Chitosan-induced modulation of secondary metabolism and stress tolerance in Salvia rosmarinus under combined drought and heat stress

When drought and heat strike together, rosemary doesn't just suffer—it fights back. And a simple sugar-derived compound may be the key to unlocking its hidden resilience.

Rosemary, a beloved herb, faces a double threat: drought and scorching heat. A new study reveals how this plant copes when both stresses hit at once—and how a natural booster can make it even tougher.

Researchers exposed rosemary to drought, heat, and a combination of both. After three weeks, they measured pigments, protective sugars, and stress markers. The combined stress caused more oxidative damage and reduced photosynthetic pigments. Yet, the plant adapted by boosting osmoprotectants and adjusting its chlorophyll ratio.

Enter chitosan, a biostimulant derived from shellfish. When sprayed on leaves, it helped rosemary retain more pigments, increase sugar levels, and reduce oxidative harm. Even better, stressed plants treated with chitosan produced more rosmarinic acid and key monoterpenes like camphor and 1,8-cineole—signs of enhanced secondary metabolism.

Antioxidant tests confirmed that chitosan-treated plants had superior free-radical scavenging and reducing power. This is the first evidence that foliar chitosan can boost rosemary's resilience against combined drought and heat, offering a sustainable way to protect crops in a warming world.

Key Points

• Chitosan boosts pigment retention and reduces oxidative damage.
• Combined stress triggers adaptive osmoprotectant and chlorophyll changes.
• First report of foliar chitosan enhancing rosemary's stress resilience.