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Vascular Puncture of Maize Kernels for the Mechanical Transmission of Maize White Line Mosaic Virus and Other Viruses of Maize. Raymond Louie, U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), Corn and Soybean Research Unit, and Department of Plant Pathology, The Ohio State University (OSU), and the Ohio Agricultural Research and Development Center (OARDC), Wooster 44691; Phytopathology 85:139-143. Accepted for publication 31 October 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, 1995. DOI: 10.1094/Phyto-85-139.

Maize white line mosaic virus (MWLMV) was efficiently transmitted (>90%) by a vascular puncture method with insect pins to maize kernels without causing teratogenic or lethal injuries to the developing seedlings. The pins, soldered to a 10-gauge copper wire, were used to puncture vascular tissues of maize kernels. The copper wire and pins were mounted in an engraving tool for machine-assisted inoculation. Effects of preinoculation soaking of kernels in water; postinoculation moisture regimes; the size, number, and configuration of pins; and the site and frequency of inoculation on rates of transmission were evaluated. Transmission rates of MWLMV were highest (average 32%) when the preinoculation soaking of kernels was done at 4 C. In contrast, transmission rates were significantly reduced when the preinoculation soaking of kernels was done at 30 C. The average rates of transmission to inoculated kernels incubated at 30 C on paper towels moistened with either 50 or 150 ml of water in a 2-L Pyrex dish for 24 h or directly planted into soil were 42, 20, and 11% (P > 0.003; LSD = 14.5%), respectively. Inoculations near the side of the embryo averaged 58% transmission whereas inoculations near the tip of the plumule averaged 33% transmission (P > 0.0001). Subjecting kernels to one, two, or three preinoculation soak (24-h) and dry (20- to 24-h) cycles or a 4- or 20-h preinoculation soak period resulted in transmission rates of 95, 90, 87, 80, and 14% (P > 0.0001), respectively. The optimum conditions for MWLMV transmission were 1) the use of a machine-assisted inoculator with minuten pins positioned like the tines of a fork, 2) preinoculation soaking of the kernels at 21 C for 4 h, 3) inoculation of kernels near the side of an embryo, and 4) incubation of kernels at 30 C postinoculation for 24 h on paper towels moistened with 50 ml of water. The ranges of transmission rates with this protocol for the following maize viruses were maize chlorotic dwarf waikavirus, 134%; maize dwarf mosaic potyvirus (strain A), 4182%; maize mosaic rhabdovirus, 119%; maize rayado fino marafivirus, 125%; maize rough dwarf fijivirus (maize Rio Cuarto disease), 1%; maize streak geminivirus, 15%; maize subtle mosaic virus, 1248%; and wheat streak mosaic potyvirus, 355%.