Agronomic and Anatomical Indicators of Dwarfism and Graft Incompatibility in Citrus Plants

Poncirus trifoliata var. monstrosa (T. Ito) Swingle is a rootstock used in Brazilian citriculture for its potential to induce dwarfism and the viability of densified crops. Its recommendation is still restricted due to lack of research on the performance and compatibility of different types of scion under specific conditions of soil and climate. The aim of this study was to correlate plant size and productive efficiency with anatomical indicators of dwarfism or graft incompatibility between citrus scion cultivars and the ‘Flying Dragon’ trifoliate orange (FD) and ‘Rangpur Lime’ (RL) as rootstocks. The experimental design was of randomised blocks with split plots, with the experiment conducted in an orchard from the fourth to the sixth year of cultivation, under localised irrigation. The treatments consisted of two rootstocks (FD and RL) in the plots and five scion cultivars (Tahiti acid lime, and Natal, Navel, Lima Sorocaba and Pera oranges) in the sub-plots, with four replications per treatment. The agronomic performance of the plants was evaluated, together with the characteristics of samples containing the cambial zone and secondary xylem below, above and within the graft region. The FD rootstock gives the smallest size and greatest productive efficiency. The ‘Navel’ orange has good anatomical plasticity, adjusting itself more efficiently to the rootstocks. Visual symptoms of incompatibility between the ‘Pera’ orange grafted onto the FD can be seen at 64 months after planting. Vessel size and frequency, as well as the size and disposition of the cambial zone, are related to dwarfism and graft incompatibility.