MOVEMENT OF BARLEY MILD MOSAIC AND BARLEY YELLOW MOSAIC-VIRUSES IN LEAVES AND ROOTS OF BARLEY

Leaves of barley plants were mechanically inoculated with barley mild mosaic virus (BaMMV) and roots were inoculated using viruliferous zoos pores of the fungus vector Polymyxa graminis. At intervals after inocu lation, leaves and roots were tested by different methods to detect vi rus coat protein (ELISA or Western blot) or nucleic acid (slot-blot or reverse transcriptase-PCR). Following inoculation with zoospores, vir us could be detected in roots after 1 wk (Western blot or PCR) but not until 3-4 wk by ELISA. Virus moved to leaves in 5-6 wk but, except at temperatures of about 20 degrees C, plants had to be cut back close t o soil level to stimulate virus movement. Following mechanical inocula tion, virus could be detected in leaves of a susceptible cultivar with in 5 days by ELISA and 3 days by the other methods. Western blots and PCR showed that virus was present in the roots by 5 days. BaMMV was no t detected by any method in leaves or roots of a resistant cultivar, i ndicating that the virus did not multiply in it. When leaves were mech anically inoculated on a small area only, BaMMV capsid protein was det ected below the inoculated site at 4 days and in young growing leaves and roots at 13 days after inoculation but never above the inoculation site or in older leaves. After stem extension began, new leaves of in fected plants were free of symptoms. The results are compared to obser vations of plants infected with barley yellow mosaic virus (BaYMV). It is proposed that movement of BaMMV and BaYMV is strongly related to t he phloem transport and to the source-sink pattern of winter barley pl ants.