Interference between Cowpea Mosaic Virus and Cowpea Severe Mosaic Virus in a Cowpea Host Immune to Cowpea Mosaic Virus

Abstract

Summary Infection of a cowpea line by cowpea severe mosaic virus (CPSMV) was inhibited by cowpea mosaic virus (CPMV) even though the plants were immune to CPMV. The inhibition was dose-dependent and was complete if CPMV was added to the inoculum in a 50-fold excess over CPSMV. Isolated CPMV RNA inhibited infection by CPSMV or by isolated CPSMV RNA. CPMV particles devoid of RNA (top component), u.v.-inactivated but intact CPMV particles or u.v.-inactivated CPMV RNA did not inhibit infection by CPSMV. Bottom component particles of CPMV, but not middle component particles, inhibited CPSMV to the same extent as unfractionated CPMV. These findings strongly suggest that the interference is not due to competition between the particles or the RNAs of the two viruses for infectible sites. It may be that CPMV infects cells of the ‘immune’ host subliminally and that the inhibition is associated with replication of at least bottom component RNA of CPMV.