Genetic architecture of apple fruit quality traits following storage and implications for genetic improvement

Accurate prediction of genetic potential and response to selection in breeding requires knowledge of genetic parameters for important selection traits. Data from breeding trials can be used to obtain estimates of these parameters so that predictions are directly relevant to the improvement program. Here, a factor allocation diagram was developed to describe the sampling design used to assess the quality of fresh and post-storage (2 months) fruit from advanced selection trial in an apple breeding program from which models for analyses were developed. Genetic variation was the largest source of variation for the fruit size, red colour type, proportion of red skin colour and lenticels, and instrumentally assessed fruit diameter, mass, puncture force and titratable acidity. In contrast, residual variation was the largest for fruit shape, juiciness, sweetness, aromatic flavour, eating and overall quality, and instrumental crispness. Genetic effects for traits were generally stable over fixed effects, except for a significant interaction with storage duration for firmness. Genetic correlations among traits were generally weak except between fruit mass (and diameter) and sensory size (0.98), titratable acidity and sensory acidity (0.97), puncture force and sensory firmness (0.96–0.90), crispness and juiciness (0.87), sweetness and aromatic flavour (0.84) and instrumental and sensory crispness (0.75). Predictions of the performance for seven commercial cultivars are presented. This study suggests that the Washington State apple production area can be treated as a single target environment and sufficient diversity exists to generate new elite cultivars. In addition, options for evaluating the efficiency of apple breeding are discussed.     

QTL analysis of fruit quality in fresh market tomato: a few chromosome regions control the variation of sensory and instrumental traits

The organoleptic quality of tomato fruit involves a set of attributes (flavour, aroma, texture) that can be evaluated either by sensory analyses or by instrumental measures. In order to study the genetic control of this characteristic, a recombinant inbred line (RIL) population was developed from an intraspecific cross between a cherry tomato line with a good overall aroma intensity and an inbred line with medium flavour but bigger fruits. A total of 38 traits involved in organoleptic quality were evaluated. Physical traits included fruit weight, diameter, colour, firmness, and elasticity. Chemical traits were dry matter weight, titratable acidity, pH, and the contents of soluble solids, sugars, lycopene, carotene, and 12 aroma volatiles. A panel of trained assessors quantified sensory attributes: flavour (sweetness and sourness), aroma (overall aroma intensity, together with candy, lemon, citrus fruit, and pharmaceutical aromas) and texture (firmness, meltiness, mealiness, juiciness, and skin difficult to swallow). RILs showed a large range of variation. Molecular markers were used to map a total of 130 quantitative trait loci (QTL) for the 38 traits. They were mainly distributed in a few chromosome regions. Major QTLs (R(2) >30%) were detected for fruit weight, diameter, colour, firmness, meltiness, and for six aroma volatiles. The relationships between instrumental measures and sensory traits were analysed with regard to the QTL map. A special insight was provided about the few regions where QTLs are related to multiple traits. A few examples are shown to illustrate how the simultaneous analysis of QTL segregation for related traits may aid in understanding the genetic control of quality traits and pave the way towards QTL characterization.     

Evaluation of the best linear unbiased prediction method for breeding values of fruit-quality traits in citrus

Fruit-quality trait improvement is an important objective in citrus breeding; however, fruit breeding programs often accumulate highly unbalanced phenotypic records, which are a serious obstacle in comparing and selecting genotypes. The best linear unbiased prediction (BLUP) method can be used to overcome these difficulties, but few fruit breeding programs have adopted the method, and to our knowledge, the method has not yet been used to predict breeding values of traits based on pedigree information and genetic correlations between traits in citrus. Accordingly, we used the BLUP method to predict the breeding values of nine fruit-quality traits (fruit weight, fruit skin color, fruit surface texture, peelability, flesh color, pulp firmness, segment firmness, sugar content, and acid content) utilizing phenotypic records collected over several years as part of the citrus breeding program conducted at the Kuchinotsu branch of the National Institute of Fruit Tree Science in Japan. Although the accumulated phenotypic records were highly unbalanced, the BLUP method was able to predict the breeding values of all 2122 genotypes (111 parental cultivars and 2011 F₁ offspring from 126 pair-cross families), as well as estimates of several genetic parameters, including narrow-sense heritability and phenotypic and genotypic correlations. These findings demonstrate the utility of the BLUP method in citrus crossbreeding and provide predicted breeding values, which can be used to select superior genotypes in the Kuchinotsu Citrus Breeding Program and related genetic selection endeavors.     

Utilization of pedigree information to estimate genetic parameters from large unbalanced data sets in apple

 Genetic parameters (narrow-sense heritabilities and genetic correlations) were estimated for major agronomical traits in apple from large unbalanced data sets, with the help of wide-pedigree information. The software REML VCE (Groeneveld 1996) took into account the complex pedigree of the French apple-breeding population, thanks to the restricted maximum likelihood procedure combined with the construction of the entire relationship matrix between hybrids planted in the field and their ancestors. Narrow-sense heritability estimates ranged from 0.34 to 0.68 for traits exhibiting a normal distribution. Heritability values around 0.35–0.40 were obtained for fruit characteristics (size, texture, flavour, juice content, attractiveness, russeting). Higher values of heritability were obtained for vigour, assessed by the circumference of the trunk (0.51), and powdery mildew resistance (0.68). Additive genetic correlations between traits were also estimated, showing a very high relationship between fruit-quality traits. Vigour and powdery mildew resistance were slightly correlated with the other traits. Utilization of the ‘individual genetic model’ for the estimation of genetic parameters and breeding values in apple is discussed. Received: 14 June 1997 / Accepted: 4 December 1997     

Mapping quantitative physiological traits in apple (Malus × domestica Borkh.)

Efficient breeding and selection of high-quality apple cultivars requires knowledge and understanding of the underlying genetics. The availability of genetic linkage maps constructed with molecular markers enables the detection and analysis of major genes and quantitative trait loci contributing to the quality traits of a genotype. A segregating population of the cross between the apple varieties `Fiesta' (syn. `Red Pippin') and `Discovery' has been observed over three years at three different sites in Switzerland and data on growth habit, blooming behaviour, juvenile period and fruit quality has been recorded. QTL analyses were performed, based on a genetic linkage map consisting of 804 molecular markers and covering all 17 apple chromosomes. With the maximum likelihood based interval mapping method, the investigated complex traits could be dissected into a number of QTLs affecting the observed characters. Genomic regions participating in the genetic control of stem diameter, plant height increment, leaf size, blooming time, blooming intensity, juvenile phase length, time of fruit maturity, number of fruit, fruit size and weight, fruit flesh firmness, sugar content and fruit acidity were identified and compared with previously mapped QTLs in apple. Although `Discovery' fruit displayed a higher acid content, both acidity QTLs were attributed to the sweeter parent `Fiesta'. This indicated homozygosity at the acidity loci in `Discovery' preventing their detection in the progeny due to the lack of segregation.     

Variation and genetic parameters of fruit colour and polyphenol composition in an apple seedling population segregating for red leaf

Red flesh colour is a relatively new target for apple breeding programmes and understanding genetic relationships between this trait and other fruit characters, including polyphenol compounds, is important for both breeders and marketers of new red flesh cultivars. In this study, fruit peel and flesh colours and concentrations of up to 20 individual fruit polyphenols within each tissue were examined in fruit harvested from a 14-family apple seedling population segregating for red and green leaf. Red leaf seedlings always produced red flesh fruit that varied from pale red to complete dark red cortical tissue (type 1 red flesh). Some (20 %) of green leaf seedlings also produced fruit with red flesh, albeit at low intensity (type 2 red flesh). Cyanidin 3-O-galactoside was the dominant anthocyanin in both fruit tissues, with concentrations being 1,900 times higher in the flesh and 2.5 times higher in the peel of fruit from red than from green leaf seedlings. Red leaf seedlings also had 59 % more flesh epicatechin and 17 % less total peel flavonols, but other polyphenols were not associated with leaf colour. Heritability estimates for red flesh colour, flesh cyanidin 3-O-galactoside, flesh and peel catechins were high in red leaf and low in green leaf seedlings. Conversely, estimates for red peel coverage and two peel anthocyanins were higher in green compared to those from red leaf seedlings. Other than these, heritability estimates were high only for dihydrochalcones and hydroxycinnamic acids from each tissue for both leaf colours but low for all other flesh and peel flavan-3-ols, procyanidins and most peel flavonols irrespective of leaf colour. Genetic correlations between polyphenol compounds varied considerably, but were broadly similar for red and green leaf seedlings. Genetic correlations were mostly moderate to high between compounds of the same metabolic group, but low between compounds from different groups. These results are discussed in relation to the genetic control of flesh colour and polyphenol accumulation in apple, as well as to implications for breeding red flesh apples with altered polyphenol composition.     

Phenotypic and genetic correlations of pork myoglobin content with meat colour and other traits in an eight breed-crossed heterogeneous population

Meat colour is one of the most important meat quality traits affecting consumption desire. Genetic improvement for meat colour traits is not so easy because pigs can be phenotyped only after slaughter. Besides the parameters from the optical instrument, other indexes that reflect the material basis of meat colour should be measured accurately and used in the genomic analysis. Myoglobin (Mb) is the main chemical component determining meat colour. However, to what extent the Mb content contributes to meat colour, and whether it can be used as a trait for pig breeding to improve meat colour, and the correlations of Mb content with complex porcine traits are largely unknown. To address these questions, we measured the muscle Mb content in 624 pigs from the 7th generation of a specially designed eight breed-crossed pig heterogeneous population, evaluated its phenotypic and genetic correlations with longissimus thoracis colour score at 24 h after slaughter. More than that, we also systematically phenotyped more than 100 traits on these animals to evaluate the potential correlations between muscle Mb content and economically important traits. Our results showed that the average muscle Mb content in the 624 pigs was 1.00 mg/g, ranging from 0.51 to 2.17 mg/g. We found that higher Mb content usually correlated with favourable meat colour, higher marbling score, less moisture content, and less drip loss. Genetic correlation analysis between muscle Mb content and 101 traits measured in this study shows that Mb content is also significantly correlated with 31 traits, including marbling, shear force, firmness, and juiciness. To our knowledge, this is one of the largest studies about the correlations of muscle Mb content with as many as 100 various traits in a large-scale genetically diversified population. Our results showed that the Mb content could be a selection parameter for the genetic improvement of meat colour. The selection for higher Mb content will also benefit marbling, shear force, firmness, and overall liking but might not affect the growth, carcass, and fat deposition traits.     

Genetic architecture of fruit quality traits in Malus x domestica (Borkh.) compared between own-rooted seedlings and vegetative propagules on ��M. 9�� rootstock

The comparative performance of vegetative propagules (VP) grafted on ‘M. 9’ rootstock and own-rooted (OR) seedlings of the same genotypes was investigated for apple [Malus x domestica (Borkh.)] fruit quality traits using offspring from 22 control-pollinated families. Fifteen fruit quality traits including fruit size and shape, skin colour, russet and sensory eating characteristics were evaluated for individual seedlings. Estimates of genetic variance–covariance matrices (G) were obtained and compared between the two treatments (OR versus VP) using Mantel’s test and regression approaches. Empirical estimates of correlations, at the individual-tree and family-mean levels, between the two treatments were compared with those obtained from deterministic simulations. Estimates of narrow-sense heritability (h ²) were higher in the VP population than in the OR population for 11 of the 15 traits. The estimated G matrices were significantly different between the two treatments. Simulation study showed that with an increase in the total genetic variance, the correspondence between the two treatments at the family-mean level improved dramatically for different family sizes. As the ratio of dominance/additive variance increased from 0 to 1, the family-mean correlations between the two treatments decreased for all family sizes. The average estimated correlations between the two treatments at the family-mean level were higher than at the individual-tree level (0.78 and 0.42, respectively). These observed correlations were very similar to our theoretical expectations. In the light of these results, caution is required when comparing apple seedlings tested on their own roots with those tested on ‘M. 9’ rootstock, as potential cultivar breeding parents.     

Influence of slaughter age and carcass suspension on meat quality in Angus heifers

This study investigated the effects of pelvic suspension and slaughter age on longissimus thoracis et lumborum (LTL) from 40 heifers with at least 75% Angus breeding. A total of 20 heifers were slaughtered directly from pasture at 18 months of age, and carcass sides were hung either by the Achilles tendon or the pelvic bone. The other 20 heifers were assigned to an additional winter housing period and slaughtered at 22 months of age; carcass sides were hung only by Achilles suspension. All carcasses were electrically stimulated and assessed according to the EUROP carcass classification system. In addition, the LTL muscles were aged for 7 or 14 days before meat quality was evaluated for intramuscular fat (IMF), drip loss, colour, shear force, compression and sensory analysis. The 22-month-old heifers were heavier, fatter and had more IMF than 18-month-old heifers. Conformation scores (muscling) did not differ between the two slaughter groups. Pelvic suspension reduced both between- and within-animal variation for peak force, total energy and compression peak force. For the 18-month-old heifers, pelvic suspension also decreased peak force, total energy and compression variables for the LTL muscles from both ageing periods, whereas Achilles-suspended samples had lower shear force values only at day 14. Sensory analysis showed that pelvic-suspended sides had greater tenderness, lower bite resistance, less threadiness, higher juiciness and meat flavour and less visible marbling than meat from Achilles-suspended sides. Pelvic-suspended sides at 18 months of age were similar in peak force and total energy values to the 22-month-old heifers. The importance of ageing the Achilles-suspended sides was more obvious for samples from 18-month-old heifers than from the 22-month-old animals. The correlations between the different instrumental measurements and sensory tenderness were considerably higher for carcasses suspended by the Achilles tendon (r = −0.55 to 0.20) than for those hung by the pelvic bone (r = −0.25 to 0.19). More correlations between sensory-evaluated tenderness and shear variables were significant after 7 days (n = 6) of ageing than after 14 days (n = 4) of ageing. This study clearly shows the benefits of pelvic suspension, which reduces the need for additional feeding after pasture.     

Dissection of genetic and environmental factors involved in tomato organoleptic quality

Background  

One of the main tomato breeding objectives is to improve fruit organoleptic quality. However, this task is made somewhat challenging by the complex nature of sensory traits and the lack of efficient selection criteria. Sensory quality depends on numerous factors, including fruit colour, texture, aroma, and composition in primary and secondary metabolites. It is also influenced by genotypic differences, the nutritional regime of plants, stage of ripening at harvest and environmental conditions. In this study, agronomic, biochemical and sensory characterization was performed on six Italian heirlooms grown in different environmental conditions.     

皱皮木瓜果实发育后期品质变化及其成熟阶段的划分初探

以湖北长阳产皱皮木瓜为材料,测定果实发育后期果实鲜质量、果长、果径、果色、果实硬度以及果肉干物质量、可溶性糖含量、总酸含量和总黄酮含量等品质指标的动态变化,划分不同成熟阶段,为判断果实适宜采收期、实现优质生产提供理论参考。结果表明:(1)皱皮木瓜果实发育后期果实鲜质量、果长、果径、果肉干物质量和可溶性糖含量均呈现上升趋势;果色由绿色、黄绿色渐变为淡黄色到黄色;果实硬度、果肉总酸和总黄酮含量呈先上升后下降趋势。(2)各品质指标快速变化的时间区域存在差异,果实鲜质量在花后105~150d增加较快,果色在150d后逐渐变黄,果实硬度在花后135~165d快速下降,果肉总酸、总黄酮含量则在花后105~120d快速增加至峰值。(3)根据主成分分析结果和各品质指标的变化特点,可初步将皱皮木瓜果实发育后期划分为未成熟(花后105d之前)、早期成熟(花后120~150d)和成熟(花后165~180d)3个阶段。研究表明,随着果实成熟度的提高,皱皮木瓜果实鲜质量、果色、果肉干物质量、可溶性糖含量等指标不断升高,果实硬度逐渐下降,其食用加工品质不断提升,而在早期成熟阶段(花后120~150d)果实的药用品质则相对较高。     

辣椒果实性状主基因+多基因遗传分析

以果实性状差异较大的一年生辣椒材料C.annuum B9431(P1)和灌木辣椒材料C.frutescens H108(P2)为亲本,构建4世代群体(P1、P2、F1、F2),应用数量性状主基因+多基因混合遗传模型方法对辣椒6个果实性状进行遗传分析,为辣椒果实性状QTL定位及分子标记辅助育种研究奠定理论基础。结果表明:6个果实性状均符合2对主基因+多基因遗传模型。其中,单果重量、果实纵径、果实横径、果形指数和果肉厚度5个性状均符合E-0模型,即2对加性-显性-上位性主基因+加性-显性-上位性多基因混合遗传模型;果柄长度最佳遗传模型为E-5,即2对完全显性主基因+加性-显性多基因模型。单果重量、果实纵径、果实横径、果形指数、果肉厚度和果柄长度主基因遗传率分别为87.64%、37.67%、82.46%、94.82%、83.33%和40.00%,多基因遗传率分别为7.50%、54.56%、10.53%、0.27%、12.96%和37.78%。     

Consistency statistics and genetic parameters for taste panel assessed meat quality traits and their relationship with carcass quality traits in a commercial population of Angus-sired beef cattle

Sensory traits, such as juiciness and tenderness, are known to be important to the consumer and thus will influence their consumption of meat, specifically beef. These traits are difficult to measure and often require the use of taste panels to assess the complex parameters involved in the eating experience. Such panels are potentially a large source of measurement error, which may reduce the effectiveness of breeding programmes based on the data they generate. The aim of this study was to assess the quality of such taste panel-derived sensory traits as well as calculating genetic parameters and residual correlations for these traits along with a further set of traditional carcass quality traits. The study examined a sample of 443 Aberdeen Angus-cross animals collected from 14 breeder-finisher farms throughout Scotland. To assess the quality of the taste panel measurements, three consistency statistics were calculated: (i) panel-member consistency, i.e. the extent to which an individual panel member varied in their scoring for a given trait over the period of the experiment; (ii) repeatability, i.e. the consistency with which an individual panel member was able to score a trait on repeated samples from the same animal; and (iii) reproducibility, i.e. the extent to which taste panel members agreed with each other when scoring a trait. These consistency statistics were moderately high, particularly for panel-member consistency and reproducibility, with values ranging from 0.48 to 0.81 and 0.43 to 0.73 respectively. Estimated heritabilities were low for most of the sensory taste-panel-evaluated traits where the maximum value was 0.16 for overall liking. Residual correlations were high between many of the closely related sensory traits, although few significant correlations were found between the carcass quality data and meat quality traits.     

Biochemical measurements of beef are a good predictor of untrained consumer sensory scores across muscles

The ability of the biochemical measurements, haem iron, intramuscular fat (IMF%), moisture content, and total, soluble and insoluble collagen contents, to predict untrained consumer sensory scores both across different muscles and within the same muscle from different carcasses were investigated. Sensory scores from 540 untrained French consumers (tenderness, flavour liking, juiciness and overall liking) were obtained for six muscles; outside (m. biceps femoris), topside (m. semimembranosus), striploin (m. longissimus thoracis), rump (m. gluteus medius), oyster blade (m. infraspinatus) and tenderloin (m. psoas major) from each of 18 French and 18 Australian cattle. The four sensory scores were weighted and combined into a single score termed MQ4, which was also analysed. All sensory scores were highly correlated with each other and with MQ4. This in part reflects the fact that MQ4 is derived from the consumer scores for tenderness, juiciness, flavour and overall liking and also reflects an interrelationship between the sensory scores themselves and in turn validates the use of the MQ4 term to reflect the scope of the consumer eating experience. When evaluated across the six different muscles, all biochemical measurements, except soluble collagen, had a significant effect on all of the sensory scores and MQ4. The average magnitude of impact of IMF%, haem iron, moisture content, total and insoluble collagen contents across the four different sensory scores are 34.9, 5.1, 7.2, 36.3 and 41.3, respectively. When evaluated within the same muscle, only IMF% and moisture content had a significant effect on overall liking (5.9 and 6.2, respectively) and flavour liking (6.1 and 6.4, respectively). These results indicate that in a commercial eating quality prediction model including muscle type, only IMF% or moisture content has the capacity to add any precision. However, all tested biochemical measurements, particularly IMF% and insoluble collagen contents, are strong predictors of eating quality when muscle type is not known. This demonstrates their potential usefulness in extrapolating the sensory data derived from these six muscles to other muscles with no sensory data, but with similar biochemical parameters, and therefore reducing the amount of future sensory testing required.     

Map position and functional allelic diversity of Md-Exp7, a new putative expansin gene associated with fruit softening in apple (Malus × domestica Borkh.) and pear (Pyrus communis)

Fruit ripening can be considered as a complex set of biochemical and physiological changes occurring at the end of the developmental stage. Ripe fruit texture notably affects overall quality and consumer appreciation. Excessive softening limits shelf-life and storability, thereby increasing disease susceptibility and economic loss. Fruit softening is a process due to the depolymerisation of different polysaccharide classes, an event controlled by a synergic and coordinated action of several enzymes among which expansins play a fundamental role. To date, six expansin genes are known to be expressed during apple fruit ontogeny, from full bloom up to fruit ripening. We identified a novel expansin apple homolog (Md-Exp7) sharing high sequence similarity with specific-ripening expansin genes of other crops. A functional marker (Md-Exp7_SSR) based on an SSR motif located within the untranslated region of the gene was developed and mapped on Linkage Group 1 of the apple and pear genomes in a region where one major apple QTL for fruit firmness had been previously identified. The allelic composition of 31 apple varieties for the SSR marker was associated with differences in fruit softening.     

Phenotypic and molecular characterization of selected tomato recombinant inbred lines derived from the cross <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> × <Emphasis Type="Italic">S. pimpinellifolium</Emphasis>

An important trait defining fresh tomato marketability is fruit shelf life. Exotic germplasm of Solanum pimpinellifolium is able to prolong shelf life. Sixteen recombinant inbred lines with differing values of shelf life and fruit weight were derived by antagonistic-divergent selection from an interspecific cross involving Solanum pimpinellifolium. The objective of this study was to evaluate these recombinant inbred lines for many fruit quality traits such as diameter, height, size, acidity, colour, firmness, shelf life and weight, and to characterize them by amplified fragment length polymorphism markers. For most traits, a wide range of genetic variability was found and a wide range of molecular variation was also detected. Both sets of data allowed the identification of recombinant inbred lines by means of cluster analysis and principal component analysis. Genetic association among some amplified fragment length polymorphism markers and fruit quality traits, suggested by the principal component analysis, could be identified by single point analysis. Potential molecular markers underlying agronomical traits were detected in these recombinant inbred lines.