Evaluation of somatic hybrids of potato with Solanum stenotomum after a long-term in vitro conservation

Screening for Resistance Resources against Bacterial Wilt in Wild Potato

Potato is an important crop, used not only for food production but also for various industrial applications. With the introduction of the potato as a staple food strategy, the potato industry in China has grown rapidly. However, issues related to bacterial wilt, exacerbated by factors such as seed potato transportation and continuous cropping, have become increasingly severe in the primary potato cultivation regions of China, leading to significant economic losses. The extensive genetic diversity of Ralstonia solanacearum (R. solanacearum), which is the pathogen of bacterial wilt, has led to a lack of highly resistant potato genetic resources. There is a need to identify and cultivate potato varieties with enhanced resistance to reduce the adverse impact of this disease on the industry. We screened 55 accessions of nine different wild potato species against the bacterial wilt pathogen R. solanacearum PO2-1, which was isolated from native potato plants and belongs to phylotype II. Three accessions of two species (ACL24-2, PNT880-3, and PNT204-23) were identified with high resistance phenotypes to the tested strains. We found these accessions also showed high resistance to different phylotype strains. Among them, only PNT880-3 was capable of flowering and possessed viable pollen, and it was diploid. Consistent with the high resistance, decreased growth of R. solanacearum was detected in PNT880-3. All these findings in our study reveal that the wild potato PNT880-3 was a valuable resistance source to bacterial wilt with breeding potential.

Global transcriptome and targeted metabolite analyses of roots reveal different defence mechanisms against Ralstonia solanacearum infection in two resistant potato cultivars

Ralstonia solanacearum (Rs), the causal agent of bacterial wilt disease in an unusually wide range of host plants, including potato (Solanum tuberosum), is one of the most destructive phytopathogens that seriously reduces crop yields worldwide. Identification of defence mechanisms underlying bacterial wilt resistance is a prerequisite for biotechnological approaches to resistance breeding. Resistance to Rs has been reported only in a few potato landraces and cultivars. Our in vitro inoculation bioassays confirmed that the cultivars 'Calalo Gaspar' (CG) and 'Cruza 148' (CR) are resistant to Rs infection. Comparative transcriptome analyses of CG and CR roots, as well as of the roots of an Rs-susceptible cultivar, 'Désirée' (DES), were carried out two days after Rs infection, in parallel with their respective noninfected controls. In CR and DES, the upregulation of chitin interactions and cell wall-related genes was detected. The phenylpropanoid biosynthesis and glutathione metabolism pathways were induced only in CR, as confirmed by high levels of lignification over the whole stele in CR roots six days after Rs infection. At the same time, Rs infection greatly increased the concentrations of chlorogenic acid and quercetin derivatives in CG roots as it was detected using ultra-performance liquid chromatography - tandem mass spectrometry. Characteristic increases in the expression of MAP kinase signalling pathway genes and in the concentrations of jasmonic, salicylic, abscisic and indoleacetic acid were measured in DES roots. These results indicate different Rs defence mechanisms in the two resistant potato cultivars and a different response to Rs infection in the susceptible cultivar.

Dynamic proteomic profile of potato tuber during its in vitro development

Potato tuberization is a complicated biochemical process, which is dependent on external environmental factors. Tuber development in potato consists of a series of biochemical and morphological processes at the stolon tip. Signal transduction proteins are involved in the source-sink transition during potato tuberization. In the present study, we examined protein profiles under in vitro tuber-inducing conditions using a shotgun proteomic approach involving denaturing gel electrophoresis and liquid chromatography-mass spectrometry. A total of 251 proteins were identified and classified into 9 groups according to distinctive expression patterns during the tuberization stage. Stolon stage-specific proteins were primarily involved in the photosynthetic machinery. Proteins specific to the initial tuber stage included patatin. Proteins specific to the developing tuber stage included 6-fructokinase, phytoalexin-deficient 4-1, metallothionein II-like protein, and malate dehydrogenase. Novel stage-specific proteins identified during in vitro tuberization were ferredoxin-NADP reductase, 34 kDa porin, aquaporin, calmodulin, ripening-regulated protein, and starch synthase. Superoxide dismutase, dehydroascorbate reductase, and catalase I were most abundantly expressed in the stolon; however, the enzyme activities of these proteins were most activated at the initial tuber. The present shotgun proteomic study provides insights into the proteins that show altered expression during in vitro potato tuberization.

Distribution of glycoalkaloids in potato tubers of 59 accessions of two wild and five cultivated Solanum species

Steroidal glycoalkaloids are naturally occurring, secondary plant metabolites that are found in foods, including potatoes and tomatoes. Their content in plants is controlled by both genetic and environmental factors. Glycoalkaloid profiles can be passed to progenies during breeding and hybridization of wild and cultivated potatoes designed to develop improved potatoes. The most common potato, Solanum tuberosum, contains primarily the glycoalkaloids, alpha-solanine and alpha-chaconine. However, wild-type potatoes being used for breeding new varieties contain other, less common glycoalkaloids. Because glycoalkaloid composition is a major criterion for the release of new potato cultivars, we used HPLC, TLC, GC, and GC/MS to determine their nature and content in several Solanum species widely used in potato breeding and hybridization programs. Solanum tuberosum, as well as S. andigena and S. stenotomum, contained alpha-solanine and alpha-chaconine. S. canasense was found to contain only dehydrocommersonine. S. acaule contained alpha-tomatine and demissine. S. juzepczukii and S. curtilobum contained demissine and two previously unidentified glycoalkaloids. We characterized them as demissidine-glucose/rhamnose (1/1 ratio) and demissidine-galactose/glucose/rhamnose (1/1/1 ratio), tentatively named dihydro-beta(1)-chaconine and dihydrosolanine, respectively. We found extensive variability in the glycoalkaloid profiles in the tested potato varieties. The possible significance of these findings for plant breeding and food safety is discussed.