Tomato: a crop species amenable to improvement by cellular and molecular methods

Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures. In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.

Integration of dinucleotide microsatellites from hexaploid bread wheat into a genetic linkage map of durum wheat.

Seventy nine microsatellite markers from hexaploid bread wheat (T. aestivum L.) were integrated into a genetic linkage map of durum wheat (T. turgidum ssp. durum (Desf.) Huns.) created by RFLP segregation data from a population of 65 recombinant inbred lines. The results indicate a relatively even distribution of microsatellite loci and demonstrate that microsatellite markers from hexaploid wheat provide an excellent source of molecular markers for use in the genetics and breeding of durum wheat

Construction and testing of a microsatellite database containing more than 500 tomato varieties

The aim of this study was to evaluate the suitability of sequence tagged microsatellite site (STMS) markers for varietal identification and discrimination in tomato. For this purpose, a set of 20 STMS primer pairs was used to construct a database containing the molecular description of the most common varieties (>500) of tomato grown in Europe. The database was built and tested by a consortium of five European laboratories each using a different STMS detection system. In this way, it could be demonstrated that the STMS markers and database were suitable for use in network activities where a common database is being established on a continuing basis with data from different laboratories. Microsatellite polymorphism in tomato was found to be relatively low. The number of alleles per locus ranged from 2 to 8 with an average of 4.7 alleles per locus. Nevertheless, more than 90␘f the varieties had different microsatellite profiles. A "blind testing" exercise showed that in general, identification of unknown samples (or detecting the most similar variety) with the 20 markers and the database was relatively easy for homogeneous varieties but less certain with heterogeneous varieties when using pools of 6 individual

Assessment of The Uniformity of Wheat and Tomato Varieties at DNA Microsatellite Loci

By analysing a number (20-38) of individuals from selected varieties of wheat and tomato, we have been able to assess intra-varietal uniformity at certain microsatellite (simple sequence repeat, SSR) loci. In total, 45 varieties of wheat were analysed at between 7-9 different SSR loci, and 10 varieties of tomato were analysed at six loci. The results showed that there was variation both between varieties and between microsatellites in the degree of non-uniformity observed, and it was possible to identify a number of different probable sources of non-uniformity. Twenty-four of the wheat varieties and nine of the tomato varieties were sufficiently uniform to meet the standards currently applied for distinctness, uniformity and stability (DUS) testing using phenotypic characteristics. The implications for the potential future use of SSRs in DUS testing are discusse

QTL mapping for resistance against cereal cyst nematode (Heterodera avenae Woll.) in wheat (Triticum aestivum L.)

The resistance to cereal cyst nematode (Heterodera avenae Woll.) in wheat (Triticum aestivum L.) was studied using 114 doubled haploid lines from a novel ITMI mapping population. These lines were screened for nematode infestation in a controlled environment for two years. QTL-mapping analyses were performed across two years (Y1 and Y2) as well as combining two years (CY) data. On the 114 lines that were screened, a total of 2,736 data points (genotype, batch or years, and replication combinations) were acquired. For QTL analysis, 12,093 markers (11,678 SNPs and 415 SSRs markers) were used, after filtering the genotypic data, for the QTL mapping. Composite interval mapping, using Haley-Knott regression (hk) method in R/QTL, was used for QTL analysis. In total, 19 QTLs were detected out of which 13 were novel and six were found to be colocalized or nearby to previously reported Cre genes, QTLs or MTAs for H. avenae or H. filipjevi. Nine QTLs were detected across all three groups (Y1, Y2 and CY) including a significant QTL "QCcn.ha-2D" on chromosome 2D that explains 23% of the variance. This QTL colocalized with a previously identified Cre3 locus. Novel QTL, QCcn.ha-2A, detected in the present study could be the possible unreported homeoloci to QCcn.ha-2D, QCcn.ha-2B.1 and QCcn.ha-2B.2. Six significant digenic epistatic interactions were also observed. In addition, 26 candidate genes were also identified including genes known for their involvement in PPNs (plant parasitic nematodes) resistance in different plant species. In-silico expression of putative candidate genes showed differential expression in roots during specific developmental stages. Results obtained in the present study are useful for wheat breeding to generate resistant genetic resources against H. avenae