Influence of media composition on gas exchange parameters, biochemical composition and growth of zygotic embryo-cultured coconut (Cocos nucifera L.) plantlets

Coconut zygotic embryo culture has practical value in collection and exchange of germplasm overseas and is done on different media protocols. Differences in plantlet survival and media composition led to a study with an objective to compare growth, leaf gas exchange characteristics and biochemical constituents of plantlets of dwarf and tall cultivars of coconut grown on four media viz., PCA-ARC, UPLB, IRD and CPCRI. A total of 960 embryos from two dwarf (COD and MYD) and two tall (WCT and LCT) cultivars of coconut were inoculated on four different media. The dwarfs germinated earlier than the talls. Maximum vitrification was observed in liquid media, viz. PCA-ARC followed by UPLB and IRD. At the time of transplantation to pots for acclimatization, plantlet morphological growth did not vary significantly. However, biochemical composition (reducing sugars, starch, total carbohydrates, free amino acids and proteins; the chl. a, b, total chlorophyll and chl. ‘a/b ratio’) of seedling leaves varied with cultivar and influenced by medium composition. Development of photosynthetic system was influenced by the composition of medium and readily usable carbon source in media seems to inhibit Pn. In general, plantlets raised on PCA-ARC and CPCRI media had higher in vitro and ex vitro survival rates followed by those raised on UPLB medium. Plantlets from IRD medium had lowest survival capacity. LCT and MYD plantlets survived better when grown on PCA-ARC medium, and WCT and COD plantlets survived better when raised on CPCRI medium. It is suggested that providing solid germinating medium to reduce vitrification loss; addition of auxins and reduction of salt concentrations in growth medium, reduction of sucrose concentration in rooting medium and gradual increase in PAR during rooting may help in early establishment of photosynthetic mechanism and better growth to increase the in vitro and ex vitro survival rates of coconut seedlings.