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Effects of Homobrassinolide on HLB-Affected Citrus Trees

At UF/IFAS, we are working on finding solutions for Florida’s citrus growers. This is a summary of one project made possible by state legislative funding for the UF/IFAS Citrus Initiative during the 2018-19 cycle. It documents how we are making progress and  providing Florida growers with reasonable, pragmatic solutions to successfully grow citrus in the new age of citrus greening.

Researchers: Fernando Alferez, Horticultural Sciences; Tripti Vashisth, Horticultural Sciences; and Christopher Vincent, Horticultural Sciences

IMPACT: Research has shown that a currently available product called homobrassinolide (HBR) can improve tree health, increase fruit yield, and improve internal fruit quality of HLB-diseased citrus trees. Growers may use this product now.

Brassinosteroids are a class of plant hormones associated with development and stress tolerance. In early 2016, a Cuban scientific study asserted a compound from this group could reduce pathogen concentrations in citrus trees affected by citrus greening disease, also known as Huanglongbing or HLB. In response, a UF/IFAS research team led by horticulturalist Fernando Alferez of the Southwest Florida Research and Education Center set out to assess the potential of a related compound, homobrassinolide.

At two UF/IFAS research facilities in central and southwest Florida, Alferez and his colleagues designed an experiment involving outdoor-grown Valencia sweet orange trees that were 6-8 years old and HLB-positive. The trees were divided into three groups and every other week for six months, each group was treated with a solution that contained a low concentration of homobrassinolide, a high concentration, or
pure water with no homobrassinolide.

Approximately one year into the study, researchers found no differences in the concentrations of HLB pathogen between the treatment groups. However, homobrassinolide apparently promoted earlier flowering, faster fruit development and earlier, larger yields, all of which are potentially beneficial to growers. Results from the second year indicate trees receivingthe lower concentration of homobrassinolide had 21% greater yield than the untreated trees, and better internal fruit quality. Trees receiving the higher concentration had 10% greater yield. Alferez has launched an additional study to determine whether homobrassinolide may help young citrus trees shrug off the HLB pathogen and remain healthy. Work continues to develop precise recommendations that growers can use to sustain productivity of HLB-diseased trees.

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