Brassinosteroids (Brs) are a natural group of hormones known for their significant impact on responses to both biotic and abiotic stresses across various plant species. Brs can also influence plant growth and fruit maturation. With the recent availability of commercial formulations, this plant growth regulator is becoming an increasingly popular management tool in agriculture. Our team has been working on understanding BRs mode of action in citrus, because information is still scarce. In Florida, citrus industry is now in decline due mainly to the citrus greening disease (HLB), which has become endemic in the state, with no potential cure in the horizon. The disease reduces internal fruit quality and compromises viability of young, newly planted citrus trees. Our work has unveiled that Homobrassinolide (HBr) may increase internal maturation in sweet orange under citrus greening endemic conditions. We have determined the optimal application rate and the most effective timing for Hamlin and Valencia cultivars. We have shown that the beneficial effects of HBr are more pronounced in the healthier trees. This has led us to adapt the use of HBr in combination with oxytetracycline (OTC) injections, as growers in Florida are now injecting OTC in mature trees to reduce HLB. Our results show that HBr, when used on OTC-injected trees, improve internal fruit quality significantly. In addition, we have found that treating young, newly planted trees with HBr induces a strong immune response by activating the salicylic acid pathway, resulting in a delay in HLB infection. We have also shown that other Br analog, Epibrassinolide (EBL) improve the cold tolerance of citrus trees when young, treated plants were exposed to -4 ℃ for 24 hours. In addition, we have also observed EBL are helpful in improving the postharvest fruit quality. This is of special interest in the northern part of the state, where fresh market citrus industry is expanding, as region often experiences frequent chilling conditions during winter months. All in all, we are showing that Brs may be a ready-to-use tool in Florida citrus industry.
