CHARACTERIZATION AND MOLECULAR-DETECTION OF THE P4 PATHOTYPE OF PEA SEED-BORNE MOSAIC POTYVIRUS

The New York isolate of pea seedborne mosaic potyvirus (PSbMV) pathotype P4 was differentiated from the more prevalent PSbMV-P1 pathotype on selected pea cultivars, serologically and by sequence-specific reverse transcription-polymerase chain reaction (RT-PCR). PSbMV-P4 was seed-transmissible at much lower rates than PI (0 to 0.7% versus 0 to 32%) in selected pea cultivars and was not detectable by enzyme-linked immunosorbent assay (ELISA) in reproductive tissues (pollen or embryo axes) of pea, whereas P1 was readily detectable in these tissues. P4 also was aphid-transmitted at lower rates (4 to 16%) than those of P1 (11 to 40%) and had distinct virus acquisition-time optima. RT-PCR detected approximately 10 pg of P4 RNA per 1.0 mu g of total nucleic acids from P4-infected tissues and provided positive pathotype identification in single or mixed infections. RT-PCR and pathotype-selective ELISA were used to determine seed-transmission rates of the two pathotypes in seedling progeny of pea (Pisum sativum) cultivars inoculated with P1, P4, or P1 + P4. There were slight variations in the frequency of P1 seed transmission in the presence of P4; P4 seed-transmission rates did not increase in the presence of P1.