Application of Lactobacillus spp. for the biological management of green mold (Penicillium digitatum) on sweet orange fruit under in vitro and storehouse conditions

This study aimed to investigate the use of probiotic lactic acid bacteria including Lactobacillus brevis, L. plantarum, L. helveticus and L. delbrueckii from dairy products against Penicillium digitatum (green mold) on sweet orange fruit. Antifungal activity of Lactobacillus spp. was first assayed using bacterial cells through the overlay method against 10(5) spore/mL suspension of P. digitatum. Also, P. digitatum growth inhibition was measured in the PDA medium containing 15 and 30% cell-free supernatant (CFS) of Lactobacillus spp. Antifungal activity of Lactobacillus spp. was evaluated under storehouse conditions by treating wounded fruits with 10(8)/mL cell suspension (CS) and 30% CFS of Lactobacillus spp., which then infected with 10(5)/mL spore suspension of P. digitatum. The CS and CFS of L. plantarum had the best antifungal activity under both in vitro and in vivo conditions followed by L. helveticus, L. delbrueckii and L. brevis. L. plantarum. The 15 and 30% L. plantarum CFS were able to inhibit the growth of P. digitatum by 30.31%, 76.82% and 97.6% respectively, under in vitro conditions. Also, L. plantarum CS and 30% CFS reduced the growth of the P. digitatum on the fruit by 92.77 and 98.9% respectively, under storehouse conditions. The total content of all sugars of treated fruits with Lactobacillus spp., CS and CFS showed significant difference compared to untreated fruits. Therefore, the present study highlights the successful application of biological fungicides based on secondary compounds of Lactobacillus spp. due to greater stability of metabolites than bacterial cells in the environment.