Validation of a functional molecular marker suitable for marker-assisted breeding for fruit texture in apple (Malus × domestica Borkh.)

Molecular markers are nowadays considered fundamental tools in breeding programs, supporting the selection of the most favourable offspring. This role is invaluable in the case of complex agronomic traits in tree fruit crop species, such as fruit texture in apple (Malus × domestica Borkh.). This work presents the validation of a previously identified functional simple sequence repeat marker, named Md-PG1_SSR10kd, suitable for the advanced selection of high texture performance seedlings. Two independent populations were chosen by marker-assisted parent selection, and a specific set of seedlings was selected by marker-assisted seedling selection, to validate the predictive power of this marker. The two groups of seedlings, further phenotyped for fruit texture, showed a clear difference in texture behaviour. The selection of this marker also showed a higher efficiency than Md-ACS1 and Md-ACO1, two functional markers currently implemented in different breeding programs. Finally, the allelic effect was estimated by computing the breeding values in a collection of 83 different apple cultivars. The results reported here confirmed the association of Md-PG1_SSR10kd with texture sub-traits, proposing this as a novel promising selection strategy suitable for apple fruit texture.     

Expression of ethylene biosynthetic and signaling genes in relation to ripening of banana fruit after cold storage

Banana fruit are highly sensitive to chilling injury (CI), while the effect of different degrees of CI on the subsequent fruit ripening is largely unknown. In the present work, ripening characteristic of banana fruit after storage at 7 °C for 3 days or for 8 days, and expression levels of eight genes associated with ethylene biosynthetic and signaling, including MaACS1, MaACO1, MaERS1, MaERS3, and MaEIL1–4, were investigated. The results showed that banana fruit stored at 7 °C for 8 days exhibited more severe chilling symptoms than those at 7 °C for 3 days. Compared with banana fruit stored at 7 °C for 8 days, which showed abnormal ripening, more decrease in fruit firmness, while higher increase in ethylene production and hue angle were observed in banana fruit stored at 7 °C for 3 days, which could ripening normally. Moreover, gene expression profiles during ripening revealed that ethylene biosynthetic and signaling genes were differentially expressed in peel and pulp of banana fruit after storage at 7 °C for 3 days and 7 °C for 8 days. In the peel of fruit storage at 7 °C for 3 days, expression levels of MaACS1, MaACO1, MaEIL1, and MaEIL2 increased remarkably while MaERS3, MaEIL1, and MaEIL4 were enhanced in the fruit after storage at 7 °C for 8 days. In the pulp, with the exception of MaACO1 and MaERS3, expression levels of other genes did not exhibit a significant difference, between the banana fruit storage at 7 °C for 3 days and 7 °C for 8 days. Taken together, our results suggest that differential expression of ethylene biosynthetic and signaling genes such as MaERS3, MaACO1, and MaEIL2, may be related to ripening behavior of banana fruit with different degrees of CI after cold storage.     

Effect of fruit maturity on UV-B-induced post-harvest anthocyanin accumulation in red Chinese sand pear

The effect of fruit maturity on UV-B-induced post-harvest anthocyanin accumulation in red Chinese sand pear (Pyrus pyrifolia Nakai) cultivar ‘Mantianhong’ was evaluated. During the irradiation, compared with the fruit harvested at 20 days before harvest (DBH) and 10 DBH, the mature fruit (harvested at commercial harvest date) had higher soluble solids content, soluble sugars concentration but lower firmness and starch content. In addition, higher content of anthocyanin has been detected in mature fruits than in immature fruits due to the significant increase in the expression of genes related to anthocyanin biosynthesis, especially PpCHS, PpF3H, PpANS, PpUFGT, PyMYB10 and PpbHLH in red Chinese sand pears. Hierarchical clustering analysis suggested that most genes related to anthocyanin biosynthesis showed a coordinate expression pattern. These findings are helpful in understanding the molecular mechanism of anthocyanin biosynthesis and regulation, which could lead to the development of new technologies for improving fruit color in Chinese sand pears and other fruits.     

Inheritance of the<Emphasis Type="Italic"> Md-ACS1</Emphasis> gene and its relationship to fruit softening in apple (<Emphasis Type="Italic">Malus</Emphasis> ×<Emphasis Type="Italic"> domestica</Emphasis> Borkh.)

The 1-aminocyclopropane-1-carboxylic acid synthase (ACS) gene is a member of the ACS gene family that is involved in apple (Malus × domestica Borkh.) fruit ripening. Presence of an allele (Md-ACS1-2) of this gene is associated with low internal ethylene concentration in some apple cultivars. In this study, inheritance of Md-ACS1 was determined for 50 apple cultivars/advanced selections and 101 F₁ seedlings from five populations. Following this, the softening pattern of apples stored at 20°C for up to 40 days was examined using 35 fruiting cultivars/selections of defined Md-ACS1 status. Md-ACS1 is inherited in a Mendelian fashion and was found to be linked to fruit softening. Maturity season of genotypes also significantly affected fruit softening. Late-season genotypes in the Md-ACS1-2/2 class had the slowest rate of softening, while early-season Md-ACS1-1/1 genotypes had the most rapid softening rate. The implications of these results are discussed in relation to parental selection and breeding for storage ability in apple.Communicated by H. Nybom     

Effects of chilling on tomato fruit texture

The effects of chilling on tomato ( Lycopersicon esculentum Mill cv. Caruso) texture were investigated using fruit stored at 22°C (nonchilled) or 5°C (chilled) for 28 days. or at 5°C for 15 days before transfer to 22°C to facilitate ripening during and additional 13 days (prechilled). Prechilled fruit exhibited symptoms of slight chilling injury, i.e. development of mealiness, accelerated softening relative to that of nonchilled fruit and nonuniform surface colour development. The firmness of all fruit decreased during ripening and chilled storage when measured by flat plate compression and puncture, especially during the early stages of ripening of nonchilled and prechilled fruit. The compression firmness of pericarp tissue similarly decreased during ripening of nonchilled and prechilled fruit, but was maintained during chilling. Total moisture content (ca 94%) of tissue, uronide content (32-35% w/w) and extracted β-galactosidase activity did not differ significantly ( P > 0.05) among fruit during ripening and chilled storage. The degree of uronide methyl esterification in ethanol-insoluble solids prepared from pericarp tissue (EIS) was relatively low for all fruit. i.e. <40%. EIS from which greater levels of pectinesterase were extracted (i.e. nonchilled>chilled>prechilled) exhibited decreased levels of uronide methyl esterification. Markedly elevated levels of β-glucosidase activity were extracted from prechilled EIS. Total polygalacturonase activity (mainly as PGI) and autolysis of enzyme-extracted EIS were inversely correlated ( P ≤ 0.05) only with the loss of nonchilled fruit and tissue firmness and prechilled fruit firmness. Results suggest a possible role for β-glucosidase in textural changes of prechilled fruit and tissue (e.g. loss of firmness, development of mealiness) and also implicate loss of skin strength in the softening of whole fruit during chilling.     

The relationship between fruit retention force at harvest and quality of feijoa after storage

Feijoa (Feijoa sellowiana, cvs Apollo and Gemini) fruits were removed from the tree and grouped into treatments according to retention force (RF) at harvest. Fruits with greater RF at harvest had higher titratable acidity and flesh firmness, lower soluble solids content and less locule clarity at harvest than fruits with lower RF. After 4 wk storage at 4 °C and 5 days shelflife at 20 °C titratable acidity, soluble solids and firmness in these fruits were similar across RF grades except that after shelflife the incidence of flesh and locule browning was greater in fruits harvested with low RF when compared with fruits picked with greater force. At harvest the total sugar and organic acids, and the sugar: acid ratio were similar irrespective of RF, whereas after storage and shelflife no consistent effect of RF existed. Taste panellists could not detect differences in the eating appeal of fruit harvested with high or with low retention force after storage and shelflife. Soluble solids, acidity and flesh firmness declined markedly over storage and shelflife irrespective of retention force at harvest and although these fruits were still acceptable for eating, they no longer had the characteristic flavour and texture of unstored feijoas.     

Comparative transcript profiling of a peach and its nectarine mutant at harvest reveals differences in gene expression related to storability

Gene expression at harvest was compared for two stone fruit cultivars, a peach and its near-isogenic nectarine mutant, using two microarray platforms, μPEACH1.0 and ChillPeach. Together, both platforms covered over 6,000 genes out of which 417 were differentially expressed between the fruits of the two cultivars at a p value of 0.05. A total of 47 genes in nectarine and 60 genes in peach were at least twofold higher relative to each other. Nectarine had much better storage characteristics than peach and could be stored for over 5 weeks at 5 °C without storage disorders. In an attempt to determine whether gene expression at harvest could give an indication of storage potential, the expression analysis of the two cultivars was compared to that of two genotypes with different sensitivities to chilling injury. Principal component analysis of gene expression results across four fruit types differing in chilling sensitivity resulted in 41 genes whose expression levels separated the fruits according to sensitivity to storage disorders, suggesting that the genes have a role in cold response adaptation.     

Cloning of cDNAs encoding cell-wall hydrolases from pear (Pyrus communis) fruit and their involvement in fruit softening and development of melting texture

'La France' pear ( Pyrus communis L.) fruit stored at 1°C for 1 month (short-term storage) before transfer to 20°C softened and developed a melting texture during ripening, whereas fruit stored for 5 months (long-term storage) before transfer to 20°C softened but did not develop a melting texture. To clarify the mechanisms involved in fruit softening and textural changes, the cDNAs encoding cell-wall hydrolases were isolated by RT-PCR, and their expression and localization were investigated in 'La France' pears. Genes encoding three polygalacturonases (PG; EC 3.2.1.15), four pectin methylesterases (PME; EC 3.1.1.11), one α -arabinofuranosidase (ARF; EC 3.2.1.55), three β -galactosidases (GAL; EC 3.2.1.23), and two endo-1,4- β - d -glucanases (Cel; EC 3.2.1.4) were isolated. Among these 13 isolated genes, PcPG1 was the only gene for which the mRNA expression levels increased in both the short- and long-term stored fruits. This suggested that PcPG1 is involved in fruit softening rather than in the development of the melting texture. In contrast, the expression levels of PcPG3 , PcPME1 , PcPME2 , PcPME3 , PcGAL1 , PcGAL2 , and PcCel2 increased during ripening only in the short-term stored fruit. These genes might thus be involved in the development of the melting texture.     

Estimation of genetic parameters and prediction of breeding values for apple fruit-quality traits using pedigreed plant material in Europe

Genetic parameters for apple (Malus x domestica) fruit external traits (fruit size, ground colour, proportion of over colour and attractiveness) and sensory traits (firmness, crispness, texture, juiciness, flavour, sugar, acidity and global taste) were estimated using 2,207 pedigreed genotypes from breeding programmes in six European countries. Data were scored for 3 years and four periods during storage. Analyses were performed with a restricted maximum likelihood method using VCE 5.1.2 software. Heritability estimates ranged from medium to high for instrumental traits. Genetic correlations between firmness and sugar were medium and low between firmness and acidity. Sensory traits showed low to high heritability, acidity and flavour being, respectively, the most and the less heritable. Global taste was strongly correlated with texture, juiciness, and flavour and relatively less correlated with crispness and acidity. Sensory sugar and acidity showed highly negative correlations whereas their instrumental measurements showed low and increasing positive correlations from harvest to 4 months post-harvest. Sugar exhibited a higher sensory/instrumental divergence. Conversely, instrumental and sensory firmness were highly correlated. Fruit external characteristics had medium heritability. Fruit attractiveness had highest and lowest correlations with fruit size and ground colour, respectively. Best linear unbiased predictors of breeding values were computed for all genotypes with the software PEST. The results were analysed with regard to the dynamic and the reliability of genetic parameters according to the scoring dates. Original issues of the study and the importance of the obtained results for efficient designs of further apple fruit quality breeding programmes were discussed.     

Genetic analysis of the slow-melting flesh character in peach

The slow-melting flesh (SMF) trait in peach [Prunus persica (L.) Batsch] defines a slower process of postharvest fruit-softening than the prevalent melting flesh (MF) types. This gives a longer shelf life and a delayed harvest-time resulting in better fruit quality. Unlike other known fruit texture traits, SMF is difficult to measure and has a complex inheritance. We examined this character over 2 years in the offspring of two crosses, both with “Big Top,” an SMF nectarine, as the female parent, and with a melting flesh (MF) nectarine as the male parent (“Armking” and “Nectaross”). Following harvest, a texturometer was used to provide a textural profile analysis, and fruit firmness evolution was measured with a penetrometer over a period of 5 days’ storage at 20 °C. Linkage maps were constructed with a high-density SNP chip, and a phenotype-genotype analysis allowed the detection of three independent genomic regions where most QTLs (quantitative trait loci) were located. Two of these, on linkage groups 4 and 5, explained the variability for two characters—maturity date and firmness loss—that is, the QTL on linkage group 4 found in the MF parents and that on linkage group 5 in Big Top. A third region on linkage group 6, which identified a QTL for maturity date only in Armking, has no apparent association to the softening process. The relationship between maturity date and fruit-firmness loss and a hypothesis on the inheritance of the SMF character are discussed.     

Effect of simultaneous down-regulation of pectate lyase and endo-β-1,4-glucanase genes on strawberry fruit softening

Strawberry is a soft fruit with a short postharvest shelf-life. The loss of fruit firmness during ripening is mainly due to the disassembly of parenchyma cell walls mediated by the expression of genes encoding enzymes acting on pectins, such as pectate lyase, or hemicellulose, e.g. endo-β-1,4-glucanase. To determine if the simultaneous down-regulation of FaplC and FaEG3 genes, encoding a pectate lyase and a endo-β-1,4-glucanase, respectively, exerted an additive effect on strawberry softening, transgenic plants expressing tandem antisense sequences of both genes under the control of the constitutive promoter CaMV35S were generated. Fifteen independent transgenic lines were obtained and fruit yields and several quality parameters of transgenic ripe fruit were recorded during two consecutive years. Fruit yield was reduced in most of the lines, especially in the first evaluation period, and five out of 15 lines (33 %) did not set fruit. The expression of FaplC and FaEG3 genes was measured in ripe fruits from six selected lines showing the highest fruit yields. All selected lines showed a high level of FaplC gene silencing, ranging from 97 to 71 %; however, FaEG3 gene expression was only significantly down-regulated in two lines. Fruit colour and soluble solids contents were similar in control and transgenic ripe fruits, while fruit weight was slightly lower than control in some of the lines. In all lines, transgenic fruits were significantly firmer than control, with an increase in firmness ranging from 19 to 32 %. The reduction of fruit softening in transgenic fruits was not correlated with the suppression of FaEG3 gene expression, and lines with the highest simultaneous down-regulation of FaplC and FaEG3 showed similar fruit firmness to lines where only FaplC was suppressed. These results indicate that pectate lyase and endo-β-1,4-glucanase do not act in an additive or synergistic way during strawberry softening, and question the role of glucanases in this process.     

Effect of 1-MCP and low-temperature storage on postharvest conservation of camu–camu

Camu–camu, a native fruit from the Amazon region, is a rich source of bioactive compounds. However, its intense metabolic activity and high-water content limit the fruit’s postharvest storage and marketing. The aim of this study, conducted in two parts, was to evaluate the effects of 1-MCP and storage temperature on the physiology and postharvest preservation of camu–camu fruit. In part 1 of the study, fruit harvested at maturity stage 3 were divided into groups: control, 1-methylcyclopropene (1-MCP; 900 nL L^?1; 12 h) and ethylene (1000 µL L^?1; 24 h) and were stored at 22?±?1 °C and 85?±?5% RH for 9 days. In part 2, fruit harvested at maturity stage 3 were stored at 5, 10, 15, 20, or 25?±?1 °C and 85?±?5% RH for 9 days. During storage, fruit were evaluated daily for decay, mass loss, respiratory activity, and ethylene production, and every 3 days they were evaluated for peel color, pulp firmness, soluble solids content, total titratable acidity, ascorbic acid, total chlorophyll, and total anthocyanins. Fruit treated with 1-MCP exhibited delayed ripening due to lower metabolic activity, as evidenced by delay to softening, reduced mass loss and no decay. Storage at 5 °C prevented ethylene production, mass loss, color changes, and maintained pulp firmness, while did not affect soluble solids content. The results indicated that storage of camu–camu fruit at 5 °C or at 25 °C following application of 900 nL L^?1 1-MCP were effective strategies to delay ripening and maintain fruit quality up to 9 days.     

Expression of expansin genes in strawberry varieties with contrasting fruit firmness.

Fruit softening is associated with cell wall disassembly mediated by the action of a complex set of enzymes and proteins. Expansins, a group of proteins with unknown enzymatic activity, are proposed to be involved in this process. In order to study the involvement of expansins in strawberry fruit softening we have analyzed the expression level of five expansin mRNAs (FaEXP1, FaEXP2, FaEXP4, FaEXP5 and FaEXP6) in the cultivars "Selva", "Camarosa" and "Toyonaka", which differ in fruit firmness during ripening. We have found a correlation between mRNA expression levels and fruit firmness for FaEXP1, FaEXP2 and FaEXP5. For these three mRNAs we have observed higher expression levels in the softest cultivar (Toyonaka) than in the other two firmer cultivars (Selva and Camarosa) at the beginning of ripening. This correlation was not found in the case of FaEXP4 and FaEXP6, although both genes displayed a different expression pattern in the three cultivars analyzed. Western-blot analysis revealed that the accumulation of expansin proteins begins earlier in the softest cultivar during ripening.     

Low temperature alters plasma membrane lipid composition and ATPase activity of pineapple fruit during blackheart development

Plasma membrane (PM) plays central role in triggering primary responses to chilling injury and sustaining cellular homeostasis. Characterising response of membrane lipids to low temperature can provide important information for identifying early causal factors contributing to chilling injury. To this end, PM lipid composition and ATPase activity were assessed in pineapple fruit (Ananas comosus) in relation to the effect of low temperature on the development of blackheart, a form of chilling injury. Chilling temperature at 10 °C induced blackheart development in concurrence with increase in electrolyte leakage. PM ATPase activity was decreased after 1 week at low temperature, followed by a further decrease after 2 weeks. The enzyme activity was not changed during 25 °C storage. Loss of total PM phospholipids was found during postharvest senescence, but more reduction was shown from storage at 10 °C. Phosphatidylcholine and phosphatidylethanolamine were the predominant PM phospholipid species. Low temperature increased the level of phosphatidic acid but decreased the level of phosphatidylinositol. Both phospholipid species were not changed during storage at 25 °C. Postharvest storage at both temperatures decreased the levels of C18:3 and C16:1, and increased level of C18:1. Low temperature decreased the level of C18:2 and increased the level of C14:0. Exogenous application of phosphatidic acid was found to inhibit the PM ATPase activity of pineapple fruit in vitro. Modification of membrane lipid composition and its effect on the functional property of plasma membrane at low temperature were discussed in correlation with their roles in blackheart development of pineapple fruit.     

Calcium nitrate delays climacteric of persimmon fruit

Calcium nitrate (20 g litre^?1) delayed persimmon (Diospyros kaki) ripening on the tree and also reduced postharvest fruit deterioration when applied prior to fruit colour break. The magnitude of the response depended on the date of treatment. Application made one month prior to the peak of estimated commercial harvest was the most efficacious, and colour development, fruit softening and ethylene production were significantly retarded by the treatment. At harvest, there was no effect on fruit size or soluble solids content. Although there was a tendency for the content of soluble solids and fruit firmness to decrease with storage period, firmness of treated fruit was maintained.     

Low temperature storage effects on two olive fruit fly parasitoids

Effects of cold storage temperatures and storage duration were evaluated for Psyttalia humilis (Silvestri) from Namibia and Psyttalia ponerophaga (Silvestri) from Pakistan, braconid parasitoids of Bactrocera oleae (Rossi) imported to California, USA. Immature stages of P. humilis were exposed to 4, 6, 8, 10, or 12 °C for 1, 2 or 4 months (pupa only at 4 and 12 °C) and then held at 24 °C for adult emergence. Less than 5 % of parasitoids in the 4–8 °C treatments survived, regardless of storage duration. At the 10 °C treatment, adult survival decreased with increased storage duration, but increased with advancing developmental stages. Survival was not affected at the 12 °C treatment. Adult P. humilis were exposed to 6, 8, 10 °C for short periods (1, 2, 4, or 6 weeks) or ambient winter conditions in Parlier, California, USA (about 9 °C). Regardless of storage temperature, P. humilis reproduction was reduced after storage of four and six weeks. Similarly, after 4 months at ambient winter temperatures, P. humilis reproduction was reduced. Psyttalia ponerophaga pupae stored at 6 °C for 41–97 days had decreased survival and increased developmental time. Survival of P. ponerophaga pupae ranged from 13.9–52.1 %, whereas under similar storage conditions survival of P. humilis was <0.7 %, suggesting P. ponerophaga is more cold tolerant than P. humilis.     

采后两种不同果肉类型油桃软化相关酶活性的变化

以软质油桃“秦光”和非软质油桃“阿姆肯”为原料,研究了果实软化过程中果实硬度和果实软化相关酶活性变化。在果实硬度迅速下降期淀粉酶和蔗糖酶活性较高,以后酶活性下降。纤维素酶多聚半乳糖醛酸酶在果实软化前期活性很低,只在要果实呼吸跃变期这两种酶活性才明显升高。果胶果酯酶活性极低而且变化不大。“秦光”油桃的这几种酶酶活化性“阿姆肯”高,因而果实软化较快。