Detection of Latent Infections of Ralstonia solanacearum Race 3 Biovar 2 in Geranium

Abstract

Ralstonia solanacearum race 3 biovar 2 is a regulated quarantine pathogen that infects solanaceous hosts such as potato as well as geranium, where it causes either bacterial wilt (also known as Southern Wilt) or a symptomless latent infection. Geranium growers and government regulators need reliable detection methods to identify infected plant material before it is exported. We previously found that R. solanacearum-infected geranium plants can shed millions of bacteria in effluent water that flows from pots. We tested a nondestructive sampling method wherein effluent water from infected plants grown under commercial conditions was both dilution plated and filter concentrated for real-time polymerase chain reaction (PCR). Under field conditions in Guatemala, effluent shedding of infected geranium plants was highly variable. Comprehensive growth chamber studies confirmed that latently infected and mildly symptomatic geranium plants often but not invariably shed detectable numbers of bacteria in their effluent. At the peak of bacterial shedding, just under 90% of infected plants shed detectable bacteria whereas, at the lowest point, 44% shed detectable numbers of pathogen cells. Bacterial shedding peaked several weeks after inoculation regardless of whether plants were symptomatic or latently infected. Bacterial stem population sizes did not correlate with either effluent population sizes or disease index rating. Finally, we found that the effluent from geranium plants grown in volcanic rock scoria medium contains inhibitors that reduce the effectiveness of real-time PCR detection methods.

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

“…To measure the survival of R. solanacearum strains in stems of susceptible geranium plants, we petiole-wound inoculated 10-week-old geranium plants (cv. "Designer Dark Red"; Ball FloraPlant, West Chicago, IL) with a suspension of R. solanacearum cells as described previously (41) to give a final cell concentration of 2.5 ϫ 10 3 CFU/plant for strain UW551 or 2.5 ϫ 10 4 CFU/plant for strain K60. The plants were incubated in a growth chamber with a cycle of 14 h light at 24°C and 10 h dark at 19°C.…”

“…The potato is only one host of R3bv2, however, as the strain also infects tomato plants, eggplant, and many wild and horticultural plants (13,25,34,47,52). Infected geranium cuttings have been accidentally introduced to North America and Europe from the highland tropics, although the bacterium has not become established in North America (25,29,40,41,53). R3bv2 most likely originated in the Andes with potato plants, since isolates from around the world are essentially clonal (14,22,39,48).…”

Fatty Acid Polymorphism of Ralstonia solanacearum in Different Egyptian Governorates and other European Countries

“…Typical morphological characteristics of virulent R. solanacearum were purified (Swanson et al, 2007). Results of biochemical and physiological characteristics identified all isolates as R. solanacearum (Table 1).…”

In silico genomic subtraction guides development of highly accurate, DNA-based diagnostics for Ralstonia solanacearum race 3 biovar 2 and blood disease bacterium

“…While this development has resulted in lowered food costs and improved choices for the consumer, it has also dramatically increased the risk of introducing plant pathogens into new environments (Janse et al 2004;Swanson et al 2007). To stem the spread of disease, we need rapid diagnostic tools to detect contaminated material so that pathogens can be contained and destroyed.…”

“…One of the greatest needs is for simple, in-the-field diagnostics that can give rapid assessment of potential contamination without the need for cumbersome or complex equipment. The immunochromatographic strip (immunostrip) is one such tool that has improved the ability of growers and regulators to manage and contain the spread of agricultural pathogens (Champoiseau et al 2009;Swanson et al 2007). While immunostrips are quick, reliable, and easy to use in the field, their limit of detection is 10 4 -10 5 cells (Champoiseau et al 2009;Paret et al 2010;Swanson et al 2007), and they rarely can distinguish between closely related strains and variants.…”