Bioactivity of various ethanolic plant extracts against Pectobacterium carotovorum subsp. carotovorum causing soft rot of potato tubers

Abstract

Bacterial soft rot of potato caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) is the most destructive disease worldwide mainly during storage. The pathogen has a wide host range affecting a number of vegetable species. Use of various chemicals and antibiotics has been reported previously against this disease with variable degrees of success, besides, excessive use of antibiotics and chemicals causes various health hazards and also leads to the development of resistance to various other human pathogenic bacteria. In the present study various ethanolic plant extracts were evaluated against Pcc (syn. Erwinia carotovora subsp. carotovora) in-vitro by both disc and Agar well diffusion method. Among them seed extract of Datura stramonium gave highest inhibition zone of 26mm (agar well method) followed by leaf extract of Urtica dioica with 25.33mm. Other plant extracts with their decreasing order of efficacy were Datura stramonium (leaves), Trigonella foenumgraecum (seeds), Syzygium aromaticum (cloves), Salix alba (leaves), Hibiscus rosa-sinesis (leaves), Eucalyptus sp. (leaves), Azadirachta indica (leaves), Conyza canadensis (leaves), Cupressus torulosa (leaves), Morus alba (leaves), Ficuscarica (leaves), Polygonum hydropiper (leaves) and Juglans regia (leaves). Extracts which were found effective under in-vitro conditions were further evaluated on potato tubers. Among them, seed extract of Datura stramonium showed highest control (18.4% disease severity), when applied 12 hours prior to the inoculation of the pathogen and 20%, when applied simultaneously with the inoculation of the pathogen followed by Urtica dioica (leaves) with severity of 20.8% when applied 12 hours prior and 21.6% when applied simultaneously with the pathogen inoculation up to 6 days of storage as against 84.8% in case of inoculated control.