Comparative Analysis of miRNA Expression Profiles Between Heat-Tolerant and Heat-Sensitive Genotypes of Flowering Chinese Cabbage Under Heat Stress Using High-Throughput Sequencing

Heat stress disturbs cellular homeostasis, thus usually impairs yield of flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee). MicroRNAs (miRNAs) play a significant role in plant responses to different stresses by modulating gene expression at the post-transcriptional level. However, the roles that miRNAs and their target genes may play in heat tolerance of flowering Chinese cabbage remain poorly characterized. The current study sequenced six small RNA libraries generated from leaf tissues of flowering Chinese cabbage collected at 0, 6, and 12 h after 38 °C heat treatment, and identified 49 putative novel miRNAs and 43 known miRNAs that differentially expressed between heat-tolerant and heat-sensitive flowering Chinese cabbage. Among them, 14 novel and nine known miRNAs differentially expressed only in the heat-tolerant genotype under heat-stress, therefore, their target genes including disease resistance protein TAO1-like, RPS6, reticuline oxidase-like protein, etc. might play important roles in enhancing heat-tolerance. Gene Ontology (GO) analysis revealed that targets of these differentially expressed miRNAs may play key roles in responses to temperature stimulus, cell part, cellular process, cell, membrane, biological regulation, binding, and catalytic activities. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis identified their important functions in signal transduction, environmental adaptation, global and overview maps, as well as in stress adaptation and in MAPK signaling pathways such as cell death. These findings provide insight into the functions of the miRNAs in heat stress tolerance of flowering Chinese cabbage.

A Brassica miRNA Regulates Plant Growth and Immunity through Distinct Modes of Action

In plants, high disease resistance often results in a reduction of yield. Therefore, breeding crops with balanced yield and disease resistance has become a major challenge. Recently, microRNA (miRNA)-mediated R gene turnover has been shown to be a protective mechanism used by plants to prevent autoimmunity in the absence of pathogens. However, whether these miRNAs play a role in plant growth and how miRNA-mediated R gene turnover responds to pathogen infection have rarely been explored. Here, we found that a Brassica miRNA, miR1885, targets both an immune receptor gene and a development-related gene for negative regulation through distinct modes of action. MiR1885 directly silences the TIR-NBS-LRR class of R gene BraTNL1 but represses the expression of the photosynthesis-related gene BraCP24 by targeting the Trans-Acting Silencing (TAS) gene BraTIR1 for trans-acting small interfering RNAs (tasiRNAs)-mediated silencing. We found that, under natural conditions, miR1885 was kept at low levels to maintain normal development and basal immunity but peaked during the floral transition to promote flowering. Interestingly, upon Turnip mosaic virus (TuMV) infection, miR1885-dependent trans-acting silencing of BraCP24 was enhanced to speed up the floral transition, whereas miR1885-mediated R gene turnover was overcome by TuMV-induced BraTNL1 expression, reflecting precise regulation of the arms race between plants and pathogens. Collectively, our results demonstrate that a single Brassica miRNA dynamically regulates both innate immunity and plant growth and responds to viral infection, revealing that Brassica plants have developed a sophisticated mechanism in modulating the interplay between growth, immunity, and pathogen infection.

Disturbance and competition drive diversity effects in cabbage-aphid-onion systems with intra-specific genetic variation

Decreased reliance on pesticides can be achieved through a clever use of eco-evolutionary knowledge via intercropping economically valuable crops with companion plants that can hamper pest outbreaks. We created a greenhouse multi-layered microcosm system to test two potato peach aphid clones, performing alone or in competition, on mixes of genetically variable cultivars of cabbage, with and without onion. The onion acted as a nuisance/disturbance for the pest, which was generally for the benefit of the cabbage albeit both plants sharing space and nutrients. The onion effect was context-specific and differed by aphid genotype. Onion variable nuisance negatively affected the numbers of one aphid genotype (green) across all contexts, while the other genotype (pink) numbers were decreased in two contexts only. However, the green performed better than the pink on all cases of cabbage di-mixes despite its numbers being capped when the onion was present. Further, there was also a general aphid propensity to wander off the plant along with a differential production of winged morphs to escape the onion-affected environments. Moreover, through a comparative increase in dry mass, which was subject to onion and aphid effects, a diversity effect was found where the cabbages of fully genetically variable microcosms sustained similar final dry mass compared with non-infested microcosms. Our findings provide fresh insights into the use of multi-layered contextual designs that not only allow disentangling the relative effects of genetic variation and modes of interaction, but also help integrate their benefits into pest management in view of companion planting.

Phytoavailability of bound residue of Carbendazim to Chinese cabbage (Brassica campestris ssp.chinensis) coexisted with Superabsorbent polymers

Understanding the bioavailability and phytotoxicity of Carbendazim (MBC) bound residues (BR) in soils incubated with different Superabsorbent polymer (SAP) amendment on succeeding crops is essential to assess their environmental fate and risks. In our research, we studied the morphological characteristics and 14C-accumulation of Chinese cabbage and released BR in three typical cultivated soils. The plant dry weight was in order of superabsorbent-hydrogels formulations (HMBC) > MBC > MBC and SAP (MBC-SAP) at 35 d in basic soil 3 (S3), with 675.40 ± 29.07 mg/plant.d.w, 575.93 ± 25.35 mg/plant.d.w and 427.86 ± 18.79 mg/plant.d.w. The whole plant accumulated 2-fold more BR when grew in neutral soil 2 (S2) treated with SAP than MBC at 7 d. The root accumulated a greater proportion of 14C-MBC residue than shoot, with order of MBC-SAP > MBC > HMBC at 21d. The results indicate MBC-BR could be released and accumulated in plant. HMBC promoted the Chinese cabbage growth with lowest 14C accumulation, while MBC-SAP inhibited plant growth with the highest 14C uptake. The released BR rate was 61.43 ± 3.75% of initial BR in MBC-SAP, with 2-fold higher than MBC and HMBC. It is assumed HMBC could be a potential environmentally friendly measure for rational use of pesticides in future.

Nitric oxide alleviates salt stress in seed germination and early seedling growth of pakchoi (Brassica chinensis L.) by enhancing physiological and biochemical parameters

The germination and seedling vigor of crops is negatively affected by soil salinity. Nitric oxide (NO) has emerged as a key molecule involved in many physiological events in plants. The objective of present study was to evaluate the impact of exogenous sodium nitroprusside (SNP, a NO donor) at different concentrations on the seed germination and early seedling growth characteristics of pakchoi (Brassica chinensis L.) under NaCl stress. 100 mM NaCl stress markedly inhibited the seed germination potential, germination index, vitality index and growth of radicles and plumules. SNP pretreatment attenuated the salt stress effects in a dose-dependent manner, as indicated by enhancing the characteristics of seed germination and early seedling growth parameters, and the mitigating effect was most pronounced at 10 μM SNP. Efficient antioxidant systems were activated by SNP pre-treatment, and which effectively increased the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), and reduced contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) and the production rate of superoxide anion radical (O₂^·-) in radicles and plumules, thereby preventing oxidative damage from NaCl stress. SNP pre-treatment also increased the contents of proline and soluble sugar in radicles and plumules under NaCl stress. In addition, SNP pre-treatment significantly increased the K⁺ contents and decreased Na⁺ contents in radicles and plumules, resulting in the increased level of K⁺/Na⁺ ratio. Our results demonstrated that SNP application on pakchoi seeds may be a good option to improve seed germination and seedling growth under NaCl stress by modulating the physiological responses resulting in better seed germination and seedling growth.

Sound waves affect the total flavonoid contents in Medicago sativa, Brassica oleracea and Raphanus sativus sprouts

BACKGROUND

Sound waves are emerging as a potential biophysical alternative to traditional methods for enhancing plant growth and phytochemical contents. However, little information is available on the improvement of the concentration of functional metabolites like flavonoids in sprouts using sound waves. In this study, different frequencies of sound waves with short and long exposure times were applied to three important varieties to improve flavonoid content. The aim of this study was to investigate the effect of sound waves on flavonoid content on the basis of biochemical and molecular characteristics.

RESULTS

We examined the effects of various sound wave treatments (250 Hz to 1.5 kHz) on flavonoid production in alfalfa (Medicago sativa), broccoli (Brassica oleracea) and red young radish (Raphanus sativus). The results showed that sound wave treatments differentially altered the total flavonoid contents depending upon the growth stages, species and frequency of and exposure time to sound waves. Sound wave treatments of alfalfa (250 Hz), broccoli sprouts (800 Hz) and red young radish sprouts (1 kHz) increased the total flavonoid content by 200%, 35% and 85%, respectively, in comparison with untreated control. Molecular analysis showed that sound waves induce the expression of genes of the flavonoid biosynthesis pathway, which positively corresponds to the flavonoid content. Moreover, the sound wave treatment significantly improves the antioxidant efficiency of sprouts.

CONCLUSIONS

The significant improvement of flavonoid content in sprouts with sound waves makes their use a potential and promising technology for the production of agriculture-based functional foods. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Morphological, transcriptomics and phytohormone analysis shed light on the development of a novel dwarf mutant of cabbage (Brassica oleracea)

Plant dwarf mutants generally exhibit delayed growth, delayed development, short internodes, and abnormal leaves and flowers and are ideal materials to explore the molecular mechanism of plant growth and development. In the current study, we first discovered a spontaneous cabbage (Brassica oleracea) dwarf mutant 99-198dw, which exhibits a dwarf stature, wrinkled leaves, non-heading, and substantially reduced self-fertility compared with the wild-type 99-198; however, the underlying molecular mechanism of its dwarfism is unknown. Here, we performed comparative phenotype, transcriptome and phytohormone analyses between 99-198 and 99-198dw. Cytological analysis showed that an increase in cell size, a reduction in cell layers, chloroplast degradation and a reduction in mitochondria were observed in 99-198dw. RNA-Seq showed that a total of 3801 differentially expressed genes (DEGs) were identified, including 2203 upregulated and 1598 downregulated genes in the dwarf mutant. Key genes in stress-resistant pathways were mostly upregulated, including salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), ethylene (ET), etc., while the DEGs reported to be related to plant height, such as those involved in the gibberellin (GA), brassinolide (BR), indole-3-acetic acid (IAA), and strigolactone (SL) pathways were mostly downregulated. In addition, the DEGs in the cell division pathway were all downregulated, which is consistent with the cytokinesis defects detected by cytological analysis. The changes in the GA4, JA, ET, SA and ABA contents measured by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) absolute quantification were consistent with the transcriptome analysis. Further hormone treatment tests showed that the exogenous application of GA, BR, 6BA, paclobutrazol (PC), etc. did not rescue the phenotype, implying that the change in phytohormones is due to but not the cause of the dwarf trait. It was speculated that mutation of certain DEG related to cell division or participating in signalling pathway of phytohormones like GA, BR, IAA, and SL were the cause of dwarf. These results are informative for the elucidation of the underlying regulatory network in 99-198dw and enrich our understanding of plant dwarf traits at the molecular level.

Screening and Assessment of Potential Plant Growth-promoting Bacteria Associated with Allium cepa Linn

Plant growth-promoting bacteria (PGPB) are beneficial microbes that increase plant growth and yield. However, limited information is currently available on PGPB in onion (Allium cepa Linn.). The aims of the present study were to isolate and identify PGPB in onion and examine the effects of isolated PGPB on germination and growth during the vegetative stage in onion, pak choy (Brassica chinensis), and sweet pepper (Capsicum annuum). Twenty-three strains of PGPB were isolated from the roots, bulbs, and rhizosphere soil of onion. All isolated bacterial strains showed one or more PGP traits, including indole acetic acid production, phosphate solubilization ability, and 1-aminocyclopropane-1-carboxylate deaminase and nitrogenase activities; most of these traits were derived from Bacillus sp., Microbacterium sp., and Pseudomonas sp. Eight bacteria that exhibited strong abilities to produce indole acetic acid were selected for a Petri dish trial, soil pot test, and vermiculate pot test. The Petri dish trial showed that strains ORE8 and ORTB2 simultaneously increased radicle and hypocotyl lengths in onion, but inhibited growth in sweet pepper after 7 d. The soil pot experiment on onion revealed that strains ORE5, ORE8, and ORTB2 strongly promoted growth during the vegetative stage with only a half dose of chemical fertilizer. The present results indicate that ORE8 (Bacillus megaterium) and ORTB2 (Pantoea sp.) are the most promising biofertilizers of onion and may simultaneously inhibit the seedling growth of other plants.

The ecological role of bacterial seed endophytes associated with wild cabbage in the United Kingdom

Endophytic bacteria are known for their ability in promoting plant growth and defense against biotic and abiotic stress. However, very little is known about the microbial endophytes living in the spermosphere. Here, we isolated bacteria from the seeds of five different populations of wild cabbage (Brassica oleracea L) that grow within 15 km of each other along the Dorset coast in the UK. The seeds of each plant population contained a unique microbiome. Sequencing of the 16S rRNA genes revealed that these bacteria belong to three different phyla (Actinobacteria, Firmicutes, and Proteobacteria). Isolated endophytic bacteria were grown in monocultures or mixtures and the effects of bacterial volatile organic compounds (VOCs) on the growth and development on B. oleracea and on resistance against a insect herbivore was evaluated. Our results reveal that the VOCs emitted by the endophytic bacteria had a profound effect on plant development but only a minor effect on resistance against an herbivore of B. oleracea. Plants exposed to bacterial VOCs showed faster seed germination and seedling development. Furthermore, seed endophytic bacteria exhibited activity via volatiles against the plant pathogen F. culmorum. Hence, our results illustrate the ecological importance of the bacterial seed microbiome for host plant health and development.

Comparative Transcriptome Analysis of the Molecular Mechanism of the Hairy Roots of Brassica campestris L. in Response to Cadmium Stress

Brassica campestris L., a hyperaccumulator of cadmium (Cd), is considered a candidate plant for efficient phytoremediation. The hairy roots of Brassica campestris L are chosen here as a model plant system to investigate the response mechanism of Brassica campestris L. to Cd stress. High-throughput sequencing technology is used to identify genes related to Cd tolerance. A total of 2394 differentially expressed genes (DEGs) are identified by RNA-Seq analysis, among which 1564 genes are up-regulated, and 830 genes are down-regulated. Data from the gene ontology (GO) analysis indicate that DEGs are mainly involved in metabolic processes. Glutathione metabolism, in which glutathione synthetase and glutathione S-transferase are closely related to Cd stress, is identified in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. A Western blot shows that glutathione synthetase and glutathione S-transferase are involved in Cd tolerance. These results provide a preliminary understanding of the Cd tolerance mechanism of Brassica campestris L. and are, hence, of particular importance to the future development of an efficient phytoremediation process based on hairy root cultures, genetic modification, and the subsequent regeneration of the whole plant.

Vernalization and Floral Transition in Autumn Drive Winter Annual Life History in Oilseed Rape

Plants with winter annual life history germinate in summer or autumn and require a period of prolonged winter cold to initiate flowering, known as vernalization. In the Brassicaceae, the requirement for vernalization is conferred by high expression of orthologs of the FLOWERING LOCUS C (FLC) gene, the expression of which is known to be silenced by prolonged exposure to winter-like temperatures [1]. Based on a wealth of vernalization experiments, typically carried out in the range of 5°C-10°C, we would expect field environments during winter to induce flowering in crops with winter annual life history. Here, we show that, in the case of winter oilseed rape, expression of multiple FLC orthologs declines not during winter but predominantly during October when the average air temperature is 10°C-15°C. We further demonstrate that plants proceed through the floral transition in early November and overwinter as inflorescence meristems, which complete floral development in spring. To validate the importance of pre-winter temperatures in flowering time control, we artificially simulated climate warming in field trial plots in October. We found that increasing the temperature by 5°C in October results in raised FLC expression and delays the floral transition by 3 weeks but only has a mild effect on flowering date the following spring. Our work shows that winter annuals overwinter as a floral bud in a manner that resembles perennials and highlights the importance of studying signaling events in the field for understanding how plants transition to flowering under real environmental conditions.

Concentration-dependent effects of tungstate on germination, growth, lignification-related enzymes, antioxidants, and reactive oxygen species in broccoli (Brassica oleracea var. italica L.)

The phyto-impact of tungstate is not frequently studied like other heavy metals especially in the sight of continuous accumulation of tungstate in the agriculture soils and water. Thus, the present study was aimed to investigate the supplementation of various tungstate concentrations (0, 1, 5, 10, 50, and 100) to germination water (mg L^-1) or clay soil (mg kg^-1) on germination and metabolism of broccoli. Lower concentrations (1-10 mg L^-1) accelerated germination process and reciprocally were recorded at the highest one (100 mg L^-1). The promoter effect of lower concentrations on seedlings growing on tungstate contaminated soil was underpinned from enhancement of pigments, metabolites, enzymatic and non-enzymatic antioxidants, and nitrate reductase. However, the highest concentration-noxious impacts perceived from oxidative damage and membrane integrity deregulation accompanied with no gain from increment of proline, superoxide dismutase, and glutathione-S-transferase. The depletion of phytochelatins and nitric oxide jointed with the enhancement of peroxidases, polyphenol oxidase, and phenylalanine ammonia-lyase at higher concentration reinforced lignin production which restricted plant growth. The results supported the hormetic effects of tungstate (beneficial at low concentrations and noxious at high concentration) on morphological and physiological parameters of broccoli seedlings. The stimulatory effect of tungstate on metabolic activities could serve as important components of antioxidative defense mechanism against tungstate toxicity.

Responses of seeds of typical Brassica crops to tetracycline stress: Sensitivity difference and source analysis

Antibiotics can induce adverse effects on plants. Brassica crop seeds, for their advantages, are used widely in seed germination test to investigate phytotoxicity of substances. However, their performances on evaluating antibiotics remain to be studied to select sensitive species for control of potential risks. In this work, common species of Chinese cabbage (Brassica rapa L.), edible rape (Brassica napus L.), and cabbage (Brassica oleracea L.) with three cultivars each were selected to compare and analyze the sensitivity difference of their seeds to tetracycline (TC) stress. Results showed that the ratio of axis to cotyledon (RAC) by fresh weight was an alternative endpoint besides radicle length (RL) in the test. The species sensitivity distribution (SSD) based on the effective concentrations causing x% inhibition (EC_x) in RL of seeds exposed to TC was applied to compare the sensitivity of seeds and estimate the hazardous concentration for x% species (HC_x). From the species-dependent sensitivity and the sensitivity difference of cultivars in the same species of seeds to TC, the performance of Chinese cabbage was the best in the study. The sensitivity of seeds to TC could be evaluated by EC₂₀ related to seed physical traits and germination indices, while the extent of seeds affected by TC could be evaluated by EC₅₀ related to the composition of seed storage reserves. We recommended that it was a new idea to analyze responses of different seeds to TC at large scale according to seed innate characteristics.

Functional Similarity and Difference among Bra-MIR319 Family in Plant Development

miR319 was the first plant miRNA discovered via forward genetic mutation screening. In this study, we found that miR319 family members had similar sequences but different expression patterns in Brassica campestris and Arabidopsis thaliana. RT-PCR analysis revealed that Bra-MIR319a and Bra-MIR319c had similar expression patterns and were widely expressed in plant development, whereas Bra-MIR319b could only be detected in stems. The overexpression of each Bra-MIR319 family member in Arabidopsis could inhibit cell division and function in leaf and petal morphogenesis. Bra-miR319a formed a new regulatory relationship after whole genome triplication, and Bra-MIR319a overexpressing in Arabidopsis led to the degradation of pollen content and affected the formation of intine, thereby causing pollen abortion. Our results suggest that Bra-MIR319 family members have functional similarity and difference in plant development.

Reclaiming Phosphate from Waste Solutions with Fe(III)-Polysaccharide Hydrogel Beads for Photo-Controlled-Release Fertilizer

Photoresponsive hydrogels from polysaccharides and Fe(III) were used as a new system to capture and release PO43- from waste solutions. Uptake of 0.6-1.5 mg of phosphate per gram of hydrogels was determined from 800 ppm phosphate solutions (pH 4.8-9.0). These beads also captured 1.2 mg g-1 of phosphate from animal waste (raw manure, 727 ppm phosphate, pH 7.6), which accounted for above 80% phosphate uptake. Irradiation of phosphate-loaded hydrogels degraded the gels due to the photochemistry of the Fe(III)-carboxylates, giving controlled phosphate release (∼81% after 7 days). No release (<2% after 7 days) was seen in the dark. Kale plant trials showed complete degradation of the hydrogels in ∼2 weeks under greenhouse conditions. Biomass analysis of kale treated with phosphate-loaded beads compared to controls indicated no signs of toxicity. These results show that Fe(III)-polysaccharide hydrogels were able to reclaim phosphates from waste solutions and can be used as a controlled-release fertilizer.

Soil-borne fungi influence seed germination and mortality, with implications for coexistence of desert winter annual plants

Soil-borne fungi influence coexistence of plant species in mesic environments, but much less is known about their effects on demographic processes relevant to coexistence in arid and semi-arid systems. We isolated 43 fungal strains that naturally colonize seeds of an invasive winter annual (Brassica tournefortii) in the Sonoran Desert, and evaluated the impact of 18 of them on seed germination and mortality of B. tournefortii and a co-occurring native annual (Plantago ovata) under simulated summer and winter temperatures. Fungi isolated from B. tournefortii seeds impacted germination and mortality of seeds of both plant species in vitro. Seed responses reflected host-specific effects by fungi, the degree of which differed significantly between the strains, and depended on the temperature. In the winter temperature, ten fungal strains increased or reduced seed germination, but substantial seed mortality due to fungi was not observed. Two strains increased germination of P. ovata more strongly than B. tournefortii. In the summer temperature, fungi induced both substantial seed germination and mortality, with ten strains demonstrating host-specificity. Under natural conditions, host-specific effects of fungi on seed germination may further differentiate plant species niche in germination response, with a potential of promoting coexistence. Both host-specific and non-host-specific effects of fungi on seed loss may induce polarizing effects on plant coexistence depending on the ecological context. The coexistence theory provides a clear framework to interpret these polarizing effects. Moreover, fungi pathogenic to both plant species could induce host-specific germination, which challenges the theoretical assumption of density-independent germination response. These implications from an in vitro study underscore the need to weave theoretical modeling, reductive empirical experiments, and natural observations to illuminate effects of soil-borne fungi on coexistence of annual plant species in variable desert environments.

Influence of photoluminophore-modified agro textile spunbond on growth and photosynthesis of cabbage and lettuce plants

Light-converting polypropylene spunbond was first used in the study of the key physiological parameters of plants. A comparative study of the functioning of the photosynthetic apparatus and the dynamics of growth in late cabbage plants (Olga variety) and leaf lettuce (Emerald variety) was conducted using the ordinary nonwoven polypropylene fabric (spunbond) (density 30 g·m-2) and the spunbond containing a photoluminophore (PL) (1.6% yttrium oxysulfide doped with europium). The plants were grown in a glass greenhouse without spunbond and under the spunbond containing and not containing the PL that transforms a part of UV-radiation into red light radiation. The use of the spunbond led to a decrease in the rate of photosynthesis, activity of the photosystem 2, and the accumulation of plant biomass and to an increase in the stomatal conductance. By contrast to unmodified spunbond, the application of the spunbond containing the PL led to an increase in the rate of photosynthesis, the water-use efficiency (WUE), and the accumulation of the total biomass of plants by 30-50% but to a decrease in the transpiration rate and the stomatal conductance. It is assumed that the positive effect of the PL is associated with an increase in the fraction of fluorescent red light, which enhances photosynthetic activity and accelerates plant growth.

Biopesticide based sustainable pest management for safer production of vegetable legumes and brassicas in Asia and Africa

Vegetables are one of the important crops which could alleviate poverty and malnutrition among the smallholder farmers in tropical Asia and Africa. However, a plethora of pests limit the productivity of these crops, leading to economic losses. Vegetable producers overwhelmingly rely on chemical pesticides in order to reduce pest-caused economic losses. However, over-reliance on chemical pesticides poses serious threats to human and environmental health. Hence, biopesticides offer a viable alternative to chemical pesticides in sustainable pest management programs. Baculoviruses such as nucleopolyhedrovirus (NPV) and granulovirus (GV) have been exploited as successful biological pesticides in agriculture, horticulture and forestry. Maruca vitrata multiple nucleocapsid NPV (MaviMNPV) was found to be a unique baculovirus specifically infecting pod borer on food legumes, and it has been successfully developed as a biopesticide in Asia and Africa. Entomopathogenic fungi also offer sustainable pest management options. Several strains of Metarhizium anisopliae and Beauveria bassiana have been tested and developed as biopesticides in Asia and Africa. This review specifically focuses on the discovery and development of entomopathogenic virus and fungi-based biopesticides against major pests of vegetable legumes and brassicas in Asia and Africa. © 2019 Society of Chemical Industry.

Effects of Earthworms and Agricultural Plant Species on the Soil Nematode Community in a Microcosm Experiment

Both earthworms and plants may affect the soil nematode community. However, the effects of earthworms and plant species interactions on soil nematode community are poorly understood. We explored how an epigeic earthworm Eisenia fetida affects the soil nematode community in systems with three representative plants (wheat, cotton and cabbage) which were grown in pots with or without added earthworms under greenhouse conditions. Earthworm presence decreased the abundance of total nematode and all four nematode trophic groups, except for the fungivore and predator/omnivore nematodes in wheat systems, but increased the genus richness of nematode in all treatments. Due to plant identity and different root exudates, plants had significant effects on soil nematode abundance. Compared with the no plant and without earthworm treatment, wheat and cabbage had the higher stimulation of the abundance of total nematode, bacterivores and fungivores, and cotton had the higher stimulation of the abundance of fungivores and predators-omnivores; whereas earthworm presence mostly weakened the stimulation effects of plant species on soil nematode abundance which indicated earthworms had the enhanced effects in the presence of plants. The interaction affected soil nematode abundance (total nematodes, bacterivore, fungivore and omnivore-predators) and community diversity indices (diversity index H', evenness index J', community maturity index ∑MI, Simpson dominance index λ and nematode channel ratio NCR). Principal component analysis showed that plant species affected soil nematode community composition. Redundancy analysis indicated plant species and biomass accounted for 41.60% and 34.13% of the variation in soil nematode community structure, respectively; while earthworms explained only 6.13%. Overall, current study suggest that earthworm could inhibit nematode abundance; whereas, plants have exerted greater influences on nematode community structure than earthworm presence due to their species-specific effects on different trophic groups of nematodes.

Potential toxicity of trace elements and nanomaterials to Chinese cabbage in arsenic- and lead-contaminated soil amended with biochars

To our knowledge, this is the first report on exploring the interactive effects of various biochars (BCs) and nanomaterials (NMs) on plant growth and bioavailability of trace elements in soil. This study evaluated the bioavailability and toxicity of arsenic (As), lead (Pb), and NMs to cabbage plants. The BCs were produced from rice husk (RB), sewage sludge, and bamboo wood (WB). The BCs at 2.5 and 5% (w w^-1), NMs for removing As (NMs-As) and heavy metals (NMs-HM) at 3000 mg kg^-1, and multi-walled carbon nanotubes (CNT) at 1000 mg kg^-1 were applied in bioassay and incubation experiments (40 days), along with the unamended soil as the control. Results showed that the NMs-As and NMs-HM decreased seed germination at 3 days after sowing; however, their toxicity was eliminated by BCs. Growth parameters of cabbage revealed that the CNT was the most toxic NMs, as it was translocated in root and leaf cells, which was confirmed by transmission electron microscopic images. Bioavailable Pb was reduced by 1.2-3.8-folds in all amended rhizosphere and bulk soils. Amendments of 2.5% WB + NMs-As and 2.5% RB + NMs-As significantly decreased both bioavailable As and Pb.

Benefits of phytoremediation amended with DC electric field. Application to soils contaminated with heavy metals

The objective of this study was to determine the influence of the DC electric current in the physicochemical properties of soil. The electric current may induce changes in pH and electric conductivity that will be reflected in the distribution of the electric potential in the soil specimen. This information will be used for the development of a phytoremediation technology amended with electric current. The results showed that low or moderate voltage gradients (0.67 V/cm) induced small changes in physicochemical properties of soil that do not compromise plant survival. The selected voltage gradient was used in electro-phytoremediation tests in soil contaminated with heavy metals (Cd, Co, Cr, Cu, Pb and Zn). Two plants species adapted to the soil and climate conditions were selected (Brassica rapa L. subsp. rapa and Lolium perenne L.). The electric field enhanced the plant growing, mainly in L. perenne, and increased the phytoremediation of the 6 metals. Mixed cultures of the two plant species showed interesting results for large scale applications.

Agronomic performance, energy analysis, and carbon balance comparing different fertilization strategies in horticulture under Mediterranean conditions

Production capacity evaluation and environmental sustainability assessment allow defining both the most appropriate fertilization strategies and the agricultural systems management. The aims of this study were to investigate the following, in a cauliflower-lettuce rotation: (i) agricultural system agronomic performance, (ii) fertilization treatments environmental sustainability through the energy inputs/outputs analysis, and (iii) carbon footprint through the GHG emissions and carbon sequestration analyses. Three fertilization strategies were compared: (i) CM, compost from municipal solid waste; ii) MIN, mineral fertilizers; iii) MIX, the CM compost plus a mineral fertilizer. Cauliflower and lettuce responses to fertilization were influenced by climatic conditions from year to year, and among the fertilizer treatments, the CM demonstrated a better resilience to the extreme weather events. It also showed the highest renewable energy (44.3%), suggesting that the substitution of mineral fertilizers with organic ones may help to reduce the non-renewable energy depletion, thus promoting the sustainability in horticultural systems. The CM was the most efficient treatment, since the energy stocked as C in the soil (145,889 MJ ha-1) and the net energy and the energy efficiency for cauliflower and lettuce (113,106 MJ ha-1 and 3.1, respectively) were the highest. Our results suggest that the application of the tested sustainable practices makes the farm a "sink" for the atmospheric CO2.

Bioaugmentation of Exogenous Strain Rhodococcus sp. 2G Can Efficiently Mitigate Di(2-ethylhexyl) Phthalate Contamination to Vegetable Cultivation

This work developed a bioaugmentation strategy that simultaneously reduced soil di(2-ethylhexyl) phthalate (DEHP) pollution and its bioaccumulation in Brassica parachinensis by inoculating the isolated strain Rhodococcus sp. 2G. This strain could efficiently degrade DEHP at a wide concentration range from 50 to 1600 mg/L and transformed DEHP through a unique biochemical degradation pathway that distinguished it from other Rhodococcus species. Besides, strain 2G colonized well in the rhizosphere soil of the inoculated vegetable without competition with indigenous microbes, resulting in increased removal of DEHP from soil (∼95%) and reduced DEHP bioaccumulation in vegetables (∼75% in the edible part) synchronously. Improved enzyme activities and DOC content in the rhizosphere of the planting vegetable and inoculating strain 2G were responsible for the high efficiency in mitigating DEHP contamination to vegetable cultivation. This work demonstrated a great potential application to grow vegetables in contaminated soil for safe food production.

Substituting organic manure for compound fertilizer increases yield and decreases NH3 and N2O emissions in an intensive vegetable production systems

Substituting organic manure for compound fertilizer may play an important role in regulating the nitrogen (N) cycle and consequently affecting crop yield in agroecosystems. However, how substituting different organic manures for compound fertilizer affects crop yield and ammonia (NH₃) and nitrous oxide (N₂O) emissions in the vegetable system during the life-cycle production (including storage and field application) remains poorly elucidated. Thus, we conducted a greenhouse experiment to investigate the effects of substituting organic manure species, i.e., stored swine manure fertilizer (SS), swine manure covered by straw (CS), stored swine fertilizer mixed with biochar (BS), and stored swine manure fertilizer with void expansion (OS) for compound fertilizer (FC) on rapeseed yield and NH₃ and N₂O emissions in a rapeseed-cropping system in China. The results showed that the total gaseous N losses (NH₃ and N₂O) were 1.6, 1.4 and 1.1 times higher in SS, CS and OS than FC, respectively. However, total gaseous N losses in BS was 0.9 times less than FC. Compared with FC, rapeseed yield and N uptake in SS and CS were decreased by 17.2-20.2% and 16.0%-28.1%, respectively, but which were increased by 7.3% and 54.1% in BS, respectively. In addition, OS decreased rapeseed yield by 17.2%, but increased N uptake by 8.5%. Therefore, the effects of substituting organic manure for compound fertilizer on rapeseed yield, N uptake, NH₃ and N₂O varied regarding different organic manure species. Adopting stored swine fertilizer mixed with biochar might be a sound management practice to reduce gaseous N losses and enhance N uptake and yield in intensive vegetable production systems.

Creek to Table: Tracking fecal indicator bacteria, bacterial pathogens, and total bacterial communities from irrigation water to kale and radish crops

The impact of microbially contaminated irrigation water on risks to produce safety and public health is a complex issue that is not well understood. This study tracked fecal indicators, pathogenic bacteria, and total bacterial communities from a creek water irrigation source to irrigated produce to assess the impact of irrigation events on soil and produce-associated microbiota. Kale and radishes were drip-irrigated using Mid-Atlantic creek water in October 2017. Plant and soil samples were collected immediately before and after irrigation, and for 3 consecutive days thereafter. All samples (n = 134), including irrigation water, were tested for generic Escherichia coli and total coliforms (TC) using standard membrane filtration or direct plating, and for Salmonella enterica and Listeria monocytogenes by selective enrichment. DNA extracted from all samples was PCR-amplified for the V3-V4 region of the 16S rRNA gene for bacterial community profiling. In soil, TC levels were significantly higher immediately and 3 days post-irrigation compared to pre-irrigation (p < 0.01). E. coli levels in soil increased after irrigation, but the difference was not significant (p = 0.31), and die-off was not observed. No E. coli were detected on kale leaves. TC increased over the study period on radish roots (p < 0.01) but not kale leaves (p = 0.43). Although target pathogens were detected in irrigation water, S. enterica was detected from only one post-irrigation kale sample and L. monocytogenes was not detected in the field. The 16S rRNA gene sequencing data revealed differences in bacterial community structure and composition across sample types and showed that radish soil and root surface bacterial communities were more strongly influenced by irrigation compared to kale samples. This study provides insights into the impact of irrigation water on fresh produce microbiota, revealing that, although irrigation did influence crop-associated microbiota (especially below ground) in the field, bacterial pathogens were not likely transferred to the crop.