Tripti Vashisth, University of Florida Institute of Food and Agricultural Sciences associate professor, has been leading the research on how plant growth regulators (PGRs) can improve the health of HLB-infected trees. She’s conducted extensive research on the use of gibberellic acid. But she has recently begun to study another hormone, cytokinin.
She gave an update on this work during the Citrus Growers’ Institute held earlier this month in Avon Park, Florida. Cytokinin is a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. It is found in commercial seaweed extracts and other products.
While Vashisth conducted limited research on cytokinin almost a decade ago, it was shelved until more recently when other hormones she was studying began to show benefits to citrus.
Last spring, she initiated a trial to evaluate the impact cytokinin might have on HLB-affected citrus. The trial was applied in a very sick Hamlin grove to see if the hormone could improve growth. The treatments were calcium nitrate, Cytogem, Ascend, Stimplex and a control.
The trial showed that two PGR treatments (Ascend and Stimplex) provided the best results with Stimplex showing the highest performance. Stimplex is a seaweed extract that contains cytokinin. In the trial, applications were made starting in the spring every 45 days for six months.
“With the Stimplex, overall leaf growth looked very good, and we were seeing some reduction in starch accumulation,” Vashisth said. “We also were able to significantly improve the yield. The (yield) numbers were not that impressive, but these were very sick trees. But it was a significant improvement (over other treatments).”
Vashisth is now evaluating the synergistic effects of cytokinin and gibberellic acid, applying the materials at the best times. Cytokinin is applied in the spring, followed by gibberellic acid in the summer and early fall. She says in addition to improved canopy and fruit retention, the applications seem to improve fruit size.
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