Parent-offspring correlation estimate of heritability for early blight resistance in tomato, Lycopersicon esculentum Mill

This study estimated the heritability (h²) of early blight (EB) resistance in filial progeny of a cross between a susceptible ('NC84173'; mid-season maturity) and a resistant ('NC39E'; late-season maturity) tomato breeding lines. It addition, it examined the potential of identifying progeny with mid-season maturity and EB resistance. A total of 162 F₂ plants were grown under field conditions in 1998 and evaluated for disease symptoms three times during the season, and the area under the disease progress curve (AUDPC) and final percent defoliation (disease severity) were determined. The F₂ plants were self-pollinated and F₃ seeds produced. The 162 F₃ progeny families, consisting of 20 plants per family, were grown in a replicated field trial in 1999 and evaluated for EB resistance (final percent defoliation) and plant maturity (days to 50% ripe fruit). The distributions of the final percent defoliation values in the F₂ and F₃ generations indicated that resistance from 'NC39E' was quantitative in nature. Estimates of h² for EB resistance, computed as the correlation coefficients between F₃ progeny family means and F₂ individual plant values, ranged from 0.65 to 0.71, indicating that EB resistance of 'NC39E' was heritable. Across F₃ families, a negative correlation (r =-0.46, p < 0.01) was observed between disease severity and earliness in maturity, indicating that plant maturity affected disease severity. However, several F₃ families were identified with considerable EB resistance and mid-season maturity, indicating that resistance from 'NC39E' might be useful for the development of commercially acceptable EB resistant tomato cultivars.