Impact of Deficit Irrigation on Growth and Water-use Dynamics of HLB-affected Citrus Trees

A greenhouse study was conducted from October 2019 to July 2021 at the Citrus Research and Education Center (CREC) in Lake Alfred, FL. The objective was to assess the impact of deficit irrigation on tree growth, soil water availability, stem water potential (SWP), sap flow and root growth of 2- to 4-year-old Huanglongbing (HLB)-affected ‘Valencia’ ( Citrus sinensis ) orange trees on ‘Kuharske citrange’ rootstock ( Citrus sinensis x Poncirus trifoliata ) using evapotranspiration (ET)-based irrigation schedule. A total of 20 trees were either HLB-positive or non-HLB affected and one-half of the trees was subjected to deficit irrigation (80% ET) and the other half to full irrigation (100% ET). For HLB-affected trees irrigated at 80% ET and 100% ET, there was no significant difference for tree height in both years. In general, there was no difference for SWP between the HLB-affected trees subjected to deficit irrigation and full irrigation. Non-HLB trees subjected to 100% ET and 80% ET had greater sap flow compared to HLB-affected trees subjected to 100% and 80% ET. Sap flow for the period of March-April and June-July 2021 was comparable between HLB-affected trees at all irrigation rates. Maximum sap flow occurred between 11 and 16 h for HLB-affected trees during for the three measurement periods. HLB-affected trees used an average of 1.6 mm day − 1 while non-HLB trees used 2.1 mm day − 1 . On average, healthy trees (non-HLB) used about 20% more water than HLB-affected trees. For HLB-affected trees, irrigating at 80% ET may be appropriate for achieving water savings under controlled environments.