Phenotyping progenies for complex architectural traits: a strategy for 1-year-old apple trees (Malus x domestica Borkh.)

International audienceThe aim of this study was to define a methodology for describing architectural traits in a quantitative way on tree descendants. Our strategy was to collect traits related to both tree structural organization, resulting from growth and branching, and tree form and then to select among these traits relevant descriptors on the basis of their genetic parameters. Because the complexity of tree architecture increases with tree age, we chose to describe the trees in the early stages of development. The study was carried out on a 1-year-old apple progeny derived from two parent cultivars with contrasted architecture. A large number of variables were collected at different positions and scales within the trees. Broad-sense heritability and genetic correlations were estimated and the within tree variability was analyzed for variables measured on long sylleptic axillary shoots (LSAS). These results were combined to select heritable and not correlated variables. Finally, the selection of variables proposed combines topological with geometric traits measured on both trunks and LSAS: (1) on the trunk, mean internode length, and number of sylleptic axillary shoots; (2) on axillary shoots, conicity, bending, and number of sylleptic axillary shoots born at order 3. The trees of the progeny were partitioned on the basis of these variables. The putative agronomic interest of the selected variables with respect to the subsequent tree development is discussed

Functional analysis and expression profiling of HcrVf1 and HcrVf2 for development of scab resistant cisgenic and intragenic apples

Apple scab resistance genes, HcrVf1 and HcrVf2, were isolated including their native promoter, coding and terminator sequences. Two fragment lengths (short and long) of the native gene promoters and the strong apple rubisco gene promoter (PMdRbc) were used for both HcrVf genes to test their effect on expression and phenotype. The scab susceptible cultivar ‘Gala’ was used for plant transformations and after selection of transformants, they were micrografted onto apple seedling rootstocks for scab disease tests. Apple transformants were also tested for HcrVf expression by quantitative RT-PCR (qRT-PCR). For HcrVf1 the long native promoter gave significantly higher expression that the short one; in case of HcrVf2 the difference between the two was not significant. The apple rubisco gene promoter proved to give the highest expression of both HcrVf1 and HcrVf2. The top four expanding leaves were used initially for inoculation with monoconidial isolate EU-B05 which belongs to race 1 of V. inaequalis. Later six other V. inaequalis isolates were used to study the resistance spectra of the individual HcrVf genes. The scab disease assays showed that HcrVf1 did not give resistance against any of the isolates tested regardless of the expression level. The HcrVf2 gene appeared to be the only functional gene for resistance against Vf avirulent isolates of V. inaequalis. HcrVf2 did not provide any resistance to Vf virulent strains, even not in case of overexpression. In conclusion, transformants carrying the apple-derived HcrVf2 gene in a cisgenic as well as in an intragenic configuration were able to reach scab resistance levels comparable to the Vf resistant control cultivar obtained by classical breeding, cv. ‘Santana’

Variation of selfing rate and inbreeding depression among individuals and across generations within an admixed Cedrus population

[EN] We investigated the variation and short-term evolution of the selfing rate and inbreeding depression (ID) across three generations within a cedar forest that was established from admixture ca 1860. The mean selfing rate was 9.5%, ranging from 0 to 48% among 20 seed trees (estimated from paternally inherited chloroplast DNA). We computed the probability of selfing for each seed and we investigated ID by comparing selfed and outcrossed seeds within progenies, thus avoiding maternal effects. In all progenies, the germination rate was high (88-100%) and seedling mortality was low (0-12%). The germination dynamics differed significantly between selfed and outcrossed seeds within progenies in the founder gene pool but not in the following generations. This transient effect of selfing could be attributed to epistatic interactions in the original admixture. Regarding the seedling growth traits, the ID was low but significant: 8 and 6% for height and diameter growth, respectively. These rates did not vary among generations, suggesting minor gene effects. At this early stage, outcrossed seedlings outcompeted their selfed relatives, but not necessarily other selfed seedlings from other progenies. Thus, purging these slightly deleterious genes may only occur through within-family selection. Processes that maintain a high level of genetic diversity for fitness-related traits among progenies also reduce the efficiency of purging this part of the genetic load. © 2011 Macmillan Publishers Limited All rights reserved. Guardar / Salir Siguiente >This work has been partially supported by Grant PPI-00-04 from the Polytechnic University of Valencia (Spain). We thank B Fady and E Klein as well as two anonymous reviewers for their helpful comments on a previous version of the paper. 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A major QTL controlling apple skin russeting maps on the linkage group 12 of 'Renetta Grigia di Torriana'

Background: Russeting is a disorder developed by apple fruits that consists of cuticle cracking followed by the replacement of the epidermis by a corky layer that protects the fruit surface from water loss and pathogens. Although influenced by many environmental conditions and orchard management practices, russeting is under genetic control. The difficulty in classifying offspring and consequent variable segregation ratios have led several authors to conclude that more than one genetic determinant could be involved, although some evidence favours a major gene (Ru). Results: In this study we report the mapping of a major genetic russeting determinant on linkage group 12 of apple as inferred from the phenotypic observation in a segregating progeny derived from 'Renetta Grigia di Torriana', the construction of a 20 K Illumina SNP chip based genetic map, and QTL analysis. Recombination analysis in two mapping populations restricted the region of interest to approximately 400 Kb. Of the 58 genes predicted from the Golden Delicious sequence, a putative ABCG family transporter has been identified. Within a small set of russeted cultivars tested with markers of the region, only six showed the same haplotype of 'Renetta Grigia di Torriana'. Conclusions: A major determinant (Ru_RGT) for russeting development putatively involved in cuticle organization is proposed as a candidate for controlling the trait. SNP and SSR markers tightly co-segregating with the Ru_RGT locus may assist the breeder selection. The observed segregations and the analysis of the 'Renetta Grigia di Torriana' haplotypic region in a panel of russeted and non-russeted cultivars may suggest the presence of other determinants for russeting in apple

Variabilité intraspécifique chez le pin maritime (Pinus pinaster Ait) dans le sud-est de la France. I. Variabilité des populations autochtones et des populations de l'ensemble de l'aire de l'espèce

Une plantation comparative de 25 provenances de pin maritime implantée en 1982 dans le sud-est de la France (massif des Maures) a été étudiée en 1988, 1989 et 1993. À l'échelle régionale, il existe une importante variabilité pour les caractères de vigueur (hauteur et diamètre) et pour la sensibilité à la cochenille Matsucoccus feytaudi mais une faible différenciation pour les caractères de forme (écart à la verticalité, coefficient de forme, angle d'insertion et grosseur des branches). Les analyses mettent, en revanche, en évidence une grande variabilité pour l'ensemble des caractères étudiés à l'échelle de l'aire de l'espèce. Les provenances atlantiques sont les plus vigoureuses et parmi les moins sensibles au ravageur. Les provenances corses sont hétérogènes pour les caractères de forme et présentent une grande sensibilité au ravageur. La provenance marocaine de Tamjout est complètement résistante à la cochenille. Les provenances du sud-est sont moyennes pour tous les caractères de forme et de vigueur mais très sensibles à M feytaudi. Ces résultats posent la question de l'intérêt des populations locales pour le développement sylvicole et la mise en œuvre d'un programme d'amélioration génétique pour le sud-est de la France. L'alternative d'une hybridation interraciale comme méthode d'amélioration de l'espèce dans la région est discutée.Intraspecific variability in maritime pine (Pinus pinaster Ait) in the south-east of France. I. Variability in autochthonous populations and in the whole range of the species. A provenance trial of maritime pine comprising 25 provenances (table I) and located in the south-east of France was studied at 8, 9 and 13 years of age. The results show a high variability for growth and sensibility to the coccid Matsucoccus feytaudi at the regional level, but no differentiation for form traits (see table III, analysis 1). At the species range level, however, significant provenance differences appear for all characters (see table III, analyses 2 and 3). Atlantic provenances are the most vigorous and among the most resistant to the coccid (see figs 1 and 2). Corsican provenances show an intraracial variation for form and a great sensibility to the insect (see figs 1 and 2). The Moroccan origin appears to be completely resistant to the insect, while the south-eastern populations are intermediate for vigor and form but quite sensitive to the pest (see figs 1 and 2). These results raise the problem of the use of the local populations as reproductive material in the south-east. In this respect, interracial hybridization may be an alternative method for genetic improvement of maritime pine