Agronomic Performance of Mandarin and Hybrid Cultivars Grafted onto Two Commercial Rootstocks Under High Disease Pressure in Brazil

Thirteen mandarin and hybrid cultivars grafted onto the commercial rootstocks Rangpur Lime and Swingle Citrumelo were comparatively assessed for vegetative growth, fruit physicochemical attributes, and field incidence and severity of Altenaria Brown Spot (ABS) and Huanglongbing (HLB). The experiment was conducted from January 2015 to December 2018 under a randomized block design, with ten replicates per scion–rootstock combination. Plant height, canopy volume, fruit mass, juice yield, acidity, soluble solids, and disease assessments were performed. RL induced greater vegetative growth but was associated with higher HLB severity, particularly in the Dekopon IAC 2009 and TM × LP 358 varieties. SC resulted in less vigorous trees but improved fruit quality, with higher acidity and soluble solids. Regarding ABS, the Loose Jacket IAC 515 and Muscia varieties showed high susceptibility, while Ortanique IAC 554 and Rainha BRS exhibited tolerance to both ABS and HLB. These findings suggest that although RL promotes vigorous growth, it may increase disease susceptibility, whereas SC is associated with reduced disease severity and improved fruit quality. Ortanique IAC 554 and Rainha BRS showed consistently low severity of ABS and HLB, combined with stable vegetative development and fruit quality, underscoring the importance of rootstock choice for guiding cultivar deployment in orchards under high disease pressure.