Genetic differentiation in leaf phenology among natural populations of Adansonia digitata L. follows climatic clines

Leafing phenology is an important component of climatic adaptation in semi-arid regions. The questions are to what extent phenology is under genetic control and represent adaptation to local climates? In the present study, we compare leaf phenology among Adansonia digitata L. trees of 27 different origins from West and East Africa and test if the differences follow climatic clines. Timing of bud burst was largely synchronized with the start of rainy season, but some few individual trees showed bud burst before the first rain. Timing of leaf senescence was under genetic control with substantial differences among origins. The timing of senescence was for some origins at the end of rainy season and for some in the beginning of the dry season. Differences among origins in timing of leaf senescence were related to the variation in drought just before- and in the first months of the rainy season at the sites of origin. Populations from drier sites had the earliest leaf shed at the common test site indicating that trees have been adapted to the prevailing climatic conditions at the sites of origin. We discuss the results in the light of possible triggering factors. Keywords: Baobab, Geographic variation, Phenological phases, Senescence, Budburst