BEAN YELLOW MOSAIC POTYVIRUS INFECTION OF ALTERNATIVE HOSTS ASSOCIATED WITH SUBTERRANEAN CLOVER (TRIFOLIUM-SUBTERRANEUM) AND NARROW-LEAFED LUPINS (LUPINUS-ANGUSTIFOLIUS) - FIELD SCREENING-PROCEDURE, RELATIVE SUSCEPTIBILITY RESISTANCE RANKINGS, SEED TRANSMISSION AND PERSISTENCE BETWEEN GROWING SEASONS/

A held screening procedure was devised to determine relative susceptib ility and resistance rankings for hosts of bean yellow mosaic potyviru s (BYMV) using BYMV-infected Trifolium subterraneum plants transplante d at each end of single row test plots. Natural spread of BYMV by aphi ds resulted in BYMV symptoms in test limes. Four test lines were ranke d as highly resistant, nine were resistant, seven were moderately resi stant, eight were susceptible and two were highly susceptible to BYMV infection. Disease progress curves plotted for each test line assisted in the ranking process. Relative rankings were independent of floweri ng data and presence of host alkaloids. Acrythosiphon kondoi, Myzus pe rsicae and Rhopalosiphum padi were the predominant aphid species caugh t in traps associated with field screening plots. Seven plant species tested were new BYMV host records. Seed of four plant species systemic ally infected following sap inoculation with BYMV was tested, and seed transmission detected in Melilotus indica (0.5%). When seed of 19 alt ernative host species that became systemically infected through natura l spread was tested, seed transmission was found in Medicago polymorph a (0.9%), Medicago truncatula (0.3%), M. indica (1%), T. arvense (0.1% ), T. campestre (0.2%) and T. glomeratum (0.05%). No seed transmission was detected in T. subterraneum. It is concluded that under broadacre agriculture in the Mediterranean climate of Western Australia, seed-b orne infection in naturalized M. polymorpha, T. arvense, T. campestre and T. glomeratum growing in T. subterraneum pastures probably provide s the principal means by which BYMV persists over the dry summer to ac t as primary sources for subsequent spread. The species most likely to contribute to BYMV spread within T. subterraneum pastures and from th em to Lupinus angustifolius crops were L. cosentinii, T. campestre, T. dubium and T. subterraneum itself.