Genetic Diversity among North American Spring Wheat Cultivars: I. Analysis of the Coeffecient of Parentage Matrix

Abstract

Genetic diversity constitutes the raw material for plant improvement, and it can provide protection against genetic vulnerability to biotic and abiotic stresses. Our objectives were to determine patterns of relatedness using the coefficient of parentage (COP) matrix among 270 spring wheat (Triticum aestivum L.) cultivars and to compute mean COP values for major regional breeding programs. The collection included most important cultivars released during this century from Canada (47), the USA (133), and Mexico (90). Cluster analysis, based on the COP matrix, resulted in 20 major clusters of four or more entries and six small clusters of two cultivars each. The first three axes from a principle coordinate analysis of the interclnster COP matrix showed (i) group ofseven clu sters inc luding most har d red spring cuitivars (HRS) from the USA, and Canada (CWRS), based mainly on a ‘Marquis’ background, (ii) group ofnine int errelated clusters including most cultivars from CIMMYT (Mexico), (iii) interrelated clusters including mostly white wheats, and (iv) two small clusters including mostly old Canadian cultivars. Mean COP values were computed among cuitivars released during three successive time periods for major regional breeding programs. The CWRS cuitivars have become progressively more interrelated based on a Thatcher background. Average COP values (0.58 among modern cultivars) for this class were higher than values reported for winter wheat, barley (Hordeum vulgare L.), and oat (Avena sativa L.) gene pools. The HRS wheats showed a fairly high but slowly decreasing interrelatedness (COP= 0.22) among modern cultivars, with some regional differences. CIMMYT cultivars were less interrelated (COP = 0.15–0.20) and comparable to levels reported for soft red winter wheat and barley. Quality requirements and kernel type have probably been major factors in maintaining relatively high COP in the CWRS but somewhat less in the HRS in the USA. CIMMYT cultivars, in general, do not have quality restrictions, allowing the introduction of more diversity.