Diversity among cultivated sunflower resources and use in breeding

The first significant breeding to high oil content in sunflowers, which took place in Russia from 1930, concerned open pollinated varieties. These were the basis of modern breeding programmes, which started in 1950-60, mainly in Europe, Canada, the USA and Argentina, but work in that period in countries such as Morocco, Australia and Chile also produced genotypes of direct agronomic interest, or which widened the genetic variability available. Studies of the structure of this variability have become possible following genotyping of large numbers of inbred lines by microsatellites (2 or 3 per linkage group) and the definition of core collections which cover a large part of the diversity in cultivated sunflower. Although some geographic effects on combining ability have been reported, the main groups which appear are characterized by cms maintenance or male fertility restoration. The collections defined should be useful in similar studies for the determination of genome sequences controlling important phenotypic characters, although for characters determined by parts of the genome poorly represented by the markers, enriched or specific collections may be necessary. Such knowledge should help to optimize the use of sunflower genetic resources in breeding.