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Almond [Prunus dulcisMiller (D.A. Webb)] is the main tree nut species worldwide. Here, genotyping-by-sequencing (GBS) was applied to 149 almond cultivars from the ex situ collections of the Italian Council for Agricultural Research (CREA) and the Spanish National Research Council (CSIC), leading to the detection of 93,119 single-nucleotide polymorphisms (SNPs). The study of population structure outlined four distinct genetic groups and highlighted diversification between the Mediterranean and Californian gene pools. Data on SNP diversity and runs of homozygosity (ROHs) allowed the definition of kinship, inbreeding, and linkage disequilibrium (LD) decay in almond cultivated germplasm. Four-year phenotypic observations, gathered on 98 cultivars of the CREA collection, were used to perform a genome-wide association study (GWAS) and, for the first time in a crop species, homozygosity mapping (HM), resulting in the identification of genomic associations with nut, shell, and seed weight. Both GWAS and HM suggested that loci controlling nut and seed weight are mostly independent. Overall, this study provides insights on the almond cultivation history and delivers information of major interest for almond genetics and breeding. In a broader perspective, our results encourage the use of ROHs in crop science to estimate inbreeding, choose parental combinations minimizing the risk of inbreeding depression, and identify genomic footprints of selection for specific traits.

Capitolo di libro, sprovvisto di abstract. Dal sito dell'editore: By adopting precise management techniques, growers can reduce the environmental impact of fruit growing, without sacrificing quality and yields, while maintaining income. This chapter discusses how improvements in sustainable peach production can be achieved by an interaction among quite varied disciplines. The chapter describes the importance of vascular flows to peach fruit growth and focuses on the significance of photosynthesis as the engine of productivity in peach production. The chapter considers the adoption of precision fruit growing, and provides a case study. Finally, the chapter looks ahead to future research trends in this area.

Leaf photosynthetic performance of a new red-skinned inter-specific hybrid pear variety called ‘PremP009’ (PIQA® BOO®) is presently unknown and therefore was compared to the Asian pear variety ‘Hosui’. The seasonal growth patterns and the final dry matter accumulation of all tree components were also investigated for both genotypes in their first year of growth after grafting. Leaf gas exchange and tree growth comparisons were assessed using an innovative grafted plant system, which involved a bi-axis tree with the presence of combinations of identical or mixed (one of each genotype) ‘PremP009’ and ‘Hosui’ scion genotypes grafted onto a single clonal rootstock (‘Buerre Hardy’ BA29). This experimental grafted plant system allowed a technique for comparing leaf photosynthesis of two scion genotypes on the same root system, thereby avoiding between-plant differences in plant water relations. ‘PremP009’ had higher leaf photosynthesis and higher leaf mass compared with ‘Hosui.’ However, by the end of the first year of growth, primary shoots of ‘PremP009’ were shorter with fewer nodes, corresponding to less dry weight gain in primary shoot leaves and stems. This vegetative behavior of ‘PremP009’ is likely a response to the smaller individual leaf area in the early season affecting light capture that greatly limits dry matter accumulation of young trees. HIGHLIGHTS - The bi-axis grafting technique never showed before in a scientific paper presents a strategic systemfor a comparative study of red/green leaf photosynthetic performance and related dry matter partitioning.

In drought-stressed apple, leaf area decrease and stem growth cessation increase are key determinants of drought avoidance. Both the genotype and its possible phenotypic plasticity contribute to the variability of responses. Under soil water restriction, plant growth is impaired by the indirect negative impact on plant carbon balance of stomata closure and hydraulic failure. The relative contributions of these two phenomena have been scarcely explored in trees under different drought-stress intensities, and even less work is published which accounts for genetic variability and phenotypic plasticity. Working on 21 apple genotypes from the same progeny, we assessed the effects of two consecutive periods of soil drought, moderate and severe, on growth and functional patterns of leaf and stem. Leaf area decreased while temporary stem growth cessation increased under drought with strong variations depending on the genotype. These results suggested that both reduction of transpiring leaf area and leaf organogenesis are key determinants for drought avoidance in the apple. Results also confirmed the pivotal role of stomatal conductance (g s) in maintaining percent loss of conductivity of the stem xylem (PLC) under values for runaway embolism (ca. 14 % under severe drought). The sorting of genotypes according to their morphological response to drought showed that genotypes with high reduction of growth were characterized by similar g s but lower PLC than genotypes with medium and low reduction of growth. This suggests that for a given level of stomatal closure the drought-related reduction of leaf area could also limit the progression of cavitation in stem xylem. As a whole, the variability of morphological responses of apple genotypes to contrasted drought conditions indicated that both genetic variability and phenotypic plasticity are involved in the range of iso-anisohydry documented for this species.

The detection of leaf functionality is of pivotal importance for plant scientists from both theoretical and practical point of view. Leaves are the sources of dry matter and food, and they sequester CO2 as well. Under the perspective of climate change and primary resource scarcity (i.e. water, fertilizers and soil), assessing leaf photo-assimilation in a rapid but comprehensive way can be helpful for understanding plant behavior under different environmental conditions and for managing the agricultural practices properly. Several approaches have been proposed for this goal, however, some of them resulted very efficient but little reliable. On the other hand, the high reliability and exhaustive information of some models used for estimating net photosynthesis are at the expense of time and ease of measurement. The present study employs a multivariate statistical approach to assess a model aiming at estimating leaf photo-assimilation performance, using few and easy-to-measure variables. The model, parameterized for apple and pear and subjected to internal and external cross validation, involves chlorophyll fluorescence, carboxylative activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), air and leaf temperature. Results prove that this is a fair-predictive model allowing reliable variable assessment. The dependent variable, called IPL index, was found strongly and linearly correlated to net photosynthesis. IPL and the model behind it seem to be (1) reliable, (2) easy and fast to measure and (3) usable in vivo and in the field for such cases where high amount of data is required (e.g. precision agriculture and phenotyping studies).