Australian macadamia industry is valued at AUD 300M, with increasing demand from both global and domestic markets. However, use of genetically variable seedling rootstocks with long lead-times for production can create variability in tree performance and inefficiencies in nursery practise. Tissue culture offers numerous benefits, including the mass production of high-quality, disease-free rootstocks that are genetically uniform and usually have vigorous root system relative to cuttings. This project is developing a commercially viable, high-throughput, meristem-tips based tissue culture, clonal propagation system. The optimization process of cultivar ‘Beaumont’ has reached large-scale multiplication and elongation stage, with over 1500 plants produced from 20 shoot tips in 6 months. The preliminary experiment on root initiation has shown promising outcomes as well. This study focused on Stage 3 (Shoot Elongation) of a tissue culture pipeline for mature ‘Beaumont’ macadamia, aiming to produce vigorous, high-quality single shoots for rooting while maintaining multiplication capacity. Two experiments were conducted over four 4-week subculture cycles to assess the integrated effects of cytokinin and auxin combinations on shoot elongation, multiplication, callus formation, and shoot abnormality. Results showed that lower auxin levels helped maintain shoot multiplication over time, while higher auxin levels often reduced multiplication after 3 cubsulture cycles. B1. 5X1 (Treatment Code) performed well across the four subculture cycles and was selected as the most suitable treatment for Stage 3. Callus formation was generally low and it was not the main problem. However, shoot abnormalities were common, especially under higher cytokinin levels, indicating that shoot quality remains the key limitation. Future work will focus on basal nutrient optimisation using a Design of Experiments approach to improve shoot quality.
Hu et al. (Tue,) studied this question.