Breeding strategies for seed protein content and trypsin inhibitors inferred from combining ability and heterosis in test-crosses of Vicia faba

The relative importance of general and specific combining ability (GCA and SCA, respectively), amount and causes of heterosis and inferences for breed ing strategies were assessed for trypsin inhibitors activity (TIA) and seed protein content (SPC) in Vicia faba test-crosses. Four lines with low ('Bo nd') and high ('H2OS', '98/Tunesien' and 'Canner Express') TIA, and two tes ters ('Rowena' and 'Felicia') with low TIA were used to produce test-crosse s. GCA accounted for 89% and 57% of the test-cross sums of squares for SPC and TIA, respectively; SCA accounted for 48% and 34%, and differences betwe en reciprocals for 6% and 9%. Specific heterosis was large only in low TIA x low TIA test-crosses and tended towards an increased TIA. Epistatic inter action explained the observed specific heterosis for high TIA. Breeding fab a bean hybrids for high SPC and low TIA is not convenient because non-addit ive gene actions exert minimal effects on SPC or are in the undesired direc tion for TIA. Selecting inbred lines which combine low TIA, good SPC and sa tisfactory grain yield is more promising: Rowena and Rowena x Bond are adeq uate as base materials.