| Avocado, Persea americana Mill., is an important fruit crop and is cultivated in tropical and subtropical regions. Despite its importance, commercial production has mostly depended on only a few rootstock and scion cultivars. Avocado improvement by conventional breeding has been slow due to a long juvenile period, low fruit set, genetic heterogeneity, lack of genetic information regarding horticultural traits and inefficiency of breeding techniques. Biotechnology, including somatic cell genetics and genetic transformation, has great potential for improving perennial fruit species, including avocado. The use of biotechnology for improving avocado is dependent on in vitro protocols, including efficient somatic embryogenesis, protoplast isolation and subsequent regeneration of plants from protoplasts, genetic transformation and shoot proliferation for propagating unique regenerants. This study was undertaken to develop the cell culture system for improving avocado.; Embryogenic cultures have been induced from several avocado genotypes and elite cultivars. Conditions for maintenance of embryogenic cultures have been determined, and efficient somatic embryo development from embryogenic cultures has been described. Protoplasts have been isolated from embryogenic cultures, and somatic embryo development from protoplast-derived cultures has been obtained. Although plant recovery from somatic embryos has been achieved, the efficiency of conversion, or germination has been low.; Interspecific protoplast fusion between embryogenic avocado cultures and leaf mesophyll protoplasts of Nectandra coriacea (Sw.) Griseb., P. borbonia (L.) Spreng. and P. pachypoda has been attempted in an effort to produce interspecific somatic hybrids with resistance to phytophthora root rot caused by Phytophthora cinnamomi Rands; however, putative hybrid plants of the former and embryogenic cultures of the latter could not be confirmed by RAPD analysis. The somatic hybridization experiments were limited by the availability of protoplasts from the non-avocado parents. Whether or not protoplast fusion is a viable method for overcoming sexual incompatibility between avocado and its wild relatives remains unresolved.; The in vitro protocols for avocado that have been developed have significant implications for avocado improvement using biotechnology. A research collaboration has already demonstrated the feasibility of genetic transformation of embryogenic cultures of avocado. |
