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Xingbin Xie, Congbing Fang and Yan Wang

Bosc is a winter cultivar of european pear (Pyrus communis) that has a relatively short storage life partially due to a high ethylene production rate (EPR) during cold storage. ‘Bosc’ pears were harvested at commercial maturity and treated with gas 1-methylcyclopropene (1-MCP) at 0, 0.15, and 0.3 µL·L−1 and stored at −1.1 °C for 8 months. Results indicated that all 1-MCP treatments inhibited EPR and respiration rate (RR), retarded the degradation of chlorophyll and titratable acidity (TA), and extended storage quality; but inhibited ripening capacity. 1-MCP at 0.15 and 0.3 µL·L−1 had the same efficacy on keeping fruit quality although its higher rate was more efficient on inhibiting EPR and RR. The expression of ethylene synthesis genes (PcACS1, PcACS2, PcACS4, PcACS5, and PcACO1) and receptor genes (PcETR1, PcETR2, and PcERS1) was upregulated in control fruit during storage and they were downregulated significantly by 1-MCP treatments. In contrast, the ethylene receptor genes of PcETR5 and PcCTR1 were downregulated in control fruit during storage and were unaffected by 1-MCP treatments. Although the transcription levels of chlorophyll degradation genes PcPPH, PcNOL, PcSGR, PcRCCR, PcNYC, and PcPAO were all upregulated in control fruit during storage and downregulated by 1-MCP; only PcCHL was downregulated in the control and 1-MCP had no consistent effect on it. The relationship of ethylene biosynthesis/perception with chlorophyll degradation and storage quality in european pears was discussed.

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Xingbin Xie, Todd Einhorn and Yan Wang

‘Starkrimson’ is a highly profitable red-skinned european pear (Pyrus communis) cultivar that has a short storage life due mainly to the development of a mealy texture upon ripening and an internal browning (IB) disorder during or after storage. In 2013, ‘Starkrimson’ pears were sprayed with aminoethoxyvinylglycine (AVG) at 0, 30, 60, and 120 mg·L−1 1 week before harvest or treated with 1-methylcyclopropene (1-MCP) at 0.3 µL·L−1 for 24 hours shortly after harvest, then stored at −1.1 °C and evaluated over a 16-week period. The experiment was repeated in 2014. After 2 weeks of storage, control fruit (nontreated) had a higher respiration rate and ethylene biosynthesis than AVG or 1-MCP-treated fruit. Following 12 weeks of storage, control fruit exhibited a greater incidence of mealy texture and greater extractable juice (EJ) after ripening, and by 16 weeks significantly higher IB relative to AVG and 1-MCP-treated fruit. AVG at 30 mg·L−1 had little effect on any of the storage responses measured compared with control. AVG at 60 mg·L−1 reduced ethylene synthesis, respiration rate, and titratable acidity (TA) loss and maintained high eating quality with low EJ. Fruit treated with 60 mg·L−1 AVG also developed markedly less IB following 16 weeks of storage than control or 30 mg·L−1 AVG treatments. AVG at 120 mg·L−1 did not improve storage quality achieved with 60 mg·L−1 but delayed ripening capacity by 1 month. 1-MCP markedly inhibited ethylene synthesis and respiration rate and eliminated IB during 16 weeks of storage; however, 1-MCP-treated fruit required 14 days at 20 °C to ripen to high eating quality following 12 to 16 weeks of storage compared with 5 days for 60 mgL−1 AVG. Both AVG and 1-MCP suppressed the expressions of ethylene synthesis (PcACS1, PcACS4, PcACS5, and PcACO1) and perception genes (PcETR1, PcETR2, and PcETR5) although 1-MCP was more efficient than AVG. In conclusion, preharvest AVG applications at 60 mg·L−1 or postharvest 1-MCP treatment at 0.3 µL·L−1 extended storage life of ‘Starkrimson’; however, 1-MCP inhibited ripening capacity whereas 60 mg·L−1 AVG did not.

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Zhuangjun Zhao, Margaret Mukami Gitau, Tao Hu, Yan Xie, Longxing Hu and Jinmin Fu

Plants growing in salt-affected soils may have retarded growth and inhibited or altered metabolic processes. This study aims at investigating the impact of subsurface soil salinity on root growth and metabolic processes in perennial ryegrass (Lolium perenne). The seeds of perennial ryegrass (cv. Quick Start II) were planted in polyvinyl chloride (PVC) tubes (10 cm diameter × 42 cm long) for 2 months. The experiment consisted of three treatments: 1) control, 40 cm filled with sand–peat mixture (7 sand : 3 peat wt/wt); 2) T20, a 20-cm-deep layer of saline soil covered with a 20-cm-deep layer of sand–peat mixture; and 3) T30, a 30-cm-deep layer of saline soil covered with a 10-cm-deep layer of sand–peat mixture. Our study showed that soil salinity at the subsurface inhibited the growth of perennial ryegrass roots. Compared with the control, the root activity in saline soil layer decreased, whereas it remained high in the mixture-soil zone. The content of amino acids in the roots obtained from the surface soil (0–10 cm) in T30 was greater than that in both the T20 and the control regimes. The content of soluble sugars in the roots went up with the decrease of the depth of sand–peat mixture. The increased root activity and free amino acids content in the roots sampled from the upper soil layers coupled with the increased soluble sugars in the roots subjected to soil salinity stress in the bottom soil layer represents some adaptive responses and regulative mechanisms in perennial ryegrass.

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Xiaoning Li, Xiaoyan Sun, Guangyang Wang, Erick Amombo, Xiuwen Zhou, Zhaohong Du, Yinkun Zhang, Yan Xie and Jinmin Fu

Phosphorus (P) is an essential nutrient element that is necessary for plant growth and development. However, most of the P exists in insoluble form. Aspergillus aculeatus has been reported to be able to solubilize insoluble forms of P. Here, to investigate the P-solubilizing effect of A. aculeatus on the performance of perennial ryegrass (Lolium perenne) under P-deficiency stress, we created four treatment groups: control [i.e., no Ca3(PO4)2 or A. aculeatus], A. aculeatus only (F), Ca3(PO4)2 and Ca3(PO4)2 + A. aculeatus [Ca3(PO4)2 + F] treatment, and Ca3(PO4)2 at concentrations of 0 and 3 g per pot (0.5 kg substrate per pot). In our results, the liquid medium inoculated with A. aculeatus exhibited enhanced soluble P and organic acid content (tartaric acid, citric acid, and aminoacetic acid) accompanied with lower pH, compared with the noninoculated regimen. Furthermore, A. aculeatus also played a primary role in increasing the soluble P content of substrate (1 sawdust: 3 sand), the growth rate, turf quality, and photosynthetic capacity of the plant exposed to Ca3(PO4)2 + F treatment, compared with other groups. Finally, in perennial ryegrass leaves, there was a dramatic increase in the valine, serine, tyrosine, and proline contents, and a remarkable decline in the glutamic acid, succinic acid, citric acid, and fumaric acid contents in the Ca3(PO4)2 + F regimen, compared with other groups. Overall, our results suggested that A. aculeatus may play a crucial role in the process of solubilizing Ca3(PO4)2 and modulating perennial ryegrass growth under P-deficiency stress.