By Davie Kadyampakeni
Huanglongbing (HLB) is a citrus disease that affects the growth of the fibrous roots of citrus trees. This means that HLB-affected trees may have reduced root volume, which impacts water uptake.
A greenhouse study was conducted from October 2019 to July 2021 at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center (CREC) in Lake Alfred to evaluate the growth and development of HLB-affected citrus trees under a deficit irrigation system. The objective was to assess the impact of deficit irrigation on tree growth, water availability, stem water potential (SWP), sap flow and root growth of HLB-affected Valencia orange trees on Kuharske citrange rootstock using an evapotranspiration (ET)-based irrigation schedule. The study hypothesized that HLB-affected citrus trees require less irrigation water to complete their biological functions than healthy citrus trees because of severe fibrous root loss.
A total of 20 potted trees were either HLB-positive or non-HLB-affected. One-half of the trees were subjected to deficit irrigation (80% ET) and the other half to full irrigation (100% ET). There was no significant difference in tree height in both years between HLB-affected trees irrigated at 80% ET and 100% ET. In general, there was no difference in SWP between the HLB-affected trees subjected to deficit irrigation and full irrigation. At 80% and 100% ET, non-HLB trees had greater sap flow than HLB-affected trees.
Sap flow for the periods of March–April and June–July 2021 was comparable between HLB-affected trees at all irrigation rates. Maximum sap flow occurred between 11 a.m. and 4:00 p.m. for HLB-affected trees. HLB-affected trees had an average water use of 1.6 millimeter per day compared to 2.1 millimeters per day for non-HLB trees. Healthy trees used about 20% more water than HLB-affected trees, equivalent to 0.5 millimeters per day. Thus, irrigating at 80% ET may be appropriate for achieving water savings in controlled environments for HLB-affected trees without causing water stress.
Acknowledgments: This was a UF/IFAS Citrus Initiative project, funded by the Florida Legislature and the U.S. Department of Agriculture.
Davie Kadyampakeni is an associate professor at the UF/IFAS CREC in Lake Alfred.