Variation in outcrossing levels in faba bean cultivars: role of ecologicalfactors

Understanding the role of pollinators in determining the outcrossing rate i s very important for the development of synthetic varieties of faba bean. I sozyme markers have been used to study the multilocus outcrossing rate in f ive cultivars under field conditions and in two locations. The study was ca rried out at Cordoba (Spain) and at Rennes (France). These two locations we re chosen because previously studies showed strong differences in cross-pol lination. Multilocus outcrossing rates at both locations, Cordoba and Renne s, were 0.65 and 0.33 respectively. Local differences in pollinator abundan ce and foraging activity were 26 and 32 times higher, respectively, at Cord oba than at Rennes which could explain an outcrossing rate twice at Cordoba compared with Rennes. So, pollinators may play a prominent role in determi ning the differences in outcrossing between locations. However, at a local level, there is a highly significant positive correlation between foraging activity and outcrossing only at Rennes (where the number of pollinators is scarce) but not at Cordoba (where pollinators are abundant). We suggest th at although pollinators have a major impact on the level of outcrossing, in circumstances where there are a Lot of pollinators the differences in outc rossing between cultivars depends on other factors among which is the abili ty of the genotype itself to outcross. No type of floral display seems to b e clearly important in the determination of the outcrossing level in such a case. The implication of our results for faba bean breeding strategies is discussed.