Climacteric and non-climacteric behavior in melon fruit: 2. Linking climacteric pattern and main postharvest disorders and decay in a set of near-isogenic lines

A set of near-isogenic lines (NILs) of melon (Cucumis melo L.) was used to test the relationship between the climacteric pattern and postharvest disorders at harvest and after 30 days at 8 °C. The NILs contained different chromosome introgressions in the linkage group III from the non-climacteric exotic Korean accession PI 161375 transferred into the genetic background of the non-climacteric Spanish cultivar ‘Piel de Sapo’ (PS). A quantitative trait locus (QTL) in this linkage group induced climacteric behavior in eight NILs accompanied by a peak of ethylene production and fruit dehiscence to different degrees. The cultivar ‘Nicolás’ and one NIL showed a non-climacteric pattern of respiration rate and ethylene production. The climacteric NILs were used to test the relationship between this pattern and postharvest disorders. The reference climacteric lines ‘Fado’ and ‘Védrantais’ were more sensitive to CI and associated Cladosporium rot than the NILs or PS. In general, a more intense climacteric behavior was accompanied by fruit dehiscence, and higher total losses and greater skin scald after storage, than in PS. A higher incidence of chilling injury (CI) in the climacteric NILs was found compared with the non-climacteric ones, although with exceptions (one NIL for CI in the form of scald; the same NIL and one more for pitting). The climacteric onset and netting scald were not related, and CI in the form of skin spots was only found in climacteric NILs and was positively correlated with the maximum peak of ethylene production. Some climacteric NILs did not follow the rule of a higher susceptibility to other disorders and decay after storage compared with PS, such as for example in fruit over-ripening (detected externally or internally), Cladosporium rot at the peduncle and Alternaria rot. Mealiness was independent of climacteric behavior. Three climacteric NILs obtained better flavor scores after storage than PS, although the maximum peak of ethylene production was positively correlated with off-flavor. Genotypic correlation between disorder data and the physiological data of climacteric fruit revealed positive (flavor index) or negative postharvest consequences (skin injuries, rots or off-flavors). At least one QTL can be assigned to most of the quality traits analyzed.     

Effect of postharvest ethylene treatment on carotenoid accumulation and the expression of carotenoid biosynthetic genes in the flavedo of orange (Citrus sinensis L. Osbeck) fruit

Degreening with ethylene is a common postharvest practice in citrus fruit. In this work we have examined the effect of ethylene treatment on carotenoid content and composition, and on the expression of carotenoid biosynthetic genes in the flavedo of Navelate orange (Citrus sinensis L.) harvested at two ripening stages. The ethylene-induced fruit coloration and carotenoid content in the flavedo increased with the ripening stage of the fruit. Analysis of the changes in individual carotenoids revealed that ethylene stimulated an increase in phytoene, phytofluene, (9Z)-violaxanthin which is the main carotenoid in fully ripened orange peel, and the apocarotenoid β-citraurin, and decreased the concentration of chloroplastic carotenoids. These changes are consistent with the effect of ethylene on the expression of carotenoid biosynthetic genes, since it up-regulated the expression of phytoene synthase, ζ-carotene desaturase and β-carotene hydroxylase genes, sustained or transiently increased accumulation of phytoene desaturase, plastid terminal oxidase, β-lycopene cyclase and zeaxanthin epoxidase mRNAs, and decreased the expression of the ɛ-lycopene cyclase gene. These data indicate that exogenous ethylene reproduces and accelerates the physiological and molecular changes in the carotenoid biosynthesis naturally occurring during maturation of citrus fruit. On the other hand, gibberellic acid, which delays fruit degreening, reduced the ethylene-induced expression of early carotenoid biosynthetic genes and the accumulation of phytoene, phytofluene and β-citraurin.     

Detached ripening of non-climacteric strawberry impairs aroma profile and fruit quality

Climacteric fruit show an autocatalytic burst in ethylene production during ripening and are therefore able to ripen detached from the plant. This detached ripening of climacteric fruit is a unique feature that is widely exploited by the postharvest industry. Non-climacteric strawberry on the other hand, ripens without the autocatalytic ethylene response. Surprisingly, we found that strawberry was capable of ripening after detachment at the green stage. This apparent ripening process was studied by comparing ethylene production and multiple fruit quality traits between strawberries that ripened on the vine versus detached. Our findings show that ethylene production is hardly influenced by the dissimilar ripening conditions, yet fruit quality is heavily affected. Importantly, detached strawberries did not reach the same fruit mass, lowering the market value of the detached ripened fruit. Furthermore, sugar and acid analysis showed that detached strawberries have a low malic acid, glucose, fructose and sucrose content compared to fruit ripened on the vine, indicating that a continuous supply of photosynthesis assimilates, water and nutrients by the plant is essential for normal fruit ripening. The unique aroma of strawberries was also heavily altered in detached ripened fruit. Detached strawberries had a lower abundance of most volatile compounds, except for alcohols, resulting in less intense aroma and unwanted off-flavors. It can be concluded that detached ripened strawberries are of inferior quality compared to normal vine-ripened strawberries and are unsuitable for marketing.     

Browning disorders in pear fruit

Disorders occurring during long-term storage of pears can cause economic loss, especially when disordered fruit cannot be distinguished externally from sound fruit. A typical category of disorders in pear fruit is related to internal browning of the flesh and the presence of cavities. In this review, information which appeared in the literature in the last decade has been integrated into a generic model for the development of storage-related browning disorders in pear. In this model it is assumed that browning disorders are caused by an imbalance between oxidative and reductive processes due to metabolic gas gradients inside the fruit, leading to an accumulation of reactive oxygen species. The latter may induce loss of membrane integrity which becomes macroscopically visible through the enzymatic oxidation of phenolic compounds to brown coloured polymers. The development of disorders during postharvest ripening and storage of fruit also depends on a range of preharvest factors such as climate conditions and crop load. Methods to evaluate the incidence of browning disorders nondestructively have been reviewed.     

Climacteric or non-climacteric behavior in melon fruit: 1. Aroma volatiles

A near-isogenic line (NIL) SC3-5 and a further nine NILs of melon contained introgressions of an exotic non-climacteric accession of Cucumis melo ‘Shongwan Charmi’ [SC (PI 161375), Conomon Group)] into the non-climacteric Spanish Inodorus type of melon cultivar ‘Piel de Sapo’ (PS). The NILs exhibited different climacteric behavior and aroma. Fruit from SC3-5 and seven NILs showed a climacteric pattern, while fruit from one NIL, both parentals and the cultivar ‘Nicolás’, were non-climacteric. The NILs were compared with the reference aromatic cultivars ‘Fado’ and ‘Védrantais’, which show climacteric behavior with high levels of respiration and ethylene production. The twenty-eight aromatic compounds common to the cultivars and NILs studied defined the aroma profile, which was composed of fifteen esters, six aldehydes, two alcohols, three derived sulfur compounds (methyldisulfanylmethane; methanethiolate; methyl 2-sulfanylacetate) and other three compounds (1,7,7-trimethylnorbornan-2-one; acetone; 2-ethylfuran). On the basis of the total ion count peak area, three compounds (isobutyl acetate; benzyl acetate; pentanal) allowed the climacteric to be distinguished from the non-climacteric NILs according to univariate analysis. Multivariate analysis of the aroma data on the basis of total ion count peak area separated the aromatic attributes of the climacteric ‘Védrantais’ and ‘Fado’ melons from the NILs that were closer to their inbred parentals when analyzed by partial least squares regression plus discriminant analysis. In the climacteric reference cultivars or NILs, esters were the predominant volatiles while aldehydes predominated in non-climacteric ones. These results support the hypothesis that at least one QTL in linkage group III boosts a series of maturation signals that are characteristic of climacteric fruit, including a different aroma profile.     

Influence of time from harvest to 1-MCP treatment on apple fruit quality and expression of genes for ethylene biosynthesis enzymes and ethylene receptors

A strong potent inhibitor of ethylene action, 1-methylcyclopropene (1-MCP) maintains apple fruit quality during storage. To understand the influence of time after harvest until 1-MCP treatment, we studied expression patterns of genes for ethylene biosynthesis enzymes and ethylene receptors in two apple cultivars, ‘Orin’ and ‘Fuji’, which differ in ethylene production. Ethylene production and expression of MdACS1, MdERS1, and MdERS2 were suppressed in all 1-MCP-treated ‘Fuji’ fruit, but in ‘Orin’, the later 1-MCP was applied after harvest, the less was the suppression of ethylene production and expression of these genes. In fruit in which 1-MCP had low efficacy (e.g., ‘Orin’ treated at 7 DAH), ethylene production and the level of MdERS1 were briefly reduced by 1-MCP treatment at 2 days after treatment, then began to increase. Since ethylene receptors negatively regulate the ethylene signalling pathway, the increased levels of ethylene production and ethylene receptors after 1-MCP treatment might reduce 1-MCP efficacy.     

Genomics of pear and other Rosaceae fruit trees

The family Rosaceae includes many economically important fruit trees, such as pear, apple, peach, cherry, quince, apricot, plum, raspberry, and loquat. Over the past few years, whole-genome sequences have been released for Chinese pear, European pear, apple, peach, Japanese apricot, and strawberry. These sequences help us to conduct functional and comparative genomics studies and to develop new cultivars with desirable traits by marker-assisted selection in breeding programs. These genomics resources also allow identification of evolutionary relationships in Rosaceae, development of genome-wide SNP and SSR markers, and construction of reference genetic linkage maps, which are available through the Genome Database for the Rosaceae website. Here, we review the recent advances in genomics studies and their practical applications for Rosaceae fruit trees, particularly pear, apple, peach, and cherry.     

灌溉方式对地表蒸发和梨果实发育的影响

为了解决地面灌溉中灌溉水利用效率低、果实品质差的问题,于2013年在河北工程大学永年校区以5年生田间梨树为试材,研究不同地面灌溉方式对土壤水分含量、地表蒸发量、梨产量与品质的影响。4种地面灌溉方式包括沟灌、畦灌、覆草畦灌和覆草非灌溉。测定不同处理的土壤含水量、地表蒸发量和果实品质。结果表明,不同灌溉方式的土壤含水量差异显著,覆草畦灌和沟灌显著高于畦灌和覆草非灌溉处理。覆草畦灌和沟灌较畦灌可显著减少地表的蒸发量,覆草非灌溉、覆草畦灌、沟灌和畦灌3—8月的累积地表蒸发量分别是77.92、114.64、163.1、203.73 mm。沟灌的灌溉水利用效率为1.99 kg/m3,显著大于覆草畦灌和畦灌,分别提高了1.45、1.06 kg/m3。沟灌显著提高了果实的单果重、可溶性固形物含量、总糖含量和维生素C含量。综上,沟灌既能减少地表蒸发又能提高果实产量和品质,是当前较好的地面灌溉方式。     

Postharvest quality of peeled prickly pear fruit treated with acetic acid and chitosan

White (Opuntia albicarpa) and red (Opuntia ficus-indica) prickly pears were peeled and submerged in chitosan solutions containing different concentrations of acetic acid (1.0 or 2.5%) to obtain ready-to-eat prickly pear products. Some physicochemical (pH, total soluble solids, color, weight loss, and firmness), antioxidant (phenolic compounds and antioxidant activity), microbiological (aerobic mesophile bacteria and yeasts plus molds), and sensory (color, firmness, aroma, flavor, and overall acceptance) characteristics were assessed during 16 d of storage at 4 ± 1 °C and 85 ± 5% of relative humidity. Chitosan coating containing 1.0% of acetic acid delayed weight loss, maintained firmness and color of white prickly pear during the storage time. Most of the sensory values for white prickly pear coated with chitosan containing 1.0 and 2.5% of acetic acid were higher than those obtained for uncoated fruit. Red prickly pear coated with chitosan with 2.5% acetic acid did not maintain its sensory quality throughout 16 d of storage. Chitosan coating with 1 and 2.5% acetic acid did not affect phenolics content and antioxidant activity in white prickly pears; however, an increase of these compounds was observed in red prickly pears. Microbe populations were unchanged in white prickly pears (<10 CFU g⁻¹) and slightly increased in red prickly pears (10–500 CFU g⁻¹) coated with chitosan during the entire storage time.     

Differential fruit gene expression in two strawberry cultivars in response to elevated CO2 during storage revealed by a heterologous fruit microarray approach

The use of a heterologous fruit microarray system to identify differentially expressed genes between strawberry cultivars with different responses to 20 kPa CO₂ (balance air) during storage has been evaluated. Specifically, a tomato cDNA microarray containing approximately 12,000 ESTs (representing 8700 unigenes) was hybridized with strawberry cDNA populations to compare gene expression differences between two cultivars: ‘Jewel’, a cultivar that accumulates acetaldehyde and ethanol in response to elevated CO₂ during storage, and ‘Cavendish’ that does not accumulate these compounds under the same storage conditions. A set of 80 tomato gene sequences gave differential hybridization signals between the two strawberry cultivar probes when they were stored in CO₂ for 48 h, suggesting homologous strawberry genes with differential expression. Within each cultivar, when RNA from fruit stored in air was compared with that from fruit stored in CO₂, 168 sequences suggested differential expression in ‘Jewel’, but only 51 were differentially expressed in ‘Cavendish’ fruit. Strawberry genes with putative homologies to enzymes involved in cell wall metabolism, ethylene action and stress were implicated by the tomato array. This research not only demonstrates the usefulness of using a heterologous microarray platform from a model species (tomato) to study a complex process in strawberry, a crop of economic importance, for which genomic resources are still limited, but also provides a foundation for investigating the molecular basis of responses to elevated CO₂ during strawberry postharvest storage.