Genetic control of maize resistance to corn stunt spiroplasma

The corn stunt spiroplasma (CSS) is transmitted by Dalbulus maidis leafhopper. The disease causes severe losses on maize production. One complete diallel genotype of two corn stunt resistant maize lines, and two corn stunt susceptible maize lines were tested by spiroplasma inoculation under insect-proof screenhouse condition, in order to elucidate the maize genetic control to this disease. The percentage of reduction on plant dry weight caused by the spiroplasma inoculation in relation to the dry weight average of the healthy plants, was calculated for each plant spiroplasma inoculated, to express maize resistance. The disease incidence for each treatment was represented by the percentage of plants with CSS symptoms. The disease severity was scored based on CSS symptoms severity, for each plant. Reductions on the dry weight were caused by the disease; the disease severity data showed a positive and strong correlation (r = 0.80). The statistical analyses indicated that genetic control of maize resistance to spiroplasma includes genes with additive effects and genes with dominance or epistatic effects, suggesting complex resistance inheritance. One line was better performing than all the others, reducing the disease damage, as well per se as in crosses.