Characterization and Management of Ralstonia Solanacearum in Louisiana

Abstract

Ralstonia solanacearum (Rs), the causal agent of bacterial wilt of tomato, can cause severe economic losses to tomato growers in Louisiana (LA). Traditional management tactics are ineffective. Resistant cultivars lack durability and have undesirable horticultural traits. In addition, disease resistance is strain specific. For these reasons, many producers in LA have abandoned their fields for tomato production. Although R. solanacearum is endemic in LA, pathogen populations have never been characterized. Tomato samples with bacterial wilt symptoms were collected from Livingston, Tangipahoa, East Baton Rouge and St. Helena parishes in 2015. Bacterial wilt was confirmed using Agdia Inc. Rs-specific immunoflow strips and bacterial streaming test. Fifteen isolates were recovered from five fields and one greenhouse. Strains from LA were characterized and belong to phylotype I and II. Thirty-three percent of the strains were characterized as biovar 1 and 20% as biovar 3. Forty-seven percent of strains were unable to utilize dulcitol, and thus belong to a new biovar 6 classification. None of the isolates belong to a select agent Race 3 biovar 2. A worldwide collection of genetically diverse eggplant, tomato and pepper varieties was screened for resistance to seven Rs strains from LA. One pepper variety (PM702) and one eggplant variety (cv. MM15) were identified as being highly resistant to all seven strains from LA. All of the tomato varieties tested were susceptible to the LA strains. Grafting with resistant rootstock varieties was explored as a sustainable management strategy for bacterial wilt in LA. Three susceptible tomato cultivars (Celebrity, Florida 91 and BHN602) that are commonly produced in LA were grafted onto cvs. MM152 and PM702 resistant rootstocks and onto tomato cv. Hawaii 7996, which is considered a model resistant variety. None of the tomato plants that were grafted to pepper cv. PM702 survived the grafting process. Tomato plants (all varieties) grafted to eggplant (cv. MM152) rootstocks were the most resistant to Rs strains from LA compared to those grafted to Hawaii 7996. This study shows that Rs strains from LA were capable of infecting putatively resistant tomato rootstocks but may be managed by using resistant eggplant rootstocks.