MICROPROPAGATION OF DARJEELING ORANGE (CITRUS-RETICULATA BLANCO) BY SHOOT-TIP GRAFTING

Micropropagation of Darjeeling orange (Darjeeling mandarin) was done b y shoot-tip grafting on the local rootstocks rough lemon, sour orange and Rangpur lime. Seedlings of these plants were raised in MS medium i n standard conditions of temperature, light duration and plant age. Mi crobuds (0.2 mm long), aseptically excised from the scion, were grafte d onto the decapitated rootstock seedlings. The micrografts in culture medium were grown under standard lighting. Rootstock seedlings showed optimum growth at 25-30 degrees C. Optimum growth of the micrografts resulted from treatment in complete darkness for 4 d after grafting fo llowed by exposure to 750 W for 16 h d(-1) for 15 d and 1500-2000 W fo r 16 h d(-1) for 39 d. The success of micrografting depended on the ag e of the rootstock seedling which was 21 d, 14 d and 14 d for sour ora nge, rough lemon and Rangpur lime respectively. The micrografts were t hen double grafted to the two year old rootstocks seedlings of the res pective species and the age of the micrografts for the successful doub le grafts was also standardized. The survival rate was high with 40 d, 45 d and 45 d micrografts on sour orange, rough lemon and Rangpur lim e respectively. The double-grafts were then indexed for tristeza virus and greening disease after six months' growth in an insect-proof scre enhouse and found to be free from these graft transmissible diseases.