Potential rootstocks for Valencia sweet orange in rain-fed cultivation in the North of São Paulo, Brazil

The North region of So Paulo has a high incidence of citrus sudden death (CSD), making Rangpur lime an inappropriate rootstock for use in this region. Identified CSD-tolerant rootstocks require supplementary irrigation. An ideal rootstock must be CSD-tolerant, provide high yields of fruits with high quality juice, be tolerant to drought, and induce some level of dwarfism in order to allow closer spacing. These characteristics were evaluated for Valencia orange trees on rootstocks of Dancy mandarin, Santa Cruz Rangpur lime (LCRSC) and 25 diverse hybrid rootstocks. The main parents of the hybrids were Citrus sunki, C. reshni, C. volkameriana, C. limonia, C. sinensis and Poncirus trifoliata. The experiment was performed in Colmbia, SP, Brazil, from 2009 to 2015 in rain-fed cultivation. At seven years of age, 54% of the rootstocks presented tree size similar to or higher than LCRSC, whereas in the others there was a reduction between 75 and 8% compared to LCRSC. Sacaton citrumelo rootstock resulted in substantial dwarfism and the hybrids of C. volkameriana x C. limonia were semi-dwarfing. All rootstocks presented juice with soluble solids varying from 9.89 to 11.06 Brix and ratio from 13.52 to 18.31. A Selection Index (SI) was developed to compare rootstocks. Twelve rootstocks exhibited SI superior to LCRSC. Citrange 25 and C. reshni x P. trifoliata Swingle 224, 287 and 71158 produced smaller tree size with greater production efficiency, soluble solids and processing index superior to LCRSC. The latter citrandarin rootstock presented incompatibility with Valencia sweet orange at age eight.