Russian apple R12740-7A is the designation for an accession grown from seed collected in Russia, which was found to be highly resistant to apple scab. The resistance has historically been attributed to a naturally pyramided complex involving three major genes: one race-nonspecific gene, Vr, conditioning resistance to all known races, plus two race-specific genes. The race-nonspecific gene was identified as an independently segregating gene by Dayton and Williams (1968) and is referred to in this paper as Vr-DW. The first researchers to study the scab resistance gene complex in Russian apple never described the phenotype conditioned by the race-nonspecific gene. Later, Aldwinckle et al. (1976) associated the name Vr with a scab resistance gene conditioning distinctive stellate necrotic reactions, which we refer to as Vr-A in order to distinguish it from Vr-DW. We show that the segregation ratios in progenies from the scab differential hosts 2 and 4 that are derived from Russian apple, crossed with susceptible cultivars were consistent with a single gene conditioning resistance in each host. The genes have been named Vh2 and Vh4, respectively. Resistant segregants from host 2 showed stellate necrotic reactions, while those from host 4 showed hypersensitive reactions. Both the phenotypes and the genetic maps for the genes in the respective hosts were very similar to those of the genes previously named Vr-A and Vx, respectively, in an F1 family of Russian apple. We showed that race 2 of V. inaequalis isolated from host 2 was able to infect resistant descendants of the non-differential accession PRI 442-23 as well as host 2. The descendants of PRI 442-23 were expected to carry the race-nonspecific Vr-DW gene, but in fact carry Vr-A. We conclude that the Vh2

Background: Assessment of allergenicity of foods is important for allergic consumers and regulators. Immunoassays to measure major food allergens are widely applied, often giving variable results. Using the major apple allergen Mal d 1 as a model, we aimed to establish at the molecular level why different immunoassays for assessing allergenicity of apple cultivars produce conflicting outcomes. Methods: Mal d 1 was measured in 53 cultivars from Italy and 35 from The Netherlands, using four different immunoassays. Purified Mal d 1 standards were molecularly characterized by size-exclusion chromatography (SEC) and mass spectrometry (MS). Results: Three immunoassays using an identical standard gave similar results. Minor differences in sample preparation already resulted in significant loss of allergenicity. The fourth assay, using a different Mal d 1 standard, gave 10- to 100-fold lower outcomes. By SEC, this standard was shown to be almost fully aggregated. This aggregation was accompanied by a decrease of the mass of the Mal d 1 molecule by ∼1 kDa as analyzed by MS. The deviating immunoassay was shown to selectively recognize this aggregated form of Mal d 1, whereas the other three assays, including the one based on IgE antibody recognition, preferentially bound non-aggregated allergen. Conclusions: Variable and poorly controllable major allergen modification in both extracts and standards hamper accurate allergenicity assessments of fruits.

No abstract

To date, molecular markers have been made available for many economically important traits. Unfortunately, lack of knowledge of their allelic variation hampers their full exploitation in commercial breeding programs. These markers have usually been identified in one single cross. Consequently, only one or two favourable alleles of the related QTL are identified and may be exploited for marker-assisted breeding (MAB), while a breeding program may include several alleles. Selection for only these alleles means that many favourable genotypes are ignored, which decreases efficiency and leads to genetic erosion.A new approach, called pedigree genotyping, allows the identification and exploitation of the majority of alleles present in an ongoing breeding program. This is achieved by including breeding material itself in QTL detection, so covering multiple generations and linking many crosses through their common ancestors in the pedigree. The principle of Identity by Descent (IBD) is utilised to express the identity of an allele of a modern selection in terms of alleles of founding cultivars. These founder alleles are used as factors in statistical analysis. Co-dominant markers, like SSR (= microsatellite) markers, are essential in this approach since they are able to connect cultivars, breeding selections and progenies at the molecular marker level by monitoring specific chromosomal segments along family trees.Additional advantages of the use of breeding genetic material are (1) a major reduction in experimental costs since plant material is already available and phenotyped by default (2) continuity over generations within breeding programs with regard to marker research (3) the testing of QTL-alleles against a wide range of genetic backgrounds, making results generally applicable (4) possibility to explore intra-as well as inter-QTL interactions. Fruit firmness in apple is used as an example to illustrate the principles of this powerful approach to detect QTLs and estimate their allelic variation. Prospects for strawberry are also indicated. INTRODUCTIONTo date, molecular markers have been identified for many loci governing important horticultural traits. These markers have usually been identified in one single cross. As a consequence, only one or two favourable alleles of a locus are identified, whereas a breeding program usually includes many favourable alleles. If a breeder focuses selection on these alleles, many favourable genotypes would be unnecessarily discarded. This reduces the efficiency of the breeding program. Moreover, the genetic diversity of the material is unnecessarily narrowed. A new approach called 'Pedigree Genotyping' makes it possible to find markers for all favourable alleles present in a breeding program. The costs of this approach are low compared to traditional marker research because it utilises data from the ongoing breeding program.

No abstract