Resistance to phloem transport of potato leafroll virus in potato plants

Abstract

A 'double-graft sandwich' technique in which sections of potato stem from different potato cultivars were grafted between a susceptible healthy stock plant and a potato leafroll virus (PLRV)-infected scion was used to study the rate of phloem transport of PLRV in cultivars differing in resistance to PLRV infection (I R) and accumulation (AR). Resistance to phloem transport (i.e. delayed PLRV systemic movement) was found in Bismark cultivar (I R AS). This was independent of I R and A R as the rate of movement in Bismark cultivar was markedly slower than that in Omega and Spunta (I R AR), Delaware (I s AR), and Desiree and Renova (I s A s) cultivars. It operated in Bismark cultivar stems of two different ages, but did not operate against potato virus X (PVX) and was not influenced by previous infection with this virus. Aphid vector (Myzuspersicae) feeding preferences and colonization rates differed between cultivars, but the cultivar characteristics responsible were unrelated to I R, A R or resistance to phloem transport. Delayed systemic movement of PLRV out of leaves inoculated with viruliferous aphids was independent of A R and resistance to phloem transport, and remained unaffected by previous infection with PVX. It was also independent of cultiwlr factors causing different aphid feeding preferences and colonization rates, but may be linked to I R.

Short and long distance spread of potato leafroll luteovirus: effects of host genes and transgenes conferring resistance to virus accumulation in potato.

“…In our experiments, the movement of PLRV through two graft unions began around 7 days after grafting and was generally complete by about 14 to 16 days, though in some experiments, virus movement was slightly slower. Very similar estimates were made by Wilson & Jones (1992). Movement of virus through grafts occurred soon after acquiring functional phloem continuity across grafts as demonstrated by 6(5)-carboxyfluorescein tracing (around 7 days after grafting ; Table 1).…”

“…It is, therefore, likely that neither the H-MR nor T-MR mechanisms present in the tested clones cause a slowing of PLRV movement along phloem strands. In similar experiments, Wilson & Jones (1992) observed that test stem pieces of potato cv. Bismark did reduce the rate of PLRV movement and suggested that this was possibly the result of the severe necrosis associated with PLRV infection in this cultivar.…”

“…In potato, there are several lines of evidence suggesting that a mechanism operates in resistant clones to restrict PLRV movement in phloem tisue (Golinowski et al, 1987 ;Derrick & Barker, 1992 ;Wilson & Jones, 1992). Likewise, restriction of virus movement in vascular tissue has been shown to be a factor in pepper lines that are resistant to cucumber mosaic virus (Dufour et al, 1989).…”

“…Host gene-mediated resistance (H-MR) and transgenemediated resistance (T-MR) in plants transformed with the PLRV coat protein gene have been shown to be effective in decreasing PLRV accumulation in infected potato plants (Barker & Harrison, 1985 ;Kawchuk et al, 1990 ;Van der Wilk et al, 1991 ;Barker et al, 1992 ;Wilson & Jones, 1992). Furthermore, in plants with either of these types of resistance, PLRV-infected cells were found to be restricted largely to internal (adaxial) phloem bundles (Barker & Harrison, 1986 ;Derrick & Barker, 1992).…”

“…Bismark (Hutton & Brock, 1953) and clone G7445(1) (Barker, 1987 b). Wilson & Jones (1992) found that the rate of systemic movement of PLRV through grafted stem sections of cv. Bismark was considerably slower than through stem tissues of susceptible potato cultivars.…”