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Resistance

Role of Vigna species in the Appearance of Pathogenic Variants of Cucumber Mosaic Virus. D. K. Lakshman, Former graduate research assistant, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; D. Gonsalves(2), and R. W. Fulton(3). (2)Associate professor, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; (3)Professor, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706. Phytopathology 75:751-757. Accepted for publication 12 February 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-751.

To determine the role of host plants in the appearance of new strains of cucumber mosaic virus (CMV), two cowpea cultivars, namely, Vigna unguiculata ssp. unguiculata 'Blackeye' and V. unguiculata ssp. cylindrica 'Catjang,' were investigated as model systems. Four strains of CMV, selected by several single-lesion transfers through Chenopodium quinoa, caused numerous necrotic lesions with diameters of 0.1- 0.2 cm and ≤0.1 cm on the inoculated primary leaves of Blackeye and Catjang, respectively. Additionally, large necrotic lesions (0.4- 0.6 cm in diameter) appeared at a rate of 0.11- 5.26% (0.53% average) of the total lesions on Catjang and only 0.02% of those on Blackeye. Inocula from large lesions derived from Catjang caused similar lesions on Blackeye. Unlike their parent strains, some large-lesion isolates became systemic to Blackeye. Large-lesion isolates were stable under continual passages through Catjang but reverted to small-lesion types after four serial passages by mass inoculation through C. quinoa, cucumber, squash, or tobacco. Cross protection and serological tests indicated that the large-lesion isolates were CMV. They were also indistinguishable from respective parent strains as determined by coat protein peptide mapping, RNA profile, and symptomatology on differential hosts. This suggested that the large-lesion isolates were mutants and not contaminants already present in the various isolates. Presence or absence of satellite RNA did not affect the appearance and/or size of large lesions on Catjang. Their initital expression on Catjang provides an example of a specific host-selection mechanism which might add to the high variability of CMV.