Different potato virus Y strains frequently co-localize in single epidermal leaf cells and in the aphid stylet

Single aphids can simultaneously or sequentially acquire and transmit multiple potato virus Y (PVY) strains. Multiple PVY strains are often found in the same field and occasionally within the same plant, but little is known about how PVY strains interact in plants or in aphid stylets. Immuno-staining and confocal microscopy were used to examine the spatial and temporal dynamics of PVY strain mixtures (PVYO and PVYNTN or PVYO and PVYN) in epidermal leaf cells of ‘Samsun NN’ tobacco and ‘Goldrush’ potato. Virus binding and localization was also examined in aphid stylets following acquisition. Both strains systemically infected tobacco and co-localized in cells of all leaves examined; however, the relative amounts of each virus changed over time. Early in the tobacco infection, when mosaic symptoms were observed, PVYO dominated the infection although PVYNTN was detected in some cells. As the infection progressed and vein necrosis developed, PVYNTN was prevalent. Co-localization of PVYO and PVYN was also observed in epidermal cells of potato leaves with most cells infected with both viruses. Furthermore, two strains could be detected binding to the distal end of aphid stylets following virus acquisition from a plant infected with a strain mixture. These data are in contrast with the traditional belief of spatial separation of two closely related potyviruses and suggest apparent non-antagonistic interaction between PVY strains that could help explain the multitude of emerging recombinant PVY strains discovered in potato in recent years.

LINKAGE CHARACTERIZATION OF RESISTANCE TO ZYMV AND WMV-2 IN THE INBRED CHINESE CUCUMBER LINE TMG-1

TMG-1 is resistant to ZYMV and WMV-2, two closely related potyviruses. Resistance to ZYMV is due to a single recessive gene (Provvidenti, 1987); however, two recessive genes appear to confer resistance to WMV-2. We sought to further characterize the resistances by studying possible linkage relationships with physiological, morphological, electromorphic, and phytopathological markers. TMG-1, WI-2757 (an inbred line susceptible to both viruses), and their F2 progeny were screened for various single gene characters that differ between the two parents. Linkages reported in the literature were also observed in this study: (1) between bitterfree (bi) and female (F), and (2) between numerous spine (ns), small spine (ss), and tuberculate (Tu). New linkages detected were between: (1) resistance to WMV-2 and F, (2) resistance to WMV-2 and ZYMV, and (3) possibly resistance to ZYMV with fusarium and ns.