GENETIC DIVERSITY OF OROBANCHE CUMANA POPULATIONS IN DIFFERENT EUROPEAN COUNTRIES
G GAGNE1,P ROECKEL-DREVET1, B GREZES-BESSET2, P SHINDROVA3, P IVANOV3, C CRAND-RAVEL4, F VEAR5, D TOURVIEILLE DE LABROUHE5, G CHARMET4 and P NICOLASl
1GREAT, UA INRA-OVGV, Université Blaise Pascal, 24 av. des Landais, 63177 Aubiere, France; 2BIOGEMMA, Domaine de Sandreau, 31700 Mondonville, France; 3IWS, Dobrudja, General Toshevo, Bulgaria; 4INRA, Station d'Amelioration des Plantes, Domaine de Crouelle, 234 av. du Brézet, 63039 Clermont-Ferrand, France; 5GREAT, INRA, Station d'Amélioration des Plantes et de Pathologie Vegetale, Domaine de Crouelle, 234 av. du Brézet, 63039 Clermont-Ferrand, France
Background and objectives
Orobanche cumana Walir. is an holoparasitic angiosperm which infects sunflower roots (Helianthus annuus L.). Because of the increased occurrence of broomrape on sunflower crops and the appearance of new races not controlled by many resistance genes, the survey and the understanding of broomrape population evolution is crucial for sunflower breeders. The previous study of variability of broomrape populations infesting sunflower was based on isozyme analysis and was restricted to Spain, although this species was first reported at the begining of the century in Eastern Europe and was only observed recently in Spain. The aim of our study was to analyse the genetic variability of eight O. cumana populations originating from highly infested countries using RAPD technique in order to gain insight into the fundamental genetic evolution of this parasitic weed and eventually to determine molecular markers of these broomrape populations.
Materials and methods
Three populations from Bulgaria, one from Romania, one from Turkey and three from Spain were collected and approximately 20 plants per population, with a total of 180 plants, were studied with RAPD. Pairwise distances were computed with the Nei and Li coefficient . Nei's  genetic diversity statistics and genetic differentiation between populations, among groups and among populations within groups were calculated (one group corresponding to the East European countries and the other the Spanish populations). Gst were calculated also for all population pairs which led to gene flow among populations.
Results and conclusions
Twenty-three primers generated a total of 57 polymorphic and 76 monomorphic bands. For all 23 primers, very similar amplification patterns were obtained, although the geographic origins and the sunflower genotypes were different. The lowest percentage similarity (80%) was found between two plants from Bulgarian and Spanish populations. The mean of intra-population genetic diversity, Hsm, is low but not negligible (0.076) compared with the total genetic diversity, Htm (0.18).
All results suggest that O. cumana populations are self-pollinated, whatever their geographic origins. Genetic diversity within populations of O. cumana is certainly due to a combination of breeding and seed dispersion systems, age of population and infestation level. The population were organized in two distinct groups: Turkish, Romanian and Bulgarian populations are in one group and Spanish populations are in a separate group. The Romanian population appears to link the two groups. Gene exchange between populations were generally low.
Our results suggest that O. cumana is a self-pollinated species with a monophyletic origin. The study of virulence of individuals from each population is in progress to determine their relationships with the molecular genetic diversity.
1. Nei M, Li WH, 1979. Proceedings of the National Academy of Sciences USA 76, 5369-5373.
2. Nei M, 1973. Proceedings of the National Academy of Sciences USA 70, 3321-3323.