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Cork spot is a common physiological disorder in pear fruits, which has been found in some pear cultivars. Mineral nutrition imbalance in fruit is regarded as the principal influence factor for disorder incidence, with some ongoing confusion and controversy. In our research, we explored the cork spot characteristics in Japanese pear 'Akizuki' (Pyrus pyrifolia Nakai), adopted metabolome and mineral content analysis for healthy and disordered fruits, and made a correlation analysis of mineral and metabolites. Cork spots are mainly distributed on the outer flesh beneath the fruit peel. In cork spotted tissues, superoxide (SOD) and peroxidase (POD) activities, as well as malondialdehyde (MDA) content, increased. A total of 1024 known metabolites were identified from all the samples and more changes in metabolism were detected between normal and cork spotted flesh tissues. Correlation analysis displayed that Ca, especially the Mg/Ca in fruits, could be used to predict whether an orchard will develop cork spot disorder; Mg and B were associated with the appearance of symptoms, and the contents of Zn, Fe, and Mg, as well as Mg/B and Zn/B, might be strongly tied to the formation of cork spots in pears. This research provides insights into the occurrence of pear cork spot disorder and clarifies the role of minerals. [ABSTRACT FROM AUTHOR]

The hard-end of pear fruit might be a disorder of the environmental abiotic stress, which is mainly caused by the reduced water intake of the fruit resulting from climate drought. To explore the factors that cause fruit hard-end, two rootstocks of Pyrus betulaefolia and P. bretschneideri with different root absorptive capacity of water and nutrients were used as base stock of 'Whangkeumbae' (P. pyrifolia) pear fruit. The results showed that the incidence of hard-end fruit in 'Whangkeumbae' pear trees using rootstock with lower rate of water absorptive increased, indicating that this physiological disorder was related with water deficiency. PpNAC187 was selected from RNA-Seq carried out on the calyx end of with and without the hard-end symptom of different rootstocks. The transgenic tobacco overexpressing PpNAC187 showed higher tolerance with drought and salt stress, which might suggest that PpNAC187 acts an important role during the hard-end occurring caused by drought or salt stress. [ABSTRACT FROM AUTHOR]

Fruit pedicel is the bridge linking the parent tree and the fruit, which is an important channel for water and nutrients transport to the fruit. The genetic specificity determines the characteristics of the pedicel and the fruit, but the relationship between the pedicel structure and the fruit characteristics is unexplored. Combining the investigation of fruit characteristics, the statistical analysis of the pedicel structural properties, and the 2D and 3D anatomical observation of the pedicel, this study found distinctive contributions of the pedicel elements to the fruit characteristics in four pear species. The European pear (Conference) showed distinct fruit shape index and pedicel structural properties compared with the oriental pears (Akizuki, Yali, and Nanguoli). The fruit size positively correlated with pedicel length, fiber area, pedicel diameter, the area percentage of the cortex, and the area percentage of phloem; however, fruit firmness and soluble solids concentration are showed a stronger positive correlation with xylem area, pith area, the area percentage of xylem, the area percentage of sieve tube, and the area percentage of pith. Pedicel elements, including pith, fiber, and cortex, likely play a certain role in the fruit growth due to the variations of their characteristics demonstrated in the four pear species. The porosity, the ratio of the surface area to the volume, and the spatial arrangement of the vessels showed significant variations across the pear species, indicating the distinction of the hydraulic conductance of the pedicels. Our findings provided direct evidence that pedicel structural elements contributed distinctively to the fruit characteristics among pear species. [ABSTRACT FROM AUTHOR]

The utilisation of interstocks or rootstocks to reduce tree size has long been used in orchards. In the present study, we characterised the dwarfing effect of "OHF51" (Pyrus communis "Old Home" × "Farmingdale") when used as interstock compared with callery pear (Pyrus calleryana Decne.). Shorter trees, smaller canopy, smaller trunk diameter and lower height of the first branch were found in trees with "OHF51" as the interstock as compared to callery pear. Metabolome analysis showed that the interstock altered the metabolite profiles of both the scion and the rootstock. The number of identified differential metabolites in scions, interstocks and roots were 8, 39 and 12, respectively, with "OHF51" interstock as compared to the same positions with callery as the interstock. Flavonoids and phenolic acids/derivatives were most altered in concentration. The concentrations of flavonoids procyanidin B2 and procyanidin B3 were remarkably higher in both the scion shoots and the interstock because of "OHF51," while the concentration of two monosucroses, D‐sorbitol and D‐mannitol, were drastically reduced in roots with "OHF51" interstock present. The reallocation of carbohydrates from shoot to root could be influenced by the interstock, which participates in the regulation of scion growth in the spring season. Flavonoids and phenolic acids/derivatives are understood to be key compounds involved in the reduction of scion growth. "OHF51" (Pyrus communis "Old Home" × "Farmingdale") could reduce the scion growth as an interstock in pear trees by altering the metabolite profiles. Flavonoids and phenolic acids/derivatives are key compounds involved in the reduction of scion growth. [ABSTRACT FROM AUTHOR]

'Akituki' (Pyrus pyrifolia Nakai.) is a very popular and profitable pear cultivar in China. However, its high susceptibility to cork spot disorder has limited its expansion of cultivated area. The mechanisms of cork spot disorder have been discussed extensively, focusing on Ca2+ deficiency, yet no consensus has been made. In this study, we applied nitrendipine (NI) as a Ca2+ uptake inhibitor to explore the role of calcium in cork spot disorder occurrence. Results showed that NI treatment on the fruit remarkably increased the incidence of cork spot disorder; alteration of mineral contents happened at the early developmental stage of the fruit, especially on the outer flesh and the peel of the fruit; and this gap was filled gradually along with the expansion of the fruit. Significant differences in the expression levels of Ca2+ transport-related genes were found in the inner flesh, outer flesh and peel during the fruit growth period. The observation of free Ca2+ localization indicated the intracellular imbalance of Ca2+ in the NI-treated fruit. In conclusion, NI treatment reduced the calcium content in the fruit at an early developmental stage, altered the related expression of genes and influenced the cellular Ca2+ balance in the fruit, which prompted the occurrence of cork spot disorder. Measures for the prevention and control of cork spot disorder should be taken at the early stage of the fruit development in the field. [ABSTRACT FROM AUTHOR]

A disorder in pears that is known as 'hard-end' fruit affects the appearance, edible quality, and market value of pear fruit. RNA-Seq was carried out on the calyx end of 'Whangkeumbae' pear fruit with and without the hard-end symptom to explore the mechanism underlying the formation of hard-end. The results indicated that the genes in the phenylpropanoid pathway affecting lignification were up-regulated in hard-end fruit. An analysis of differentially expressed genes (DEGs) identified three NAC transcription factors, and RT-qPCR analysis of PpNAC138, PpNAC186, and PpNAC187 confirmed that PpNAC187 gene expression was correlated with the hard-end disorder in pear fruit. A transient increase in PpNAC187 was observed in the calyx end of 'Whangkeumbae' fruit when they began to exhibit hard-end symptom. Concomitantly, the higher level of PpCCR and PpCOMT transcripts was observed, which are the key genes in lignin biosynthesis. Notably, lignin content in the stem and leaf tissues of transgenic tobacco overexpressing PpNAC187 was significantly higher than in the control plants that were transformed with an empty vector. Furthermore, transgenic tobacco overexpressing PpNAC187 had a larger number of xylem vessel elements. The results of this study confirmed that PpNAC187 functions in inducing lignification in pear fruit during the development of the hard-end disorder. [ABSTRACT FROM AUTHOR]

• Performance of X-ray CT in characterizing cork spot of pear fruit. • Larger pores formation closely correlates with the disorder of cork spot. • Pore network influences the cork spot disorder. • The feasibility of STL format 3D image analysis in the internal observation of cork spot disorder. Healthy and disordered fruit of Chinese 'Chili' (Pyrus bretschneideri Rehd.), a well-known pear cultivar in China, are used to investigate the cork spot disorder by non-destructive X-ray computed microtomography (μCT) scanning technology, with pixel resolution of 67-70 μm and scanning time of 60 min on intact fruit. The results suggested that X-ray μCT could clearly and accurately distinguish the internal organization, size and location of cork spot in the pear fruit. CT images showed that the spots mostly locate in the pulp tissue between the calyx end and the equator of disordered fruit, and usually within 14 mm below the pericarp. STL format 3D images had great potential to distinguish cork spotted fruit core from healthy one. In addition, total number of pores is strongly decreased while larger pores bigger than 900 μm are considerably increased in disordered fruit as compared to healthy fruit, which indicates that larger pores maybe formed by the extension and interconnection with adjacent pores of some small pores. Further analysis in pore skeleton-network shows that extremely higher porosity and highly branched, more connected and thicker pores are observed in cork spotted fruit than those in healthy fruit. In addition, the average length of the healthy pore throat is 160.08 μm, which is significantly smaller than that of disordered fruit (277.91 μm). Moreover, the coordination number of pores in cork spotted fruit is 2, while it is 0 in healthy fruit. All the above results indicate that X-ray μCT provides a new perspective to the non-destructive visualization, quantification and knowledge of the 3D image structure of pear fruit with cork spot, and it is highly essential for early diagnosis and further study of the pathogenic mechanism of this disorder. [ABSTRACT FROM AUTHOR]

• Mere Ca2+ concentration is not suggested as the cork spot biochemical marker. • Intracellular partitioning of Ca2+ is important to CSPD. • Ca2+ distribution inside the fruit is important to CSPD. Cork spot is one of the most damaging physiological disorders in pear. However, the mechanism of cork spot is unclear. Ca2+ deficiency is considered as the major agent to cork spot. In this study, we investigated cork spot characteristics in Chinese 'Chili' (Pyrus bretschneideri Rehd.) and analyzed the relationship between mineral elements alteration and cork spot occurrence. We found early initiation of cork spot disorder in 'Chili' at 80 days after full bloom (DAFB). Cork spot in disordered fruit mostly distributed around the fruit eye with necrotic and brown tissues at the spotted site in flesh. At harvest time, cork spot disordered fruit had a smaller size, higher firmness, lower titratable acidity, higher lignin and cellulose content than healthy fruit, while starch concentration was the same between disordered and healthy fruit. Differences of mineral elements content were also found in both leaves and fruits, and Ca2+ distribution was visualized to be concentrated inside cell wall in disordered fruit cells. Principal components analysis (PCA) of mineral elements data showed that fruit samples could be separated according to their healthy or disordered condition at 80 and 160 DAFB. However, no significant correlation was found between cork spot disorder and mineral elements data. Ca2+ concentration was not suggested as the cork spot biochemical marker in our study. At last, we hypothesized the relationship between cork spot occurrence and Ca2+ distribution in 'Chili' and summarized the factors probably contributing to Ca2+ deficiency disorder, which would be useful in designing orchard strategies against cork spot. [ABSTRACT FROM AUTHOR]