Distribution of genetic variability in a durum wheat world collection.

A durum wheat world collection of 349 entries has been used to study the amount and distribution of genetic variability based on isoenzymatic characters involving a minimum of 13 loci. Genetic variability has been studied in a hierarchical fashion: between origins and within origins, further divided into between entries per origin and within entries. Factorial analysis of correspondences and chi-square distance were the basic statistical tools. The effect of domestication is deduced by comparing isozymic frequencies between wild emmer and durum wheat. It involves changes in frequencies mainly towards the accumulation of "null" alleles. The richest origins of genetic variation for durum wheat were Iran, Mexico, Ethiopia, Egypt and Afghanistan. Generally, between-entry variability was larger than the withinentry component. Exceptions were the accessions from Mexico, Greece, Argentina and Cyprus. The relationships between origins were greatly affected by their within-variability, the logic in the grouping is mostly along geographical or political lines. Egypt might be considered a microcenter of diversity for durum wheat within the Mediterranean center, although it is certainly related to Ethiopia (included in the Abisinic center). Mexico has become a new microcenter of diversity, quite likely man-made, and is distant from other centers of durum wheat diversity as far as gene frequency is concerned.