Genetic Control of O3 Sensitivity in a Cross Between Two Cultivars of Snap Bean

Abstract

Identification of genetic control of ozone (O 3 ) sensitivity is desirable for selection of plant cultivars which are indicators of O 3 stress. A cross was made between two cultivars of snap bean ( Phaseolus vulgaris L . ), `Oregon 91' (P 1 ) and `Wade Bush' (P 2 ), an O 3 -sensitive and O 3 -insensitive cultivar, respectively. Ten genetic populations (generations), `Oregon 91' (P 1 ), `Wade Bush' (P 2 ), F 1 , F 2 , backcrosses to both parents, and all reciprocal crosses, were field planted in each of two summers and evaluated for injury to O 3 . Ozone responses for the reciprocal crosses were not significantly different for any generation, so injury ratings from the reciprocal crosses were combined for each generation to provide six populations (P 1 , P 2 , F 1 , F 2 , BC 1 , and BC 2 ) for analysis. When components of genetic variation were estimated from the six generations, additive genetic variance was the most important component in the total genetic variance available, although dominance variance was also a significant component. There was an inconsistency in the magnitude and the direction of the factors contributing to the dominance effects and also a large environmental component making up the phenotypic variance. Estimates of broad-sense heritability and narrow-sense heritability were 60% and 44%, respectively. Results suggest that O 3 -sensitive and O 3 -insensitive selections could be screened and evaluated in an ambient O 3 environment. Several generations will be necessary, however, to develop `Bush Blue Lake' type selections that vary only in sensitivity to O 3 .