RESUMO
Potato bacterial wilt is caused by the devastating bacterial pathogen Ralstonia solanacearum. Quantitative resistance to this disease has been and is currently introgressed from a number of wild relatives into cultivated varieties through laborious breeding programs. Here, we present two methods that we have developed to facilitate the screening for resistance to bacterial wilt in potato. The first one uses R. solanacearum reporter strains constitutively expressing the luxCDABE operon or the green fluorescent protein (gfp) to follow pathogen colonization in potato germplasm. Luminescent strains are used for nondestructive live imaging, while fluorescent ones enable precise pathogen visualization inside the plant tissues through confocal microscopy. The second method is a BIO-multiplex-PCR assay that is useful for sensitive and specific detection of viable R. solanacearum (IIB-1) cells in latently infected potato plants. This BIO-multiplex-PCR assay can specifically detect IIB-1 sequevar strains as well as strains belonging to all four R. solanacearum phylotypes and is sensitive enough to detect without DNA extraction ten bacterial cells per mL in complex samples.The described methods allow the detection of latent infections in roots and stems of asymptomatic plants and were shown to be efficient tools to assist potato breeding programs.
Assuntos
Ralstonia solanacearum , Solanum tuberosum , Reação em Cadeia da Polimerase Multiplex , Óperon , Doenças das Plantas , Ralstonia solanacearum/genéticaRESUMO
Ralstonia solanacearum is the causative agent of bacterial wilt of potato. Ralstonia solanacearum strain UY031 belongs to the American phylotype IIB, sequevar 1, also classified as race 3 biovar 2. Here we report the completely sequenced genome of this strain, the first complete genome for phylotype IIB, sequevar 1, and the fourth for the R. solanacearum species complex. In addition to standard genome annotation, we have carried out a curated annotation of type III effector genes, an important pathogenicity-related class of genes for this organism. We identified 60 effector genes, and observed that this effector repertoire is distinct when compared to those from other phylotype IIB strains. Eleven of the effectors appear to be nonfunctional due to disruptive mutations. We also report a methylome analysis of this genome, the first for a R. solanacearum strain. This analysis helped us note the presence of a toxin gene within a region of probable phage origin, raising the hypothesis that this gene may play a role in this strain's virulence.