and BCMNV isolates using differential

cuitivars, and to screen for resistance of popular bean varieties to the virus isolates. Two

surveys were conducted during the short and the long rain seasons in 15 sub counties of

western Kenya covering the following AEZS: Lower Midland I, Lower Midland 2,

Lower Midland 3, Lower Midland 4, Upper Midland 1, Upper Midland 3, and Lower

Highland 1. Symptomatic leaf samples were collected for serological and pathogenic

analysis. Three virus isolates X, Y and Z were characterized using 7 differential

cultivars. BCMD mean incidence varied across the agro ecological zones (AEZ), it was

highest in Lower Midland 2 (17.90%) and lowest in Lower Midland 3 (3.75%).

However, the incidences were not statistically different across AEZ (p=0.36). There was

a strong significant positive correlation between BCMD incidence and severity (r=0.883;

p

Pathogroup VII. Two new pathogroups IV and VII are shown to occur for the first time

in the region. The presence of two SCAR DNA markers, SWI3 and SBD5, associated

with dominant I gene and recessive be-T resistant genes to BCMV and BCMNV in the

popular Andean diversity panel lines from western Kenya confirmed the presence of bc-

12 gene in twenty out of twenty four varieties screened, three had I gene while one had

neither of the two resistance genes. In conclusion, viral disease is widespread in bean

growing areas of western Kenya. Integrated management of BCMD is highly

recommended.