Induction of high frequency of somatic embryoids in Indian cotton cv. Surabhi through temperature stress

An elite Indian cultivar of cotton (Gossypium hirsutum L.) Surabhi was tested for its embryogenic protential. Callus was induced from three explants viz. roots, cotyledons and hypocotyls on MS medium supplemented with auxins and cytokinins in different combinations. The hypocotyls were amenable to callus induction than roots or cotyledons. The ideal combination for callus induction was MS containing 0.5 NAA + 0.5 BA, 0.5 2, 4 D + 0.25/0.5 Kin and 0.5 2, 4-D + 0.25/0.5 BA. The friable callus was cultured on the same media combinations except that only KNO₃ was provided as nitrate source. The cultures were divided into two sets with one being maintained at optimum temperature (28± 2°C) and other exposed to a higher temperature stress (33± 2°C). Under controlled temperature, there was good callus production but no embryoids were formed even after forty day of culture. Irrespective of the hormonal combinations, the callus exposed to temperature stress of 33°C entered into embryogenesis. The callus maintained on 2, 4-D as auxin source formed embryoids which were watery and turned brown with time. A combination of 0.5 NAA + 0.5 BA was found to be the best which lead to production of embryoids in eighty per cent of the cultures. However, when these embryoids were transferred to maturation medium devoid of hormones, they failed to germinate.