Interspecific Potato Breeding Lines Display Differential Colonization Patterns and Induced Defense Responses after Ralstonia solanacearum Infection

Abstract

Potato (Solanum tuberosum L.) is one of the main hosts of Ralstonia solanacearum, the causative agent of bacterial wilt. This plant pathogen bacteria produce asymptomatic latent infections that promote its global spread, hindering disease control. A potato breeding program is conducted in Uruguay based on the introgression of resistance from the wild native species S. commersonii Dun. Currently, several backcrosses were generated exploiting the high genetic variability of this wild species resulting in advanced interspecific breeding lines with different levels of bacterial wilt resistance. The overall aim of this work was to characterize the interaction of the improved potato germplasm with R. solanacearum. Potato clones with different responses to R. solanacearum were selected, and colonization, dissemination and multiplication patterns after infection were evaluated. A R. solanacearum strain belonging to the phylotype IIB-sequevar 1, with high aggressiveness on potato was genetically modified to constitutively generate fluorescence and luminescence from either the green fluorescence protein gene or lux operon. These reporter strains were used to allow a direct and precise visualization of fluorescent and luminescent cells in plant tissues by confocal microscopy and luminometry. Based on wilting scoring and detection of latent infections, the selected clones were classified as susceptible or tolerant, while no immune-like resistance response was identified. Typical wilting symptoms in susceptible plants were correlated with high concentrations of bacteria in roots and along the stems. Tolerant clones showed a colonization pattern restricted to roots and a limited number of xylem vessels only in the stem base. Results indicate that resistance in potato is achieved through restriction of bacterial invasion and multiplication inside plant tissues, particularly in stems. Tolerant plants were also characterized by induction of anatomical and biochemical changes after R. solanacearum infection, including hyperplasic activity of conductor tissue, tylose production, callose and lignin deposition, and accumulation of reactive oxygen species. This study highlights the potential of the identified tolerant interspecific potato clones as valuable genetic resources for potato-breeding programs and leads to a better understanding of resistance against R. solanacearum in potato.

Comparison of type 5d autotransporter phospholipases demonstrates a correlation between high activity and intracellular pathogenic lifestyle

“…aeruginosa and R. solanacearum (37)(38)(39) showed a low enzymatic efficiency when exposed to 4-MuH compared to those from the intracellular pathogens B. pseudomallei (40), F. nucleatum (10) and the facultative intracellular pathogen A. hydrophila (41,42). This activity difference may indicate a primarily intracellular role for the type 5d phospholipases.…”

Anatomical and Biochemical Changes Induced by Gluconacetobacter diazotrophicus Stand Up for Arabidopsis thaliana Seedlings From Ralstonia solanacearum Infection

“…The phylogenetic assignment of R. solanacearum strains was also determined based on analysis of the partial nucleotide sequences of the endoglucanase (egl) gene. PCR amplification of a 750-bp region of the egl gene was performed using the Endo-F and Endo-R primers pair as previously described (Fegan et al, 1998). Reactions were performed in a total in a total volume of 25 μl containing 1× DNA polymerase buffer, 1.5 mM MgCl2, 0.2 mM of each dNTP, 10 pmol of each primer, 1 U of Taq DNA polymerase (Promega), and 50 ng of DNA template.…”

Sound Vibration-Triggered Epigenetic Modulation Induces Plant Root Immunity Against Ralstonia solanacearum

“…Studies show that the expression of lignin biosynthesis genes is up-regulated in plants infected with various pathogens such as necrotrophic bacteria, biotrophic bacteria, and fungi (Bonello et al, 2003;Ponce de Leon et al, 2007;Chezem et al, 2017). In potato (Solanum tuberosum) and tomato, R. solanacearum-resistant cultivars contain higher lignin content than susceptible cultivars (Ishihara et al, 2012;Ferreira et al, 2017). Therefore, SV-induced LAC2, LAC17, and IRX12 activation in our study possibly contributed to plant cell wall reinforcement, thus strengthening the barrier against R. solanacearum in Arabidopsis root.…”