Development of EST-derived markers in Dendrobium from EST of related taxa

Public databases are useful for molecular marker development. The major aim of this study was to develop expressedsequence tag (EST)-derived markers in Dendrobium from available ESTs of Phalaenopsis and Dendrobium. A total of 6063sequences were screened for simple sequence repeats (SSRs) and introns. Primers flanking these regions were generated andtested on genomic DNAs of Phalaenopsis and Dendrobium. Twenty-three percent of amplifiable Phalaenopsis EST-derivedmarkers were cross-genera transferable to Dendrobium. Forty-one markers from both Phalaenopsis and Dendrobium thatamplified in Dendrobium were assessed on six commercial cultivars and six wild accessions. All of them were transferableamong Dendrobium species. High polymorphism and heterozygosity were observed within wild accessions. Sixteen polymorphic markers were evaluated for linkage analysis on an F1 segregating population. Seven markers were mapped into threelinkage groups, two of which showed syntenic relationship between dendrobium and rice. This relationship will facilitatefurther quantitative trait loci (QTL) mapping and comparative genomic studies of Dendrobium. Our results indicate thatPhalaenopsis EST-derived markers are valuable tools for genetic research and breeding applications in Dendrobium

Resistance to tomato yellow leaf curl virus-Thailand isolate (TYLCTHV-[2]) and markers loci association in BC2F1 population from a cross between Seedathip 3 and a wild tomato, Solanum habrochaites ‘L06112’ clone no.1

The BC2F1 population from a cross between wild tomato, Solanum habrochaites ‘L06112’ and recurrent susceptiblevariety, Seedathip 3 was investigated for a resistance to Tomato yellow leaf curl Thailand virus (TYLCTHV-[2]). Five stemcuttings from each of the 196 lines were inoculated with TYLCTHV-[2] using viruliferous whiteflies as the inoculation vector.Disease response was recorded weekly intervals and scored for three weeks according to the severity of the symptoms. Thepresence of TYLCTHV-[2] was confirmed by enzyme-linked immunosorbent assay (ELISA) at three weeks after inoculation.ELISA readings showed a normal distribution for the BC2F1 population ranging from 0.055 (resistant) to 0.930 (susceptible).DNA samples from BC2F1 population were analyzed for genes and markers association; Ty-2 on chromosome 11 using AVRDCprimer number 11-090.0 (TG105A), and Ty-3 on chromosome 6 using marker C2_At3g11210. Results showed that Ty-2 waslost during stepwise selection at BC1F1 generation, while Ty-3 showed no relationship to marker C2_At3g11210 and theamount of virus detected from ELISA reading. This indicated that the TYLCTHV-[2] resistant phenotype response in theBC2F1 population neither came from Ty-2 nor linked to the Ty-3 gene

Novel PCR Primers for Specific Detection of Xanthomonas citri subsp. citri the Causal Agent of Bacterial Citrus Canker

ABSTRACT The new primers were developed for specific detection of Xanthomonas citri subsp. citri (Hasse) (Xcc) [syn. X. axonopodis pv. citri (Xac)], the causal agent of Asiatic citrus canker disease. Twenty three strains of Xcc and 34 strains of other xanthomonads including X. fuscans subsp. aurantifolii, X. alfalfae subsp. citrumelonis, X. campestris pv. campestris, X. campestris pv. glycines, X. citri subsp. malvacearum and X. fuscans subsp. fuscans were tested for specificity of new primers by classical PCR. The results showed that these 354 F/R primers specifically amplified all of Xcc strains but not other xanthomonad strains. The 354-bp PCR fragment was sequenced and its nucleotide sequences were compared for similarity with Genbank database. The 354-bp nucleotide sequences were 99.7% similar to gene XAC2443 of Xac strain 306 (Accession AE011881). The sensitivity of these specific primers for detection of viable cells and total DNA of Xcc were 70 CFU/µl and 50 pg/µl, respectively. Therefore, these novel primers can be used as an alternative application for rapid and specific detection of Xcc

Identification of a resistance gene Rpi-dlc1 to Phytophthora infestans in European accessions of Solanum dulcamara

Initial screening of 14 Solanum dulcamara accessions enabled the identification of individuals resistant and susceptible to Phytophthora infestans. Crosses between contrasting genotypes resulted in three F2–BC1 populations segregating for resistance to late blight in a laboratory assay and under field conditions. Genetic profiling of one of these populations using 128 AFLP primers generated three markers linked to the resistant phenotype. Blast analysis of the sequenced markers resulted in a plausible gene position on the distal end of the long arm of chromosome 9 that could be confirmed by CAPS markers. Thus, we describe a first resistant gene, named Rpi-dlc1, from S. dulcamara, a Solanum species native to Europe. In addition, one population was tested for broadness of resistance responses using a set of seven additional P. infestans isolates, varying in virulence. This indicated the possible presence of additional Rpi genes

Development of di-nucleotide microsatellite markers and construction of genetic linkage map in mango (Mangifera indica L.)

Forty-two di-nucleotide microsatellite, or simple-sequence repeat (SSR), markers were developed using CA and CTenriched genomic libraries of Mangifera indica L. Six cultivated mangoes and two wild species were tested for primer amplifications. Most loci could amplify M. caloneura Kruz and M. foetida. The average number of alleles per locus was 4.4. The average expected heterozygosity and the maximum polymorphism information content value were 0.57 and 0.53, respectively. The SSRs developed in this study together with 65 SSRs and 145 restriction fragment length polymorphism (RFLP) markers reported previously were used in the genetic linkage analysis. A partial genetic linkage map was constructed based on 31 F1 progenies from a cross between ‘Alphonso’ and ‘Palmer’. The map spanned a distance of 529.9 centiMorgan (cM) and consisted of 9 microsatellite markers (6 from this study) and 67 RFLP markers. The new SSR markers and the present map will be useful for mango genetic studies and breeding applications in the future