Rootstock selection for 'Swatow' Mandarin trees grown at different locations throughout the Brazilian subtropics.

Evaluating citrus rootstocks is of paramount importance in determining their suitability for a certain region and promoting resilience in orchards by increasing the genetic pool, thereby potentially contributing to a more strategic establishment of new plantings. This long-term field study (2000-2013) aimed to evaluate different rootstocks for 'Swatow' mandarin grown at two locations (Paranavaí and Londrina) in the Brazilian subtropics. Nine rootstocks were evaluated, including 'Rangpur' lime, 'Swingle' citrumelo, 'Volkamer' lemon, 'Caipira DAC' sweet orange, 'Cleopatra' and 'Sunki' mandarins, 'Trifoliate' orange, 'Carrizo', and 'Fepagro C-13' citranges. Trees were assessed for vegetative growth, yield, fruit quality, density, and yield estimates. The experimental design was a randomized block arranged in a 9 × 2 setting (rootstock × location) with 6 replicates and 4 trees per plot. 'Swatow' trees grew more vigorously in Londrina than Paranavaí, particularly for 'Cleopatra' and 'Sunki' pairings. Tree vigor was reduced with 'Trifoliate', resulting in higher tree density estimates and yield efficiency. This rootstock, along with 'Rangpur', 'Swingle', and 'Carrizo' provided superior yield to the scion. All tested rootstocks conferred good fruit quality. Fruits were larger and heavier in 'Sunki' pairings, showing higher soluble solids (SS) content, along with 'Caipira DAC', 'Trifoliate', 'Swingle', and 'Carrizo' at both locations. Our findings confirm the suitability of 'Trifoliate' orange, 'Carrizo' citrange, or 'Caipira DAC' orange rootstocks as promising candidates for 'Swatow' mandarin cultivation in humid subtropical and analogous regions. Further investigations are invoked to improve the horticultural performance of 'Swatow' mandarin trees grafted onto these rootstocks.