Trifoliate hybrids as rootstocks for Pêra sweet orange tree

Abstract

The Rangpur lime (Citrus limonia) has been used as the main rootstock for Pêra sweet orange (C. sinensis) trees. However, its susceptibility to citrus blight and citrus sudden death has led to the use of disease-tolerant rootstocks, such as Cleopatra mandarin (C. reshni), Sunki mandarin (C. sunki) and Swingle citrumelo (C. paradisi x Poncirus trifoliata), which are more susceptible to drought than the Rangpur lime. These mandarin varieties are also less resistant to root rot caused by Phytophthora, and the Swingle citrumelo showed to be incompatible with the Pêra sweet orange. In search of new rootstock varieties, this study aimed at assessing the fruit precocity and yield, susceptibility to tristeza and blight and occurrence of incompatibility of Pêra sweet orange trees grafted on 12 trifoliate hybrids, on Rangpur lime EEL and Goutou sour orange, without irrigation. Tristeza and blight are endemic in the experimental area. The Sunki x English (1628) and Changsha x English Small (1710) citrandarins and two other selections of Cleopatra x Rubidoux provided the highest cumulative yields, in the first three crops and in the total of six crops evaluated. The Cleopatra x Rubidoux (1660) and Sunki x Benecke (1697) citrandarins induced early yield, while the Cravo x Swingle citromonia and C-13 citrange induced later yield. None of the rootstock varieties caused alternate bearing. Pêra sweet orange trees grafted on Swingle citrumelo, Cleopatra x Swingle (1654) citrandarin and on two selections of Rangpur lime x Carrizo citrange showed bud-union-ring symptoms of incompatibility. None of the plants presented symptoms of tristeza or blight.