Development of a temporary immersion system (RITAA®) for mass production of sugarcane (Saccharum spp. interspecific hybrids)

Commercial micropropagation of sugarcane is largely determined by the clonal fidelity and the cost of plants produced. Rapid production of plants in vitro reduces the frequency of offtypes in many species. By exploiting the concept of transverse thin cell layer culture, we have developed a rapid, high frequency direct plant regeneration system, called SmartSettA (R), for commercial sugarcane cultivars grown in Australia. Similar to conventional micropropagation, labour remains the major cost of this plant production system. Hence, to reduce the labour component, we have integrated the SmartSettA (R) system with the RITAA (R) temporary immersion bioreactor. Thin transverse leaf sections or fragmented leaves cultured on agar-based SmartSettA (R) shoot induction medium were used as the starting material for RITAA (R). Shoot initiation on semi-solid medium prior to transferring to RITAA (R), culture immersion frequency, explant size and genotype determined the productivity (number of plants produced per unit culture) of the system. Results obtained with cultivar Q165 indicate that explants cultured for 45 d on SmartSettA (R) shoot induction medium were the most prolific, producing on average 275 shoots per vessel after 45 d of culture in RITA with 1 min immersion every 12 or 24 h. Using the fragmented tissue, 14-d-old explants and 3-mm leaf tissue fragments were the most productive. Experiments with three cultivars (Q117, Q165 and Q205) showed that RITAA (R) culture conditions need to be optimised for each cultivar for maximum plant production.