Pollination system and effective pollinators of Argania spinosa (L. Skeels)

Abstract

This work deals with Argania spinosa breeding system and its associated pollinators in two different sites located in Souss valley. The main objective of this work was to study the effect of three pollination treatments on the percentage of fruit set of argan tree as well as to determine its potential pollinators. To study the breeding system, three treatments were applied for flower buds. The first treatment is an open pollination for insects and wind, the second one concerns only wind pollination, and the third one is a self-pollination. On the other hand, flower visitors were assessed to evaluate their frequency (F) and their activity rate (AR) which were exploited to calculate the index of visitation rate (IVR = F × AR) for each visitor. Pollen loads were also counted for the main pollinators as well as their foraging behavior. A highly significant fruit set was obtained from insect open pollination compared to the other treatments (p < 0.001), which ensures up to 88.05% of fruit set. However, 7.94% and 4.01% of fruit set were obtained from wind pollination and self pollination respectively. Forty three species visit argan flowers at both sites (43 insects visitors in Belfaa vs 38 in Azrarag). Highly significant frequency for Hymenoptera was recorded in Azrarag 53.2% than Belfaa (25.4%). On the other hand, a highly significant frequency for Diptera was recorded in Belfaa (61.9%) than Azrarag (36%). However, no significant difference was recorded for Coleoptera frequency in both sites (P = 0.08). Based on pollen loads and IVR, Apis mellifera, Halictidae bees, and Syrphidae species were the most pollinators for the argan tree. IVR computed for A. mellifera and their pollen loads were highly significant compared with other visitors. Breeding system of argan tree is closely dependent on insect pollination. Management of argan forest and orchards should be designed to increase and preserve insects community.