Assessing Potato Cultivar Sensitivity to Tuber Necrosis Caused by Tobacco rattle virus

Elimination of Tobacco rattle virus from viruliferous Paratrichodorus allius in greenhouse pot experiments through cultivation of castle russet

Corky ringspot (CRS) is a widespread potato tuber necrotic disease caused by Tobacco rattle virus (TRV) infection. In the Pacific Northwest, this virus is transmitted by the stubby root nematode (SRN) within the genus Paratrichodorus. Remediating CRS affected fields is a major challenge that can be mitigated by growing plant varieties that are resistant to TRV infection. Growing alfalfa has been shown to reduce TRV levels in CRS infested fields over time but the development of a potato cultivar with these same capabilities would be of great economic benefit to potato growers. Castle Russet is a new potato clone that does not develop symptoms of CRS disease. To assess its ability to reduce soil virus load, Castle Russet, tobacco var. “Samsun NN”, alfalfa var. “Vernema”, and Russet Burbank potato were grown for a period of 1 to 3 months in soils containing viruliferous SRN populations at two different inoculation pressures (60 nematodes/pot and 1060 nematodes/pot) in greenhouse pot experiments. SRN population size and the presence of TRV were assessed over several months post inoculation. Results indicate that plant host and length of exposure significantly influence SRN population dynamics, whereas the TRV infection status of bait plants was significantly affected by both of these factors as well as inoculation pressure. These results suggest that both alfalfa var. “Vernema” and Castle Russet are resistant to TRV infection and may potentially be used to eliminate the virus from fields affected by CRS.

Potato Tuber Necrosis Induced by Alfalfa Mosaic Virus Depends on Potato Cultivar Rather Than on Virus Strain

Alfalfa mosaic virus (AMV) was identified as the causal agent of internal tuber necrosis in the potato cultivar Innovator in New Brunswick, Canada. Further pathological characterization of the isolate (designated as isolate CaM) was performed on six potato cultivars and one breeding clone. Upon mechanical inoculation, four cultivars (Innovator, Yukon Gold, Rochdale Gold-Dorée, and Shepody) showed needle-sized necrotic spots and increasing calico symptoms on new leaves, whereas the remaining cultivars only developed calico symptoms on new leaves. All tubers of CaM-infected Innovator and Shepody plants developed sporadic internal necrotic spots, as did ca. 23 and 8% tubers of CaM-infected Yukon Gold and Rochdale Gold-Dorée, respectively. Sequence analysis of the CP gene of CaM with AMV isolates from potato, all presumed belonging to the "non-necrotic" strain and retrieved from GenBank, indicated that CaM shared >97.1% sequence identity with all but four Egyptian isolates. At the complete genome level, phylogenetic analysis of all available sequences demonstrated that RNA 1 and RNA 3 can be grouped into three major clades each, whereas RNA 2 can be clustered into two clades. CaM and Ca175-1, an AMV isolate that was deemed non-necrotic in a previous study, had different phylogenetic clade patterns, indicating different RNA 1-RNA 2-RNA 3 haplotypes: IA-I-IB (CaM) versus Ca175-1 (IB-II-IA). Despite the difference in haplotype composition, CaM and Ca175-1 induced similar levels of internal necrosis in tubers of Innovator and its parent Shepody. The results suggest that the internal necrosis in AMV-infected tubers depends on potato cultivar rather than on AMV strain/haplotype, and CaM is just a "regular" isolate of AMV.