Factors influencing in vitro shoot regeneration of Macadamia Integrifolia

A study was carried out to investigate the effect of culture medium factors that influence the shoot regenerative potential of Macadamia nodal segments in vitro. Explants were obtained from shoots of current growth flush of Macadamia integrifolia and inoculated onto different test media. Woody plant medium (WPM) gave results comparable to MS medium whose macronutrients had been reduced to half rate. Explants cultured on media gelled with Biotec agar No. 1 and Purified agar had significantly higher bud breaking frequency and shoot number per explant than Phytagel and Gelrite. Optimum culture performance was obtained on MS medium enriched with 30 g/L sucrose. Highest bud breaking frequency (98%), shoot number per explant (8.1) and shoot length (3.3 cm) were obtained when WPM was supplemented with 2 mg/L BAP, 1 mg/L IBA and 1 mg/L GA3. When elongated shoots were cultured on to medium supplemented with cytokinins for rooting, only excessive callusing was obtained but no roots were formed within the culture period. The results of this study indicate that M. integrifolia is amenable to tissue culture but further studies are required to obtain rooting of in vitro shoots to come up with an optimized commercially feasible protocol for Macadamia tissue culture.