Pseudomonas Isolates as Potential Biofungicides of Green Mold (Penicillium Digitatum) on Orange Fruit

ABSTRACT Green mold, caused by Penicillium digitatum, is a serious disease of citrus fruit during postharvest. The focus of this study was to evaluate possible biological alternatives to chemical fungicides for P. digitatum control. Four Pseudomonas isolates (Q110B, Q125B, Q112B, and Q004B) were isolated from rhizospheric soil and evaluated for their antagonistic activity against P. digitatum. The in vitro evaluations of these isolates by dual culture revealed an important zone of inhibition after 3 days of incubation at 25 ± 2°C. The Q004B isolate provided a high zone of inhibition in vitro at 45 mm diameter. Four Pseudomonas isolates tested showed antagonistic activity against P. digitatum on orange fruit after 7 days of inoculation under postharvest conditions. Inhibition percentage of P. digitatum on orange fruit ranged from 22 to 85% for Q004B and Q112B, respectively. Regarding the mechanism of action, the four tested isolates produced volatile compounds in vitro with inhibition percentage ranging from 35% to 79%, respectively for Q004B andQ125B. The Q004B isolate caused a high spore inhibition rate of 46%, while Q110B had no effect on spore germination. The four isolates of Pseudomonas produced siderophores in CAS medium. Additionally, Q125B, Q112B, and Q004B showed a positive chitinolytic activity, whereas Q110B provided negative results to the chitinase assay. These isolates represent potential candidates for biological control of citrus green mold and may be effectively used as a sustainable alternative measure to chemical fungicide control.