Evaluation of Resistance to Ralstonia solanacearum in Tomato Genetic Resources at Seedling Stage

Abstract

Bacterial wilt of tomatoes caused by Ralstonia solanacearum is a devastating disease that limits the production of tomato in Korea. The best way to control this disease is using genetically resistant tomato plant. The resistance degree to R. solanacearum was evaluated for 285 tomato accessions conserved in the National Agrobiodiversity Center of Rural Development Administration. These accessions of tomato were originated from 23 countries. Disease severity of tomato accessions was investigated from 7 days to 14 days at an interval of 7 days after inoculation of R. solanacearum under greenhouse conditions. A total of 279 accessions of tomato germplasm were susceptible to R. solanacearum, resulting in wilt and death in 70 to 90% of these plants. Two tomato accessions were moderately resistant to R. solanacearum. Only four accessions showed high resistance against R. solanacearum. No distinct symptom of bacterial wilt appeared on the resistant tomato germplasms for up to 14 days after inoculation of R. solanacearum. Microscopy of resistant tomato stems infected with R. solanacearum revealed limited bacterial spread with thickening of pit membrane and gum production. Therefore, these four resistant tomato germplasms could be used in tomato breeding program against bacterial wilt.

Keywords: Ralstonia solanacearum; bacterial wilt; genetic resource; resistance; tomato.

Fig. 1

The symptoms of resistant (A, IT 201664) and moderately resistant (B, K177647) accessions of tomato germplasms to bacterial wilt at 14 days after inoculation of Ralstonia solanacearum at concentration of 1×10⁸ cfu/ml. Susceptible (C, cv. Hoyong) and resistant control (D, cv. Support) showed wilt or non-wilt symptom, respectively.

Fig. 2

Light micrographs of transverse sections from the hypocotyls of a susceptible (A) and resistant (B) plant at 3 days after inoculation of Ralstonia solanacearum. A large number of bacteria (arrows) were present in the vessel lumen of susceptible tomato (cv. Hoyong) stem at 3 days after inoculation (A). Transverse section of resistant tomato (IT 201664) stem showed the absence of colonization or vessel reaction (B).

Fig. 3

Electron micrographs of transverse (A and B) and longitudinal (C and D) sections from the xylem tissues in the hypocotyls of susceptible (A and C) and resistant (B and D) plants at 3 days after inoculation of Ralstonia solanacearum. (A) Bacterial cells conolized in companion cell (cc) and intercellular space. Secondary cell walls (CW) adjacent to bacteria are structurally loosened by bacteria. The Primary cell walls were disconnected (arrows). (B) A vessel colonized with bacteria showing degeneration of parenchyma cell. V: vessel; PC: parenchyma cell; P: connecting pit membrane. (C) The secondary cell walls (CW) and pit membrane (P) are structurally loosened in susceptible plants. (D) Two vessels with secondary cell wall (CW) connecting pit membrane (P) and gums (g). Pit membranes that are thick and high in electron density are indicated by arrow.