Joseph Riov* (1), Anat Madmoni (2), Leonid Korol (3), Zvi Mendel (3), Rakefet David Schwartz (3), Galina Shklar (3), Ailon Calev (4) and Robert Sitbon (5)
1 Faculty of Agriculture, the Hebrew University of Jerusalem, Rehovot
2 Beit Berl College, Kfar Saba
3 Agricultural Research Organization, Volcani Center, Bet Dagan
4 Forest Department, Keren Kayemeth LeIsrael – Jewish National Fund (KKL-JNF), Eshtaol
5 Southern Region, KKL-JNF, Gilat
*
riov@agri.huji.ac.il Natural hybrids of Pinus brutia × Pinus halepensis were first discovered in Italy in the 1920s and later in Greece. Although there is a phenological barrier between the two species, i.e., their flowering periods do not fully overlap, there is some overlapping between the female flowering of P. brutia and the male flowering of P. halepensis, which enables formation of hybrids. In controlled hybridization performed in Greece it was observed that hybrids could be formed only when P. brutia was the female parent. The growth rate of these hybrids, which were planted in various sites in Greece, was significantly higher than that of the two parents, particularly in inferior sites.
Natural hybrids of P. brutia × P. halepensis were also discovered in various forests in Israel, in light of their exceptional dimensions.
These hybrids appear in pure stands of P. brutia or in mixed stands of the two parents, whose seed sources were imported to Israel from abroad, probably from Greece. Several research programs in Israel have addressed various characteristics of these hybrids, focusing particularly on morphological, biochemical, and molecular markers for their identification.
Recently, a new method, Cleaved Amplified Polymorphic Sequencing has been successfully employed for identification of the hybrids. Local natural hybrids also occur in several sites in Israel.
Controlled hybridization between P. brutia and P. halepensis performed in Greece and Israel revealed that the proportion of hybrids exhibiting heterosis was very low. These results clearly show that in practice it would not be possible to produce the hybrids by using seeds originated from controlled pollination; it would be preferable to use vegetative propagation to produce seedlings from the successful hybrids that appear in the forests. A method for vegetative propagation of pines, including hybrids, was developed in Israel; it also enables propagation of mature cuttings that are usually difficult to root.
However, for mass propagation it would be necessary to utilize other methods, such as rooting cuttings developed from needle fascicles (brachiblasts) following pruning or somatic embryogenesis. In experiments conducted in Israel, hybrids of P. brutia × P. halepensis proved to be highly resistant to Matsucoccus josephi, but their resistance was somewhat lower than that of P. brutia.
The climate changes, particularly the long drought periods that occurred in recent years in Israel, and the resulting mortality of P. halepensis trees, require the utilization of drought-resistant species.
The exceptional development of hybrids in stands in various regions in Israel, including the northern Negev, indicate that they are suitable for this purpose. This topic is currently being investigated.
Tables and figures available in English in full Hebrew version (PDF below)