Potato tuber necrosis induced by alfalfa mosaic virus depends on potato cultivar rather than on virus strain

Citation

Nie, X., Dickison, V., Singh, M., de Koeyer, D., Xu, H., Bai, Y., Hawkins, G. (2020). Potato tuber necrosis induced by alfalfa mosaic virus depends on potato cultivar rather than on virus strain. Plant Disease, [online] 104(2), 340-347. http://dx.doi.org/10.1094/PDIS-04-19-0827-RE

Plain language summary

In a previous study, we identified alfalfa mosaic virus (AMV) as the disease-causing agent of tuber flesh necrosis (internal death of the tuber tissue) in potato cultivar Innovator in New Brunswick (Nie et al. 2015). In this study, the virus isolate (designated as CaM) was further investigated for its disease-causing ability in six potato cultivars and one breeding clone. Four cultivars (i.e., Innovator, Yukon Gold, Rochdale Gold-Dorée and Shepody) developed needle-sized necrotic (dead tissue) spots and increasing yellow mosaic (aka calico) symptoms on new leaves, whereas the remaining cultivars only developed calico symptoms on new leaves. All tubers of CaM-infected Innovator and Shepody developed internal necrosis, as did about 23% and 8% tubers of CaM-infected Yukon Gold and Rochdale Gold-Dorée, respectively. Molecular analysis showed that CaM and Ca175-1, an AMV isolate that was deemed non-necrotic in a previous study (Xu and Nie 2006), had different genetic types (i.e., haplotypes): IA-I-IB (CaM) vs. Ca175-1 (IB-II-IA). Interestingly, 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.

Abstract

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 “nonnecrotic” 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 nonnecrotic 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.

Publication date

2020-01-01