Magnesium accelerates changes in the fruit ripening and carotenoid accumulation in Satsuma Mandarin pulp

Biocontrol ability and possible mechanism of Metschnikowia pulcherrima against major diseases of postharvest citrus fruit and its biopreservative application

The capability of Metschnikowia pulcherrima to control postharvest citrus diseases was analyzed, with its action mechanisms and preservation performance during storage further explored. In vitro and in vivo tests demonstrated M. pulcherrima significantly inhibited the growth of Penicillium digitatum (P.d), Penicillium italicum (P.i), and Geotrichum citri-aurantii (G.c), and markedly controlled the incidence and progression of these three postharvest diseases. The non-cellular components of M. pulcherrima did not significantly inhibit three pathogens' growth, while its volatile compounds (VOCs) displayed notable inhibitory effects. Moreover, M. pulcherrima exhibited no parasitic effects on the mycelia of three pathogens. Nutritional competition experiment revealed that M. pulcherrima outcompeted the pathogens, utilizing fructose and glucose more rapidly and efficiently in nutrient-poor fruit wounds. Additionally, M. pulcherrima demonstrated a rapid proliferation and colonization ability on citrus fruit wounds and exhibited biofilm formation, thereby effectively preventing pathogen from contacting the fruit. Iron competition experiments indicated that exogenous FeCl3 significantly reduced M. pulcherrima's antifungal activity against P.d, P.i, and G.c, and its diseases control efficacy. Induced resistance tests demonstrated that M. pulcherrima significantly enhanced citrus fruit resistance to three diseases, with a particularly strong effect against sour rot. Storage tests over 180 d revealed that M. pulcherrima treatment significantly decreased the natural decay rate and maintained the quality indicators of citrus fruits. Overall, M. pulcherrima presented considerable potential as a biocontrol agent for effectively managing postharvest diseases in citrus fruits.

Changes in Bioactive and Physicochemical Composition of Rubus During Three Developmental Stages

Blackberries, underexploited wild fruits, are not widely recognized by the general population. Maturation in berries (Rubus ulmifolius) modifies their quality attributes, hence, this study aimed to examine the variations in physicochemical, phytochemical, antioxidant properties and minerals of the berries at the three maturity stages viz., unripe, half-ripe and full ripe. The results indicated an increase in TSS from 7.0 to 10.5 °B, moisture content from 80 to 86%, vitamin C from 19.0 to 27.50 (mg/100 g FW), sugars from 5.40 to 9.30% and anthocyanins from 69.72 to 139.44 (mg/100 g FW), while acidity from 1.21 to 0.33% citric acid, ash from 1.68 to 0.84%, total phenolic content 1021.0 to 875.0 (mgGAE/100 g FW), total flavonoid content from 372.30 to 274.30 (mgQE/100 g FW), decreased with the advancement of maturity from unripe to full ripe. Antioxidant activity measured through DPPH and FRAP assays, increased from 86.3 to 92% inhibition and 172.30 to 226.06 µmol Fe2+/g (FW), respectively. Gallic acid, quercetin decreased from 737.14 to 107.14, 953.35 to 364.80 (mg/kg FW), respectively, while cyanidin-3-glucoside and 3,4-dihydroxy benzoic acid values increased from 3.67 to 27.27, 43.46 to 101.70 (mg/kg FW), respectively. Rutin and vanillic acid, were not detected in the early stages of maturation but were later detected in the full ripe stage of Rubus, with concentrations of 16.82, 2.66 (mg/kg FW), respectively. The study highlights ripening induced changes in physicochemical properties and bioactive compounds of blackberries with half ripe stage possessing better quality attributes to be further used for food applications.

Microbial and organic manure fertilization alters rhizosphere bacteria and carotenoids of Citrus reticulata Blanco 'Orah'

BACKGROUND

Citrus reticulata Blanco 'Orah' is one of the most widely grown citrus varieties in southern China. It has been proven that microbial and organic manure fertilization improve the yields and appearances of 'Orah' fruits. However, details regarding the mechanisms underlying the effects of combined fertilization on the agronomic traits and rhizosphere bacterial community of plants still need to be elucidated.

RESULTS

This study compared the rhizosphere bacterial community and carotenoids of 'Orah' with (WYT group) and without (WYCK group) combined fertilization in a local orchard in Wuming town from Nanning, Guangxi, China. The WYT group was sprayed with 50 ml Strongreen and 250 g of Yumeiren five times while WYCK group did not sprayed. Combined fertilization increased fruit weight and the Citrus color index (CCI) significantly (p < 0.05). By 16s rRNA sequencing, 7,126 operational taxonomic units (OTU) were obtained. A higher Shannon index was observed in the WYT group compared to that in the WYCK group. Comparison between the two groups showed that Pseudomonas was enriched in the WYT group with LDA (log10) score of 4.32, and Cyanobacteria was enriched in the WYCK group with LDA (log10) score of -4.11. At the family level, Phyllobacteriaceae (abundance mean: 0.0046 in WYCK vs. 0.0073 in WYT) was significantly abundant in the WYT group, whereas Thermosporothrix (abundance mean: 0.00053 in WYCK vs. 0.0019 in WYT) and Sphingobium (abundance mean: 0.00053 in WYCK vs. 0.0013 in WYT) were significantly abundant in the WYCK group. A total of 51 carotenoid components were tested by UPLC-MS/MS. In the pulp tissues, 37 carotenoid components were decreased in the WYT group compared to those in the WYCK group. In fruit skin, 24 significantly different components (7 downregulated and 17 upregulated) were identified in WYT compared to those in WYCK. Correlation analysis revealed that the network between OTUs and carotenoids contained seven carotenoid components and four OTUs. Four OTUs, strain TRA3-20 (a eubacterium), Roseiflexus, OPB35, and Fictibacillus correlated to carotenoid accumulation regulation in fruit skin.

CONCLUSIONS

This study demonstrates the impact of the fertilization on soil microorganisms and carotenoid components. It constructs the regulatory network contained four OTUs for seven carotenoid components, providing evidence on precise fertilization in Orah.