Rapid and visual detection of milk vetch dwarf virus using recombinase polymerase amplification combined with lateral flow strips.

BACKGROUND: Milk vetch dwarf virus (MDV) is an important ssDNA virus which causes yellowing, stunting and leaf rolling symptoms on legumes. In China, the virus causes great economic losses and has recently been found to infect tobacco. The expansion of its host range and its ability to spread rapidly has given rise to the urgent need for a sensitive, specific and rapid diagnostic assay that can assist in effective disease control. METHODS: Assays based on the polymerase chain reaction combined with lateral flow strip detection (PCR-LFS) and recombinase polymerase amplification combined with LFS (RPA-LFS) were developed targeting the coat protein (CP) gene of MDV. RESULTS: The PCR and RPA assays could detect respectively 103 copies or 101 copies of MDV by agarose gel electrophoresis. The PCR-LFS and RPA-LFS assays developed could both detect as few as 101 copies per reaction at 37 °C. Both methods could detect MDV in crude leaf extracts. CONCLUSIONS: The RPA-LFS assay developed is a rapid, sensitive and specific method for detecting MDV, which is convenient and has great potential for use in the field.

Reduction mechanism of Cd accumulation in rice grain by Chinese milk vetch residue: Insight into microbial community.

Chinese milk vetch is an efficient approach to reduce Cd accumulation in rice, nevertheless, its reduction mechanism is not well understood. In this study, we investigated the rice grain Cd, soil properties and microbial community in a Cd-polluted paddy field amended with milk vetch residue (MV) or without (CK) during rice growth period. We found that milk vetch residue averagely decreased the Cd content in rice grain by 45%. Decrease of Cd in rice mainly attributed to the inhibition of Cd activation by milk vetch residue at heading stage probably by the formation of HA-Cd (Humic Acid) and CdS. Increased pH and organic matter (OM) promoted the reduction of available Cd. In addition, nonmetric multidimensional scaling (NMDS) analysis revealed that microbial community structure was significantly different between MV and CK treatment (r = 0.187, p = 0.002), and the core functions of differentially abundant genera were mainly associated with N-cycling, organic matter degradation and sulfate-reducing. The application of milk vetch residue increased the abundance of sulfate-reducing bacteria (SRB) by 8-112% during the rice growth period, which may involve in promoting the transformation of Cd to a more stably residual Cd (CdS). Canonical correspondence analysis (CCA) and mantel test analysis indicated that available K (p = 0.004) and available N (p = 0.005) were the key environmental factors of shaping the SRB. Altogether, changes in soil properties affected microbial structure and functional characteristics, especially the response of SRB in MV treatment would provide valuable insights into reducing the bioavailability of Cd in soil.

Full genome sequence analysis and putative host-shifting of Milk vetch dwarf virus infecting tobacco (Nicotiana tabacum) in China.

BACKGROUND: Tobacco production in China has been affected by plant viruses with Milk vetch dwarf virus (MDV) as a recent invader posing serious concern. According to most of the studies, MDV mainly infects hosts from Fabaceae family but in our previous study we reported its infection in tobacco plant (Nicotiana tabacum L.) in Shandong province. FINDINGS: In current study (2016-2017), tobacco plants (Nicotiana tabacum) with severe stunting, yellowing and axillary bunch of new leaves were observed in Zhengning, Gansu province. Isolate GSZN yielded into eight genomic circular single-stranded DNA components while no alphasatellite DNA was obtained. High percent identity of this isolate was recorded in overall nucleotide and amino acid assembly with reported MDV isolates worldwide. Phylogenetic analysis fetched into a separate sub-clade comprising of new isolate along with other tobacco infecting isolates of MDV. While recombination was predicted in DNA-C encoding Clink protein and DNA-U1, which may attribute towards the potential host-shifting phenomenon and ability of this virus to expand its host range. CONCLUSION: To our knowledge this is the first full genome annotation of a Nanovirus, infecting tobacco in natural field conditions, also this is the first extended analysis on host-shifting behavior of MDV.

Genetic analyses of Astragalus sect. Humillimi (Fabaceae) resolve taxonomy and enable effective conservation.

PREMISE OF THE STUDY: Astragalus sect. Humillimi is distributed across the southwestern United States and contains two endangered taxa, A. cremnophylax var. cremnophylax and A. humillimus. The former was originally described from the South Rim of the Grand Canyon. Analysis of individuals discovered on the North Rim of the Grand Canyon yielded some evidence that the population represented a distinct species. To enable effective conservation, we clarify the group's taxonomy and characterize the genetic diversity of A. cremnophylax and A. humillimus. METHODS: We used AFLPs to genotype most species in sect. Humillimi, focusing on the two endangered forms. We examined patterns of genetic diversity using complementary analytical approaches. KEY RESULTS: Our results demonstrate that North Rim populations group with A. c. var. cremnophylax. We found low levels of genetic diversity at certain localities and strong differentiation among populations. Astragalus humillimus, which has suffered recent and severe population declines, exhibits weak differentiation among and low diversity within populations. CONCLUSIONS: Our results clarify the taxonomy of sect. Humillimi and define the boundaries of A. c. var. cremnophylax, which is shown to inhabit both rims of the Grand Canyon. This clarification, and detailed analysis of genetic variation within both endangered taxa, may advance ongoing efforts to conserve these taxa. Our results suggest that range-wide genetic analysis of A. humillimus may inform recovery strategies for this taxon.

Design of species-specific PCR method for the detection of pathogen Embellisia astragali in standing milk vetch seeds.

UNLABELLED: Embellisia astragali is an important seedborne pathogenic fungus responsible for yellow stunt and root rot of standing milk vetch (Astragalus adsurgens). The current detection methods that are based on culture and morphological identification are time-consuming, laborious and not always reliable. A PCR-based diagnostic method was developed with the species-specific primer pairs AatpF and AatpR designed from the sequence of the plasma membrane ATPase gene of E. astragali. The specificity of the primers was verified by PCR analysis of DNA from three strains of E. astragali and 19 isolates of nontarget fungi from other genera. A single 135-bp amplicon was detected only from E. astragali isolates, and no cross-reactions were observed with any other tested isolates. The detection limit of this new method was 5 pg of template DNA. The specific primers enabled the detection of E. astragali from the seed of standing milk vetch. This species-specific PCR method provides quick, simple, powerful and reliable detection of E. astragali. SIGNIFICANCE AND IMPACT OF THE STUDY: PCR-based detection is fast, convenient, precise and sensitive compared to the traditional methods of pathogen detection. This study develops the first PCR method for the detection of Embellisia astragali in standing milk vetch seeds. The species-specific primer set designed from the plasma membrane ATPase gene of E. astragali can detect the pathogen. This assay could be applied in the standing milk vetch seed industry.

Host-plant dependent population genetics of the invading weevil Hypera postica.

Population genetics of invading pests can be informative for understanding their ecology. In this study, we investigated population genetics of the invasive alfalfa weevil Hypera postica in Fukuoka Prefecture, Japan. We analyzed mitochondrial tRNALeu-COII, nuclear EF-1α gene fragments, and Wolbachia infection in relation to three leguminous host plants: Vicia angustifolia, Vicia villosa, and a new host Astragalus sinicus cultivated as a honey source and green manure crop. A parsimony network generated from mitochondrial gene sequences uncovered two major haplotypic groups, Western and Egyptian. In contrast to reported Wolbachia infection of the Western strain in the United States, none of our analyzed individuals were infected. The absence of Wolbachia may contribute to the stable coexistence of mitochondrial strains through inter-strain reproductive compatibility. Hypera postica genetic variants for the mitochondrial and nuclear genes were associated neither with host plant species nor with two geographic regions (Hisayama and Kama) within Fukuoka. Mitochondrial haplogroups were incongruent with nuclear genetic variants. Genetic diversity at the nuclear locus was the highest for the populations feeding on V. angustifolia. The nuclear data for A. sinicus-feeding populations indicated past sudden population growth and extended Bayesian skyline plot analysis based on the mitochondrial and nuclear data showed that the growth of A. sinicus-feeding population took place within the past 1000 years. These results suggest a shorter history of A. sinicus as a host plant compared with V. angustifolia and a recent rapid growth of H. postica population using the new host A. sinicus.

The nanovirus U2 protein suppresses RNA silencing via three conserved cysteine residues.

Nanoviruses have multipartite, circular, single-stranded DNA genomes and cause huge production losses in legumes and other crops. No viral suppressor of RNA silencing (VSR) has yet been reported from a member of the genus Nanovirus. Here, we demonstrate that the nanovirus U2 protein is a VSR. The U2 protein of milk vetch dwarf virus (MDV) suppressed the silencing of the green fluorescent protein (GFP) gene induced by single-stranded and double-stranded RNA, and the systemic spread of the GFP silencing signal. An electrophoretic mobility shift assay showed that the U2 protein was able to bind double-stranded 21-nucleotide small interfering RNA (siRNA). The cysteine residues at positions 43, 79 and 82 in the MDV U2 protein are critical to its nuclear localization, self-interaction and siRNA-binding ability, and were essential for its VSR activity. In addition, expression of the U2 protein via a potato virus X vector induced more severe necrosis symptoms in Nicotiana benthamiana leaves. The U2 proteins of other nanoviruses also acted as VSRs, and the three conserved cysteine residues were indispensable for their VSR activity.

Joint utilization of Chinese milk vetch and lime materials mitigates soil cadmium risk and improves soil health in a double-cropping rice system.

Cadmium (Cd) in paddy soil poses significant risks to humans due to its strong biological migration and toxicity. Chinese milk vetch (MV) is commonly used as green manure in the paddy fields of southern China and its potential to decrease the availability of Cd has been identified. Nevertheless, the effects of MV combined with lime materials (lime, L; limestone, LS) on Cd availability, soil properties, enzyme activity and comprehensive benefits are still not fully understood in double-cropping rice system. A field study was conducted to investigate these changes. The results indicated that all treatments notably decreased soil available Cd (Avail-Cd) by 19.3-44.3% and 14.9-43.1% during early and late rice, compared with CK. Moreover, the Cd fractions transformed to more stable forms. Compared to CK, all treatments reduced brown rice Cd content by 34.6-64.2% and 12.7-52.5% during the two periods. Furthermore, the translocation factors root to shoot, as well as shoot to brown rice, decreased. The combination led to improvements in soil properties, soil enzyme activity. Meantime, Cd in iron-manganese plaque (IMP) decreased by 31.9-51.1% and 29.0-42.7% respectively during two periods in amendments treatments. Soil pH and DOC were more important factors for Cd bioavailability than other properties. Additionally, rice Cd uptake was positively correlated with Cd in IMP. Enzyme activity exhibited a negative correlation with soil active Cd. Partial Least Squares Path Model (PLS-PM) indicated that the mitigation of Cd pollution helped to improve soil enzyme activity. Grey correlation analysis (GRA) indicated that MVLS showed the best comprehensive benefits in soil-plant system. Overall, the combination of MV and lime materials could reduce Cd availability, enhance soil properties and enzyme activity. And this could be strengthened by the combination. These findings will provide valuable insights for Cd-contaminated soil remediation.

Predispersal seed predation is higher in a rare species than in its widespread sympatric congeners (Astragalus, Fabaceae).

PREMISE OF THE STUDY: Rare plants may be rare, in part, because they are more susceptible to damage by predispersal insect seed predators than widespread congeneric species; thus, seed predation may be an important determinant of plant rarity. Scant evidence exists to either support or reject this hypothesis, limiting our ability to predict herbivore effects on plant rarity. We used a comparative framework to test this hypothesis in rare-common, sympatric congeners. METHODS: We compared seed consumption by insect type and seed production among a rare Astragalus (Fabaceae) species and two sympatric, widespread congeners. We measured plant traits and tested whether traits were correlated with seed damage within and among rare-common species. KEY RESULTS: Seed predation was significantly higher in a rare species than in common congeners over 2 yr. Seed production per pod was significantly lower in the rare species. Seed weevils exclusively consumed seeds of the rare species. Higher seed predation in the rare species is related to a combination of factors: plant phenology, dispersal ability, and vigor; seed predator identity; and insect phenology. CONCLUSIONS: Our results support the hypothesis that a rare plant is more susceptible to seed predators than two common, sympatric congeners. Seed predator reduction is a promising management tool to increase seed-set, recruitment, and survival of the rare species. Further studies that compare rare-common, sympatric congeners are greatly needed to broadly evaluate the hypothesis concerning rarity and susceptibility to seed predators and to inform conservation plans for rare species.

Potential effect of key soil bacterial taxa on the increase of rice yield under milk vetch rotation.

Legume crop rotation is often adopted in rice cultivation to improve soil productivity. However, little is known about the role of microbes under legume rotation in affecting soil productivity. To elucidate this, a long-term paddy cropping experiment was set up to study the relationship between crop yield, soil chemical properties, and key microbial taxa under a double-rice and milk vetch rotation. Milk vetch rotation significantly improved soil chemical properties compared to no fertilization treatment, and soil phosphorus was a major factor correlated with crop yield. Long-term legume rotation increased soil bacterial alpha diversity and changed soil bacterial community. After milk vetch rotation, the relative abundances of Bacteroidota, Desulfobacterota, Firmicutes, and Proteobacteria increased while those of Acidobacteriota, Chloroflexi, and Planctomycetota decreased. Moreover, milk vetch rotation increased the relative abundance of phosphorus-related gene K01083 (bpp), which was significantly correlated with soil phosphorus content and crop yield. Network analysis showed that taxa of Vicinamibacterales were positively correlated with total phosphorus and available phosphorus, which was a potential taxon contributing to the availability of soil phosphorus stock. Our results indicated that milk vetch rotation could enrich key taxa with latent phosphate-solubilizing ability, increase the content of soil available phosphorus, and finally enhance crop yield. This could provide scientific guidance for better crop production.

[Effects of Chinese Milk Vetch Returning Incorporated with Chemical Fertilizer Reduction on the Composition and Function of Soil Bacterial Communities in Paddy Fields].

Chinese milk vetch (Astragalus sinicus L.) is an important organic nutrient resource in the southern Henan rice-growing area. Thus, the effects of Chinese milk vetch (MV) returning incorporated with reduced chemical fertilizer on the physicochemical properties and bacterial community characteristics in paddy soil were studied. These results can provide a certain theoretical basis for the improvement of soil fertility and reduction of chemical fertilizer in this area. A field experiment was conducted for 12 consecutive years, involving six fertilization treatments (blank control, CK; 100% chemical fertilizer, F100; 80% chemical fertilizer+22.5 t·hm-2 MV, MV1F80; 80% chemical fertilizer+45 t·hm-2 MV, MV2F80; 60% chemical fertilizer+22.5 t·hm-2 MV, MV1F60; and 60% chemical fertilizer+45 t·hm-2 MV, MV2F60). The high-throughput sequencing method was used to compare the effects of different fertilization treatments on soil bacterial community diversity, composition, and structural characteristics. The FAPROTAX function prediction method was used to analyze the abundance differences of functional groups between different fertilization treatments. Additionally, combined with soil physicochemical properties and bacterial community characteristics, we explored the key soil environmental factors that changed the structure and functional characteristics of the soil bacterial community. Compared with that under CK, the soil bulk density (BD) under the MV returning incorporated with reduced chemical fertilizer treatment was decreased, whereas soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) were increased by 12.7%-35.5%, 38.2%-65.7%, 66.7%-95.2%, and 20.3%-31.6%, respectively. Compared with that under the F100 treatment, the Sobs index and Shannon diversity index of the bacterial community under the MV returning incorporated with reduced chemical fertilizer were decreased, and the Sobs index and Shannon diversity index were significantly positively correlated with BD (P<0.05) but significantly negatively correlated with SOC and TN (P<0.05). Compared with that under the F100 treatment, the relative abundances of Firmicutes under the MV1F80 and MV2F60 treatments were significantly increased by 82.2% and 67.4% (P<0.05), but the relative abundances of Acidobacteria were significantly reduced by 32.6% and 40.5% (P<0.05), respectively. The relative abundance of Actinobacteria under the MV2F60 treatment was significantly increased by 30.0% (P<0.05) compared with that under the F100 treatment. According to RDA analysis, soil SOC, TN, and TK were the main soil environmental factors that significantly affected bacterial community (P<0.05). Compared with that under CK and the F100 treatment, the abundance of functional groups of chemoheterotrophy, nitrogen fixation, fermentation, and ureolysis under the MV returning incorporated with reduced chemical fertilizer treatment were improved, whereas the abundance of functional groups of animal parasites or symbionts, all human pathogens, and human pathogen pneumonia were reduced, particularly under MV1F80 and MV2F60. To summarize, the long-term MV returning to the field incorporated with reduced chemical fertilizer improved the soil physical and chemical properties, thus changing the structure and functional characteristics of the soil bacterial communities, contributing to the improvement in the soil fertility, stability, and health of micro-ecosystems in paddy fields, thus ensuring the green and sustainable development of regional agriculture.

Combined application of chemical fertilizer with green manure increased the stabilization of organic carbon in the organo-mineral complexes of paddy soil.

The influence of the combined application of chemical fertilizer with green manure on the stabilization of organic carbon (C) was explored in the organo-mineral complexes of paddy soil. The organo-mineral complexes were isolated from paddy soil treated with no fertilizer, chemical fertilizer alone, and chemical fertilizer combined with increasing amounts of Chinese milk vetch (CMV). The stability (reflected by mineralizable carbon proportion), the content and chemical composition of organic C, the Fe/Al oxides and their associated organic C in the organo-mineral complexes were investigated. The application of chemical fertilizer in combination with CMV significantly improved the stability of organic C in the organo-mineral complexes. The combined application of chemical fertilizer with CMV slightly decreased the proportion of O-alkyl C (easily decomposed) yet somewhat increased the proportions of carbonyl C and aromatic C (difficultly decomposed) and aromaticity index in the organo-mineral complexes. The treatments of chemical fertilizer combined with CMV showed more Fe oxides and Fe/Al-associated organic C and higher proportion of Fe/Al-associated organic C in the total organic C of the organo-mineral complexes. The mineralizable carbon proportion displayed significantly negative correlations with carbonyl C and Fe/Al oxide-associated organic C in the organo-mineral complexes. The Fe/Al oxides were likely to be preferentially bound with the aromatic C and carbonyl C in the organo-mineral complexes. Overall, the combined application of chemical fertilizer with CMV facilitated the association of difficultly decomposed carbon and Fe/Al oxides, which significantly improved the stabilization of organic C in the organo-mineral complexes of paddy soil.

Cadmium-Tolerant Bacterium Strain Cdb8-1 Contributed to the Remediation of Cadmium Pollution through Increasing the Growth and Cadmium Uptake of Chinese Milk Vetch (Astragalus sinicus L.) in Cadmium-Polluted Soils.

Cadmium (Cd) pollution has attracted global attention because it not only jeopardizes soil microbial ecology and crop production, but also threatens human health. As of now, microbe-assisted phytoremediation has proven to be a promising approach for the revegetation of Cd-contaminated soil. Therefore, it is important to find such tolerant microorganisms. In the present study, we inoculated a bacteria strain tolerant to Cd, Cdb8-1, to Cd-contaminated soils and then explored the effects of Cdb8-1 inoculation on the performance of the Chinese milk vetch. The results showed plant height, root length, and fresh and dry weight of Chinese milk vetch grown in Cdb8-1-inoculated soils increased compared to the non-inoculated control group. The inoculation of Cd-contaminated soils with Cdb8-1 also enhanced their antioxidant defense system and decreased the H2O2 and malondialdehyde (MDA) contents, which alleviated the phytotoxicity of Cd. The inoculation of Cdb8-1 in Cd-contaminated soils attenuated the contents of total and available Cd in the soil and augmented the BCF and TF of Chinese milk vetch, indicating that the combined application of Cd-tolerant bacteria Cdb8-1 and Chinese milk vetch is a potential solution to Cd-contaminated soils.

Milk vetch returning reduces rice grain Cd concentration in paddy fields: Roles of iron plaque and soil reducing-bacteria.

Milk vetch (MV, Astragalus sinicus L.) is used in agricultural production as a green manure; however, its impact on accumulation levels of heavy metals (e.g., Cd) in rice remains poorly understood. This study investigated the effects of MV on Cd accumulation in rice, iron plaque formation, soil properties, and the soil microbial community structure through field experiments. The results showed that MV reduced Cd concentration in the roots, stem, leaves, and grains by 33%, 60%, 71%, and 49%, respectively. Chemical fertilizer and MV treatment promoted iron plaque formation, and MV considerably increased the Fe/Mn ratio in the iron plaque. More importantly, MV inhibited Cd transportation from the root iron plaque to the root by 74%. The concentrations of CaCl2-extractable Cd, available phosphorus, and available potassium, as well as the cation exchange capacity and urease activity, were significantly reduced in the MV treatment. Furthermore, 16 S rDNA high-throughput sequencing results of the soil microbial community structure showed that compared with the control, MV increased the soil microbial richness, increased the relative abundance of anaerobic microorganisms, and significantly increased the relative abundance of Thermodesulfovibrio and Geobacter at the genus level. The increase in anaerobic microbial abundance was closely related to the decrease in CaCl2-extractable Cd concentration. The application of MV promoted the formation of iron plaque, inhibited the transport of Cd, increased the abundance of anaerobic microorganisms, decreased the CaCl2-extractable Cd concentration, and reduced the Cd concentration in rice grain.

Astragalus sinicus Incorporated as Green Manure for Weed Control in Corn.

Astragalus sinicus L. (milk vetch), one of the most widespread green manure species, is widely planted in the temperate zone. Eleusine indica L. (goosegrass), a serious annual weed in the world, has evolved resistance to some non-selective herbicides. The use of milk vetch as green manure for weed control in paddy fields was proposed. Aqueous extracts of milk vetch are known to exert a different level of phytotoxicity on weeds and crops. Phytotoxic substances contained in green manure were released into the soil by leaching at the initial stage and decomposition at the later stage after the return of green manure. Considering the need for searching new sustainable strategies for weed control, a question arises: "if milk vetch could be applied in goosegrass control, which stage is the most important to control goosegrass after milk vetch returned to the field, and at the same time, will the subsequent crop, corn (Zea mays L.), be affected by the side effects from milk vetch phytotoxicity?" In this study, the potential of milk vetch for goosegrass control was approached by repeated laboratory experiments, which include the aqueous extract experiment, decomposed experiment, and pot experiment. The effects of milk vetch returning to the field on maize were simulated by a pot experiment. The extract of milk vetch could significantly inhibit the germination of goosegrass at 2% concentration, and the inhibition enhanced with the increase of concentration. In the decomposed liquid experiment, decay time within 15 days, with the increase of decay days or concentration, goosegrass inhibition effect of decomposed liquid was enhanced. When decay time was more than 15 days, the inhibition ability of the decomposed liquid to goosegrass decreased. According to the RI accumulated value, aqueous extract and decomposed liquid have a "hormesis effect" on the germination and growth of goosegrass. Pot experiment proved that the addition of 1-10% (w/w) of milk vetch significantly reduced the germination and growth of goosegrass. On the contrary, the comprehensive analysis showed that the participation of milk vetch was conducive to the growth of corn. Our results constitute evidence that the incorporation of milk vetch into the soil could be a feasible practice to reduce weed infarctions in the corn-based cropping system.

Nitrogen application practices to reduce cadmium concentration in rice (Oryza sativa L.) grains.

Cadmium (Cd) pollution in paddy soils creates challenges in rice grain production, thereby threatening food security. The effectiveness of different base-tillering-panicle urea application ratios and the combined basal application of urea and Chinese milk vetch (CMV, Astragalus sinicus L.) in minimizing Cd accumulation in rice grains was explored in a Cd-contaminated acidic soil via a field experiment. The results indicated that under similar nitrogen (N) application rates, an appropriate amount of urea applied at the panicle stage or the combined basal application of urea and CMV decreased Cd absorption by rice roots and its accumulation in rice grains, as compared with that of conventional N application (control). Furthermore, under a 3:4:3 base-tillering-panicle urea application ratio or under a high basal application of CMV (37,500 kg hm-2), Cd concentrations in brown rice were significantly lower (40.7% and 34.1%, respectively) than that of control. Cadmium transport coefficient from root to straw was significantly higher than that of control when an appropriate amount of urea was applied at the panicle stage or when urea and CMV were applied basally, whereas the Cd transport coefficient from straw to brown rice was relatively lower. Moreover, soil pH, or the CEC and CaCl2-Cd concentrations under different N fertilizer treatment was not significantly different. However, the rice grain yield increased by 29.4% with basal application of a high CMV amount compared with that of control. An appropriate amount of urea applied at the panicle stage or the combined basal application of urea and CMV decreased Cd absorption by rice roots and inhibited its transport from straw to brown rice, thus reducing Cd concentration in brown rice. Therefore, combined with the key phase of Cd accumulation in rice, a reasonable urea application ratio or a basal application of high CMV amounts could effectively reduce Cd concentration in brown rice.

Weed suppression and antioxidant activity of Astragalus sinicus L. decomposition leachates.

Astragalus sinicus L. (milk vetch), a versatile plant that has a soil-enriching effect as green manure, is widely planted in the temperate zone of China. In previous experiments, milk vetch incorporated into the soil as green manure showed potential for goosegrass control. However, "what exactly happens at the chemical level?" and "what are the compounds that are potentially responsible for the phytotoxic effects observed during those previous assays?" In a recent study, in vitro phytotoxicity bioassays and chemical analyses of milk vetch decomposition leachates were carried out to explore the relationship between the temporal phytotoxic effects and the dynamics of chemical composition. For that, milk vetch decomposition leachates with a decay time of 12 h, 9 days, 12 days, 15 days, and 18 days were analyzed for organic compounds by liquid chromatography. The main results were as follows: (1) three compounds with goosegrass suppression potential produced during the decomposed process, i.e., 4-ethylphenol, N-acrylimorpholine, and allyl isothiocyanate. 2-Hydroxyethyl acrylate was present in the 12-h decomposition leachates but was at its highest concentration of 127.1 µg ml-1 at 15 days. (2) The cultures were configured according to the four concentrations of goosegrass-resistant active substances measured in the 15-day decomposition leachate and, as with the 15-day decomposition leachate, the mixture cultures inhibited 100% of goosegrass germination at the high concentrations (≥ 30%), which suggests that these substances have goosegrass suppression potential. (3) The high total phenolic content (302.8-532.3 mg L-1), the total flavonoid content (8.4-72.1 mg L-1), and the reducing activity of the decomposition leachates for different decay times may explain why the incorporation of milk vetch into the soil did not lead to peroxidation of goosegrass in the previous study. (4) Finally, the changes in acid fraction and total content (1.9-4.2 mg ml-1) for different decay times explain the variations in pH of the decomposition leachates, which, when discussed in conjunction with previous studies, may lead to changes in soil nutrient effectiveness and consequently affect crop growth. This study can provide a reference for green weed control research.

Co-utilizing milk vetch, rice straw, and lime reduces the Cd accumulation of rice grain in two paddy soils in south China.

The danger posed by cadmium (Cd) pollution to rice production is continuously increasing. Co-utilizing milk vetch (Astragalus sinicus L.) and rice straw is a good practice for rice yield and soil fertility in south China. However, its effects on Cd availability in soil-rice systems remain unclear. A micro-plot trial of two typical paddy soils (alluvial sandy soil and reddish clayey soil) in south China was conducted to investigate the effects of milk vetch, rice straw, lime, and their combined application on Cd availability and the related mechanisms. Soil chemical properties, CaCl2-extractable Cd (CaCl2-Cd), total content of Cd (Total-Cd), Cd fractionation (BCR sequential-extraction method), and Cd accumulation in rice were measured. Results showed that the co-utilization of milk vetch, rice straw, and lime (GRFL) decreased the Cd content in rice grain by 91.43% and 15.63% in early rice of two soils, respectively. Cd was not detected in late rice grains. CaCl2-Cd decreased by 0.025 mg kg-1 in late rice of alluvial sandy soil, 0.057 and 0.044 mg kg-1 decreased in early and late rice of reddish clayey soil, and Total-Cd decreased by 19.4% and 9.1% for early rice of two soils, respectively. Co-utilizing milk vetch, rice straw, and lime changed the distribution of different chemical forms of Cd, decreased the content of bioavailable Cd in soil by reducing the Aci-Cd and RedCd, and benefited the formation of more stable residual fraction (ResCd). Redundancy analysis showed that the improvement in soil pH, dissolved organic matter (DOM), and other soil properties was the main cause of the transformation of Cd form. Among the soil properties, pH and DOM had the greatest impacts on Cd availability. In conclusion, co-utilizing milk vetch and rice straw can alleviate the danger of soil Cd in rice production, and this effect could be strengthened by applying lime.

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Root exudates are important carriers for material exchange and information transfer between plant and soil, and important regulators of crop-soil-microorganism interaction in intercropping systems. We examined the interaction between crops in intercropping system by setting three treatments, monoculture Chinese milk vetch, monoculture rape and Chinese milk vetch intercropped with rape. The responses of root exudates were emphatically analyzed. The results showed that 391 root exudates were detected, with 93 of which being identified and divided into nine types of metabo-lites. Among them, organooxygen compounds were the most abundant, mainly in the form of ribitol. Under different planting patterns, root exudates of Chinese milk vetch and rape were significantly different. The characteristics of root exudates in intercropping were similar to monoculture rape, but significantly different from monoculture Chinese milk vetch. Among the root exudates in different planting modes, only 9-fluorenone 1 was negatively correlated with others. The differential root exudates were mainly benzenoids, lipids and lipid-like molecules, organic acids and derivatives, and organooxygen compounds. The benzenoids, lipids and lipid-like molecules were important types that characterized the changes of root exudates of Chinese milk vetch and rape. Chinese milk vetch intercropping with rape changed the characteristics of root exudates, which were closely related to benzenoids, lipids, and lipid-like molecules.

Succession of fungal community and enzyme activity during the co-decomposition process of rice (Oryza sativa L.) straw and milk vetch (Astragalus sinicus L.).

The co-incorporation of rice straw (RS) and milk vetch (MV) into paddy fields has been increasingly applied as a sustainable farming practice in southern China. Our previous study revealed the contribution of bacteria to the co-decomposition of the RS and MV mixture, although additional underlying factors driving the co-decomposition process need to be clarified. The present study further determined the succession of fungal communities and enzyme activity in the co-decomposition process of the RS and MV mixture. The results showed that non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled RS and MV mixture during the co-decomposition process, stimulating mixture decomposition. Overall fungal abundance was 19.6-30.6% higher in the RS and MV mixture throughout the study than in the single residue. Fungal diversity and community structure were mainly affected by the sampling date rather than the type of residue. Specifically, mixing RS and MV significantly increased the abundance of Peziza sp. and Reticulascus tulasneorum (lignocellulose- and lignin-decomposing fungi) and exhibited higher activities of C- and N-related hydrolases than monospecific residues. Random forest (RF) models showed that bacteria contributed more to the residue decomposition and activities of C-related hydrolases, N-related hydrolases, and oxidases than fungi. However, both RF and partial least squares path models revealed that fungal abundance and community structure directly or indirectly affected the residue decomposition rate. These findings showed that mixing RS and MV could stimulate their decomposition by enhancing C-related hydrolase activity and Peziza sp. and Reticulascus tulasneorum abundance.