THE INFLUENCE OF GENOTYPE ON THE INDUCTION OF SOMATIC EMBRYOS FROM IN VITRO CULTURED ZYGOTIC EMBRYOS AND ADVENTITIOUS SHOOT REGENERATION FROM COTYLEDONS OF PEACH AND NECTARINE

Abstract

Genotype-independent transformation of peach (Prunus persica (L.) Batsch) is difficult to achieve, primarily due to its high recalcitrance to produce adventitious shoots or somatic embryos in vitro. In spite of sporadic reports of adventitious shoot organogenesis or somatic embryogenesis from peach tissue cultures, there is no universal method for peach regeneration that can be reliably used for peach transformation. In order to determine the relative efficacy of regenerative competence in peach, one to three mm long immature zygotic embryos excised from 25 peach and nectarine genotypes were cultured on Raj Bhansali et al. (1990) medium containing 2,4-dichloro phenoxy acetic acid (2,4-D). Somatic embryos were produced from 23 peach and nectarine genotypes, but the number of explants forming somatic embryos varied widely between genotypes. In general, those zygotic embryos that were small in size produced the highest numbers of somatic embryos. Accordingly, zygotic embryos of 1 mm in size are more regenerative than 2 or 3 mm in size. Thirty-seven percent of 1 mm size zygotic embryos produced somatic embryos, whereas only 27 percent of 2 mm and 16 percent of 3 mm size zygotic embryos produced somatic embryos. Among genotypes, high percentages of somatic embryos were obtained from 'Bell of Georgia', 'Bailey', 'Tennessee Natural' and 'Nemaguard'. Besides 2,4-D, other synthetic auxins such as dicamba (3,6-dichlo-o-anisic acid), picloram (4-amino 3,5,6-trichloroapicolinic acid), and centrophenoxine (4-chlorophenoxyacetic acid 2-dimethylaminoethyl ester) also induced somatic embryogenesis from zygotic embryos of 'Encore'. A 1-week pre-culture of 5-7 mm long cotyledons in dark on MS (Murashige and Skoog, 1962) medium + 5 μM 2,4-D + 0.5 μM benzyladenine (BA) followed by subculture onto MS + 12.5 μM thidiazuron (TDZ) + 0.4 μM α-naphthaleneacetic acid (NAA) induced adventitious shoots upon transfer to light in the peach genotypes 'Bounty' and 'Bailey'.