Dynamics of Polymyxa graminis and Indian peanut clump virus (IPCV) infection on various monocotyledonous crops and groundnut during the rainy season

Abstract

The progress of Indian peanut clump virus (Hyderabad isolate; IPCV-H) and its vector Polymyxa graminis in various monocotyledonous crops and groundnut was studied during the 1994, 1995 and 1996 rainy seasons in a naturally infested field in India. The roles of rainfall and temperature in the dynamics of infection by both the virus and its vector were analysed by exposing young seedlings for short periods in the field. Of the host crops studied, wheat, followed by barley, showed the highest virus incidence, although P. graminis was rarely observed in roots of wheat and was not detected in those of barley. The roots of maize, pearl millet and sorghum plants infected by P. graminis showed intense colonization by sporosori. IPCV accumulated in systemically infected maize plants; the sorghum and pearl millet cultivars studied showed a transient presence of IPCV-H. Rice was seldom infected by the virus and P. graminis was not detected in its roots. Groundnut was a systemic host for the virus, although during these experiments no P. graminis was found in its roots. Groundnut appeared to be susceptible to infection, mostly in the early stages of crop development, and the rate of IPCV-H transmission in groundnut seeds was highest (13%) for plants infected when young. The seed-transmission rate quickly decreased in plants showing symptoms 1 month after sowing. Time of infection had little influence on groundnut pod yield, which was always reduced by >60% in infected plants. There was some evidence that the quantity and distribution of rainfall influenced the incidences of IPCV-H and P. graminis: high rainfall resulted in high incidences of the virus and P. graminis, and a weekly rainfall of 14 mm was sufficient for P. graminis to initiate infection. Temperatures prevailing during the rainy season ranged from 23 to 30degreesC and were found to be conducive to natural virus transmission. These results suggest measures to be explored for controlling peanut clump disease