variation in virus content among individual leaves and roots of barley and wheat infected with a bydv-pav isolate

elisa values (o.d.s) of extracts of separately roots and individual leaves of barley and wheat plants infected by a french bydv-pav isolate (pav-4), were assessed for five dif-ferent virus incubation periods in controlled conditions (5, 10, 15, 20 and 25 days after in-oculation). in most cases, virus contents of individual roots or leaves were not statistically different for barley and wheat. for both plant species, elisa values peaked sooner in roots than in leaves and in most harvesting dates were higher in roots. the old leaf had a significantly lower virus titre than other leaves. upper leaves exhibited the highest elisa values. these results indicate that the upper part of infected plants is the most suitable for virus acquisition by aphids. a scheme for bydv-pav spread in young plants is proposed, and compared to the distribution of vectors on the plants.