Detection of Pathogenic and Non-Pathogenic Ralstonia solanacearum in Bell Pepper and Lettuce Cultivation Lands in Sri Lanka

Abstract

Ralstonia solanacearum is a soil-borne, gram-negative, phytopathogenic bacterium that critically threatens global agriculture. R. solanacearum comprises two distinct strains: one pathogenic and the other non-pathogenic. This bacterium exhibits extensive genetic diversity, infecting over 200 crop species, including bell pepper and lettuce. This study aimed to identify pathogenic and non-pathogenic strains of R. solanacearum in bell pepper and lettuce cultivation across diverse agricultural sites. Samples were collected from lettuce and bell pepper cultivation lands in Sri Lanka, including Divulapitiya, Mirahawatta, Keppetipola, and Nuwara Eliya, along with control sites such as Jaffna, Colombo, and Kegalle. Soil, water, and infected plants were collected, kept in sealed bags, and transported to the laboratory under cool conditions. The samples were processed for R. solanacearum isolation using (TTC) agar medium. Based on the recorded results in Divulapitiya sampling site, 87.5% and 100% of soil samples were contaminated with virulent and non- virulent R. solanacearum respectively. Further, 70% and 100% of collected water and plant samples were respectively contaminated with virulent R. solanacearum species in Divlapitiya sampling site. Further, at the Mirahawatta sampling site, 0% contamination was recorded for virulent strains of R. solanacearum whereas 78% contamination was recorded for non-virulent R. solanacearum. Similarly, none of the samples from Keppetipola and Nuwaraeliya sites, were positive for virulent R. solanacearum whereas 100% samples of those sites were positive for non-virulent. Importantly, none of the samples from Jaffna control site were positive for virulent R. solanacearum whereas 100% of samples were positive for non-virulent strain. Moreover, 50% and 60% of samples from Kegalle and Colombo control sites were respectively contaminated with virulent strains whereas 100% of samples of those sites were contaminated with non-virulent strain. The finding of the present study reveals that the prevalence level of R. solanacearum in selected agricultural lands giving an alarming condition for Sri Lankan   agriculture.

Keywords: R. solanacearum, Bell pepper, Lettuce, Agricultural contamination