Genetic variation for wheat spike fertility in cultivars and early breeding materials

Grain yield in bread wheat is often tightly associated with grain number/m(2). In turn, spike fertility (SF), i.e., the quotient between grain number and spike chaff dry weight, accounts for a great proportion of the variation in grain number among cultivars. In order to examine the potential use of SF as a breeding target, (1) variation for the trait was assessed in six datasets combining commercial cultivars under different environmental conditions, (2) trait heritability was estimated in a set of F-1 hybrids derived from controlled crosses between cultivars with contrasting SF and (3) SF distribution pattern was analysed in two F-2 segregating populations. Analysis of commercial cultivars revealed considerable variation for SF, under both optimal and sub-optimal conditions. In addition, genotypic variation was consistently larger than genotype x environment interaction variation in all datasets. Narrow sense heritability, estimated by the mid-parent-offspring regression of 20 F-1 hybrids and their respective parents, was 0.63. Data from two F-2 populations exhibited bell-shaped and symmetric frequency distributions of SF, with a SF mean intermediate between the parental values. Substantial transgressive segregation was detected in both F-2 populations. In conclusion, SF appears to be a heritable trait with predominantly additive effects. This warrants further investigation on the feasibility of using SF as an early selection criterion in wheat breeding programs aimed at increasing grain yield.