Host range and overwintering sources of bean leaf roll and pea enation mosaic viruses in England

SUMMARY Bean leaf roll virus (BLRV) and pea enation mosaic virus (PEMV) were each transmitted by Acyrthosiphon pisum (Harris) to fifteen of thirty species of legumes in the glasshouse; eleven species were susceptible to both viruses. The only biennial or perennial species infected by BLRV were hop trefoil (Medicago lupulina L.), lucerne (M. sativa L.) and red clover (Trifolium pratense L.), but naturally infected sainfoin (Onobrychis viciifolia Scop.) and white clover (T. repens L.) were found. The only perennial species infected with PEMV in the glasshouse was kidney vetch (Anthyllis vulneraria L.). Eggs of A. pisum , which seems to be the main vector of BLRV and PEMV in England, were found in winter on several species of cultivated perennial legumes, most on lucerne, fewest on white clover. In spring, more viviparae of A. pisum were found on lucerne than on other perennial legumes, and many on lucerne, but few on red or white clover, were infective with BLRV. Lucerne is probably the main overwintering source of BLRV in areas where lucerne is common, but elsewhere red and white clovers are probably as important. No aphid collected from perennial legumes between 1965 and 1968 was infective with PEMV, but this virus can overwinter in common vetch (Vicia sativa L.). Lucerne infected with BLRV was usually symptomless or showed only transient mild yellowing of young leaves. Lucerne plants showing vein‐yellowing, similar to that previously reported as a symptom of BLRV, were possibly infected with an aberrant strain of BLRV but more probably with BLRV and another aphid‐transmitted agent. Inoculations from lucerne with vein‐yellowing symptoms sometimes caused vein‐yellowing, and sometimes typical BLRV‐symptoms, in crimson clover (Trifolium incarnatum L.).