HLB, or citrus greening, can infect most citrus trees and even some citrus relatives. Because it is so easily vectored by the Asian citrus psyllid, citrus farmers can expect to combat this disease at some point. Chronically infected HLB trees become weakened due to a blockage of nutrient movement from the leaves to the root system, as a result of the HLB pathogen damage to the phloem. Fruit from HLB-infected citrus trees is small and lopsided, with juice that is abnormally bitter, high in acids and has no marketable value. Affected trees often die due to other pre-existing stresses such as blight, phytophthora, tristeza and others that they cannot overcome.
The UF/IFAS Citrus Research and Education Center says HLB is now confirmed in all commercial citrus-growing counties in Florida and also identified in most non-commercial citrus-growing counties on residential properties. With such a high disease rate and billions of dollars in financial impacts over the years, planting the right citrus is essential in this time of HLB. The Citrus Research and Development Foundation (CRDF) has been working with breeders to develop greening-tolerant citrus rootstocks and scions and conducting field trials of three promising CDRF rootstocks in 2020. Ongoing research aims to eradicate HLB but there is so much that can be done to make the disease functionally inconsequential, allowing the infected citrus trees to have a lower titer of the pathogen, resulting in less damage and better growth.
Using HLB-tolerant rootstocks and scions can help keep trees producing marketable fruits at a good yield. Dr. Hailing Jin at the University of California Riverside is working with natural peptides to combat HLB. The UCR technology is in the early stage but has promising results in the laboratory and greenhouse demonstrating that citrus-derived, stable antimicrobial peptides (SAMPs) were effective in preventing HLB infection on young citrus trees, and in treating young HLB-infected trees. This peptide is found in the fruit of greening-tolerant Australian finger limes, which has been consumed for hundreds of years, according to Jin.
The peptide treatment only needs to be applied a few times per year, making it a more cost-effective option for growers to keep HLB under control. Furthermore, UCR researchers say this peptide can be used in a vaccine-like solution to protect young healthy plants from infection because it is able to induce the plant’s innate immunity to the HLB bacteria. Planting rootstocks that have shown great success in trials is a great idea to start outright. Keeping an eye on the latest research in other areas of preventing and reducing infections will help put you on the positive side of this disease with innovative solutions.