Occurrence and distribution of groundnut rosette disease in Western Kenya

Groundnut (Arachis hypogaea Linn) is an important legume in western Kenya, but yields are low and declining. Pests and diseases are ranked high among the yield reducing factors. Groundnut rosette disease (GRD) is the main disease and can cause upto 100% yield loss. Distinct chlorotic, green and mosaic rosette symptoms caused by synergism among groundnut rosette assistor luteovirus (GRAV), groundnut rosette umbravirus (GRV) and its satellite RNA (sat-RNA), make it a unique and fascinating virus disease, whose origin and perpetuation in nature still remains inconclusive in spite of substantial advance in knowledge since 1907 when it was first reported. Limited information is available on the occurrence and distribution of the disease in western Kenya. This study determined the distribution and tolerance/resistance of local germplasm to GRD pathogens. A survey of GRD was conducted in Bungoma and Kakamega counties in short and long rains of 2016- 2017. Symptomatic leafy samples were collected and analyzed by molecular means. Data on incidence and severity was recorded and analyzed by Statistical Analysis Software (SAS) program version 9.3. Screenhouse experimental study was conducted at KALRO Kakamega. Five popular legume varieties and one solanaceous Physalis peruviana Linn plants at three leaf-stage in a 4x6 factorial design, were mechanically inoculated with GRD inoculum prepared from leaves of RT-PCR positive samples. The plants were monitored for symptom development in the screenhouse for 8 weeks. A total of 301 samples from 144 farms were collected. Rosette incidence was significantly higher in Bungoma (66.51%) followed closely by Kakamega (60.52%). All tested plants from the screenhouse developed symptoms typical of GRD. The fact that GRD occurs wherever groundnuts are grown in western Kenya, is of great concern and may be the reason for the observed low yields. Incorporation of GRD resistant genes in the local cultivars/varieties may be the only practical solution.