Calcium Reduces Fruit Abscission in Persimmon by Targeting Cell Wall Integrity

Area of Science:

• Horticulture
• Plant Physiology
• Agricultural Science

Background:

• Persimmon ('Rojo Brillante') in the Mediterranean faces significant yield loss (up to 90%) due to multiple fruit drop waves.
• Summer fruit drop, induced by heat and water stress, is the primary cause of yield reduction in persimmons.
• Organ abscission is a complex process influenced by genetics, hormones, nutrition, and environment.

Purpose of the Study:

• To investigate the protective role of calcium (Ca) in the abscission zone (AZ) of persimmon fruits.
• To determine if calcium application can mitigate heat and drought-induced fruit drop.
• To elucidate the molecular mechanisms underlying calcium's effect on abscission.

Main Methods:

• Calcium (Ca) was applied every 15 days from anthesis onwards to persimmon trees.
• Fruit drop, polar auxin transport (via DkPIN1 expression), and gene expression in the AZ (DkIDL6) were monitored.
• Polygalacturonase (PG) and pectin methylesterase (PME) activities were measured in treated and untreated fruits.

Main Results:

• Calcium applications significantly reduced premature fruit drop by approximately 30% under heat-drought stress.
• Treatments maintained polar auxin transport and inhibited stage C of abscission, indicated by decreased DkIDL6 gene expression.
• Ca-treated fruits showed significantly lower PME and PG activities, confirming stabilized AZ integrity and preserved fruit firmness.

Conclusions:

• Pre-anthesis calcium sprays are effective in reducing heat and drought-induced persimmon fruit drop.
• Calcium stabilizes the AZ by inhibiting cell wall-degrading enzymes and down-regulating key abscission genes (DkIDL6, DkPG20, DkPME41).
• Calcium treatments represent a climate-smart strategy to improve persimmon yield stability and fruit quality.