REGULATION OF SOMATIC EMBRYOGENESIS IN LONG-TERM CALLUS-CULTURES OF SUGARCANE (SACCHARUM-OFFICINARUM L)

Embryogenically competent callus was induced from in vitro grown Sacch arum officinarum L. (NCo 310) plantlets by plating young leaf segments on MS basal medium supplemented with 30 mu M dicamba for 21 d in dark ness, and subsequently transferring to a medium (EFDM) on which embryo s could form and develop. Embryogenic response was improved if the EFD M was supplemented with 1 or 5 mu M dicamba, casein hydrolysate (1 g l (-1)), and 6% maltose or 6-9% corn syrup. Calli maintained their embry ogenic competence for up to 16 months under these conditions, and with alternate weekly subcultures on to fresh media containing 20 mu M and 30 mu M dicamba in the dark, embryogenic callus proliferation could b e further increased. Additional improvements in embryogenic competence were optimized to over 40 months when primary callus was alternately precultured at weekly intervals either with 10(-5) M ABA or 5% sorbito l and then transferred to a medium containing 20 or 30 mu M dicamba du ring maintenance. In general, medium plant growth regulator and nutrit ional cues, especially dicamba concentration, maltose/corn syrup level s and ABA/sorbitol preconditioning, were observed to influence critica lly both embryogenic callus proliferation and the frequency of somatic embryogenesis. The data are discussed within the context that these t reatments can be successfully manipulated to enhance long-term embryog enic competence and high-frequency somatic embryogenesis in sugarcane.