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Differential Transmission of Mississippi and Ohio Corn Stunt Agents by Graminella nigrifrons. M. M. Choudhury, Graduate Research Assistant, Department of Plant Pathology and Weed Science, Mississippi State University, State College 39762; E. Rosenkranz, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, and Adjunct Associate Professor, Department of Plant Pathology and Weed Science, Mississippi State University, State College. Phytopathology 63:127-133. Accepted for publication 1 August 1972. DOI: 10.1094/Phyto-63-127.

Graminella nigrifrons was established as a vector of the Mississippi corn stunt agent (CSA-MS), in addition to being a vector of the Ohio corn stunt agent (CSA-OH). This leafhopper recovered CSA-MS from corn plants inoculated with CSA-MS by the more efficient vector, Dalbulus maidis. Adults of G. nigrifrons also acquired CSA-MS from corn plants naturally infected in the field in Mississippi. The shortest latent period of CSA-MS in G. nigrifrons was 15-18 days, compared to 12 days for the same agent in D. maidis. The minimum incubation periods of CSA-OH and CSA-MS in corn, infected by G. nigrifrons, were 11 and 15 days, respectively. The efficiency of transmission of CSA-MS by G. nigrifrons was 3-4%; that of CSA-OH, 34%. Beyond 24 hr, transmission efficiency of CSA-MS by this vector was independent of the length of acquisition access or the duration of transmission feeding. Female leafhoppers appeared to transmit CSA-OH more efficiently than did their male counterparts. The occurrence of CSA-OH in field corn in Mississippi was proved for the first time. When noninfective G. nigrifrons were exposed to field-diseased corn plants with typical corn stunt symptoms, some of the leafhoppers acquired CSA-OH, others CSA-MS from the same plants. While attempting to recover the transmitted corn stunt agents from test plants, inoculated by leafhoppers that had acquired the agents from field-diseased corn, a few G. nigrifrons transmitted both CSA-MS and CSA-OH from test plants that showed symptons of only Mississippi corn stunt. In serial transmission experiments, when a colony of G. nigrifrons contained some transmitters of CSA-OH and some of CSA-MS, such a colony would invariably transmit CSA-OH in the first 1 or 2 transfers, then CSA-MS to the subsequent test plants in the series. A few individual leafhoppers were able to transmit both CSA-OH and CSA-MS to the same test plant. Doubly infected test plants always developed symptoms first of CS-OH and later of CS-MS. When noninfective G. nigrifrons were exposed to such doubly diseased plants and then divided into subcolonies, some of these subcolonies transmitted CSA-OH, fewer transmitted CSA-MS, and an intermediate number transmitted both pathogens.

Additional keywords: maize, mycoplasmalike organism, leafhopper transmission.