Diallel analysis of yield components of snap beans exposed to two temperature stress environments

Ten snap beans ('Barrier', 'Brio', 'Carson', 'Cornell 502', 'CT 70', 'HB 1880', 'Hystyle', 'Labrador', 'Opus' and 'Venture') were selected for differential temperature tolerance and used as parents in a complete diallel mating design. The 45 F-1 hybrid lines (with reciprocals) and parents were screened at 32 degrees C day/28 degrees C night, and in a separate experiment, 16 degrees C day/10 degrees C night, during reproductive development in replicated controlled environments. Variation for yield under temperature treatments was observed among parents and hybrids, with certain hybrids exceeding parental performance. Significant (P <= 0.0001) general combining ability (GCA), and significant (P <= 0.05) specific combining ability (SCA) were observed for yield components including pod number, seed number, and seeds per pod. There was evidence that pod number and seeds per pod under temperature stress are under separate genetic control. Reciprocal effects and heterosis were not significant. GCA could not be predicted from parental performance. The breeding line 'Cornell 502' had the highest GCA under high temperature, and the cultivar 'Brio' had the highest GCA under low temperature. The cross 'Brio' x 'Venture' was high yielding in both temperature treatments. Heat tolerance and chilling tolerance were associated in certain parents and hybrids. However, performance under high and low temperature treatments was not generally correlated in the parents and hybrids, indicating that these traits should be selected separately.