In vitro regeneration of hybrid plantlets of cashew (Anacardium occidentale L.) through embryo culture

Embryos from immature nuts of cashew (Anacardium occidentale L.) were cultured in vitro to regenerate improved hybrid plantlets. Explants (embryo) were excised from developing F1 hybrid immature nuts derived from diallel cross and harvested at 2-, 4-, 6- and 8-weeks after pollination (WAPo) for in vitro culture. The explants were surface sterilized, aseptically dissected and cultured into pure basal Murashige and Skoog (MS) agar medium and MS medium supplemented with 1 mu M each of naphthaleneacetic acid (NAA), benzyladenine (BA) and gibberellic acid (GA sub(3)) and subsequently observed for germination and survival rates until successful ones were transferred to the field. Age of explants was found to significantly influence both the germination and survival rates. Explants of 6 weeks old and above were found to give better germination rate and highest survival percentage in this study. Only MS medium supplemented with 1 mu M of gibberellic acid (MS+GA sub(3)) supported germination and growth at 2-WAPo, suggesting the essentiality of GA sub(3) as a growth regulator to a very young cashew embryo. Analysis also showed that factors such as medium composition, age of embryo and genotype (accession) significantly influence the germination rate of cashew embryo. It was observed that cashew embryos were found to be autonomy of growth regulator as the age increases and medium composition is only critical at very young age of the embryo. Successful germinated explants simultaneously produced shoot and root and were ready for transfer to field and acclimatization, between 90 and 112 days after inoculation.