2018 ASHS Annual Conference

Huanglongbing or greening disease increased the need for new plantings and resetting in the field. To meet the high tree demand, citrus nurseries need high-quality, fast-growing rootstocks. Vegetative propagation is an alternative to the traditional seedling production due to the increased turnaround in the nursery. However, it may induce changes in the root system architecture and the development of adventitious roots instead of the taproot, altering root morphology and potentially the water uptake performance. The objective of this study was to compare the plant water uptake of citrus rootstocks propagated using different methods. We tested four citrus rootstocks {‘Swingle’ [Citrus paradisi × Poncirus trifoliata], ‘US-942’ [‘Sunki’ (Citrus reticulata) × ‘Flying Dragon’ (Poncirus trifoliata)], ‘US-897’ [‘Cleopatra’ (Citrus reticulata) × ‘Flying Dragon’ (Poncirus trifoliata)], and ‘US-802’ [‘Siamese’ (Citrus grandis) × ‘Gotha Road’ (Poncirus trifoliata)]} and three propagation methods (seed propagation, stem cuttings and tissue culture). The study was arranged in a split-plot design with rootstocks as the main plot factor, and propagation methods as the subplot factor. Main plots were arranged in a completely randomized design with four replications with four trees each. Trees were planted in November/2017, spaced 1.2 × 7.0 m apart, and received the same cultural practices. Microsprinklers were set under a daily irrigation schedule, and trees were fertilized using control-released fertilizer. Plant water uptake was measured using 48 sap flow sensors (SF3; Edaphic Scientific, Port Macquarie, Australia) to estimate transpiration rate. Data were obtained every 15 minutes using a set of data loggers (CR1000X; Campbell Scientific, Logan, UT) and multiplexers (AM16/32B; Campbell Scientific) installed in the field in waterproof boxes. The system was completely powered by rechargeable batteries and solar panels. The 3-needle sap flow sensor was inserted into the trunk of 1-cm diameter young trees selected randomly in the field. Daily water uptake followed the evapotranspiration pattern as reported by the Florida Automated Weather Network. ‘US-802’ propagated by stem cuttings and tissue culture presented lower transpiration rates, while seed propagation the higher values. ‘Swingle’ and ‘US-897’ presented the lowest transpiration rates when propagated by seeds. Propagation methods affected the water uptake in field conditions for the initial tree development stages (4-6 months after planting) in some rootstocks tested. New propagation methods have the potential to accelerate rootstock production and meet the existing tree demand without interfering in adequate water uptake. However, long-term effects are unknown and still under evaluation.