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.

The cropping potential of almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) cultivars is determined by their adaptation to edaphoclimatic and environmental conditions. The effects of scion–rootstock interactions on vigor have a decisive impact on this cropping success. Intensively planted orchards with smaller less vigorous trees present several potential benefits for increasing orchard profitability. While several studies have examined rootstock effects on tree vigor, it is less clear how rootstocks influence more specific aspects of tree architecture. The objective of this current study was to identify which architectural traits of commercially important scion cultivars are influenced by rootstock and which of these traits can be useful as descriptors of rootstock performance in breeding evaluations. To do this, 6 almond cultivars of commercial significance were grafted onto 5 hybrid rootstocks, resulting in 30 combinations that were measured after their second year of growth. We observed that rootstock choice mainly influenced branch production, but the effects were not consistent across the different scion–rootstock combinations evaluated. This lack of consistency in response highlights the importance of the unique interaction between each rootstock and its respective scion genotype.

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 in the prevention of various diseases, 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 use 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 and of the possible increase of their aggressiveness. They will also have to offer the premises of economic production, respectively yield and the quality, according to multiple destinations of nuts in the current consumption and food industry, but also the increasing exigencies of the consumer market and the profile industry.

The rootstock genotype plays a crucial role in determining various aspects of scion development, including the scion three-dimensional structure, or tree architecture. Consequently, rootstock choice is a pivotal factor in the establishment of new almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) intensive planting systems, demanding cultivars that can adapt to distinct requirements of vigor and shape. Nevertheless, considering the capacity of the rootstock genotype to influence scion development, it is likely that the scion genotype reciprocally affects rootstock performance. In the context of this study, we conducted a transcriptomic analysis of the scion/rootstock interaction in young almond trees, with a specific focus on elucidating the scion impact on the rootstock molecular response. Two commercial almond cultivars were grafted onto two hybrid rootstocks, thereby generating four distinct combinations. Through RNA-Seq analysis, we discerned that indeed, the scion genotype exerts an influence on the rootstock expression profile. This influence manifests through the modulation of genes associated with hormonal regulation, cell division, root development, and light signaling. This intricate interplay between scion and rootstock communication plays a pivotal role in the development of both scion and rootstock, underscoring the critical importance of a correct choice when establishing new almond orchards.

Significant strides have been made by researchers aiming to understand the crucial role of the plant cell wall (PCW) in defending against pathogens. Numerous reviews have synthesized findings on plant–pathogen interactions, shedding light on the role of the PCW in defence, the generation of cell wall damage-associated molecular patterns (DAMPs), perception, and signalling response. However, the role of the PCW in responses to herbivory remains underexplored. This review aims to fill this gap, offering a comprehensive analysis of the current knowledge in this area. For the first time, it consolidates studies focusing on the involvement of the PCW in pest response. The review examines key aspects, including the structural changes in the PCW following pest infestation, the role of cell wall-derived DAMPs, and the phenotypic traits of transgenic plants with modified cell wall components. Additionally, it delves into the genetic underpinnings of cell wall plasticity and the mechanisms of DAMP perception. Lastly, the article identifies promising research pathways to further unravel the complex role of the PCW in pest defence, encouraging advancements in this relatively nascent field. Through this effort, it aims to bridge the knowledge gap and inspire deeper investigations into the interplay between the PCW and pest resistance.

Almond breeding programs aimed at selecting cultivars adapted to intensive orchards have recently focused on the optimization of tree architecture. This multifactorial trait is defined by numerous components controlled by processes such as hormonal responses, gravitropism and light perception. Gravitropism sensing is crucial to control the branch angle and therefore, the tree habit. A gene family, denominated IGT family after a shared conserved domain, has been described as involved in the regulation of branch angle in several species, including rice and Arabidopsis, and even in fruit trees like peach. Here we identified six members of this family in almond: LAZY1, LAZY2, TAC1, DRO1, DRO2, IGT-like. After analyzing their protein sequences in forty-one almond cultivars and wild species, little variability was found, pointing a high degree of conservation in this family. To our knowledge, this is the first effort to analyze the diversity of IGT family proteins in members of the same tree species. Gene expression was analyzed in fourteen cultivars of agronomical interest comprising diverse tree habit phenotypes. Only LAZY1, LAZY2 and TAC1 were expressed in almond shoot tips during the growing season. No relation could be established between the expression profile of these genes and the variability observed in the tree habit. However, some insight has been gained in how LAZY1 and LAZY2 are regulated, identifying the IPA1 almond homologues and other transcription factors involved in hormonal responses as regulators of their expression. Besides, we have found various polymorphisms that could not be discarded as involved in a potential polygenic origin of regulation of architectural phenotypes. Therefore, we have established that neither the expression nor the genetic polymorphism of IGT family genes are correlated to diversity of tree habit in currently commercialized almond cultivars, with other gene families contributing to the variability of these traits.