Frost avoidance: sodium alginate + CaCl2 can postpone flowering of ‘Kawanakajima Hakuto’ peach trees

Abstract

The rise in early spring temperatures due to climate change has been advancing the flowering period of peach trees. This phenomenon increases the possibility of frost damage in early spring and consequently reduces the productivity of peach trees, causing economic losses. Under aberrant spring temperatures, delaying peach flowering could be used to avoid frost damage. Thus, the objective of this study was to investigate whether treatment with sodium alginate and CaCl2 in the 2nd (swollen bud) blooming stage could delay peach flowering as a strategy to avoid frost. Regarding the expression rate at the 3rd (calyx green) stage, the control treatment (CT, distilled water) showed a sharp increase from 8 days after treatment (DAT), peaking at 14 DAT. However, the 5AG group (5% sodium alginate + 100 mM CaCl2) and the 7AG group (7% sodium alginate + 100 mM CaCl2) had the maximum expression rate at 17 DAT. After maximum expression, expression in the CT sharply diminished, whereas the 5AG and 7AG treatments showed gentle decreases. At the 4th (calyx red) stage, the CT, 5AG, and 7AG treatments reached peak expression at 20 DAT (43.5%, 31.9%, and 40.2%, respectively). However, maximum expression levels of all treatments were below ~ 50%. The 5th (first pink) stage was first expressed in all treatments when the expression rate at the 4th stage peaked in all groups at 20 DAT. Maximum expression was 50.7% in the CT, 33.7% in the 5AG treatment, and 49.2% in the 7AG treatment. This tendency was similar to that at the 4th stage. Particularly, expression in the 5AG treatment diminished more slowly than that in the CT and 7AG treatment at the 3rd, 4th, and 5th stages. The CT group bloomed first at 20 DAT, reaching full bloom at 81.4%, ahead of the AG treatments at 28 DAT, while the 7AG and 5AG groups bloomed fully at 34 and 37 DAT, respectively. Our results suggest the 5AG treatment is suitable to delay peach flowering when phenological development of the flower buds reaches the 2nd stage.