Influence of additives on adhesion of Penicillium frequentans conidia to peach fruit surfaces and relationship to the biocontrol of brown rot caused by Monilinia laxa.

Additives, such as sucrose, d-sorbitol, glycerol, sodium alginate, carboxymethyl cellulose, silica gel, gelatine, non-fat skimmed milk and a commercial adhesive were added to conidia of Penicillium frequentans at two different points in the production process of the formulation of this fungus to improve conidial adhesion. Conidial adhesion was estimated as the number of P. frequentans conidia (no. conidia cm(-2)) and colony-forming units of P. frequentans per unit area (cfu cm(-2)) that adhered to glass slides or to peach surfaces. The P. frequentans conidial concentration had a significant effect on conidial adhesion, while the shelf life of conidia did not have any effect. The highest adhesion of P. frequentans conidia to glass slides was observed when conidial concentrations were greater than 10(6) conidia ml(-1). P. frequentans conidial adhesion was improved when 1.5% sodium alginate or 1.5% carboxymethyl cellulose were added to the conidial mass obtained after production and before drying by the fluid bed drying process. Conidial adhesion was also enhanced when 1.5% sodium alginate, 1.5% carboxymethyl, or 1.5% gelatine were added to conidia after fluid bed drying. P. frequentans formulations with 1.5% sodium alginate or 1.5% carboxymethyl cellulose were more effective in reducing brown rot caused by Monilinia laxa than dried P. frequentans conidia alone. Our results show that additives can improve adhesion of P. frequentans conidia to fruit surfaces, resulting in more effective control of brown rot in peaches.