Genetic diversity in bread wheat, as revealed by coefficient of parentage and molecular markers, and its relationship to hybrid performance

Variable results have been obtained in different crop species using genetic similarity (GS) estimates based on molecular markers and coefficient of parentage (COP) to predict heterosis. This study was designed: i) to assess the level of GS among 40 bread wheat (Triticum aestivum L.) cultivars selected in Central and South Europe; ii) to compare GS with COP; iii) to correlate the estimates of parental diversity with the heterotic effects detected on 149 F-1 hybrids obtained by crossing the 40 cultivars according to three mating designs. The parental cultivars and the F-1 hybrids were grown in several locations at normal seed density. Significant heterotic effects were detected for grain yield and other traits including quality attributes. The parental cultivars were assayed for DNA polymorphisms using two classes of markers: 338 RFLP and 200 AFLP(R) bands were scored. GS estimates were computed considering each molecular marker set separately (GS(RFLP), GS(AFLP)) and together (GS(TOT)). Ample differentiation among the parental cultivars was detected with the two marker sets. Although the average GS(TOT) (0.43) was higher than COP (0.10), the two measurements were significantly correlated (r = 0.36, p < 0.01). Correlations between the different estimates of genetic diversity and F1 performance or mid parent heterosis for grain yield and other related traits were in general low although statistically significant. A more detailed analysis was conducted on 28 F-1 hybrids produced in a half diallel cross of eight parental cultivars characterized by high heterotic effects for grain yield. The GS estimates based on RFLP, AFLP(R) markers and also on RAPD were partitioned into general and specific components. Correlations with general and specific combining ability effects for the measured traits were in several cases statistically significant but too low to be predictive and therefore exploitable in practical breeding.