PATH COEFFICIENT ANALYSIS OF OZONE EFFECTS ON SEED YIELD AND SEED YIELD COMPONENTS OF BEAN (PHASEOLUS-VULGARIS L)

Field experiments were conducted to determine the effects of ozone (O3) on seed yield, number of seeds plant-1, number of seeds pod-1, seed size, number of pods plant-1, number of branches plant-1, and plant height of sensitive and insensitive bean, Phaseolus vulgaris L. genotypes. The genetic materials used in these studies were derived by crossing 'BBL 254' with PI 300657, and 'BBL 290' with PI 304833. The two cultivars BBL 290 and BBL 254 are sensitive to O3 injury, whereas PIs 300657 and 304833 are insensitive to O3 injury. Path coefficient analysis is presented for the data combined over a two-year field experiment in which the effects of eight genetic materials used on seed yield, seed yield component, and O3 injury rating were assessed. The most important path of influence on seed yield was via plant height and seed number pod-1 and pod number plant-1. The two variables, plant height and pod number plant-1 are also the most affected by O3. Therefore, selection based on seeds pod-1 and plant height, and pod number plant-1 is likely to increase seed yield in beans. Significant differences were observed for all traits studied within the genetic materials used. The sensitive parents BBL 254 and BBL 290 had significantly higher O3 injury rating and lower seed yield than either the insensitive parents PI 300657 or PI 304833, or their corresponding F2 and F3 progenies. This result indicates that genetic materials are available for further hybridization and selection. The mean O3 injury ratings of the F2s and F3s do not differ significantly from their mid-parent values, suggesting that the expression of O3 insensitivity is primarily additive. The phenotypic and genotypic correlation coefficients agreed closely in each comparison, with the genotypic coefficients being usually higher than the phenotypic ones. Bean seed yield showed significant positive associations with seed number plant-1, seed number pod-1, seed size, and plant height at both genotypic and phenotypic levels. All these traits including seed yield showed significant negative associations with O3 injury rating ranged from 1 (0-20% injury) to 5 (> 80% injury).