Callusing and regeneration of three genotypes of Oryza sativa ssp. indica by 2,4 dichlorophenoxy acetic acid (2,4-D)

Abstract

Consistent callus induction and regeneration of material cultured in vitro is a prerequisite for somatic cell genetic improvement of plants, through methods such as genetic engineering. This study aims to induce rapid in vitro callusing and regeneration on three local rice varieties by exposure to different culture media. When mature embryos were exposed to three levels of 2,4-dichlorophenoxyacetic acid (2,4-D) and one level of thidiazuron (TDZ) (with a short hormone free period in between), all varieties showed rapid regeneration in the absence of a visible callus phase. When the seeds were cultured in 2,4-D for three weeks, at a decreasing concentration of 2,4-D every 7 days, and subsequently treated with TDZ, non-embryogenic calli were obtained that failed to regenerate on hormone free medium. When exposed to 2,4-D for 5 days and subculturcd in hormone free medium for two weeks, embryogenic calli and greening were observed within that period. The concentration and period of exposure to 2,4-D are critical factors for callus induction and regeneration in the genotypes tested.