Budbreak patterns and phytohormone dynamics reveal different modes of action between hydrogen cyanamide- and defoliant-induced flower budbreak in blueberry under inadequate chilling conditions

Abstract

Under inadequate chilling conditions, hydrogen cyanamide (HC) is often used to promote budbreak and improve earliness of Southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrids). However, HC is strictly regulated or even banned in some countries because of its high hazardous properties. Development of safer and effective alternatives to HC is critical to sustainable subtropical blueberry production. In this study, we examined the efficacy of HC and defoliants as bud dormancy-breaking agents for ‘Emerald’ blueberry. First, we compared water control, 1.0% HC (9.35 L ha–1), and three defoliants [potassium thiosulfate (KTS), urea, and zinc sulfate (ZS)] applied at 6.0% (28 kg ha–1). Model fitting analysis revealed that only HC and ZS advanced both defoliation and budbreak compared with the water control. HC-induced budbreak showed an exponential plateau function with a rapid phase occurring from 0 to 22 days after treatment (DAT), whereas ZS-induced budbreak showed a sigmoidal function with a rapid phase occurring from 15 to 44 DAT. The final budbreak percentage was similar in all treatments (71.7%–83.7%). Compared with the water control, HC and ZS increased yield by up to 171% and 41%, respectively, but the yield increase was statistically significant only for HC. Phytohormone profiling was performed for water-, HC- and ZS-treated flower buds. Both chemicals did not increase gibberellin 4 and indole-3-acetic acid production, but they caused a steady increase in jasmonic acid (JA) during budbreak. Compared with ZS, HC increased JA production to a greater extent and was the only chemical that reduced abscisic acid (ABA) concentrations during budbreak. A follow-up experiment tested ZS at six different rates (0–187 kg ha–1) but detected no significant dose-response on budbreak. These results collectively suggest that defoliants are not effective alternatives to HC, and that HC and ZS have different modes of action in budbreak induction. The high efficacy of HC as a dormancy-breaking agent could be due to its ability to reduce ABA concentrations in buds. Our results also suggest that JA accumulation is involved in budbreak induction in blueberry.

Hydrogen Cyanamide Application Accelerates Vegetative Bud Break and Causes Earlier Yield in ‘Optimus’ and ‘Colossus’ Southern Highbush Blueberry

“…This suggests that both cultivars can potentially benefit from HC application. In previous studies, HC applications led to higher total yields in blueberry (Lin and Agehara 2021;Wang et al 2021;Williamson et al 2002) and other woody perennial crops (Ghrab and Mimoun 2014). Here, HC-treated 'Optimus' or 'Colossus' did not exhibit higher seasonal yields than controls.…”

Enhancing Uniform Sprouting, Yield, and Quality in Grapevines: The Impact of Hydrogen Cyanamide (50% S.L) Treatment

“…In all treatments, the final budbreak percentage ranged from 71.7% to 83.7%. ZS and HC both enhanced yield in comparison to the water control by up to 41% and 171%, respectively, however only Hydrogen Cyanamides' yield increase was statistically significant [23]. The fruits of the treated vines had significantly reported the highest fruit weight, total soluble solids (TSS) and the Titratable acidity (TA) and it was the only treatment that exceeded the TSS level.…”

Influencia del ácido giberélico (AG3), etanol y cianamida hidrogenada (Dormex) sobre la brotación de yemas a partir de tubérculos de Solanum tuberosum L. var. Cecilia.

“…Durante este período, los brotes se mantienen inactivos debido a la presencia de inhibidores endógenos y a la falta de estímulos para la brotación 39 . La cianamida hidrogenada actúa como un agente rompedor de la latencia al inhibir la actividad de los inhibidores endógenos 40 .…”