SPREAD OF POTATO LEAFROLL VIRUS IS DECREASED FROM PLANTS OF POTATO CLONES IN WHICH VIRUS ACCUMULATION IS RESTRICTED

Tubers of eight potato clones infected with potato leafroll luteovirus (PLRV) were planted as 'infectors' in a field crop grown, at Invergow rie, of virus-free potato cv. Maris Piper in 1989. The mean PLRV conte nts of the infector clones, determined by enzyme-linked immunosorbent assay (ELISA) of leaf tissue, ranged from c. 65 to 2400 ng/g leaf. Myz us persicae colonised the crop shortly after shoot emergence in late M ay and established large populations on all plants, exceeding 2000/pla nt by 27 June. Aphid infestations were controlled on 30 June by insect icide sprays. Aphid-borne spread of PLRV from plants of the infector c lones was assessed in August by ELISA of foliage samples from the neig hbouring Maris Piper 'receptors'. Up to 89% infection occurred in rece ptor plots containing infector clones with high concentrations of PLRV . Spread was least (as little as 6%) in plots containing infectors in which PLRV concentrations were low. Primary PLRV infection in guard ar eas of the crop away from infectors was 4%. Some receptor plants becam e infected where no leaf contact was established with the infectors, s uggesting that some virus spread may have been initiated by aphids wal king across the soil.