The effects of rootstocks on performances of three late-ripening navel orange varieties

Selection of rootstock is very important for citrus production. Besides its major role on resistance, the rootstock also can affect fruit production and quality. Currently, the main concerns on selection of rootstock for citrus production are compatibility and resistance, due to less information on the impacts of rootstock to the performance of scion varieties. This study aims to provide information on performances of navel orange varieties on different rootstocks. Three late-ripening navel orange varieties (Citrus sinensis var. Powell, Chislett and Banfield) grafted on seven rootstocks (Swingle citrumelo (C. paradisi×P. trifoliata), Carrizo citrange (C. sinensis×P. trifoliata), X639 (C. reticulata×P. trifoliata), MXT (C. sinensis×P. trifoliata), Hongju (C. reticulata), Ziyang Xiangcheng (C. junos) and trifoliate orange (P. trifoliata)) were used as plant materials for comprehensive comparison of the performances on tree growth, fruit yield and quality in 21 scion–stock combinations. Investigation was carried out in these combinations in field nine years after planting. Vigorous growth of all the three late-ripening navel orange varieties was observed on Carrizo citrange with the largest canopy volume at 33.34 m³ and the highest yield at 29.43 kg per tree, but a low yield efficiency at 2.87 kg m⁻³. On the contrary, those on trifoliate orange had the smallest canopy volume at 10.79 m³ and the lowest fruit yield at 12.51 kg per tree, but the highest yield efficiency at 3.95 kg m⁻³. Rootstocks did not show significant effects on fruit size, fruit shape index, peel thickness and the edible rate of the fruits, but fruit quality was significantly affected by the rootstocks. Fruits from the trees grafted on trifoliate orange presented the best quality with significantly higher total soluble solids (TSS) content than those on Ziyang Xiangcheng and Hongju, and also the highest ratio of TSS/titratable acidity (TA). The TA content was observed from the fruits on X639 at 0.59 g 100 mL⁻¹. Vitamin C (Vc) content of fruits on Hongju was the highest at 49.25 mg 100 mL⁻¹. Growth vigor of the trees was positively correlated with fruit yield at an extremely significant level. The canopy volume was negatively correlated with yield efficiency, but positively correlated with compatibility index. Results of this study indicated that the rootstock has great impacts on the growth vigor of the tree, yield efficiency and quality of the fruit. In order to achieve good quality and yield efficiency for navel orange production, less growth vigor rootstock such as trifoliate orange is highly recommended.