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The production and consumption of nuts are increasing in the world due to strong economic returns and the nutritional value of their products. With the increasing role and importance given to nuts (i.e., walnuts, hazelnut, pistachio, pecan, almond) in a balanced and healthy diet and their benefits to human health, breeding of the nuts species has also been stepped up. Most recent fruit breeding programs have focused on scion genetic improvement. However, the use of locally adapted grafted rootstocks also enhanced the productivity and quality of tree fruit crops. Grafting is an ancient horticultural practice used in nut crops to manipulate scion phenotype and productivity and overcome biotic and abiotic stresses. There are complex rootstock breeding objectives and physiological and molecular aspects of rootstock-scion interactions in nut crops. In this review, we provide an overview of these, considering the mechanisms involved in nutrient and water uptake, regulation of phytohormones, and rootstock influences on the scion molecular processes, including long-distance gene silencing and trans-grafting. Understanding the mechanisms resulting from rootstock × scion × environmental interactions will contribute to developing new rootstocks with resilience in the face of climate change, but also of the multitude of diseases and pests.

Eastern filbert blight (EFB), caused by Anisogramma anomala, is the primary limiting factor for hazelnut (Corylus sp.) production in the United States. In this study, 82 cultivars and selections shown to be resistant or tolerant to EFB in Oregon were field planted in New Jersey in 2017 and 2019 and evaluated for their EFB response under high disease pressure. The trees carry known single resistance (R) genes with most mapped to their respective linkage groups (LG), including LG2, LG6, and LG7, or they express quantitative resistance (QR, horizontal resistance). Disease incidence and severity was documented, stem cankers counted and measured, and the proportion of diseased wood calculated. The EFB disease response of some cultivars/selections varied considerably between New Jersey and Oregon while others were consistent. Trends were observed in relation to resistance source origin and LGs, which provide insight into durability and usefulness of resistance. In striking contrast to Oregon, nearly all selections with R-genes mapped to LG6, including those carrying the ‘Gasaway’ resistance allele, exhibited severe EFB infections (232 of 266 [87%]). This finding is of consequence since the U.S. hazelnut industry currently relies solely on LG6 resistance for EFB resistance. Further, for the first time, EFB was observed on several selections carrying LG7 resistance, specifically offspring of ‘Ratoli’ from Spain. Interestingly, selections carrying LG7 resistance from origins other than ‘Ratoli’ remained free of EFB, with one exception, all selections carrying LG2 (n=9) resistance also remained free from EFB. Interestingly, the EFB responses of selections expressing QR (n=26) more closely resembled the disease phenotypes they exhibited in Oregon. Overall, the divergence in EFB response between Oregon and New Jersey, where pathogen populations differ, supports the presence of pathogenic variation in A. anomala and highlights potential limitations of using single R-genes to manage the disease. Results also suggest trees expressing QR may be more stable across pathogenic populations. [ABSTRACT FROM AUTHOR]

European hazelnut (Corylus avellana L.) is the only economically important nut crop in the family Betulaceae. Because of its small genome size (~385 Mb / 1C), relatively short life cycle, availability of a dense linkage map, and amenability to transformation by Agrobacterium, the European hazelnut could serve as a model plant for the Betulaceae. Here we report the construction of a bacterial artificial chromosome (BAC) library for 'Jefferson' hazelnut using the cloning enzyme MboI and the vector pECBAC1 (BamHI site). The library consists of 39 936 clones arrayed in 104 384-well microtitre plates with a mean insert size of 117 kb. The genomic coverage of the library is estimated to be about 12 genome equivalents. This library provides a valuable resource for the map-based cloning of two important genes, the resistance gene from 'Gasaway' that confers resistance to eastern filbert blight caused by the fungus Anisogramma anomala (Peck) E. Muller and the S locus that controls pollen-stigma incompatibility. Fine-resolution mapping near the two loci was carried out using random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers. Fine mapping at the disease resistance locus showed that markers W07-375 and X01-825 flanked the resistance locus at distances of 0.06 and 0.05 cM, respectively. The S locus is flanked by markers 204-950 and KG819-200 at distances of 0.14 and 0.24 cM, respectively. Assuming that 1 cM corresponds to a physical distance of 430 kb, it will take approximately two to three chromosome walks to assemble BAC contigs that span both loci. Key words: Anisogramma anomala, Corylus avellana, filbert, fine mapping, map- based cloning. Le noisetier commun (Corylus avellana L.) est la seule espece nucifere importante au sein des betulacees. En raison de la petite taille de son genome (~385 Mb / 1C), de son cycle de vie relativement court, de la disponibilite d'une carte genetique dense, et du fait qu'il se prete a la transformation par Agrobacterium, le noisetier commun pourrait servir d'espece modele chez les betulacees. Les auteurs rapportent la production d' une banque de clones BAC (chromosomes bacteriens artificiels) pour le noisetier 'Jefferson' au moyen de l'enzyme MboI et du vecteur pECBAC1 (site BamHI). La banque totalise 39 936 clones repartis dans 104 plaques de 384 puits et dont la taille moyenne des inserts est de 117 kb. La couverture genomique conferee par une telle banque est estimee comme equivalent a 12 genomes. Cette banque s'est averee une ressource precieuse pour le clonage positionnel de deux genes importants, le gene 'Gasaway' qui confere la resistance a la brulure orientale du noisetier causee par le champignon Anisogramma anomala (Peck) E. Muller et le locus S qui controle l'incompatibilite pollen-stigmate. Une cartographie fine a proximite des deux genes a ete realisee avec des marqueurs RAPD (ADN polymorphe amplifie au hasard) et microsatellites (SSR). La cartographie fine autour du locus de resistance a la brulure a montre que les marqueurs W07-375 et X01-825 bordaient ce locus a des distances respectives de 0,06 et 0,05 cM respectivement. Le locus S etait flanque des marqueurs 204-950 et KG819-200 a 0,14 et 0,24 cM respectivement. En supposant qu'un cM correspond a une distance physique de 430 kb, deux a trois etapes de marche chromosomique seraient necessaires pour assembler des contigs de clones BAC permettant de relier les marqueurs voisins. Mots-cles : Anisogramma anomala, Corylus avellana, noisette, cartographie fine, clonage positionnel. [Traduit par la Redaction], Introduction The family Betulaceae contains more than 130 species (Chen 1994) and includes alder (Alnus sp.), birch (Betula sp.), and hazelnut (Corylus sp.). The European hazelnut (Corylus avellana L.) is [...]

Abstract: A linkage map for European hazelnut (Corylus avellana L.) was constructed using random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers and the 2-way pseudotestcross approach. A [...]