INCREESING THE SURVIVAL RATE OF SHOOT-TIP GRAFTING (STG) AND ITS APPLICATION IN PRODUCTION OF DISEASE-FREE CITRUS SEEDLINGS

By putting a drop of O.lppm kinetin or zeatin at the cut of rootstock before grafting, the survival rate of shoot-tip grafting(STG) could come up to 40-60% by using 0.18-0.20 mm long shoot apices and 13-18 days old rootstocks. It differ significantly in different shoot-stage of shoot apices collected in different varieties. The survival rate was much higher than that of transplantation when rnicrografted seedlings in tube were directly grafted on 1-yr-old tangerine cv. Fuju (Citrus tangerina Hort. ix Tan.) seedlings 100% and 78% of elimination rates were obtained for Huanglungbin and citrus tristeza virus (CTV), respectively.Of the 13 citrus cvs. obtained from STG mentioned above, 2 sweet orange cvs. Chuangxia and Shaohe (C. sinensis var. Sekken(L.) Osbeck) and 2 mandarin cvs. Tianma and Shaohe (C.pooncnsis Tanaka) have been indexed, free from virus or virus-like diseases known, and transplanted to disease-free mother tree fundation. The other 9 cvs. such as mandarin cv. Huimi No.28 (C.unshiu Marc.) etc. have been propagating and identifying.