Prospects for hybrid breeding in winter triticale: I. Heterosis and combining ability for agronomic traits in European elite germplasm

Triticale (XTriticosecale Wittmack) (genomes AABBRR, 2n = 6x = 42) hybrid breeding and heterosis have received increased attention in recent years, but a comprehensive study is lacking. We investigated (i) the level of heterosis, (ii) the relative importance of general combining ability (GCA) vs. specific combining ability (SCA), (iii) correlations between GCA and line per se performance, (iv) trait correlations in parents and hybrids, and (v) prospects for hybrid breeding. Two hundred nine F-1 hybrids of winter triticale, produced by a chemical hybridizing agent, together with their 57 female parents and five tester (male) lines were evaluated in six environments in Germany during the season 2001-2002. Midparent heterosis for grain yield averaged 10.3% and varied from -11.4 to 22.4%, whereas better-parent heterosis averaged 5.0% and varied from -16.8 to 17.4%. Midparent heterosis was also positive for 1000-kernel weight, number of kernels per spike, test weight, and plant height but negative for number of spikes per square meter, falling number, and protein concentration. GCA variance (sigma(2)(GCA)) was more important than SCA variance (sigma(2)(SCA)) for all traits except grain yield and protein concentration. For most traits, GCA X location and SCA X location interaction variances were small relative to sigma(2)(GCA) and sigma(2)(SCA), respectively. Genetic correlations between midparent and hybrid performance and between GCA effects and line per se performance showed similar trends, being moderate for grain yield and protein concentration and higher for the other traits. We concluded that grain yield heterosis in winter triticale crosses from parents in the current European germplasm pool is adequate to justify continuing research on hybrid breeding. By selecting parents for combining ability and establishing genetically diverse heterotic groups, a midparent grain yield heterosis of 20% could presumably be surpassed. Further information is needed on F-1 seed production and the cytoplasmic male sterility system.