Heritability of early blight resistance in a Lycopersicon esculentum x Lycopersicon hirsutum cross estimated by correlation between parent and progeny

Sixteen-hundred BC1 plants of a cross between an early blight (EB) suscepti ble tomato (Lycopersicon esulentum Mill.) breeding line ('NC84173'; materna l and recurrent parent) and a resistant accession ('PI126445') of the tomat o wild species Lycopersicon hirsutum Humb. and Bonp1, were grown in a field in 1998. This population was segregating (among other traits) for growth h abit, self-incompatibility and earliness in maturity. To eliminate confound ing effects of these factors on disease evaluation and h(2) estimation, pla nts that were self-incompatible, indeterminate and/or late-maturing were el iminated. The remaining plants (146), which were self-compatible and determ inate (sp./sp.) in growth habit, with early- to mid-season maturity, were e valuated for EB resistance and self-pollinated to produce BC1S1 seed. The 1 46 BC1S1 progeny families, consisting of 30 plants per family, were grown i n a replicated field trial in 1999 and evaluated for EB resistance and plan t maturity. For each of the 146 BC1 plants and corresponding BC1S1 families , the area under the disease progress curve (AUDPC) and final disease sever ity (final percentage defoliation) were determined and used to measure dise ase resistance. The distributions of the AUDPC and final percentage defolia tion values in the BC1 and BC1S1 generations indicated that resistance from 'PI126445' was quantitative in nature. Estimates of h2 for EB resistance, computed by correlation between BC1S1 progeny family means and BC1 individu al plant values, ranged from 0.69 to 0.70, indicating that EB resistance of 'PI126445' was heritable. Across BC1S1 families, a small, but significant, negative correlation (r = -0.26, P < 0.01) was observed between disease re sistance and earliness in maturity. However, several BC1S1 families were id entified with considerable EB resistance and reasonably early maturity. The se families should be useful for the development of commercially acceptable EB-resistant tomato lines.