SPREAD OF MAIZE CHLOROTIC DWARF VIRUS FROM INFECTED CORN AND JOHNSONGRASS BY GRAMINELLA-NIGRIFRONS

Early emerged adults (males and females) or last instar nymphs (males, females, or males and females together) of the leafhopper Graminella nigrifrons were allowed to acquire maize chlorotic dwarf virus (MCDV) from corn or johnsongrass source plants positioned in the center of maize plots in 1990. In 1991, two planting dates of maize were tested by using newly emerged adult males, females, or males and females. After leafhopper acquisition and potential flight to other plants, disease incidence was assessed throughout the plots. The log-logistic model provided an acceptable fit to the observed disease gradients. MCDV incidence was higher when infected corn was used as a virus source compared to johnsongrass in 1990 and both plantings of 1991. Leafhopper sex did not influence disease incidence. The intercept of the linearized log-logistic model (a) was higher for corn virus source only in 1990. The slope parameter (b), a gradient steepness, was not affected by leafhopper sex or virus source plant.