Characterization of the recessive resistance gene cyv1 of Pisum sativum against Clover yellow vein virus

Two recessive resistance genes against Clover yellow vein virus (ClYVV), cyv1 and cyv2, have been previously reported. We recently screened resistant peas from a separate set of pea lines and classified them into two groups according to their distinct modes of resistance. We later revealed that one group carries cyv2, encoding eukaryotic translation initiation factor 4E (eIF4E), in linkage group (LG) VI. We explored the possibility that the resistance gene, tentatively designated non-cyv2, that confers resistance to the other group, was actually cyv1. We found that PI 236493, which carries cyv1, had restricted cell-to-cell movement of ClYVV similar to that in non-cyv2 peas including PI 429853. PI 429853 was crossed with susceptible line PI 250438. Mapping of F₂ progeny revealed that non-cyv2 was 4?cM from the simple sequence repeat marker AB40, whose loci are close to cyv1, mo, and sbm-2 mapped in LG II, which mediates resistance to other potyviruses. Moreover, PI 429853 crossed with PI 236493 produced F₁ progeny resistant to ClYVV, raising the possibility that non-cyv2 is allelic to cyv1. Because mo was previously mapped with eIF(iso)4E in LG II, we examined the possibility that non-cyv2, cyv1, and mo encoded eIF(iso)4E. However, there was no difference in the nucleotide sequence of the eIF(iso)4E-coding region between susceptible and resistant pea lines. The eIF(iso)4E gene was equivalently expressed in both PI 429853 and PI 250438 before and after ClYVV infection. Our results suggest that these resistance genes are unlikely to encode eIF(iso)4E on LG II.