Development and evaluation of multiple regression models for prediction of sweet cherry liking

Morphological Changes to Fruit Development Induced by GA3 Application in Sweet Cherry (Prunus avium L.)

Cherry (Prunus avium) fruits are important sources of vitamins, minerals, and nutrients in the human diet; however, they contain a large stone, making them inconvenient to eat 'on the move' and process. The exogenous application of gibberellic acid (GA3) can induce parthenocarpy in a variety of fruits during development. Here, we showed that the application of GA3 to sweet cherry unpollinated pistils acted as a trigger for fruit set and permitted the normal formation of fruit up to a period of twenty-eight days, indicating that gibberellins are involved in the activation of the cell cycle in the ovary wall cells, leading to fruit initiation. However, after this period, fruit development ceased and developing fruit began to be excised from the branch by 35 days post treatment. This work also showed that additional signals are required for the continued development of fully mature parthenocarpic fruit in sweet cherry.

Options for the generation of seedless cherry, the ultimate snacking product

This manuscript identifies cherry orthologues of genes implicated in the development of pericarpic fruit and pinpoints potential options and restrictions in the use of these targets for commercial exploitation of parthenocarpic cherry fruit. Cherry fruit contain a large stone and seed, making processing of the fruit laborious and consumption by the consumer challenging, inconvenient to eat 'on the move' and potentially dangerous for children. Availability of fruit lacking the stone and seed would be potentially transformative for the cherry industry, since such fruit would be easier to process and would increase consumer demand because of the potential reduction in costs. This review will explore the background of seedless fruit, in the context of the ambition to produce the first seedless cherry, carry out an in-depth analysis of the current literature around parthenocarpy in fruit, and discuss the available technology and potential for producing seedless cherry fruit as an 'ultimate snacking product' for the twenty-first century.

Fruit Development in Sweet Cherry

Fruits are an important source of vitamins, minerals and nutrients in the human diet. They also contain several compounds of nutraceutical importance that have significant antioxidant and anti-inflammatory roles, which can protect the consumer from diseases, such as cancer, and cardiovascular disease as well as having roles in reducing the build-up of LDL-cholesterol in blood plasma and generally reduce the risks of disease and age-related decline in health. Cherries contain high concentrations of bioactive compounds and minerals, including calcium, phosphorous, potassium and magnesium, and it is, therefore, unsurprising that cherry consumption has a positive impact on health. This review highlights the development of sweet cherry fruit, the health benefits of cherry consumption, and the options for increasing consumer acceptance and consumption.

Plant-Based Biostimulant as Sustainable Alternative to Synthetic Growth Regulators in Two Sweet Cherry Cultivars

Sweet cherry is a high value crop and the economic success of its cultivation depends not only on yield but also on fruit visual and nutritional quality attributes that influence consumer acceptability, as well as on fruit post-harvest performance and resistance to cracking. During the last few decades, cherry growers have tried to achieve these goals through exogenous applications of synthetic plant hormones and/or nutrients, but there is growing concern about the sustainability of the extensive use of these compounds in agriculture. For this reason, there is increasing interest in the possible adoption of different classes of biostimulants as sustainable alternatives to plant growth regulators. This research aimed to study the impact of foliar application of a novel tropical-plant extract, performed between full bloom and fruit set, on the yield and fruit quality of two important commercial sweet cherry cultivars, Kordia and Regina. The experimental design included a commercial control involving the application of a cytokinin promoter. In both cultivars, the tropical-plant extract induced significant increases in fruit yield. In addition, in the cultivar Kordia, the tropical-plant extract enhanced fruit calcium concentration, soluble solids content, flesh firmness, and skin color by 26.2%, 11.8%, 6.7%, and 12.0% (of fruits with mahogany skin color), respectively. Our results suggest that the tropical-plant extract tested as a biostimulant may be a sustainable and effective alternative to the exogenous application of synthetic hormones for sweet cherry cultivation.

Development of a Non-Destructive Method for Detection of the Juiciness of Pear via VIS/NIR Spectroscopy Combined with Chemometric Methods

Juiciness is a primary index of pear quality and freshness, which is also considered as important as sweetness for the consumers. Development of a non-destructive detection method for pear juiciness is meaningful for producers and sellers. In this study, visible-near-infrared (VIS/NIR) spectroscopy combined with different spectral preprocessing methods, including normalization (NOR), first derivative (FD), detrend (DET), standard normal variate (SNV), multiplicative scatter correction (MSC), probabilistic quotient normalization (PQN), modified optical path length estimation and correction (OPLECm), linear regression correction combined with spectral ratio (LRC-SR) and orthogonal spatial projection combined with spectral ratio (OPS-SR), was used for comparison in detection of pear juiciness. Partial least squares (PLS) regression was used to establish the calibration models between the preprocessing spectra (650-1100 nm) and juiciness measured by the texture analyzer. In addition, competitive adaptive reweighted sampling (CARS) was used to identify the characteristic wavelengths and simplify the PLS models. All obtained models were evaluated via Monte Carlo cross-validation (MCCV) and external validation. The PLS model established by 19 characteristic variables after LRC-SR preprocessing displayed the best prediction performance with external verification determination coefficient (R2v) of 0.93 and root mean square error (RMSEv) of 0.97%. The results demonstrate that VIS/NIR coupled with LRC-SR method can be a suitable strategy for the quick assessment of juiciness for pears.

Multiple-population QTL mapping of maturity and fruit-quality traits reveals LG4 region as a breeding target in sweet cherry (Prunus avium L.)

Sweet cherry maturity date and fruit quality are relevant traits for its marketability, transport, and consumer acceptance. In this work, sweet cherry fruit development time, maturity date, and commercial fruit-quality traits (size, weight, firmness, soluble solid content, and titratable acidity) were investigated to improve the knowledge of their genetic control, and to identify alleles of breeding interest. Six sweet cherry populations segregating for these traits were used for QTL analyses. These populations descend from cross- and self-pollinations of local Spanish sweet cherries 'Ambrunés' and 'Cristobalina', and breed cultivars ('Brooks', 'Lambert', or 'Vic'). The six populations (n = 411), previously genotyped with RosBREED Cherry 6 K SNP array, were phenotyped for 2 years. QTL analyses were conducted using a multifamily approach implemented by FlexQTL™. Fruit development time, soluble solid content, and titratable acidity QTLs are first reported in sweet cherry in this work. Significant QTLs were detected for all the traits. Eighteen were more stable as they were detected for 2 years. Of these, nine are first reported in this work. The major QTLs for fruit development time, maturity date, firmness, and soluble solid content were identified on the same narrow region of linkage group 4. These traits also showed significant positive correlation (long fruit development time associated with late maturity, high firmness, and high SSC). NAC transcription factor genes identified on this LG4 region may be candidate genes for the regulation of these traits in sweet cherry, as previously described in syntenic regions of other Rosaceae species. Haplotypes of breeding interest on this LG4 genomic region were identified and will be useful for sweet cherry breeding from this and related plant material.

Inter-correlation of apple firmness determinations and development of cross-validated regression models for prediction of sensory attributes from instrumental and compositional analyses

The texture of apples is paramount for determining fruit quality. This research explored the correlations among firmness determinations from the Sinclair iQ™ Firmness Tester (SiQ™), the Aweta Acoustic Firmness Sensor (AFS), and eight measurements from the Mohr Digi-Test-2 (MDT) instrument. Assessments were conducted on a collection of nine apple cultivars (Ambrosia, Aurora Golden Gala™, Honeycrisp, Fuji, Imperial Gala, McIntosh, Pink Lady™, Silken, Salish™), with a broad range of firmness values, in each of two years. Sensory analysis of the apples was conducted using a semi-trained panel (n = 10) to evaluate crispness, hardness, juiciness and skin toughness, in quadruplicate at two testing dates, providing eight data points per cultivar per year. Inter-correlations of the instrumental firmness determinations (SiQ™, AFS, MDT) revealed that most values were highly correlated with one another (r > 0.500 n = 72). This suggested that the instruments were tracking similar, but not identical, underlying characteristics. Multiple regression models were developed using the 2016 data to predict the sensory attributes from the instrumental and compositional (titratable acidity, soluble solids concentration, absorbed juice) analyses. Models with the highest R² were cross-validated using the 2015 data. Accuracy of these models was evaluated using R² and prediction standard errors (PSEs) - an index quantifying the difference between the predicted and actual values. In general, simple 1- and 2-variable models satisfactorily predicted hardness and crispness, with the R² values ranging between 85 and 89%, while more complex non-linear models were required to predict juiciness and skin toughness. Correlations coefficients reported in this research allow for interconversion of experimental firmness data, as determined by the SiQ™, AFS and MDT. Regression models predicting hardness, crispness and juiciness from instrumental/compositional analyses, revealed that the quality factor (QF) variable was particularly important for estimation of textural characteristics. Therefore the MDT, among the instruments evaluated, was the instrument of choice for quality assessment of apples. Since cross-validation of the models accounted for a high proportion of the variance (70-82%) in a new data set with small PSEs (2.67-6.36) (on a 100-unit scale), the developed models were appropriate for estimating the apple textural attributes.

Quality of sour cherry juice of different clones and cultivars (Prunus cerasus L.) determined by a combined sensory and NMR spectroscopic approach

Juice was manufactured from seven different sour cherry clones/cultivars and evaluated by quantitative descriptive sensory analysis and (1)H NMR spectroscopy. The sensory evaluation showed a large variation in several sensory attributes between the sour cherry clones/cultivars, which could be divided into two groups on the basis of both the sensory data and the NMR spectroscopic data. These groups were closely related to the genetic background of the clones. Kelleris clones were distinctly different from Stevnsberry and Fanal clones. Hence, (1)H NMR spectroscopic data seem to correlate with sensory quality of different sour cherry clones. In addition, malic acid was the most important metabolite for modeling the two highly correlated sensory attributes sweetness and sourness, whereas the glucose content had a slight effect and the fructose content had no impact on sweetness/sourness. Other metabolites (ethyl acetate, asparagine, ethanol) could be correlated with sensory attributes; however, a direct causal connection could not be established.

Assignation of sweet cherry selections to 3 taste groupings based on perceived sweetness and sourness

Providing consumers with basic taste properties of sweet cherries at point of purchase would allow consumers to make purchase decisions based on fruit's intrinsic sensory attributes. The objective of this study was to develop a model to predict taste-grouping assignation of cherries into the following categories: (1) low sweetness/high sourness, (2) balance between sweetness and sourness, and (3) high sweetness/low sourness. A sensory panel (n = 10) was trained to recognize sweetness and sourness in 5 cultivars of sweet cherries and assign a taste grouping based on the perceived balance of sweetness and sourness. Four of these same cultivars were then evaluated for sweetness and sourness by a consumer panel (n = 117) and instrumentally for titratable acidity (TA) and soluble solids concentration (SSC). Results showed that for 3 of the 4 cherry cultivars, the sweetness/sourness balance of the cherries was not significantly different as evaluated instrumentally or by the trained panel. However, the balance determined by the consumer and the trained panel was different for 3 of the 4 cherry cultivars (P < 0.05). Based on trained panel perceived sweetness and sourness, a multinomial logit model was developed to predict the assignation of cherry taste grouping. The likelihood of group assignment depended on both the perceived sweetness and sourness of the cherry, with taste groupings agreed upon for 3 of 5 sweet cherry cultivars. As previous studies have indicated a positive relationship between cherry sweetness and sourness to consumer acceptance, these groupings show promise for assisting consumers in cherry selection at the point of purchase.

PRACTICAL APPLICATIONS

The prediction models proposed in this study suggest that both sweetness and sourness are important in the cherry characterization and the ratio between the 2 attributes may be appropriate for making taste-grouping assignments. These groupings may then be used to provide additional sensory information to consumers to assist them in cherry selection at the point of purchase.