Search

Linkage disequilibrium can be used for identifying associations between traits of interest and genetic markers. This study used mapped diversity array technology (DART) markers to find associations with resistance to stem rust, leaf rust, yellow rust, and powdery mildew, plus grain yield in five historical wheat international multienvironment trials from the International Maize and Wheat Improvement Center (CIMMYT). Two linear mixed models were used to assess marker-trait associations incorporating information on population structure and covariance between relatives. An integrated map containing 813 DArT markers and 831 other markers was constructed. Several linkage disequilibrium clusters bearing multiple host plant resistance genes were found. Most of the associated markers were found in genomic regions where previous reports had found genes or quantitative trait loci (QTL) influencing the same traits, providing an independent validation of this approach. In addition, many new chromosome regions for disease resistance and grain yield were identified in the wheat genome. Phenotyping across up to 60 environments and years allowed modeling of genotype x environment interaction, thereby making possible the identification of markers contributing to both additive and additive x additive interaction effects of traits.

In a comparison of susceptible and resistant genotypes, studies show that the disease Peronospora parasitica increases the competitive ability of the resistant genotype in the plant Arabidopsis thaliana. However, in the absence of P. parasitica, the susceptible genotype is the stronger competitor, while the resistant genotype increases seed generation.

Maize dwarf mosaic, caused by maize dwarf mosaic virus (MDMV), is the most widespread virus disease of maize (Zea mays L.) in the USA. The objectives of this study were to determine the effectiveness of selecting for resistance to MDMV under greenhouse conditions and to determine if the resistant selections had a gene, presumably Mdm1, for resistance to MDMV that was linked to the endosperm color locus, Y1, on Chromosome 6. One resistant selection was developed from each of six different races of corn crossed with a susceptible hybrid, and two additional resistant selections were obtained out of a synthetic developed in Mississippi. All selections were resistant in field trials in Mississippi. All except one had a higher level of resistance than the field resistant checks in greenhouse tests in Ohio. Three selections had infection levels similar to the highly resistant check inbred, Pa405. Except one, all resistant selections had a gene for resistance linked to the endosperm color locus on Chromosome 6. Apparently, the Mdm1 gene is common in many resistant lines, but the data on one line, Mp92:448, suggest resistance is possible without this gene.