Efficiency of essential oils against Pectobacterium carotovorum subsp. carotovorum causing potato soft rot and their possible application as coatings in storage

Abstract

This research was conducted to exploit an innovative approach for potato soft rot disease management by application of natural compounds as coatings. The activity of three novel essential oils (EOs) extracted from indigenous plants including Hyssopus officinalis, Satureja khuzistanica and Zataria multiflora was investigated against Pectobacterium carotovorum subsp. carotovorum (Pcc) under in vitro and in vivo conditions. The effect of sub-MIC concentrations of the oils was analyzed on different pathogenicity determinants of Pcc including motility, biofilm forming activity and enzyme secretion. The potential of the EOs to reduce soft rot was also evaluated in tuber maceration trial and under semi-practical storage conditions. The effect of the EOs application on decay progression and prevalence in potato tubers was determined by in vivo preventing and curing assays. The highest suppressive effects were displayed by S. khuzistanica and Z. multiflora EOs with MIC at 0.19 and 0.38 g L−1. Studied compounds were considerably able to inhibit virulence determinants of Pcc with higher efficiency than streptomycin. Biofilm-forming ability was sharply repressed in tested strains within the range of 24.8–47.6%. A significant induced motility was observed in oil-treated cells which is adversary with surface adhesion and biofilm development. Secretion of plant cell wall degrading enzymes (PCWDEs) was decreased in the range of 37.6–100% and among them, pectate lyase (Pel) and polygalacturonase (Peh) were considerably inhibited (53.4–100% and 65.4–100%). Sub-MIC values of S. khuzistanica and Z. multiflora EOs led to reduce maceration ability of Pcc strains in the range of 1.4 to 2.9 times compared with control. The results of in vivo trial indicated that tuber rot development was more efficiently controlled in preventive than curative conditions. Disease incidence was reduced by 38.4–70.6% as compared with non-coated samples in preventing assessment. In conclusion, the EOs were capable to control soft rot disease under in vitro and in vivo conditions. GC-MS analysis revealed that cis-pinocamphone, carvacrol and thymol were the main active constituents in H. officinalis, S. khuzistanica and Z. multiflora volatile oils, respectively. Studied test phytochemicals could be promising antibacterial agents for preserving potato tubers against soft rot and preventing storage loss. This is the first report on the activity of herbal antimicrobial compounds against a postharvest bacterial disease of potato as a practical solution which can be suggested as preserver coatings for the tubers and incorporated with other disease management strategies.