Effect of some plant extracts in controlling soft rot disease in some economic plants associated with molecular studies

Pectobacterium carotovorum strains were isolated from onion, pepper and carrot to investigate the molecular and physiological characters as well as efficiency of plant extracts, nano-particles and bioagents to control the bacterial pathogen. The results of molecular characterization revealed that P. carotovorum strain PB-1 (carrot), strain PB-2 (onion) and strain PB-3 (pepper). The results of phylogenetic tree displayed that the three strains were similar and characterized as P. carotovorum, and the genomic sequencing assured these results. Additionally, the pathogenicity test displayed that the strain PB-1 was very aggressive compared with strains PB-2 and PB-3. Antimicrobial activity using plant extracts, nanoparticles and bioagents were conducted. Application of fourteen plant extracts resulted that the plant extract of Tamarindus indica (fruit) showed highest diameter zone of inhibition (17.5 mm) against the P. carotovorum pathogen followed by Hibiscus sabdariffa (16 mm), Rhus coriaria (15.8 mm), Punica granatum (13.6 mm), Citrus paradise (11.6 mm), Psidium guajava (11.6 mm), Citrus sinensis (7.1 mm) and Citrus limon (6.6 mm) on carrot. Plant extract of Punica granatum (fruit peel) showed highest diameter zone of inhibition on P. carotovorum strains which isolated from onion and pepper followed with Hibiscus sabdariffa (14.25,13.75 mm) and Rhus coriaria (11.8,11.05 mm) compared with control (streptomycin 150 ppm). Nano-copper (Cu) and nano-silver (Ag) gave significant inhibition against the three strains. Nano-Cu showed 15.12, 7.6 and 14 mm inhibition however, nano-Ag showed 10.5, 10.7 and 9.75 mm inhibition on carrot, onion and pepper respectively. Bacillus subtilis as a biocontrol agent gave the best and significant results as antibacterial effect against P. carotovorum which showed 13.6 and 13 mm inhibition on carrot and onion respectively compared with Streptomyces spp., Trichoderma spp. and Saccharomyces spp.