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Etiology

Leafhopper Transmission and Host Plant Range of Maize Chlorotic Dwarf Waikavirus Strains. João R. S. Lopes, graduate fellow, Department of Entomology, The Ohio State University (OSU), Ohio Agricultural Research and Development Center (OARDC), Present address: Departamento de Entomologia, Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo, Piracicaba, SP, Brazil; Lowell R. Nault(2), and Roy E. Gingery(3). (2)professor, Department of Entomology, The Ohio State University (OSU), Ohio Agricultural Research and Development Center (OARDC); (3)research chemist and adjunct professor, Corn and Soybean Research Unit, U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS), Department of Plant Pathology, OSU-OARDC, Wooster 44691, Present address: USDA-ARS National Program Staff, Room 230, Bld. 005, BARC-West, Beltsville, MD 20705. Phytopathology 84:876-882. Accepted for publication 12 May 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/Phyto-84-876.

Two strains of maize chlorotic dwarf waikavirus (MCDV), the type strain MCDV-T and the recently isolated MCDV-M1, were compared for leafhopper transmission, vector specificity, and host plant range. Leafhopper species tested as vectors and their estimated transmission rates (by single insects) of MCDV-T and MCDV-M1, respectively, were Graminella nigrifrons, 27.0 and 20.4%; Amblysellus grex, 17.5 and 6.7%; Planicephalus flavicostatus, 7.9 and 1.0%; Stirellus bicolor, 5.9 and 1.2%; G. sonora, 1.2 and 2.5%; and Dalbulus maidis, 0.8 and 1.7%. Euscelidius variegatus, Macrosteles quadrilineatus, and Ollarianus strictus were tested as well but did not transmit either strain. No vector was found that transmitted only one of the strains; however, A. grex, P. flavicostatus, and S. bicolor transmitted MCDV-T at rates significantly higher than those for MCDV-M1. Rates of loss of inoculativity of MCDV-T and MCDV-M1 by G. nigrifrons after virus acquisition were similar but were slower at 15 C than at 30 C. Estimated retention half-lives at 15 C for MCDV-T and MCDV-M1 were 7.7 and 12.5 h, respectively. The corresponding half-lives at 30 C were 3.4 and 4.8 h, respectively. A sample of grass species representing the major groups of Gramineae was tested for susceptibility to MCDV strains with G. nigrifrons as a vector. Of 46 grass species tested, 19 (mostly panicoids and andropogonoids) were found to be susceptible to each strain on the basis of symptomatology and detection assays (dot blot hybridization and Western blots). Two symptomless differential hosts were found: Sorghastrum nutans tested positive to MCDV-T but not to MCDV-M1, whereas the reverse was observed for Schizachyrium scoparium. Tertiary veinbanding symptoms induced by MCDV-T in susceptible grasses were always more pronounced than those caused by MCDV-M1. The differences in symptom severity and transmission efficiency observed between MCDV-M1 and MCDV-T support previous conclusions that MCDV-M1 should be considered a new MCDV strain.