Identification of crop and weed hosts of Ralstonia solanacearum biovar 2 in the hills of Nepal

Abstract

Common agricultural weeds and crops that grow in the high hills of Nepal were examined after artificial inoculation and under natural conditions in the UK and Nepal to determine whether such plant species could act as hosts to biovar 2 of Ralstonia solanacearum. Bacterial populations in the roots were determined 1 and 2 months after inoculation, and at various intervals after harvesting infected potato crops under natural conditions. Inoculated roots of the summer weeds Drymaria cordata and Polygonum capitata and the winter weeds Cerastium glomeratum and Stellaria media yielded 10 2 210 7 colony-forming units per g root. High populations of the bacterium were recovered from these plants even after partial surface sterilization, indicating that systemic infection had occurred. Ralstonia solanacearum populations were recovered from root extracts of 75% of naturally growing D. cordata plants when sampled 3 months after harvest of a potato crop with bacterial wilt. Similarly, root extracts of 25% of P. capitata plants carried the bacterium. No potential winter weed hosts were infected under natural conditions when sampled 5 and 6 months after harvest of infected potato, indicating that winter conditions in the high hills of Nepal are not conducive to infection. Among crops, mustard (Brassica juncea cv. Fine White) developed typical wilt symptoms after artificial inoculation in warm glasshouse conditions (20±288C). Mustard and barley are winter crops in Nepal. However, neither mustard (Brassica juncea var. Lumle Tori) nor barley (Hordeum vulgare cv. Bonus) was infected when planted into heavily infested plots under natural conditions. The results indicated that the role of nonsolanaceous summer weeds in the persistence of biovar 2 of R. solanacearum in the environment may have been previously underestimated.

Determination of Races and Biovars of Ralstonia solanacearum Causing Bacterial Wilt Disease of Potato

“…He added that five races have been identified within the species. Strains of R. solanacearum have also been divided into five host-specific races by Pradhanang et al (2000). However, the results of this study primarily indicated that bacterial wilt pathogen of potato; R. solanacearum is belonging to race 3 although no wilt symptom was observed in tomato.…”

Genetic diversity of the bacterial wilt pathogen Ralstonia solanacearum using a RAPD marker

“…He added that five races have been identified within the species. Strains of R. solanacearum have also been divided into five host-specific races by Pradhanang et al [46]. The dendrogram based on Nei's [34] genetic distance using the Unweighted Pair Group Method of Arithmetic Means (UPGMA) indicated the segregation of 28 isolates of R. solanacearum grouped into seven, which were clustered into two major clusters: cluster 1 and cluster 2.…”

Management of Bacterial Wilt [Rhalstonia solanacearum Yabuuchi et al., 1995] of Potatoes: Opportunity for Host Resistance in Kenya

“…It mainly attacks potato, tomato (especially when planted after infected potato), geranium, occasionally Pelargonium zonale, eggplants, capsicum, and some solanaceous weeds like Solanum nigrum and Solanum dulcamara (Martin & French, 1985;Janse, 1991;French, 1994). Race 3 also infects a number of non-solanaceous weeds asymptomatically (Wenneker et al, 1999;Pradhanang et al, 2000). This race has a long association with potatoes and has an optimum temperature of 27 -28°C (French, 1994).…”