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Mingjun Li, Xuesen Chen, Pingping Wang, and Fengwang Ma

The objective of this study was to investigate ascorbic acid (AsA) accumulation, mRNA expression of genes involved in AsA biosynthesis as well as recycling, activity of key enzymes, and the relationship of them to AsA levels during the development of apple fruit (Malus ×domestica cv. Gala). AsA concentration, which mainly depends on biosynthesis, was the highest in young fruit post-anthesis and then decreased steadily toward maturation. However, AsA continued to accumulate over time because of the increase in fruit mass. Transcript levels of guanosine diphosphate (GDP)-L-galactose phosphorylase, GDP-mannose pyrophosphorylase, D-galacturonate reductase, and the post-transcriptionally regulated L-galactono-1,4-lactone dehydrogenase were not correlated with AsA accumulation in apple. In contrast, patterns of expression for L-galactose dehydrogenase, L-galactose-1-phosphate phosphatase, and GDP-mannose-3′,5′-epimerase showed a pattern of change similar to that of AsA accumulation. Although activities and expression levels of monodehydroascorbate reductase and dehydroascorbate reductase in fruit, which had less capacity for AsA recycling, were much lower than in leaves, they were not clearly correlated with AsA level during fruit development.

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Chunyu Zhang, Xuesen Chen, Hongwei Song, Yinghai Liang, Chenhui Zhao, and Honglian Li

Volatile compounds have a tremendous impact on fruit quality. We evaluated the volatile compound profiles of ripening wild apple fruit (10 Malus baccata accessions and three Malus prunifolia accessions) in the National Field Genebank for Hardy Fruits at Gongzhuling, China. Alcohols, esters, aldehydes, terpenes, hydrocarbons, ethers, heterocycles, carboxylic acids, and ketones were detected in the M. baccata and M. prunifolia fruit, with the first four being the main volatile compounds present. Of the 92 volatiles detected, esters were the most diverse (49 compounds). This wide range of abundant volatile compounds suggests that M. prunifolia is a good resource for breeding apple cultivars with novel and interesting flavors. The M. baccata accession ‘Zhaai Shandingzi’ and the M. prunifolia accession ‘Bai Haitang’ had the widest range of volatile compounds and the highest volatile compound contents of the accessions examined, and will therefore be good breeding materials for developing commercial lines with enhanced flavor and for widening the genetic diversity. The number of different ester compounds present was significantly positively correlated (r = 0.877) with the cube root of the weight of an individual ripe fruit. Principal component analysis (PCA) showed that the contents of ester compounds could be used to distinguish between M. baccata and M. prunifolia species. Therefore, ester compounds could be used as a reference of parental choice in apple breeding.

Open access

Ran Chen, Weitao Jiang, Haiyan Wang, Fengbing Pan, Hai Fan, Xuesen Chen, Xiang Shen, Chengmiao Yin, and Zhiquan Mao

Apple replant disease (ARD) has been reported in all major fruit-growing regions of the world and is often caused by biotic factors (pathogen fungi) and abiotic factors (phenolic compounds). Soil chemical fumigation can kill soil pathogenic fungi; however, the traditionally used fumigant methyl bromide has been banned because of its ozone-depleting effects. There is thus a need to identify greener fumigant candidates. We characterized the effects of different fumigants on the replanted soil environment and the growth characteristics of Malus hupehensis Rehd. seedlings. All five experimental treatments [treatment 1 (T1), metham-sodium; treatment 2 (T2), dazomet; treatment 3 (T3), calcium cyanamide; treatment 4 (T4), 1,3-dichloropropene; and treatment 5 (T5), methyl bromide] promoted significantly the biomass, root growth, and root respiration rate of M. hupehensis seedlings and the ammonium nitrogen (NH4 +-N) and nitrate nitrogen (NO3 -N) contents of replanted soil. Metham sodium (T1) and dazomet (T2) had stronger effects compared with 1,3-dichloropropene (T4) and calcium cyanamide (T3). At 172 days after T1, the height, root length, and root respiration rate of Malus hupehensis Rehd. seedlings, and the NH4 +-N and NO3 -N contents of replanted soil increased by 91.64%, 97.67%, 69.78%, 81.98%, and 27.44%, respectively, compared with the control. Thus, dazomet and metham sodium were determined to be the optimal fumigants for use in practical applications.