Bacterial wilt (BW) caused by Ralstonia solanacearum is responsible for substantial losses in cultivated potato (Solanum tuberosum) crops worldwide. Resistance genes have been identified in wild species; however, introduction of these through classical breeding has achieved only partial resistance, which has been linked to poor agronomic performance. The Arabidopsis thaliana (At) pattern recognition receptor elongation factor-Tu (EF-Tu) receptor (EFR) recognizes the bacterial pathogen-associated molecular pattern EF-Tu (and its derived peptide elf18) to confer anti-bacterial immunity. Previous work has shown that transfer of AtEFR into tomato confers increased resistance to R. solanacearum. Here, we evaluated whether the transgenic expression of AtEFR would similarly increase BW resistance in a commercial potato line (INIA Iporá), as well as in a breeding potato line (09509.6) in which quantitative resistance has been introgressed from the wild potato relative Solanum commersonii. Resistance to R. solanacearum was evaluated by damaged root inoculation under controlled conditions. Both INIA Iporá and 09509.6 potato lines expressing AtEFR showed greater resistance to R. solanacearum, with no detectable bacteria in tubers evaluated by multiplex-PCR and plate counting. Notably, AtEFR expression and the introgression of quantitative resistance from S. commersonii had a significant additive effect in 09509.6-AtEFR lines. These results show that the combination of heterologous expression of AtEFR with quantitative resistance introgressed from wild relatives is a promising strategy to develop BW resistance in potato.

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Plant domestication by selective breeding may reduce plant chemical defense in favor of growth. However, few studies have simultaneously studied the defensive chemistry of cultivated plants and their wild congeners in connection to herbivore susceptibility. We compared the constitutive glycoalkaloids (GAs) of cultivated potato, Solanum tuberosum, and a wild congener, S. commersonii, by liquid chromatography coupled to mass spectrometry. We also determined the major herbivores present on the two species in field plots, and tested their preference for the plants and their isolated GAs in two-choice bioassays. Solanum commersonii had a different GA profile and higher concentrations than S. tuberosum. In the field, S. tuberosum was mostly attacked by the generalist aphids Myzus persicae and Macrosiphum euphorbiae, and by the specialist flea beetle Epitrix argentinensis. In contrast, the most common herbivore on S. commersonii was the specialist sawfly Tequus sp. Defoliation levels were higher on the wild species, probably due to the chewing feeding behavior of Tequus sp. As seen in the field, M. persicae and E. argentinensis preferred leaf disks of the cultivated plant, while Tequus sp. preferred those of the wild one. Congruently, GAs from S. commersonii were avoided by M. persicae and preferred by Tequus sp. The potato aphid performed well on both species and was not deterred by S. commersonii GAs. These observations suggest that different GA profiles explain the feeding preferences of the different herbivores, and that domestication has altered the defensive capacity of S. tuberosum. However, the wild relative is still subject to severe defoliation by a specialist herbivore that may cue on the GAs.

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.

Escalona (2017) Compositional changes on colored and light-yellow-fleshed potatoes subjected to two cooking processes, CyTA -