Evaluation of alternatives for Penicillium digitatum imazalil resistant strains postharvest management

Abstract

The control of Green mold caused by Penicillium digitatum in Uruguayan packinghouses is based in imazalil (IMZ) application. As a result, resistant strains appeared. The aim of this work was to evaluate different alternatives for postharvest control of IMZ resistant (1.0 mg l^-1 in vitro) P. digitatum strains. Valencia and Ellendale fruit were inoculated with P. digitatum S22 (IMZ sensitive) and R20 (IMZ resistant) strains. Afterwards, they were treated by a 15 s immersion in IMZ, pyrimethanil (PYR) or fludioxonil (FLU) alone or combined with salts: sodium bicarbonate (BCS), sodium carbonate (CS) or potassium sorbate (SP). After 15 days of storage at 20 ± 2 ºC pathogen incidence was registered. For Ellendale, IMZ was the best fungicide for sensitive strain management, achieving 100% control with 500 mg l^-1. Although disease incidence was lower than 25% with 500 μL l^-1 PYR or FLU application, control efficacy was lower than for IMZ treatment. For resistant strain PYR and FLU were as effective as IMZ (1500 mg l^-1), with 80% of healthy fruit. BCS applied at 1, 2 or 3% reduced pathogen incidence, being significantly superior in mixture with IMZ 500 mg l^-1. For Valencia oranges an incidence reduction higher than 90% was obtained by IMZ 1500 mg l^-1 and IMZ + PYR 750 μL l^-1. These alternatives reveal that is possible to develop anti-resistance strategies for P. digitatum IMZ resistant strains management.