Geographical diversity for quantitative spike characters in a world collection of durum wheat.

Crop germplasm collections are formidable to plant breeders and others who wish to draw samples by virtue of their large number of entries and muliplicity of potentially interesting characters. We have examined discriminant and clustering methods for their utility in revealing germplasm groupings that are useful for selection of parental stocks and for revealing evolutionary patterns. More than 3000 entries of durum wheat (Triticum turgidum L., durum group) representing 26 countries of origin were obtained from the U.S. National Small Grains Collection and grown in a common environment in northern California. Eight quantitative measurements on spike characters were made, including awn and spike length, awn/spike length ratio, spikelet number, rachis internode length, number and weight of kernels per spike, and mean single kernel weight. Five clusters were delineated among the 26 country origins: (i) 11 countries in Europe and North Africa; (ii) France, USSR, and USA; (iii) nine countries in the eastern Mediterranean area; (iv) Ethiopia and India; (v) Afghanistan. An east to west clinal pattern was detected that represents a gradient in unimproved to improved types. Some countries with contrasting agroecological conditions clustered together, probably because a high percentage of breeding lines and cultivars shared parents from among the clustered countries. These results revealed wide variation in numbers of entries from among countries. Certain areas should be sampled morextensively. Documentation data are less complete than desired to establish evolutionary and ecological relationships. The methods used here helped focus upon groups of materials for use in plant breeding and research.