Study of the variability and evolution of Orobanche cumana populations infesting sunflower in different European countries

The parasitic plant Orobanche cumana Wallr. has become a limiting factor for sunflower crops in infested countries. Over the past few years the progression of this parasitic plant, its introduction into new countries, and the development of new and more virulent races have all been observed. Consequently, the survey and understanding of broomrape population evolution is now crucial for the establishment of efficient breeding programmes. With this in prospect. the genetic variability of O. cumana populations from infested European countries, Bulgaria, Romania, Turkey and Spain, was studied using RAPD markers. Eight populations with a total of 180 plants were analysed. Twenty three primers were used to obtain 133 reproducible bands which led to a binary matrix. This matrix was subjected to various complementary analyses including pairwise distances computed with the Nei and Li coefficient, AMOVA. Nei's genetic diversity statistics, and an estimation of gene flow among populations with the infinite-island formula. The results gave consistent conclusions whatever the method used for data treatment. We show that this parasitic plant is probably self-pollinated, that there is little intra-population variability, and very little gene exchange appears to occur between different geographic regions. Populations were well structured and organized into two distinct groups tone group corresponding to the East European countries, Bulgaria, Romania and Turkey, and the other group corresponding to Spanish populations) and could have a monophyletic origin. These results are discussed in relation to the applied uses of RAPD markers in the determination of true O. cumana races instead of populations.