Root density distribution and water uptake of citrus trees infected with huanglongbing
Citrus production in Florida is the largest in the United States with a value of production of $1.34 billion. Yields of bearing citrus trees affected by Huanglongbing (HLB, also known as Citrus greening) (Candidatus Liberibacter asiaticus) and infected with Canker (Xanthomonas axonopodis) diseases have declined steadily by 30% or more. HLB has been shown to limit root mass that could lower water and nutrient uptake. With such biological threats limiting citrus production, it is important to evaluate root distribution and water use patterns in HLB affected trees to develop appropriate recommendations for optimizing production. Studies conducted on soils in Florida Flatwoods and Ridge growing areas showed that about 64% to 82% of the fibrous roots (< 0.04 inch diameter) of healthy trees were concentrated in the irrigated zones of drip- and microsprinkler-irrigated trees and the rest were found in the non-irrigated zones. The root densities (for roots < 0.02 inch diameter) of non-HLB affected trees at 0–6-inch soil depth at the Ridge site were 1.7- to 4-fold greater than the HLB affected trees at the Flatwoods site in the irrigated and non-irrigated zones, respectively. Mixed results were observed where HLB affected trees under drip irrigation at the Flatwoods site used 8-fold more water per unit canopy volume and 3.4-fold per unit leaf area than the smaller non-HLB affected trees at the Ridge site under the same irrigation system. However, similar water use patterns between HLB and non-HLB affected trees were observed in Summer 2011. The data show that HLB affected and non-HLB affected trees have similar irrigation water requirements as long as the trees have sufficient canopy and leaf mass.