Micrografting of pistachio (Pistacia vera L. cv. Siirt)

Abstract

Pistacia vera L. is a dioecious tree species cultivated widely in the Mediterranean regions of Europe and North Africa, the Middle East, China and California, USA. Development of pistachio plantations is limited by the absence of adequate nursery stock due to the difficulty of propagating Pistacia plants by conventional methods, such as cutting and grafting. Consequently, many efforts have focused on establishing in vitro propagation procedures for Pistacia vera and several other Pistacia species (Hansman & Owens, 1986; Barghchi & Alderson, 1989; Onay & Jeffree, 2000; Onay, 2003; Onay et al., 2004a,b,c; Onay, 2005). The initiation of cultures from mature material usually involves pruning, grafting as well as BA and GA3 spray treatments that stimulate new growth of shoots (Barghchi, 1986; Gonzales & Frutos, 1990). There has been some success in establishment of mature pistachios by direct organogenesis (Yang & Lüdders, 1993; Dolcet- Sanjuan & Claveria, 1995; Onay, 2000) and somatic embryogenesis (Onay et al., 1995, 1996, 1997, 2000; Onay et al., 2004a). Onay (2000) harvested 3-4 cm long terminal lignified stem sections from 30-year-old pistachio trees and immersed the cut ends in plant growth regulator solutions, before placing them in a greenhouse medium. New, softwood shoots were forced in the greenhouse under a 24 h photo period until they were sufficiently large to excise, surface disinfest and place in vitro. However, despite this progress, establishment and multiplication of field- grown mature P. vera clones remain problematic. In vitro micrografting can overcome these limitations. The first attempts to rejuvenate mature materials by micrografting in vitro mature scion shoot tips onto juvenile P. vera rootstocks were reported by Barghchi (1986). However, the growth of scion was very slow and elongation did not occur. Micrografting was investigated in vitro as well as in vivo by Abousalim & Mantell (1992), but rejuvenation was not reported when mature trees were used as scions. Recently, pistachio has been successfully micrografted both in vivo and in vitro (Onay et al., 2003a,b, 2004b). This chapter contains a detailed protocol for in vitro micrografting of pistachio. The vigor of the proliferated shoots was restored, and complete plants were established in soil and grown in the greenhouse. This method can also be suitable for many other recalcitrant species.