CONICET | Buscador de Institutos y Recursos Humanos

tZiziphus comprises important fruit trees that inhabit arid environments of tropical and subtropical regionsof the world and are able to adapt to drought and salt stress. Species of this genus are characterized bysynchronous protandrous dichogamy and self-incompatibility; however, reduced seed set after handself-pollination indicates that self-fertilization is possible and that it causes a strong inbreeding depres-sion. We characterize the reproductive biology of Ziziphus mistol, a species typical of saline environmentsof Chaco American forests. For this purpose, we studied floral biology, observed foraging behavior andpollen load of captured floral visitors, and tested the breeding system through the assessment of fruitand seed set and pollen tube growth following self-, cross-, and open pollinations treatments. In addition,the dependence of a pollinator and autonomous self-pollination were evaluated by excluding floral vis-itors and airborne pollen. Cross-compatibility between individuals was tested through controlled handpollinations. Results indicate that Z. mistol is predominantly outcrossing and depends on its pollinatorsto produce fruits and seeds. We observed high synchrony of flowering between individuals, as well as infloral anthesis between/within inflorescences within individuals. The flowers exhibit complete intrafloraldichogamy that fully prevents autonomous self-pollination, while sexual phases overlap within inflores-cence; thus geitonogamy can easily occur. Manipulative experiments show that Z. mistol can set fruitsand seeds after self- as well as cross-pollinations. However, reduction in fruit set and seed set after selfingand/or cessation of pollen tube growth in the style suggest a self-incompatible system. From reciprocalcrosses tested (N = 95), we have identified only 32.6% compatible crosses via fruit and seed trials. Wesuggest that in Z. mistol, as well as in other species of the genus, both synchrony in floral developmentand partial self-incompatibility would be evolved to reduce the costs of inbreeding.

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