Diallel analysis of winter wheat at two nitrogen levels

Price reduction and environmental concerns advocate a lower use of nitrogen (N) fertilizer on the wheat (Triticum aestivum L.) crop. It is a common hypothesis that hybrids would be more valuable in stressed environments such as limited fertilizer conditions. The objective of this study was to assess heterosis and combining ability at two N levels. Seven winter wheat cultivars were used to produce a 7 X 7 diallel cross without the reciprocals. The 21 171 hybrids and parental lines were tested in replicated plots over 2 yr without N fertilizer (N0) or with 150 kg N ha(-1) (N+). The diallel analysis was conducted according to Griffing with year, genotype, and treatment as fixed effects. Mid-parent heterosis for grain yield was 12.2% ** at NO and +8.9%** at N+ in 1997 and +1.7% at NO and -0.4%(ns) at N+ in 1998. This was directly related to high mid-parent heterosis for abo-'eground dry "eight in 1997 (+11.2%** at NO and -10.9%** at N+) and low heterosis in 1998 (+1.2%(ns) at NO and + 0.0%(ns) N -). General (GCA) and specific (SCA) combining ability effects were always significant. The GCA/SCA ratio ranged from 3.6 to 14.8. The GCA X N level interaction was generally significant indicating different parental contributions at low or high N levels. The SCA X N level interaction was never significant. There was a tendency toward higher GCA/SCA ratio at NO than at N. The choice of parents will be dependent upon the N level under which the new hybrids will be grown.