Low temperature is one of the main environmental factors affecting the growth, yield and distribution of sugarcane. It is of great significance to explore the physiological response characteristics of sugarcane under low temperature stress and screen strong cold-tolerant sugarcane parent materials for guiding sugarcane breeding and promoting the development of sugarcane industry. In this study, eight different sugarcane varieties and one sugarcane wild species (Erianthus fulvus 99-1 clone) were used as the experimental materials to study the physiological index response after low temperature stress treatment, and the cold tolerance of the nine materials was comprehensively evaluated by principal component analysis, fuzzy membership function method and cluster analysis. The contents of malondialdehyde (MDA), chlorophyll (Chl), soluble sugar (SS) and soluble protein (SP) in most materials were higher than those of CK after low temperature stress (3 ℃, 3 days). The content of proline (Pro) in all materials was higher than that of CK, while the activity of superoxide dismutase (SOD) was lower. The activities of peroxidase (POD) and catalase (CAT) in most materials were higher than those of CK. According to the comprehensive evaluation value (D) and cluster analysis, the nine materials were divided into three groups: strong cold resistance type (E. fulvus 99-1, Yacheng 89-9, ROC10), moderate cold resistance type (ROC20, Yuetang 93-159, Huangjiali, ROC16) and weak cold resistance type (Dianzhe 01-58, ROC22). The results indicate that different sugarcane varieties have different adaptability to low temperature. Strong cold-tolerant sugarcane varieties can quickly adjust themselves under adversity, reasonably increase the content of osmotic adjustment substances and the activity of antioxidant enzymes, further remove harmful substances such as reactive oxygen species (ROS) in the body, and balance cell metabolism process, so as to better adapt to low temperature environment. This study would lay a foundation for exploring the regulation mechanism of sugarcane response to low temperature stress and breeding new sugarcane varieties with strong cold tolerance.

Seed germination is a key link for plants to enter the vegetative growth stage. During the germination of rice (Oryza sativa L.) seeds, the aleurone layers synthesize and secrete a series of acid hydrolases (such as α-amylase, protease) to degrade the storage substances in the endosperm and provide nutrition for the growth of rice seedlings. The degradation of storage proteins is inseparable from the role of proteasome and protease in rice seeds. In order to explore the involvement of 26S proteasome, 20S proteasome and its subunit PBA1 in the regulation of GA on the storage proteins in the aleurone layers of germinated rice seeds, the rice hybrid Teyou 128 was used as the experimental material. The activity of 26S proteasome, 20S proteasome and PBA1, the transcription level of OsPBA1 and the change of total protein content were detected by enzyme-linked immunosorbent assay and real-time fluorescence quantitative PCR. GA significantly promoted the degradation of storage proteins in aleurone cells and accelerated the germination of rice seeds. When GA synthesis was blocked, the degradation process of storage protein in aleurone layer cells was delayed, thus delaying the germination of rice seeds. Under normal culture conditions, the peak values of 26S proteasome activity and 20S proteasome activity in the aleurone layers of rice seeds appeared at 6 d and 7 d, respectively, while the OsPBA1 expression level and PBA1 activity showed peaks at 5 d and 8 d. Further studies showed that GA could induce the activity of PBA1, 20S proteasome and 26S proteasome, thereby accelerating the process of seed germination. The 26S proteasome activity inhibitor MG132 inhibited the growth of germinated rice seeds, but increased the activity of 20S proteasome and PBA1. The above studies preliminarily revealed the role of 26S proteasome in GA regulating the degradation of storage proteins in rice aleurone layers and its effect on the germination of rice seeds.

In order to explore the effects of nitrogen fertilizer application rate and planting density on the source-sink relationship and yield of sweet potato during ridge-sealing period, and to improve the cultivation techniques of sweet potato in Hainan, a field experiment was carried out from 2019 to 2020. The fresh-eating sweet potato variety Gaoxi14 was used as the test material, and three planting densities were set up, namely 47 600 plants/hm² (D₁), 71, 400 plants/hm² (D₂) and 142 900 plants/hm² (D₃). Four nitrogen application rates (0 kg/hm² (N₀), 60 kg/hm² (N₁), 120 kg/hm² (N₂), 180 kg/hm² (N₃) were designed in a double-factor split plot design with planting density as the main plot and nitrogen application rate as the subplot to study the effects of different planting densities and nitrogen application rates on photosynthetic characteristics, the relative chlorophyll content (SPAD), stem and leaf growth, dry matter accumulation and distribution in source and sink, tuber characteristics in ridge-sealing period, yield and its components and commodity in harvest period of Gaoxi14. Under the same planting density, the net photosynthetic rate (P_n), fresh weight of stem and leaf, number of branches, longest vine length, number of tubers per plant and single tuber weight of commercial sweet potato increased first and then decreased with the increase of nitrogen application rate, and reached the maximum at N₁ treatment. The yield of sweet potato increased first and then decreased with the increase of nitrogen application rate, and reached the maximum under N₂ treatment, which was 32.0% higher than that under N₀ treatment, but there was no significant difference between N₂ and N₁ treatments. Under the same nitrogen application rate, the dry matter distribution ratio of sweet potato roots increased first and then decreased with the increase of planting density. The D₂ treatment reached the maximum but there was no significant difference between D₂ and D₃ treatments. The root shoot ratio and yield increased significantly with the increase of planting density, and reached the maximum at D₃ treatment. The yield of D₃ was 30.9% and 24.1% higher than that of D₁ and D₂, respectively. The results of correlation analysis showed that the nitrogen application rate and planting density had significant effects on the dry matter accumulation and distribution of root tubers, while the planting density had a significant positive correlation with the yield of sweet potato at harvest stage, and the correlation coefficient was 0.704. Based on the results of this experiment, when the nitrogen application rate was 60 kg/hm² and the planting density was 142 900 plants/hm² (D₃N₁), the yield of Gaoxi 14 was the highest, reaching 30.1 t/hm², and the corresponding potato commodity rate was 94.3%, which was the best among all treatments.

The yield and quality of sweetpotato root tubers can be significantly improved by applying paclobutrazol (PBZ), and sucrose-degrading enzymes play important roles in the development of storage roots of sweetpotato. However, the physiological and biochemical mechanisms underlying PBZ-regulated storage root development is still unclear, and especially it remains to be investigated whether sucrose metabolism is involved in the PBZ-regulated development of storage roots. In this paper, sweetpotato cultivar Kokei 14 was used, a predominant cultivar planting in Hainan. After applying PBZ treatment in the early stage of cultivation (20-30 d after planting, dap), the following phenotypic parameters were investigated at 120 dap including the fresh weight of storage root per plant, fresh weight per storage root and storage root number per plant. To elucidate the physiological and biochemical mechanisms relevant to sucrose metabolism underlying PBZ-regulated storage root development, the following physiological and molecular parameters were also examined in storage roots at different development stages (30, 60, 90 and 120 dap) including the content of starch and soluble sugars (glucose, fructose and sucrose), the activities of sucrose-degrading enzymes and expression levels of the gene families. PBZ increased the yield of sweetpotato by increasing the fresh weight per storage root, but without affecting storage root number per plant. PBZ increased the content of soluble sugar and starch in storage root. However, the effect of PBZ on the yield and quality of storage roots only occurred in the early stage (30-60 d after planting) after treatment, and in the late stage (90-120 d), PBZ treatment had no significant effect on yield and quality. PBZ treatment significantly increased the activities of sucrose synthase (Sus), cell wall invertase (CWIN) and cytoplasmic invertase (CIN). However, PBZ had no significant effects on vacuolar invertase (VIN). As compared to CWIN and CIN, Sus activity was induced by PBZ treatment much earlier and more dramatic. Sus activity was significantly induced at 30 dap, whereas the activity of CWIN and CIN were significantly induced at late stage i.e. 60 dap. In other periods (especially 90-120 d), PBZ treatment had no significant effect on the activities of Sus, CWIN and CIN. The determination of the expression level of Sus, CWIN and CIN genes showed that IbSus2, IbSus5-7 and IbSus9 highly expressed in storage tuber were all significantly induced by PBZ at 30 dap. IbCIN3, IbCIN7 and IbCIN8 expressed in storage roots, and IbCWIN2 and IbCWIN4 expressed in storage roots were significantly induced by PBZ at 60 dap. However, in other periods (especially 90-120 d), PBZ treatment had no significant effect on the expression level of the relevant genes. It is speculated that the increase of Sus expression and activity under PBZ treatment is earlier and more dramatic, which can promote the rapid and biosynthesis and accumulation of starch and the rapid expansion of storage roots, while the subsequent increase of CWIN and CIN expression and activity can increase the content of soluble sugar in root tubers thus improving the quality of storage roots, and can also provide energy supply for starch biosynthesis and storage root expansion. The specific members of Sus, CWIN and CIN genes induced by PBZ had also been identified. Notably, the effects of PBZ on the yield and quality of storage roots, and activities and gene expression levels of sucros-degarding enzymes in storage roots mainly occurred in the short period after PBZ treatment. With the extension of time, the effects of PBZ on the above indicators gradually disappeared. Therefore, in order to improve the yield of sweetpotato in production, it is necessary to conduct PBZ treatment throughout the entire growth period of sweetpotato. The above results can provide a theoretical basis for achieving high-quality and high-yield sweetpotato production by variety breeding or cultivation measures.

The intercropping of Mallotus peltatus under the forest helps to break the bottleneck of land use. It is of great significance to apply green nanotechnology to improve the benefits of its compound planting. In order to clarify the regulatory role of nano-iron in the intercropping of M. peltatus under the coconut forest, the annual seedling of M. peltatus was taken as the research object to carry out the cultivation experiment. We investigated the comprehensive effects of five concentrations of nano-iron treatments (CK: 0 mg/L, T₁: 25 mg/L, T₂: 50 mg/L, T₃: 75 mg/L, T₄: 100 mg/L) on the leaf growth, photosynthetic and chemical characteristics of M. peltatus. After the first nano-iron treatment, the leaf length, width and dry weight of M. peltatus in T₃ treatment were significantly higher than those in CK, while the leaf number in each treatment was significantly more than that in CK. Compared with CK, the chlorophyll content of M. peltatus treated with four nano-iron concentrations increased significantly by 14.96% (T₁), 16.18% (T₂), 17.91% (T₃) and 20.58% (T₄). As the concentration of nano-iron increased, the leaf net photosynthetic rate, transpiration rate, stomatal conductance, efficiency of primary conversion of light energy of PSⅡ, actual photochemical efficiency of PS Ⅱ and electron transport rate of M. peltatus overall increased. After the second nano-iron treatment, leaf length, width, dry weight and number of M. peltatus treated with T₁, T₃ and T₄ were significantly higher than those of CK. Compared with CK, the chlorophyll content of M. peltatus in each treatment significantly increased by 10.28% (T₁), 7.53% (T₂), 11.13% (T₃) and 11.41% (T₄). With the increase of nano-iron concentration, the leaf net photosynthetic rate, transpiration rate and stomatal conductance of M. peltatus increased significantly, but decreased when the concentration reached T₃ treatment. The potential activity of PSⅡ and efficiency of primary conversion of light energy of PSⅡ of M. peltatus also decreased significantly in T₃ treatment. After two treatments, the contents of flavone, fat and ash of M. peltatus increased significantly in T₁ treatment compared with CK. The contents of fat and ash decreased with the increase of nano-iron concentration. To sum up, nano-iron has a positive regulatory effect on the growth of M. peltatus under the coconut forest, but high concentration will inhibit its photosynthesis and growth. We recommend that the appropriate concentration is 25-50 mg/L. This study could provide theoretical reference for the application of nano-iron in intercropping M. peltatus under the coconut forest.

Tea quality is closely related to the growth and ecological environment of tea plant (Camellia sinensis). The difference between day and night temperature (DIF) affects the synthesis and accumulation of tea plant metabolites, which in turn affects the quality of tea. In this study, Fuyun No. 6 was selected as the research object, and four DIF treatments (0 ℃, 5 ℃, 10 ℃ and 15 ℃) were simulated to explore the effects of DIF on photosynthesis and volatile and non-volatilequality components of tea fresh leaves. The results showed that the net photosynthetic rate (P_n), stomata conductance (G_s) and transpiration rate (T_r) of tea plants increased significantly with the increase of DIF (P<0.05). Increasing DIF significantly increased the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (a+b) [Chl (a+b)] and carotenoids (Car), and reached the maximum when DIF was 10 ℃. In addition, the change of DIF had an effect on the volatile components and relative contents of main components in fresh tea leaves, and the relative contents of alcohols and aldehydes were the largest in the volatile components of fresh tea leaves. The increase of DIF could significantly enhance the relative contents of aldehydes, and the relative contents of volatile components and main aroma components in fresh tea leaves were different with the change of DIF. The content of hexanal increased with the increase of DIF, with the highest value of 39.94% at DIF=15 ℃, while the relative content of cis-3-hexenol decreased with DIF increasing. The change of DIF significantly affected the activities of β-glucosidase, β-primeverosidase and lipoxygenase. The activities of β-glucosidase and β-primeverosidase first increased and then decreased with the increase of DIF, and reached the maximum when the DIF was 5 ℃, while the activity of lipoxygenase was opposite. Furthermore, the contents of free amino acids and caffeine increased significantly with the increase of DIF, which were 2.44 and 2.55 times at DIF=15 ℃ than those at DIF=0 ℃, respectively. The total flavonoids content and ratio of tea polyphenols to amino acids decreased significantly with the increase of DIF (P<0.05), with the lowest value of 2.84% and 3.24 at DIF=15 ℃. The contents of free amino acids in fresh tea leaves were significantly positively correlated with P_n, while the ratio of tea polyphenols to amino acids showed significantly negatively correlated with P_n (P<0.01). This study indicated that the increase of DIF could significantly affect the volatile aroma substances of fresh tea leaves and improve the taste and quality of tea, which could provide a certain theoretical basis for tea plantation site selection and tea planting.

Wampee [Clausena lansium (Lour.) Skeels] is a species of Rutaceae family and native to Southern China, which contains a large number of bioactive compounds that are beneficial to human health. However, because of the thin pericarp and soft pulp, wampee fruit is susceptible to the mechanical damage and the quality deterioration symptoms of fruit rot, pericarp browning and storage characteristic loss, and thus reducing the commercial value and edible value of harvested wampee fruit. Therefore, it is necessary to develop a safe and environmentally friendly postharvest storage technology for enhancing the storage behavior and quality, and prolonging storage time of harvested wampee fruit. Oxyresveratrol (OXY) is a naturally active product, with the efficacies of anti-browning, anti-oxidation, antibacterial, anti-inflammatory and antiviral. OXY has been studied more in the field of medicinal health care, but less in the field of food preservation. However, there are no reports on increasing the storage behavior and postharvest quality of wampee fruit by the usage of exogenous OXY. The study was aimed to study the effects of exogenous OXY treatment on the preservation of harvested wampee fruit. The fruit of wampee cv. Jixin was used as the experiment material, and the wampee fruit was treated by OXY solution with concentration of 0.2 g/L and distilled water (CK) for 30 min, separately. Then, the fruit was air-dried and packaged (50 fruits per bag), and stored at relative humidity 85% and temperature (25±1)℃ for 10 days. The changes of related indices of the storage behavior and postharvest quality in wampee fruit were observed and measured every two days. Compared to CK, OXY treatment could delay the increments of pericarp cell membrane permeability, browning degree and browning index, and maintain a higher commercially acceptable fruit rate but a lower weight loss percentage of harvested wampee fruit. Furthermore, OXY treatment might keep the higher values of L^* and hue angle, a higher total phenolics content, but the lower activities of phenolases such as peroxidase and polyphenol oxidase in pericarp of harvested wampee fruit. Moreover, OXY treatment could retain the higher contents of total soluble solids, vitamin C, titratable acidity, sucrose and total soluble sugar in pulp of harvested wampee fruit. Therefore, the treatment of exogenous OXY could effectively enhance the storage behavior, and retain the pericarp appearance quality and pulp nutritional quality, and thus prolong the storage time in harvested wampee fruit.

The study was aimed to explore the differences in physical and chemical indexes and volatile components of different types of Amomum tsaoko powder. The physicochemical indexes of A. tsaoko powder such as color difference, essential oil content, moisture content, particle size and surface microstructure were investigated. The volatile components of A. tsaoko powder were analyzed by headspace solid-phase microextraction and gas chromatography-mass spectrometry. The color difference ∆E of seven different fruit types of A. tsaoko powder was from 19.17±0.29 to 25.15±0.17, L^* value was from 72.50±0.23 to 76.87±0.07, a^* value was from 5.17±0.05 to 6.97±0.15, b^*value was from 12.35±0.43 to 16.91±0.43. The content of volatile oil was from (0.76±0.01)mL/100 g to (1.30±0.26)mL/100 g. The moisture content was from 11.13%±0.12% to 15.05%±0.23%. In terms of particle size, NL5 and NL6 fruit powder particles had the largest difference. A total of 31 volatile components were detected in the seven fruit powder, and 17 common components were detected, mainly aldehydes and alcohols, including 2-decenal, (E)-, eucalyptol, citral, geraniol, geranyl acetate, etc. Among them, 28 volatile components were detected in NL2 fruit types, and the relative content of 2-decenal, (E)- was the highest (22.24%±2.29%). The relative content of eucalyptol in NL5 fruit type was the highest (17.52%±2.16%). Therefore, there are some differences in color difference, essential oil content, moisture content, particle size and surface microstructure of the powder of different fruit types. The volatile components of different fruit types of A. tsaoko fruit powder have both common characteristics and differences. The research could provide theoretical guidance for the production and application of high-quality pure natural A. tsaoko powder.

The study was aimed to analyze the genetic diversity of the phenotypic traits and chemotypes of different Ocimum basilicum germplasm resources, to provide theoretical reference for the innovative utilization of basil germplasm resources and variety selection. The botanical traits of 15 basil germplasm resources and the volatile components of the leaves investigated and determined using gas chromatography-mass spectrometry (GC-MS), together with the relative odour activity values (ROAV). At the same time, principal component analysis and cluster analysis were carried out on the tested germplasms. The 15 basil germplasms differed significantly in plant height, plant width, leaf length, leaf width and stem thickness, except for the number of branches. 104 volatile compounds were identified, including 37 alkanes, 32 terpenes, 8 esters, 5 phenols, 4 alcohols, 3 aldehydes, 1 ether, and 14 other compounds, of which there are two types of common components, 2,4-di-tert-butylphenol and heptadecane. According to the ROAV values obtained from the enquiries and calculations, the key aroma substances were found to be eugenol, linalool, eucalyptol, cis-citral, methyl cinnamate, 4-allyl anisole, etc. The principal component analysis and cluster analysis of the volatile substances the germplasms could be classified into five groups, namely, Thai basil, Anise basil, Siam queen basil and Sweet basil were grouped together, Jiu Cengta basil, Genovese basil, Red rubin basil, Purple dark opal basil and Purple ruffles basil were grouped together, Clove basil and Lemon basil were grouped together, Tuscany basil, Pluto basil and Italian large leaf basil were grouped together, Cinnamon basil was grouped one category. The phenotypic trait cluster analysis also classified basil into five groups, with Pluto basil into a group, Clove basil, Anise basil and Purple dark opal basil into a group, Thai basil into a group, Italian large leaf basill and Cinnamon basil into a group. The remaining eight germplasm were clustered into a group. The 15 germplasms have significant differences in botanical characters and volatile components, and are rich in genetic diversity, which could be targeted for breeding of basil-specific germplasms.

Papaya is an economically important tropical fruit. Papaya ringspot virus (PRSV) is an important virus disease of papaya, often causing significant yield losses and quality deterioration. Since the introduction of the first transgenic papaya in 1998, PDR-based breeding strategies for disease resistance have been successfully applied. The contradiction between disease resistance based on sequence homology and increased virus genetic diversity became a new challenge for papaya breeding. In this study, we propose to use RNAi strategies aim at nuclear inclusion b gene (Nib) to obtain broad-spectrum resistance to PRSV papaya. With optimized embryo callus generation-Agrobatium meidated transformation-shoot regeneration, 52 shoots were obtained after resistance screening and a total of 24 transgenic positive shoots were obtained by specific PCR screening for the T₀ generation. In the T₀ generation field natural disease test, the transgenic papaya strains were significantly more resistant to disease than the non-transgenic control, with NibB5-2 having the best resistance in the field. Molecular charaterization of the insertion site of Nib5-2 was located at position 1976766 on chromosome 2 supercontig_30 by hiTAIL-PCR method. Green house inoculation test of NibB5-2 T1 generation, there was no virus accumulation and no disease symptoms, confirmed the resistance. Our resulst reveal that RNAi silcencing the Nib gene enhance the papaya virus resistance, meanwhile enriched the candidated genes for virus resistance breeding.