Resistance of Cowpeas to Cowpea Mosaic Virus and to Tobacco Ringspot Virus

Summary

Cowpea mosaic virus (CPMV) and tobacco ringspot virus (TobRV), though members of distinct virus groups, each have two genomic RNAs separately encapsidated and generate functional proteins by the specific proteolysis of polyproteins. CPMV and TobRV infect most cowpea (Vigna unguiculata) lines, including line Blackeye 5. Cowpeas of line Arlington did not support a detectable increase of CPMV, as previously reported, or of TobRV. In F₂ progeny of cowpea crosses the resistances to CPMV and to TobRV were inherited as distinct, simple dominant traits. Extracts of Arlington cowpea leaves have three activities that are candidate mediators of resistance to CPMV: proteinase(s) that degrade CPMV proteins, inhibitor(s) of the translation of CPMV RNAs, and an inhibitor of proteolytic processing of the polyprotein precursor to the coat proteins. These activities were tested for their virus specificity and inheritance in the progeny of cowpea crosses. The proteinase inhibitor showed the specificity and co-inheritance expected for a mediator of resistance to CPMV. No inhibitor of the processing of TobRV polyproteins was detected in similar extracts, indicating that the resistances to CPMV and to TobRV may be controlled by different mechanisms as well as by different genes.