Development and assessment of DArT markers in triticale.

Triticale (X Triticosecale Wittm.) is a hybrid derived by crossing wheat (Triticum sp.) and rye (Secale sp.). Till date, only a limited number of simple sequence repeat (SSRs) markers have been used in triticale molecular analyses and there is a need to identify dedicated high-throughput molecular markers to better exploit this crop. The objective of this study was to develop and evaluate diversity arrays technology (DArT) markers in triticale. DArT marker technology offers a high level of multiplexing. Development of new markers from triticale accessions was combined with mining the large collection of previously developed markers in rye and wheat. Three genotyping arrays were used to analyze a collection of 144 triticale accessions. The polymorphism level ranged from 8.6 to 23.8% for wheat and rye DArT markers, respectively. Among the polymorphic markers, rye markers were the most abundant (3,109) followed by wheat (2,214) and triticale (719). The mean polymorphism information content values were 0.34 for rye DArT markers and 0.37 for those from triticale and wheat. High correlation was observed between similarity matrices derived from rye, triticale, wheat and combined marker sets, as well as for the cophenetic values matrices. Cluster analysis revealed genetic relationships among the accessions consistent with the agronomic and pedigree information available. The newly developed triticale DArT markers as well as those originated from rye and wheat provide high quality markers that can be used for diversity analyses and might be exploited in a range of molecular breeding and genomics applications in triticale.

Microsatellite markers for powdery mildew resistance in pea (Pisum sativum L.).

Powdery mildew is a common disease of field pea, Pisum sativum L., and is caused by the ascomycete fungus Erysiphe pisi. It can cause severe damage in areas where pea is cultivated. Today breeders want to develop new pea lines that are resistant to the disease. To make the breeding process more efficient, it is desirable to find genetic markers for use in a marker-assisted selection (MAS) strategy. In this study, microsatellites (SSR) were used to find markers linked to powdery mildew resistance. The resistant pea cultivar '955180' and the susceptible pea cultivar 'Majoret' were crossed and F2 plants were screened with SSR markers, using bulked segregant analysis. A total of 315 SSR markers were screened out of which five showed linkage to the powdery mildew resistance gene. No single marker was considered optimal for inclusion in a MAS program. Instead, two of the markers can be used in combination, which would result in only 1.6% incorrectly identified plants. Thus SSR markers can be successfully used in marker-assisted selection for powdery mildew resistance breeding in pea.

A simple sequence repeat-based linkage map of barley.

A total of 568 new simple sequence repeat (SSR)-based markers for barley have been developed from a combination of database sequences and small insert genomic libraries enriched for a range of short simple sequence repeats. Analysis of the SSRs on 16 barley cultivars revealed variable levels of informativeness but no obvious correlation was found with SSR repeat length, motif type, or map position. Of the 568 SSRs developed, 242 were genetically mapped, 216 with 37 previously published SSRs in a single doubled-haploid population derived from the F(1) of an interspecific cross between the cultivar Lina and Hordeum spontaneum Canada Park and 26 SSRs in two other mapping populations. A total of 27 SSRs amplified multiple loci. Centromeric clustering of markers was observed in the main mapping population; however, the clustering severity was reduced in intraspecific crosses, supporting the notion that the observed marker distribution was largely a genetical effect. The mapped SSRs provide a framework for rapidly assigning chromosomal designations and polarity in future mapping programs in barley and a convenient alternative to RFLP for aligning information derived from different populations. A list of the 242 primer pairs that amplify mapped SSRs from total barley genomic DNA is presented.

Estimating genetic variation in sugar beets and wild beets using pools of individuals.

The study describes the genetic structure in sugar beets and in wild beets (Beta vulgaris) using 30 RFLP markers. Samples consisting of pooled plant material of 100 individuals from each line and population were used to analyse 120 sugar beet breeding lines and 91 wild beet populations. Greater variation was found among the wild populations than among the breeding lines. Although the two major groups of breeding lines, monogerm and multigerm, had approximately equal amounts of genetic variation, in the monogerm group more of this variation was partitioned among the lines than within the lines. Furthermore, despite most of the variation being shared by the two groups, the two groups were found to be separated along the first two components in a principal component analysis. Computer simulations were carried out to evaluate the usefulness of the pooled-sample strategy employed in the investigation. These simulations showed the use of pooled samples to be a better alternative than that of analysing a few plants individually.

A high density RFLP linkage map of sugar beet.

A high density sugar beet RFLP map with an average distance of 1.5 cM between markers has been constructed. The map covers 621 cM and includes 413 markers distributed over the nine linkage groups of sugar beet. The map is based on two F2 populations representing two different pairs of parents. The two sets of data were integrated into a single map using 90 markers that were common to both data sets. The quality of the map was assessed in several ways. The common markers were used to investigate how often the loci had been mapped in the same order in the two F2 populations. For closely situated markers (<1.5 cM) the order specified in the map is uncertain, but for markers separated by more than 2 cM the locus order is highly reliable. The error rate of the overall process was estimated at 0.3% by independently repeating the analysis of 41 markers. The map is comparatively short, with a map length corresponding to approximately 1.4 crossovers per bivalent. Another feature of the map is a high degree of clustering of markers along the linkage groups. With the possible exception of linkage group 2, each linkage group shows one major cluster, which in most cases is situated in the centre of the linkage group. Our interpretation is that sugar beet, in comparison with most other species, has an extreme localization of recombination. Key words : sugar beet, linkage, RFLP, clustering.