In Vitro Induction of Autotetraploids In Wild Peanut (Arachis paraguariensis).

Several wild Arachis species that constitute important sources of novel genes for improving the cultivated peanut are diploid (2n = 2x = 20) whereas the cultivated peanut is tetraploid (2n = 4x = 40). In an attempt to overcome the ploidy barriers that exist in gene transfer between the wild species and cultivated peanut, this study investigated the capacity of the antimitotic agent colchicine for in vitro induction of tetraploidy in wild peanut Arachis paraguariensis Chodat & Hassl. The experiment was laid out in a split plot with 4 (colchicine concentration) x 5 (treatment duration) factorial main plot and 3 explant-types as the subplot. Quarter-seed, callus and shoot tip explants were immersed in aqueous solutions of colchicine (0.05%, 0.1%, 0.2% and 0.5%) dissolved in 1% dimethyl sulfoxide for 4, 8 , 16, 20 and 24 hours. Controls were held in sterile, distilled water for similar durations. The treated explants were then regenerated on semi-solid MS callus induction medium supplemented with 4.4 g^-1 thidiazuron (TDZ) and 2.2 g^-l 6-(ɣ, ɣ-dimethylallylamino) purine (2iP). Plantlets were rooted on MS basal medium with no growth regulators before ex-vitro acclimatization. Ploidy levels of plantlets were determined via flow cytometry after two months in culture. Results showed that colchicine treatment was effective at inducing tetraploidy. Overall, tetraploid induction rates of 18.4% and 12% were observed among plantlets initiated from quarter-seeds and shoot tips respectively. However, the colchicine-treated callus explants did not produce any true tetraploid but 26% of the regenerated plants were chimeras. Further experimental research is underway to compare the morphological and reproductive characteristics of regenerated tetraploids with the normal diploids. The tetraploids generated from this study will be useful as new sources of genetic variation for overcoming hybridization barriers in peanut breeding programs.