Anti-bacterial activity of Guizotia scabra L. and Maesa lanceolata L. extracts on Erwinia carotovora L. responsible for Irish potato soft rot in Rwanda

Abstract

Food security is handicapped by the postharvest losses caused by pathogenic bacteria such as Erwinia carotovora L. (L: is a Swedish botanist called Linnaeus). Nowadays in Rwanda as well as in the different developing countries, harvested Irish potatoes undergo losses due to rotting caused by different pathogenic microorganisms found in soil, water, and other vectors. In Musanze District, Irish potato seeds or small tubers and table potatoes are spoiled by the bacterial species called Erwinia carotovora. Curative chemicals imported from developed countries are very expensive and not available in all regions of rural areas. There is a need to find local alternatives in terms of traditional treatment methods practiced by traditional healers for animals and human body. Medicinal plants roots, barks, leaves and flowers were collected from the Institute of Higher Education (called INES-Ruhengeri) botanical garden established near Volcanoes of Rwanda. Dried crude extracts were prepared in the laboratory for anti-microbial activity assay on identified Erwinia carotovora from infected samples of rotten Irish potatoes collected from Musanze District. Targeted medicinal plants were Guizotia scabra L. and Maesa lanceolata L. with a good reputation in traditional healing of human diseases. The objective of this research work was to assess or evaluate the anti-bacterial activity of crude extracts of Guizotia scabra L. and Maesa lanceolata L. on Erwinia carotovora L. identified from rotten Irish potatoes from Musanze District in Rwanda. Crude extracts were used in order to determine the minimum volume in micro-litres (minimum dose) to be used in order to inhibit Erwinia carotovora L. isolated from rotten Irish potatoes. It was found that crude extracts of Maesa lanceolata L., especially from leaves and roots exhibit a better antimicrobial effect on identified Erwinia carotovora L. For Maesa lanceolata L., the minimum dose was 5 μl with 3 mm of inhibition zone found on antibiogram, while for Guizotia scabra L., the minimum volume was 10 μl with 5mm of inhibition zone diameter. It was concluded that both medicinal plants were similarly active against Erwinia carotovora L. responsible for Irish potato soft rot in Musanze conditions. Thus, the two endangered medicinal plants species should be protected, multiplied and promoted at industrial level for the contribution to sustainable development of the country.

Keywords: Anti-bacterial activity, Crude extract, Erwinia carotovora, Guizotia scabra, Maesa lanceolata, Irish potato, pathogenic bacteria, rot