RELATIONSHIPS AMONG EUROPEAN BARLEY GERMPLASM .2. COMPARISON OF RFLP AND PEDIGREE DATA

Information about the genetic relationships among genotypes is of great importance to breeders of barley (Hordeum vulgare L.) and other self-pollinated crops. In the past, genetic similarity was mainly estimated by Malecot's coefficient of coancestry (f). However, estimates of f may not always reflect the true relationship between genotypes because of selection, random genetic drift, and other causes. In this study, we analyzed 24 winter and 24 spring barley cultivars from the European barley germplasm by means of restriction fragment length polymorphism (RFLP) and pedigree analyses. Our main objective was to compare genetic similarity (GS) based on RFLP data of 136 clone-enzyme combinations (CEC) with coancestry (f) for their ability to quantify the degree of relatedness among barley genotypes. Rank correlations between GS and f for related (f greater than or equal to 0.10) pairs of cultivars were weak for both winter (r(s) = 0.21) and spring barley cultivars (r(2) = 0.42). Based on linear regression of GS on f, coancestry explained 6 and 14% of the variation in GS for related (f greater than or equal to 0.10) pairs of winter and spring barley cultivars, respectively. The weak correlations can be explained primarily by (i) unrealistic assumptions in calculation off and (ii) substantial variation in GS estimates of unrelated cultivars. In conclusion, coancestry seems less suited than RFLP-based GS estimates to quantify the genetic relationships among barley cultivars for many applications in breeding.