Bacterial wilt management : a prerequisite for a potato seed certification program in Mali

Abstract

Potato is one of the most important cash crops in Mali and has been well adapted to the Malian cropping systems and food habit. Bacterial wilt caused by Ralstonia solanacearum (Smith) Yabuuchi et al., (1995) has become a major problem causing important damage in production. The Race and biovar of the bacterium present in Mali were not known at the start of this thesis research and the objective of this research was to identify the race/biovar and to evaluate integrated control methods with the aim to produce high quality disease free seed potato in Mali. We have initially identified the biovar and Race of R. solanacearum affecting potato in Mali as Race 1 biovar 3. ELISA tests were used on soil and water samples to detect the presence of R. solanacearum. Three detections methods of the bacteria (bacterial streaming test, Agdia immunostrip test and Tetrazolium chloride media) in plant samples were compared; weeds and crops hosting the bacteria as sources of inoculums were identified using Agdia immunostrip test.

Race was determined by hypersensitivity test, pathogenicity tests and by biochemical tests with disacharides and alcohol hexoses. The level of soil infestation in soil samples collected throughout Mali was determined by growing tobacco plant susceptible to R. solanacearum Race 1. ELISA tests showed the presence of R. solanacearum in irrigation water from Farako creek, Samogossoni well in Sikasso, and canal water in Baguineda. Other places such as Borko's soils were found free from the disease. Plant hosts identified as inoculum sources were Commelina forskalaei Vahl, tomato, egg plant and pepper. Out of the three techniques for bacterial detection in plant samples, the best detection was achieved with bacterial streaming test and Agdia immunostrip test. In varietal tests, three of the six varieties tested (Appoline, Claustar and Spunta) showed a better tolerance compared to Mondial, Daifla and Liseta in presence of high bacterial wilt disease pressure. These results will be used to design and implement an integrated bacterial wilt control program in Mali.