Mutation in sunflower showing altered resistance to phoma black stem disease

A study was undertaken to evaluate the genetic variability among gamma-irradiation induced sunflower mutants for partial resistance to phoma black stem. A population of 60 mutant lines and the original line AS613 were evaluated with an aggressive French isolate of Phoma macdonaldii (MP6) under the controlled condition. High genetic variability was observed among the mutant lines for resistance to black stem. Genetic analysis revealed that partial resistance in the mutant line M6-54-1 was controlled by recessive gene(s). The F1 hybrid developed by crossing M6-54-1 to a susceptible inbred ENSAT-B4 was, however, significantly less susceptible than the susceptible parent, indicating that the difference between the F1 hybrid and its parents in reaction to phoma black stem can not be fully explained by the recessive gene model. Dominance between alleles (epistasis) caused reduced susceptibility in the F1 progeny, which were also clearly reflected in distributions of phenotypic reactions of F2 and backcross seed lings. Generation mean analysis confirmed that epistatic effects contributed significantly to genetic variation in phoma black stem resistance in M6-54-1.