Testing maize hybrids for susceptibility to maize rough dwarf reovirus by experimental inoculation with the vector Laodelphax striatellus.

Maize rough dwarf virus (MRDV), a plant fijivirus persistently transmitted by the planthopper Laodelphax striatellus, causes, sometimes, severe epidemics in North- Western Italy. During 1988, in an experimental field not designedad hoc,MRDV showed different incidence on different hybrids. To check the field observations, six hybrids were chosen for inoculation with an isolate of MRDV by the vector in controlled conditions. Plants were grown in pots, in an insect-proof glasshouse, and individually inoculated with two hoppers each. After removal of insects, the plants were observed for symptoms for at least 30 days, then sampled and tested for MRDV by ELISA. None of the symptomless plants gave positive ELISA results. The collected insects were frozen and later tested for MRDV by ELISA. The survival of hoppers was similar on different maize hybrids. To overcome the variability of transmission efficiencyamong different groups of insects, only those plants were considered which had really been exposed to infective insects, as determined by ELISA of the insects recovered. The hybrids 'Furia' and 'Radiant' (mean P= 0.36) were significantly less susceptible than the other hybrids tested ('Alvarado ', 'Basic', 'Itala ' and 'Sprint') (mean P= 0.68).