Interspecific Crosses in Ziziphus Species

Three species of Ziziphus Mill. [Z. jujuba Mill., Z. mauritiana Lam. and Z. spina-christi (L.) Willd.] comprising a total of seventeen cultivars/genotypes were selected to perform interspecific crosses over a period of two flowering seasons under semi-arid conditions in the Negev desert of Israel. Twenty one cross combinations were done, comprising a total of 724 controlled pollination events, and resulted in 51 fruits (7.0 %). Among the crosses that set fruits, that of Z. mauritiana x Z. spina-christi resulted in the highest total percent of fruit set (11.7 %), and the reciprocal cross, resulted in a total fruit set of 8.7 %. Only few fruits were obtained from the crosses Z. jujuba x Z. spina-christi and Z. mauritiana x Z. jujuba with 7.4 and 2.5 % fruit set, respectively. With the exceptions of Z. jujuba x Z. mauritiana and Z. spina-christi x Z. jujuba, aborted and/or viable embryos were obtained in all cross combinations, showing that interspecific fertilization may occur among the studied species. The largest number of viable embryos was obtained from the cross Z. mauritiana x Z. spina-christi. Few hybrids germinated and developed, but none survived. Our study showed that gene flow among these three species may be possible in natural conditions or can be used in future breeding programs to create reproductively viable cultivars specifically adapted to semi-arid regions. However, it is uncertain whether these hybrids can germinate, grow and become established under current environmental conditions.