Enhancing yield efficiency and fruit quality in citrus through use of tetraploid rootstocks

The devastating bacterial disease huanglongbing (HLB), also known as citrus greening, is compromising citrus production worldwide. No cure for HLB exists at present and most scion cultivars are susceptible and decline quickly without proper disease management. One way to enhance the lifespan of trees and increase productivity of affected orchards is using superior rootstocks in combination with high-density planting. High density plantings are more effective with small-size trees compared to large-size trees, but few dwarfing rootstocks are currently available in Florida. One way to induce dwarfing is through manipulation of the ploidy level via somatic hybridization. In this study we compared novel tetraploid rootstocks against diploid rootstocks for their potential to induce dwarfing of the grafted sweet orange scion and enhance yield efficiency and productivity under heavy HLB pressure. Two field trials were established in 2015 in different locations in Florida, USA. The soil in one location is sandy and well-drained, while in the other it is poorly drained, requiring raised beds and furrows for drainage. Trees were assessed over three production seasons from 2019 to 2021. The different rootstocks varied significantly in their effects on tree size, yield, and yield efficiency. With some exceptions, diploid rootstocks induced a larger tree size than tetraploid rootstocks and produced higher cumulative yields. However, most of the tetraploid rootstocks induced higher yield efficiency and better fruit quality. These rootstocks have therefore good potential for use in high-density plantings to increase revenue in an HLB-endemic production environment such as Florida.