VIEW ARTICLE

Genetics

Cry, the Resistance Locus of Cowpea to Cucumber Mosaic Virus Strain Y. Yoshiko Nasu, Faculty of Agriculture, Tohoku University, Tsutsumidori-Amamiyamachi 1-1, Aoba-ku, Sendai 981, Japan; Akira Karasawa, Shuu Hase, and Yoshio Ehara. Faculty of Agriculture, Tohoku University, Tsutsumidori-Amamiyamachi 1-1, Aoba-ku, Sendai 981, Japan. Phytopathology 86:946-951. Accepted for publication 3 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-946.

Most cowpea cultivars are resistant to infection by cucumber mosaic virus strain Y (CMV-Y) that causes a hypersensitive reaction followed by the development of necrotic local lesions. It has been anticipated that resistance to CMV-Y depends upon the existence of a resistance (R) gene in cowpea. To define the nature of the R gene, we screened 38 cowpea cultivars to isolate susceptible ones. The cultivar PI 189375 was identified as susceptible based on symptoms and the presence of progeny virions on noninoculated upper leaves. Protoplasts prepared from both ‘PI 189375’ and the resistant cultivar Kurodane-Sanjaku supported virus multiplication. This result suggested that there was no difference between the capacities for virus multiplication in both cultivars at a single-cell level, implying an expression of the specific R gene in intact ‘Kurodane-Sanjaku’ plants. F₁ and F₂ populations were then constructed by reciprocal crosses between ‘Kurodane-Sanjaku’ and ‘PI 189375’. Reactions of F₁ and F₂ populations to CMV-Y inoculation demonstrated that the R gene was inherited as a single dominant gene. We designated this resistance locus as Cry (cowpea R gene to CMV-Y).