GENE DISPERSAL BY BUMBLEBEES BETWEEN 2 LINES OF FABA BEAN

Faba bean (Vicia faba L.) is pollinated by several apoid species which trip the flowers and cause either self or cross fertilization. Great variations in hybridization rate occur under field conditions. A bette r understanding of gene dispersal among faba bean is required to impro ve breeding programs. Our objective was to determine the contribution of foreign pollen to the fertilization of recipient flowers according to their position in the visitation sequence. Single workers of Bombus terrestris L. were used with caged faba bean. They foraged 10 flowers of a donor line (D-27) prior to those of a recipient line (D-23). Sev enteen bumblebee workers visited 1261 flowers of D-23. The mean number of D-23 flowers visited per individual run was 74. The 17 runs induce d 2812 seeds which were harvested and analyzed by starch-gel electroph oresis to estimate the cross-fertilization rates by allozyme markers. These rates were 21.3 and 17.5% for the first five and 10 flowers visi ted, respectively. The percentage of pods containing one? two, or thre e hybrid seeds was 78.0, 13.5, and 8.5%, respectively. These proportio ns were affected neither by the floral node level nor by the ovule pos ition in ovary. After the first visits to the recipient flowers, the i nsect foraging rapidly loses its efficacy in terms of cross fertilizat ion. Therefore, hybridization between lines requires a high frequency of alternate foraging which can be influenced by the breeding procedur es, in particular by the spatial arrangement of parental lines.