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 geneticsimilarity (GS) estimates based on molecular markers and coefficient ofparentage (COP) to predict heterosis.This study was designed: i) to assess the level of GS among 40 breadwheat (Triticum aestivum L.) cultivars selected in Central and SouthEurope; ii) to compare GS with COP; iii) to correlate the estimates ofparental diversity with the heterotic effects detected on 149 F1hybrids obtained by crossing the 40 cultivars according to three matingdesigns.The parental cultivars and the F1 hybrids were grown in severallocations at normal seed density. Significant heterotic effects were detectedfor grain yield and other traits including quality attributes. The parentalcultivars were assayed for DNA polymorphisms using two classes ofmarkers: 338 RFLP and 200 AFLP® bands were scored. GS estimates werecomputed considering each molecular marker set separately (GSRFLP,GSAFLP) and together (GSTOT). Ample differentiation amongthe parental cultivars was detected with the two marker sets. Although theaverage GSTOT (0.43) was higher than COP (0.10), the twomeasurements were significantly correlated (r = 0.36, p < 0.01).Correlations between the different estimates of genetic diversity andF1 performance or mid parent heterosis for grain yield and otherrelated traits were in general low although statistically significant.A more detailed analysis was conducted on 28 F1 hybridsproduced in a half diallel cross of eight parental cultivars characterized byhigh heterotic effects for grain yield. The GS estimates based on RFLP,AFLP® markers and also on RAPD were partitioned into general andspecific components. Correlations with general and specific combiningability effects for the measured traits were in several cases statisticallysignificant but too low to be predictive and therefore exploitable in practicalbreeding.