Genome-wide association analysis of Monilinia fructicola lesion in a collection of Spanish peach landraces.

Brown rot, caused by the Monilinia spp., is the disease that causes the greatest losses in stone fruit worldwide. Currently, M. fructicola has become the dominant species in the main peach production area in Spain. The fruit cuticle is the first barrier of protection against external aggressions and may have a key role in the susceptibility to brown rot. However, information on the role of skin fruit on the resistance to brown rot in peach is scarce. Previous genetic analyses in peach have demonstrated that brown rot resistance is a complex and quantitative trait in which different fruit parts and resistance mechanisms are involved. To search for genomic areas involved in the control of the cultivar susceptibility to brown rot and to elucidate the role of fruit skin against this infection, we have studied, for two consecutive seasons (2019 and 2020), the fruit susceptibility to M. fructicola, together with fruit cuticle thickness (CT) and density (CD), in a collection of 80 Spanish and 5 foreign peach cultivars from the National Peach Collection at CITA (Zaragoza, Spain). Brown rot incidence, lesion diameter, and severity index were calculated after 5 days of inoculation on non-wounded fruit. The peach collection has also been genotyped using the new peach SNP chip (9 + 9K). Genotypic and phenotypic data have been used to perform a genome-wide association analysis (GWAS). Phenotyping has shown a wide variability on the brown rot susceptibility within the Spanish germplasm as well as on CD and CT. The GWAS results have identified several significant SNPs associated with disease severity index (DSI), CD, and CT, five of which were considered as reliable SNP-trait associations. A wide protein network analysis, using 127 genes within the regions of the reliable SNPs and previously identified candidate genes (169) associated with Monilinia spp. resistance, highlighted several genes involved in classical hypersensitive response (HR), genes related to wax layers as ceramidases and lignin precursors catalyzers, and a possible role of autophagy during brown rot infection. This work adds relevant information on the complexity resistance mechanisms to brown rot infection in peach fruits and the genetics behind them.

Impact of Chill and Heat Exposures under Diverse Climatic Conditions on Peach and Nectarine Flowering Phenology.

The present study aims to generalize cultivar-specific tree phenology responses to winter and spring temperatures and assess the effectiveness of the Tabuenca test and various chill and heat accumulation models in predicting bloom dates for a wide range of climatic conditions and years. To this end, we estimated the dates of rest completion and blooming and correlated them with observed bloom dates for 14 peach and nectarine cultivars that were evaluated in 11 locations across Europe (Greece, France, Italy, Romania and Spain), within the EUFRIN cultivar testing trial network. Chill accumulation varied considerably among the studied sites, ranging from 45 Chill Portions (CP) in Murcia-Torre Pacheco (Spain) to 97-98 CP in Cuneo (Italy) and Bucharest (Romania). Rest completion occurred latest or was not achieved at all for some cultivars in the southern sites in Murcia. Dormancy release happened earliest in Bucharest and Cuneo, sites where heat accumulation had a strong influence on the regulation of bloom time. Blooming occurred earliest in the moderately cold regions of Lleida (Spain) and Bellegarde (France), and 7-11 days later in the warmer locations of Rome (Italy) and Naoussa (Greece), suggesting that bloom timing is strongly influenced by delayed rest completion in these locations. The Dynamic Model resulted in both more homogeneous chill accumulation across years and better predictions of bloom dates, compared with the Utah, Positive Utah and Chilling Hours models. Prediction of bloom dates was less successful for low-chill cultivars than for medium- and high-chill cultivars. Further climatic and experimental data are needed to make estimates of the climatic needs of peach cultivars more robust and to generate reliable advice for enhancing the resilience of peach production under varying and changing climatic conditions.

Effects of Consumers' Sensory Attributes Perception on Their Willingness to Pay for Apple Cultivars Grown at Different Altitudes: Are They Different?

Per capita apple consumption is decreasing in many European countries due to the perception that apples have inferior sensory traits and to the dissatisfaction of some consumers with mainstream apple cultivars. Previous studies on the consumers' acceptance of apples state that sensory attributes have a large influence on consumers' willingness to pay (WTP). Following this previous evidence and with the aim of reversing this decreasing consumption trend, our objective was to study the effect of apple sensory attributes on consumers' WTP for a mainstream ('Golden Delicious') and a local traditional apple cultivar ('Reineta'), grown at two different altitudes (high and low). A total number of 195 apple consumers participated in one experiment with two tasks. In the first task, participants were asked to rate five external and internal sensory attributes, and in the second, to indicate their maximum WTP in an experimental auction for the four apple samples. Results indicated that the WTP and the effect of sensory attributes on the WTP were different among the four apple samples. Our findings indicate that sweeter and juicer apples might be marketed at higher prices and that firmness is only appreciated in the case of the local cultivar grown at low altitudes.

Genetic Diversity and Genome-Wide Association Study of Morphological and Quality Traits in Peach Using Two Spanish Peach Germplasm Collections.

Peach [Prunus persica (L.) Batsch] is one of the most important stone fruits species in world production. Spanish peach production is currently the second largest in the world and the available cultivars in Spain includes a great source of genetic diversity with variability in fruit quality traits and postharvest disorders tolerance. In order to explore the genetic diversity and single nucleotide polymorphism (SNP)-trait associations in the Spanish germplasm, the new peach 18K SNP v2 array was used to genotype 287 accessions belonging to the two National Peach Germplasm Collections placed at the Agrifood Research and Technology Centre of Aragon (CITA) and at the Experimental Station of Aula Dei (EEAD)-CSIC. The high density of the new SNP array allowed the identification of 30 groups of synonymies, which had not been identified before using low-density markers. In addition, a possible large-scale molecular event in 'Starcrest', a sport of 'Springcrest', was detected showing a possible chromosome replacement of a 13.5 Mb region. Previous suggestions about Spanish diversification regions agreed with our genetic diversity and linkage disequilibrium (LD) decay results using high-density markers. A genome-wide association study (GWAS) detected 34 significant SNP-trait association with the type of leaf glands (TLG), fruit hairiness (FH), and flesh texture (FT). The impact of the significant SNPs was studied with SnpEff. Candidate genes encode several important family proteins involved in trichome formation and powdery mildew resistance (linked to TLG in peach). The genetic distance among cultivars obtained, together with SNP-trait associations found, provide new knowledge for marker-assisted selection and crossing approaches in peach breeding programmes.

Intrinsic and extrinsic attributes related to the influence of growing altitude on consumer acceptability and sensory perception of fresh apple.

BACKGROUND: Growing altitude might have an effect on the quality of fresh apple and therefore on the perception of sensory attributes and on acceptance by consumers. On the other hand, extrinsic information provided to the consumer might affect consumer acceptability and sensory perception of the fruit's main quality traits. The main objective of this work was to study the effect of the growing altitude on the physico-chemical attributes (soluble solid content (SSC), flesh firmness, fruit weight (g), and titratable acidity (TA)), consumer acceptability, and perception of the main sensory attributes (sweetness, acidity and texture) of two reference apple cultivars ('Golden D.' and 'Reineta') by using a panel of 195 consumers. A secondary objective was to study whether extrinsic information about cultivar and growing place have an effect on the consumer perception and acceptance of fresh apple. RESULTS: Significant effects on physico-chemical and sensory attributes were found for 'Golden D.' and 'Reineta' apple cultivars due to the growing altitude, and they were perceived by consumers. Moreover, extrinsic information about the cultivar and the growing site influenced consumers' sensory perceptions significantly. CONCLUSIONS: This work demonstrated that differences between apple fruit grown at different altitudes can be perceived by consumers. We demonstrated the importance of providing consumers with information about the cultivar and the growing place to increase their acceptance and support local produce. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The apple REFPOP-a reference population for genomics-assisted breeding in apple.

Breeding of apple is a long-term and costly process due to the time and space requirements for screening selection candidates. Genomics-assisted breeding utilizes genomic and phenotypic information to increase the selection efficiency in breeding programs, and measurements of phenotypes in different environments can facilitate the application of the approach under various climatic conditions. Here we present an apple reference population: the apple REFPOP, a large collection formed of 534 genotypes planted in six European countries, as a unique tool to accelerate apple breeding. The population consisted of 269 accessions and 265 progeny from 27 parental combinations, representing the diversity in cultivated apple and current European breeding material, respectively. A high-density genome-wide dataset of 303,239 SNPs was produced as a combined output of two SNP arrays of different densities using marker imputation with an imputation accuracy of 0.95. Based on the genotypic data, linkage disequilibrium was low and population structure was weak. Two well-studied phenological traits of horticultural importance were measured. We found marker-trait associations in several previously identified genomic regions and maximum predictive abilities of 0.57 and 0.75 for floral emergence and harvest date, respectively. With decreasing SNP density, the detection of significant marker-trait associations varied depending on trait architecture. Regardless of the trait, 10,000 SNPs sufficed to maximize genomic prediction ability. We confirm the suitability of the apple REFPOP design for genomics-assisted breeding, especially for breeding programs using related germplasm, and emphasize the advantages of a coordinated and multinational effort for customizing apple breeding methods in the genomics era.

The Multisite PeachRefPop Collection: A True Cultural Heritage and International Scientific Tool for Fruit Trees.

Plants have evolved a range of adaptive mechanisms that adjust their development and physiology to variable external conditions, particularly in perennial species subjected to long-term interplay with the environment. Exploiting the allelic diversity within available germplasm and leveraging the knowledge of the mechanisms regulating genotype interaction with the environment are crucial to address climatic challenges and assist the breeding of novel cultivars with improved resilience. The development of multisite collections is of utmost importance for the conservation and utilization of genetic materials and will greatly facilitate the dissection of genotype-by-environment interaction. Such resources are still lacking for perennial trees, especially with the intrinsic difficulties of successful propagation, material exchange, and living collection maintenance. This work describes the concept, design, and realization of the first multisite peach (Prunus persica) reference collection (PeachRefPop) located across different European countries and sharing the same experimental design. Other than an invaluable tool for scientific studies in perennial species, PeachRefPop provides a milestone in an international collaborative project for the conservation and exploitation of European peach germplasm resources and, ultimately, as a true heritage for future generations.

Identification of a new allele of the Dw gene causing brachytic dwarfing in peach.

OBJECTIVE: Peach brachytic dwarfism determined by Dwarf gene (Dw) is an undesired trait segregating in some peach breeding programs. Recently, a single nucleotide polymorphism (SNP) mutation in the gibberellin insensitive dwarf 1 (GID1) peach gene causing brachytic dwarfism was described. In this research we wanted to validate this marker in an F2 population of the 'Nectavantop' peach cultivar (Nv) to include it as a marker assisted selection tool for peach breeding programs. RESULTS: The observed segregation of the trait was in agreement with that of a recessive gene, the individuals homozygous for the recessive allele (dwdw) presenting the dwarf genotype. Dw was mapped to the distal part of linkage group 6 as previously described. The SNP marker based on the causal mutation previously described did not segregate in Nv F2 population. The sequence of the GID1c gene in Nv revealed a second SNP in its coding sequence which cosegregated with the dwarf phenotype. This SNP was predicted by the SNAP2 software to cause a major functional change and was validated in the dwarf peach cultivar 'Small sunning'. These results suggest the existence of at least two independent mutations of the Dw gene causing the peach brachytic dwarf phenotype.

Influence of antioxidant compounds, total sugars and genetic background on the chilling injury susceptibility of a non-melting peach (Prunus persica (L.) Batsch) progeny.

BACKGROUND: To identify genotypes with good organoleptic properties, antioxidant-rich content and low susceptibility to chilling injury (CI), fruits from 130 peach cultivars were studied over three consecutive years. Pomological traits, l-ascorbic acid, flavonoids, total phenolics, relative antioxidant capacity (RAC) and sugars were determined. Major symptoms of CI developed at 5 °C, such as leatheriness, flesh browning, bleeding and loss of flavor, were evaluated. RESULTS: The population exhibited wide phenotypic variation in agronomic and biochemical traits. Six genotypes with high total phenolics, RAC, flavonoids and total sugars were selected. The progeny also showed variability for all evaluated CI symptoms, and 16 genotypes showed considerably lower susceptibility to CI. After 2 weeks of cold storage, leatheriness and bleeding were the main CI symptoms observed, whereas flesh browning was predominant after 4 weeks. CONCLUSION: It was possible to find varieties with high phenolic concentration and relatively low or intermediate CI susceptibility (22, 33, 68, 80, 81, 96 and 120). However, the correlations observed between CI and phenolic contents highlight their potential influence on susceptibility to internal browning. This relationship should be considered in the current breeding programs to select cultivars with high bioactive compound contents, health-enhancing properties and good postharvest performance.

Copigmentation triggers the development of skin burning disorder on peach and nectarine fruit [Prunus persica (L.) Batsch].

Skin burning is a new type of skin damage related to exposure to high pH values during the brushing-waxing postharvest operations that has been observed recently on some newly released peach and nectarine [Prunus persica (L.) Batsch] cultivars. In this work, we described this skin disorder for the first time and studied its triggers and biological basis. Different skin burning susceptibility was observed after screening 21 peach and nectarine cultivars. The stability of the skin phenolic extracts to pH in the range 7-10 was studied by UV-visible spectroscopy. This study demonstrated that fruit skin phenolics are not stable at high pH and that the transformations occurring at high pH are reversible and time-dependent. The changes on the UV-visible absorption spectra at different pH values pointed out the copigmentation of anthocyanins as the mechanism beyond the skin burning disorder. Finally, some recommendations to minimize this postharvest damage are also discussed.

Evaluation of the antioxidant capacity, phenolic compounds, and vitamin C content of different peach and nectarine [ Prunus persica (L.) Batsch] breeding progenies.

Antioxidant capacity and contents of total phenolics, anthocyanins, flavonoids, and vitamin C were evaluated in 218 genotypes from 15 peach and nectarine breeding progenies. Significant differences were found among progenies on the fruit antioxidant profile, corroborated by the high contribution showed by cross to the phenotypic variance of each phytochemical trait analyzed (16-45%). Phytochemical profile varied depending on peach/nectarine and yellow/white flesh color qualitative traits. On the other hand, no significant effect of year was found on the bioactive profile of peaches and nectarines. Antioxidant capacity was linearly correlated to total phenolic content, but correlation varied depending on the progeny. No correlation was found for vitamin C versus any other phytochemical trait. The results suggest the importance of genetic background on the antioxidant profile of peaches and nectarines and stress its relevance for the ultimate objective of this work: selecting new peach and nectarine genotypes rich in bioactive compounds to benefit consumer's health.