A novel approach to locate Phytophthora infestans resistance genes on the potato genetic map

Mapping resistance genes is usually accomplished by phenotyping a segregating population for the resistance trait and genotyping it using a large number of markers. Most resistance genes are of the NBS-LRR type, of which an increasing number is sequenced. These genes and their analogs (RGAs) are often organized in clusters. Clusters tend to be rather homogenous, viz. containing genes that show high sequence similarity with each other. From many of these clusters the map position is known. In this study we present and test a novel method to quickly identify to which cluster a new resistance gene belongs and to produce markers that can be used for introgression breeding. We used NBS profiling to identify markers in bulked DNA samples prepared from resistant and susceptible genotypes of small segregating populations. Markers co-segregating with resistance can be tested on individual plants and directly used for breeding. To identify the resistance gene cluster a gene belongs to, the fragments were sequenced and the sequences analyzed using bioinformatics tools. Putative map positions arising from this analysis were validated using markers mapped in the segregating population. The versatility of the approach is demonstrated with a number of populations derived from wild Solanum species segregating for P. infestans resistance. Newly identified P. infestans resistance genes originating from S. verrucosum, S. schenckii, and S. capsicibaccatum could be mapped to potato chromosomes 6, 4, and 11, respectively

Broad spectrum insect resistance and metabolites in close relatives of the cultivated tomato

Wild relatives of tomato possess effective means to deal with several pests, among which are a variety of insects. Here we studied the presence of resistance components against Trialeurodes vaporariorum, Myzus persicae, Frankliniella occidentalis, and Spodoptera exigua in the Lycopersicon group of Solanum section Lycopersicon by means of bioassays and comprehensive metabolite profiling. Broad spectrum resistance was found in Solanum galapagense and a few accessions of S. pimpinellifolium. Resistance to the sap sucking insects may be based on the same mechanism, but different from the caterpillar resistance. Large and highly significant differences in the leaf metabolomes were found between S. galapagense, containing type IV trichomes, and its closest relative S. cheesmaniae, which lacks type IV trichomes. The most evident differences were the relatively high levels of different methylated forms of the flavonoid myricetin and many acyl sucrose structures in S. galapagense. Possible candidate genes regulating the production of these compounds were identified in the Wf-1 QTL region of S. galapagense, which was previously shown to confer resistance to the whitefly B. tabaci. The broad spectrum insect resistance identified in S. galapagense will be very useful to increase resistance in cultivated tomato

Broad spectrum insect resistance and metabolites in close relatives of the cultivated tomato

Wild relatives of tomato possess effective means to deal with several pests, among which are a variety of insects. Here we studied the presence of resistance components against Trialeurodes vaporariorum, Myzus persicae, Frankliniella occidentalis, and Spodoptera exigua in the Lycopersicon group of Solanum section Lycopersicon by means of bioassays and comprehensive metabolite profiling. Broad spectrum resistance was found in Solanum galapagense and a few accessions of S. pimpinellifolium. Resistance to the sap sucking insects may be based on the same mechanism, but different from the caterpillar resistance. Large and highly significant differences in the leaf metabolomes were found between S. galapagense, containing type IV trichomes, and its closest relative S. cheesmaniae, which lacks type IV trichomes. The most evident differences were the relatively high levels of different methylated forms of the flavonoid myricetin and many acyl sucrose structures in S. galapagense. Possible candidate genes regulating the production of these compounds were identified in the Wf-1 QTL region of S. galapagense, which was previously shown to confer resistance to the whitefly B. tabaci. The broad spectrum insect resistance identified in S. galapagense will be very useful to increase resistance in cultivated tomato

Stepwise screening of candidate antagonists for biological control of Blumeria graminis f. sp. tritici

Antagonists for the biological control of Blumeria graminis f. sp. tritici were selected using a stepwise screening approach. Fungal colonizers of powdery mildew pustules were isolated from leaves of cereals and other plant species. Spore production, cold tolerance, drought tolerance and UV-B resistance as important characteristics for application of biocontrol candidates in the phyllosphere were tested in in vitro assays and preliminary risk assessments were conducted. Amongst 850 tested isolates 58% belonged to various taxonomical groups of Cladosporium. Only 3% belonged to species that have been reported in literature as antagonistic to powdery mildews. The stepwise screening approach allowed to reduce the number of candidate antagonists using screening criteria that can be tested reliably and cost-effectively in in vitro assays and by data mining from initially 1237 isolates down to 143 candidate antagonists belonging to 42 taxonomical groups. The potential of these isolates to reduce conidia production of B. graminis f. sp. tritici. in wheat was assessed in bioassays on potted winter wheat plants under controlled conditions. A set of ten superior isolates was subsequently tested in a series of trials on potted spring wheat plants under open field conditions. Isolates Tilletiopsis pallescens BC0441 and T. pallescens BC0850 significantly reduced the number of powdery mildew pustules per flag leaf by 30 to 62%. Slopes of the regression lines fitted to data on number of powdery mildew pustules during time were significantly reduced by the antagonists indicating that the powdery mildew epidemics were slowed down. Treatments with T. pallescens BC0441 and T. pallescens BC0850 also reduced leaf coverage with powdery mildew pustules in a small-scale field trial in spring wheat.</p