Evaluation of Maize Chlorotic Dwarf Virus Resistance in Maize with Multiple Inoculations by Graminella nigrifrons (Homoptera: Cicadellidae)

Abstract

Disease escapes have hindered the progress of evaluation of maize, Zea mays L. subspp. mays , germ plasm for maize chlorotic dwarf virus (MCDV)resistance. The behavior of the primary leafhopper vector, Graminella nigrifrons (Forbes), is the least controllable variable in the disease evaluation process. This variable was minimized in a compact, multiple-inoculation method in a growth chamber where maize seedlings (2-3 d old) were exposed to a different group of viruliferous leafhoppers at 2-d intervals over a 6-d period. The reactions of fourteen resistant maize inbreds and the standard susceptible inbred Oh28 were determined in three comparative tests between the previous single inoculation method and this multiple-inoculation method. At 2 wk after inoculation, infections were >90% in most inbreds in the multiple-inoculation method. At 3 wk after inoculation (except for one plant in inbred Pall in one test), all plants were infected. In contrast, at 2 and 3 wk after inoculation in the single-inoculation method, MCDV infections averaged 78 and 82%, respectively. In all three tests, the mean percentage transmission at the second and third evaluation was greater in plants with the multiple-inoculation method.