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Wageningen Universiteit (2006)

Reproduction et diversité génétique chez Parkia biglobosa (Jacq.) G.Don

Sina, S

Titre : Reproduction et diversité génétique chez Parkia biglobosa (Jacq.) G.Don

Auteur : Sina, S.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2006

Résumé partiel
Parkiabiglobosa(Jacq.)G.Don, African locust bean, is one of the 34 known species of the genusParkiawhose centre of origin isSouth America. It is anagroforestrytree species spread throughout the Africansudaniansavannas, fromSenegalin the West toUgandain the East. P.biglobosa is also an important socio-economic species in high demand by local communities for its multiple amenities and uses (food, traditional medicine and pharmacy, preservation and improvement of soil fertility, rites and customs, etc.). Such an importance engenders several diverse research programmes on this species that have been undertaken inWest Africa. However, the species remains under pressure as a result of its over-exploitation by human population, shortage of rainfall and inappropriate agricultural practices, leading to the degradation and/or lack of regeneration of P .biglobosaparklands in many zones. In this context, the present study was undertaken in order to understand the reproductive biology and the genetic diversity of P.biglobosa, which are essential for the elaboration of an efficient strategy for sustainable use and conservation of genetic resources. We investigated the mating system of the species in the semi-arid zones ofBurkina Faso. Two populations were selected inBissighinandNagaré, with 153 and 209 trees, respectively, and were weekly monitored during two seasonal cycles of fruit formation. The floralphenologicalsurvey revealed relatively high synchronism index values of 0.78 forNagaréand 0.79 forBissighin. This was an indication that although the fruiting period lasts over about 5 months, the majority of the trees flowered synchronously in these two populations. Thephenologicalobservations have highlighted a seasonal profile of P.biglobosa , which mainly occurs in the dry season, like most of thesudaniansavannah species. The high values ofmultilocusoutcrossingfor both, family level and within populations (tm = 0.941 and 0.981), suggest that the species presents partial self-incompatibility, which is also a common feature in many hermaphrodite species. Genetic (protandry, self-incompatibility) and environmental (elevated level of floral synchronism) factors could explain such high values of multi-locusoutcrossing. We demonstrated that there was a weak parental relationship between the trees that were analyzed (low tm-tsvalues, between 0 and 0.086). The paternity correlation (rp= 0.299 forBissighinand 0.502 forNagaré) showed that each tree was pollinated by only two or three pollen donors, probably involving bees as the main pollinators.

Mots clés : parkia biglobosa / genetic diversity / reproduction / gene flow / plant genetic resources / resource conservation / west africa / burkina faso

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