Microspheres containing carnosic acid for the treatment of basil fungal diseases

Microspheres loaded with carnosic acid (CA) as an active ingredient which was extracted from various species of Salvia L., were prepared by a spray drying technology. The matrix of the microspheres consisted of 85% deacetylated chitosan (average MW 55000 kDa), poloxamer P407 and carnosic acid. Briefly, chitosan and poloxamer P407 were dissolved in 1% v/v acetic acid followed by dispersion of carnosic acid under vigorous stirring. The dispersion was then fed into a spray dryer (190 Mini, Büchi, Flawil, Switzerland) and processed under the following operative conditions: T inlet 180°C, T outlet 120°C, air aspiration 70% and peristaltic pump 15% (feeding rate 4 mL/min). This process yielded microspheres with 5-8 μm in diameter containing 17% active ingredients corresponding to an encapsulation efficiency of 45% and a practical yield of 34%. To investigate the protective effect against mycelial growth of Botrytis cinerea and Sclerotinia sclerotiorum an 0.1% aqueous dispersion of microspheres was sprayed on 4 groups of 200 plants of basil. After 14d the disease incidence (DI) was 10% (B. cinerea) and 2 % (S. sclerotiorium) as compared to the untreated control (B. cinerea 45% DI; S. sclerotiorum 18% DI).This protective effect of the microsphere-formulation was comparable to that of equal amounts of carnosic acid in methanol, whereas the solvent alone provoked a quite lower mycelial growth inhibition. These results highlight for the first time the antifungal activity of carnosic acid and its potential application, most likely favoured by the presence of chitosan [1], of the above formulation for plant protection against fungi.