Repeatability of large-scale germplasm evaluation results in durum wheat

Large-scale trait evaluation may enhance the utilization of germplasm collections by breeders. However, there is concern that this information may not be repeatable outside the area of testing because of large genotype x location interaction, Our objective was to assess the repeatability of large-stale evaluation results for durum wheat [Triticum turgidum (L.) Thell. ssp. turgidum conv. durum (Desf,) MacKey] across two areas of the Mediterranean region. A subset of 600 entries from a world collection was evaluated for six agronomic traits at one site in northern Syria and one in Sicily, Pearson's and Spearman's rank correlations of entry values between locations indicated that the repeatability as measured by both coefficients was high for heading time (r greater than or equal to 0.73), moderately high for kernel weight and plant height (0.48 less than or equal to r less than or equal to 0.57), relatively low for grain yield and kernels per spike (0.18 less than or equal to r less than or equal to 0.30), and non-significant for early vigor score. Comparison between phenotypic and genetic correlations suggested that not only genotype x location interactions but also experimental errors contributed substantially to departures from complete repeatability. When each location alternated as the selection site and the other as the test site, at least 50% of the advantage shown by the top 10% entries over the remaining accessions at the selection site could be maintained at the test location for early or late heading, high kernel weight, and short or tall stature, for which 30 to 57% of selected entries were common to both sites. At least 20% of the selection advantage was maintained for high kernels per spike and grain yield. The results support the potential usefulness of large-scale germplasm evaluation trials for crop improvement.