Resistance of tropical maize inbreds to major virus and fungal diseases.
A germplasm collection of open-pedigree inbreds of tropical background, assembled in Hawaii, was evaluated. A brief summary is given of data for all diseases tested, and data from viral disease evaluations, which included 100-200 inbreds, are examined in detail. The proportion of inbreds showing high or moderate resistance to maize dwarf mosaic potyvirus was 49%, to maize mosaic nucleorhabdovirus 42% and to sugarcane mosaic potyvirus 33%. Fewer were resistant to maize streak monogeminivirus (17%) and very few or none to 2 temperate viruses. Combined resistance to more than 2 viruses was very rare among 55 inbreds tested. The only significant correlation between virus responses was that between the related potyviruses maize mosaic potyvirus and sugarcane mosaic potyvirus (r = 0.49). Major virus resistance genes were verified for maize mosaic potyvirus, maize mosaic nucleorhabdovirus and maize streak monogeminivirus. Resistance was best sought from regions where the virus is endemic. A method of studying inbred from single-seed descent is outlined for identification of major genes influencing quantitative traits.