DIVERSITY AMONG NORTH-AMERICAN SPRING BARLEY CULTIVARS BASED ON COEFFICIENTS OF PARENTAGE

Maintenance of genetic diversity is an important safeguard against vulnerability to biotic and abiotic stresses. The coefficients of parentage, r, among cultivars computed from known pedigree information can be used as an index of genetic diversity. Because of the emphasis placed on developing barley (Hordeum vulgare L.) cultivars for the malting and brewing industry, it seemed likely that barley may have a narrower gene pool than other crop species where less emphasis has been placed on quality traits. Our objective was to examine the diversity among North American spring barley cultivars and the contribution of major ancestors to the two- and six-rowed barley gene pools using the coefficient of parentage as an index of diversity. Coefficients of parentage were computed for all pairs of 167 spring barley cultivars. Mean r with major ancestors was computed for cultivars categorized by row type and era of release. A cluster analysis, performed on the coefficient of parentage matrix, produced 30 disjoint clusters. The five ancestors with highest mean r with cultivars contributed 45 and 62% of the germplasm to the early and recent two-rowed cultivars and 52 and 44% of the germplasm pool in the six-rowed cultivars for the two respective time periods. Mean r within the two- and six-rowed cultivars was 0.11 and 0.10, respectively. Mean r within cultivars increased 180% in the two-rowed and 36% in the six-rowed cultivar groups from the early to recent cultivar groups. Cultivar groups formed by the cluster analysis produced mean within-cluster r values ranging from 0.29 to 0.57. Principal coordinate analysis of the between cluster matrix showed that the two- and six-rowed gene pools are essentially unrelated. Major six-rowed malting cultivars grouped into two clusters and the major two-rowed malting cultivars grouped into one cluster. These results show that malting barley cultivars are based on a limited sample of germplasm.