Callusing from rice root explants: Adventitious root formation precedes callus initiation response

The phenomenon of adventitious root induction from various parts of the plant system under specific experimental conditions is widely practised. We note in this study that roots excised from 7-day-old rice seedlings when cultured on Murashige and Skoog's nutrient medium supplemented with a,4-dichlorophenoxyacetic acid produced a large number of adventitious roots. It was further noted that the basal cells of the adventitious roots dedifferentiate to form calli masses. This response of adventitious root formation and callusing was 100% as all the tested root explants formed adventitious roots. Apart from four different cultivars of rice, three other genera namely wheat, maize and brassica showed formation of adventitious roots and calli under culture conditions. The monocot genera (rice, wheat and maize) showed more conspicuous rooting and callusing response as against brassica (a dicot). Adventitious root-derived rice calli were shown to regenerate shoot primordia with high frequency (88%) upon transfer to the same medium devoid of 2,4-dichlorophenoxyacetic acid.