Growth and net photosynthetic rates of Eucalyptus tereticornis Smith under photomixotrophic and various photoautotrophic micropropagation conditions

The growth and net photosynthetic rates of shoot cultures of Eucalyptus tereticornis Smith grown under various photoautotrophic conditions (without sucrose in the nutrient medium and with enriched CO₂ and high photosynthetic photon flux or PPF) were compared with those of shoot cultures grown under conventional photomixotrophic conditions (30 g 1^-1 sucrose and 0.3 mg 1^-1 BA). The shoot height (1.1 cm), number of new nodal segments generated per active explant (3.0) and the multiplication coefficient (2.8) were significantly higher under photomixotrophic conditions (CO) than under various photoautotrophic cultural conditions. The latter included the following treatments; agar with high PPF and CO₂ non-enrichment (AL), agar with high PPF and CO₂ enrichment (AH) and Florialite with high PPF and CO₂ non-enrichment (FL). The difference in growth was less noticeable between Florialite (a mixture of vermiculite and cellulose fiber) in combination with high PPF and CO₂ enrichment (FH), and CO. Estimated net photosynthetic rate (NPR) of shoots grown under photomixotrophic conditions was negative at each measuring day (days 7, 14, 21 and 28), whereas the NPR of shoots grown under high PPF and CO₂ non-enrichment was positive and increased during the first 14 days of culture and decreased thereafter. Shoots grown under high PPF and CO₂ enrichment exhibited an increase in NPR for 21 days and a decrease in NPR for the next 7 days.