EFFECT OF NUTRIENT MEDIA COMPOSITION ON SUGAR-FREE GROWTH AND CHLOROPHYLL FLUORESCENCE OF PINUS RADIATA SHOOTS IN VITRO

Nutrient media commonly used in conventional micropropagation may not be entirely suitable for cultures grown under sugar-free, CO₂ enriched conditions. Pinus radiata D. Don. shoots were cultured for 12 weeks in vitro under CO₂ enrichment (850 ppm) on 4 sugar-free media: modified Le Poivre medium (LP); sugar-free LP medium (SFLP); LP medium containing activated charcoal (LPCH); and new LP medium (NLP), a blend of LP and hydroponic media. The best growth of shoots (height and fresh weight increase) occurred on sugar free LPCH media and then on sugar-free NLP, LP and SFLP, and LP 3% sucrose media in descending order respectively. Chlorophyll fluorescence indicated greater photosynthetic efficiency in shoots grown on LPCH media than in shoots grown on all other media. A relationship between relative colour of shoots and chlorophyll fluorescence was also found; shoots on LPCH media were greener than shoots on other media. These results suggest that the role of charcoal for sugar-free growth of shoots requires further elucidation, the addition of charcoal to NLP medium may give further improvements and chlorophyll fluorescence may be a useful indicator of nutrient or physiological stress of shoots grown in vitro.