Occurrence and estimated losses caused by cassava viruses in Migori County, Kenya

Cassava is the second most important staple crop after maize in Migori County. A farm survey was conducted in Kuria East and Suna West sub-counties to determine the incidence, severity and estimated losses of cassava brown streak disease (CBSD) on cassava crops in farmers’ fields. A total of 70 farms (Kuria East = 40; Suna West = 30), with cassava crop aged 7-12 months after planning (MAP), were sampled using stratified random sampling procedure. Data were collected on CBSD incidence (foliar and root), root necrosis score, percent loss (roots) and yield traits (number and weight of fresh roots). Results showed mean foliar incidences of 58.5% and 53.9% in Kuria East and Suna West sub-counties, respectively. High foliar CBSD incidences were recorded in Kuria East sub-county with range of 54.0-74.0% observed in five local varieties; Manchoberi, Amakuria, Mwitamajera, Weite and Nyakohanda. A similar result trend was recorded in Suna West sub-county with a range of 52.1-77.5% in six varieties; Mary go round, MH95/0183 (improved), Ondielo, Nyakasanya, Nyakasamuel and Obarodak. Highest root necrosis scores and percent root loss were observed in two local varieties, Amakuria (2.4; 36.7%) and Agric IV (3.7; 40%), in Kuria East and Suna West sub-counties, respectively. Correlation analysis revealed strong positive correlation between root necrosis, root necrosis incidence and percent root loss; which implies that susceptible varieties suffer greatest loss. The estimated mean root yield loss caused by CBSD stood at 10.5% (equivalent: US 405 ha-1) and 7.2% (equivalent: US 384.30 ha-1) in Kuria East and Suna West sub-counties, respectively. The findings of this study are expected to provide impetus for the development and promotion of new high yielding, locally adapted and CBSD resistant cassava varieties.