Effect of environmental conditions and leafhopper gender on Maize chlorotic dwarf virus transmission by Graminella nigrifrons (Homoptera: Cicadellidae).

To determine the most economical and efficient means to maintain cultures of Maize chlorotic dwarf virus (MCDV) and to screen for host plant resistance to MCDV, we evaluated the effects of temperature, light intensity, daylength, atmospheric pressure, and leafhopper gender on the frequency of transmission of MCDV by Grarminella nigrifrons Forbes (Homoptera: Cicadellidae). Female leafhoppers transmitted at higher frequencies than males under most conditions. In temperature studies, transmission rates for both male and female leafhoppers progressively increased as temperatures rose from 20 to 30 degrees C. At high light intensities, both males and females transmitted at greater frequencies than they did at low. Similarly, longer day lengths were correlated with higher transmission rates for both sexes. No significant differences in transmission rates were observed in response to differences in atmospheric pressure. The results also showed that transmission rates under most conditions are high enough to overcome potential ambiguities caused by inoculated susceptible plants that do not become infected (disease escapes) when screening for resistance.

Accumulation of maize chlorotic dwarf virus proteins in its plant host and leafhopper vector.

The genome of Maize chlorotic dwarf virus (MCDV; genus Waikavirus; family Sequiviridae) consists of a monopartite positive-sense RNA genome encoding a single large polyprotein. Antibodies were produced to His-fusions of three undefined regions of the MCDV polyprotein: the N-terminus of the polyprotein (R78), a region between coat proteins (CPs) and the nucleotide-binding site (NBS) (R37), and a region between the NBS and a 3C-like protease (R69). The R78 antibodies react with proteins of 50 kDa (P50), 35 kDa (P35), and 25 kDa (P25) in virus preparations, and with P35 in plant extracts. In extracts of the leafhopper vector Graminella nigrifrons fed on MCDV-infected plants, the R78 antibodies reacted with P25 but not with P50 and P35. The R69 antibodies bound proteins of approximately 36 kDa (P36), 30 kDa (P30), and 26 kDa (P26) in virus preparations, and P36 and P26 in plant extracts. Antibodies to R37 reacted with a 26-kDa protein in purified virus preparations, but not in plant extracts. Neither the R69 nor the R37 antibodies bound any proteins in G. nigrifrons. Thus, in addition to the three CPs, cysteine protease and RNA-dependent RNA polymerase, the MCDV polyprotein is apparently post-transitionally cleaved into P50, P35, P25, P36, P30, and P26.