Cytology of callus and regenerated plants of sweet potato (Ipomoea batatas L.)

Abstract

The cytogenetics of fast-growing, embryogenic as well as non-embryogenic callus derived from short- and long-term cultures of sweet potato, were evaluated. Frequencies of hypo- and hyperhexaploid cells were higher (25 to 33%) in fast proliferating callus grown in 2 mg/l 2,4-D or 0.5 mg/l NAA supplemented medium, than in the embryogenic callus grown in 0.5 mg/l 2,4-D medium. Chromosomal variation was the least in embryogenic tissue grown in 0.2 mg/l 2,4-D + 2.5 g/l NaCl supplemented medium. The stability of ploidy was greatly affected by the culture age in fast-growing callus. Double hexaploid cells as low as 2-3% were observed only in the callus tissues grown and maintained for more than 2 years on 2 mg/l 2,4-D supplemented media. Root-tip cytology of regenerants developed from each passage of short-term (2 months) and long-term (2 years) cultures revealed normal hexaploidy (2n = 6x = 90) implying chromosomal stability of the hexaploids despite the occurrence of heteroploids in the callus cultures.