In vitro plant regeneration from immature cotyledon explants of macadamia (Macadamia tetraphylla L. Johnson)

Abstract

The macadamia tree, an Australian native, is highly valued for its nuts. Macadamia improvement pro- grams so far have relied on conventional breeding and selec- tion. The production of improved cultivars required to meet future demands could be accelerated by the application of modern biotechnological techniques, but this requires an efficient and reproducible regeneration system that has not yet been established for macadamia. We report here shoot regeneration from immature cotyledon explants of macadamia. Adventitious buds were induced on the cotyle- don explants from fruits collected at 140 and 190 days af- ter full bloom (DAFB) on MS medium supplemented with either 10 or 15 µM TDZ. The addition of 2% coconut milk (CM) to 10 µM TDZ containing media resulted in enhanced adventitious bud induction from 190 DAFB ex- plants. Further shoot development from the induced buds was depressed in media containing TDZ + CM; the addi- tion of 0.001 µM IAA to this combination doubled shoot development, from 1.9–3.9 shoots per explant. The trans- fer of bud clumps to media supplemented with 8.8 µM BA alone or in combination with either 0.14 µM GA3 or 0.001 µM IAA significantly increased shoot production from the previously induced explants by 1.5–2 times of that observed in TDZ + CM medium.