Moderate Temperature Fluctuations Rapidly Reduce the Viability of Ralstonia solanacearum Race 3, Biovar 2, in Infected Geranium, Tomato, and Potato Plants

Abstract

Most Ralstonia solanacearum strains are tropical plant pathogens, but race 3, biovar 2 (R3bv2), strains can cause bacterial wilt in temperate zones or tropical highlands where other strains cannot. R3bv2 is a quarantine pathogen in North America and Europe because of its potential to damage the potato industry in cooler climates. However, R3bv2 will not become established if it cannot survive temperate winters. Previous experiments showed that in water at 4°C, R3bv2 does not survive as long as native U.S. strains, but R3bv2 remains viable longer than U.S. strains in potato tubers at 4°C. To further investigate the effects of temperature on this high-concern pathogen, we assessed the ability of R3bv2 and a native U.S. strain to survive typical temperate winter temperature cycles of 2 days at 5°C followed by 2 days at ؊10°C. We measured pathogen survival in infected tomato and geranium plants, in infected potato tubers, and in sterile water. The population sizes of both strains declined rapidly under these conditions in all three plant hosts and in sterile water, and no culturable R. solanacearum cells were detected after five to seven temperature cycles in plant tissue. The fluctuations played a critical role in loss of bacterial viability, since at a constant temperature of ؊20°C, both strains could survive in infected geranium tissue for at least 6 months. These results suggest that even when sheltered in infected plant tissue, R3bv2 is unlikely to survive the temperature fluctuations typical of a northern temperate winter.

Tropical Strains of Ralstonia solanacearum Outcompete Race 3 Biovar 2 Strains at Lowland Tropical Temperatures

“…There were no significant differences between growth rates of the antibiotic-resistant strain and its wild-type parent over a 144-h period in minimal broth at either 24/19°C or 28°C, indicating that the antibiotic resistance genes did not cause a measurable fitness loss (data not shown). R. solanacearum strains carrying the spontaneous rifampin resistance used in this study retain wild-type bacterial wilt virulence on tomato (30,31).…”

Bacteriophages and Bacterial Plant Diseases

“…The bacterium has global distribution (Sanchez Perez et al, 2008), and with regard to tomato and potato production, has quarantine status in the EU (Anonymous, 2000). The species has considerable economic impact: for example, brown rot of the potato has been estimated to exceed more than €950 million in losses per year worldwide (Scherf et al, 2010). Infection begins by the bacterium entering the host plant though its roots where it will then colonize the xylem.…”

Trehalose Synthesis Contributes to Osmotic Stress Tolerance and Virulence of the Bacterial Wilt PathogenRalstonia solanacearum

“…Three-week-old Bonny Best tomato plants grown in Magenta boxes were inoculated by placing a droplet containing 2,000 R. solanacearum cells on the surface of a freshly cut leaf petiole to ensure that any pathogen cells in the soil had passed through the plant, because passage through plants primes R. solanacearum for soil survival (Scherf et al 2010). When plants reached disease index 4, they were uprooted from their box.…”