DDT resistance in barley, Hordeum vulgare—I : Induced mutants for resistance

Abstract

Most barley cultivars are susceptible to DDT; resistance is recessive and is dependent on one or two pairs of genes. Resistant mutants were induced with γ-rays and ethylene imine in a susceptible biotype. The M 2 mutant seedling frequencies for 10 krads and 20 krads of γ-rays were 6·35and 12·20 (× 10 −5), respectively. The frequencies for 0·68 and 0·08% ethylene imine were 18·72 and 28·96 (× 10 −5), respectively. These data, along with the frequencies of chlorophyll mutations observed, suggested a mutagen-locus specificity response. The degree of resistance for 124 mutants was determined by measuring the chlorophyll content in treated leaf tissue. This classification showed that some of the mutants were only partially resistant, ranging from almost completely resistant to fully susceptible. Segregation ratios of progenies from crosses of the mutants to the susceptible parent indicated that in most cases, the mutation does not reduce its gametic transmissibility. The segregation data and the reduction in chlorophyll content of treated leaf tissue suggested that some of the mutants were temperature sensitive and that possibly more than one type of gene action was responsible for resistance.