SUNN-HEMP MOSAIC-VIRUS FACILITATES CELL-TO-CELL SPREAD OF SOUTHERN BEAN MOSAIC-VIRUS IN A NONPERMISSIVE HOST

Accumulation of the cowpea strain of southern bean mosaic sobemovirus (SBMV-C) in bean, a nonpermissive host, was facilitated by coinfection with sunn-hemp mosaic (SHMV), a tobamovirus. The rate of spread in bean of SBMV-C in the presence of SHMV was compared with the rate of spread of the bean strain of SBMV (SBMV-B) coinoculated with SHMV. Virus accumulation in the leaf blade, lateral veins, midrib, petiole, stem, and roots revealed similar amounts of both strains in the nonvascular tissue of the inoculated leaf; however, a sharp decline in SBMV-C accumulation was observed starting from the lateral veins towards the mid- and distal parts of the petiole, where virtually no virus could be found. This contrasted with the uniform presence of SBMV-B throughout these plant parts. Bean protoplasts sustained replication of SBMV-C in single infection upon in vitro inoculation. Antigen accumulation of the bean and the cowpea strains of SBMV in bean protoplasts was similar, and coinoculation of bean protoplasts with SHMV and SBMV-C showed no effect on the accumulation of the latter.