Susceptible Plants Research Articles

A tripartite rheostat controls self-regulated host plant resistance to insects

Plants deploy receptor-like kinases and nucleotide-binding leucine-rich repeat receptors to confer host plant resistance (HPR) to herbivores1. These gene-for-gene interactions between insects and their hosts have been proposed for more than 50 years2. However, the molecular and cellular mechanisms that underlie HPR have been elusive, as the identity and sensing mechanisms of insect avirulence effectors have remained unknown. Here we identify an insect salivary protein perceived by a plant immune receptor. The BPH14-interacting salivary protein (BISP) from the brown planthopper (Nilaparvata lugens Stål) is secreted into rice (Oryza sativa) during feeding. In susceptible plants, BISP targets O. satvia RLCK185 (OsRLCK185; hereafter Os is used to denote O. satvia-related proteins or genes) to suppress basal defences. In resistant plants, the nucleotide-binding leucine-rich repeat receptor BPH14 directly binds BISP to activate HPR. Constitutive activation of Bph14-mediated immunity is detrimental to plant growth and productivity. The fine-tuning of Bph14-mediated HPR is achieved through direct binding of BISP and BPH14 to the selective autophagy cargo receptor OsNBR1, which delivers BISP to OsATG8 for degradation. Autophagy therefore controls BISP levels. In Bph14 plants, autophagy restores cellular homeostasis by downregulating HPR when feeding by brown planthoppers ceases. We identify an insect saliva protein sensed by a plant immune receptor and discover a three-way interaction system that offers opportunities for developing high-yield, insect-resistant crops.

Transcription Factor PecS Mediates Agrobacterium fabrum Fitness and Survival.

The transcriptional regulator PecS is encoded by select bacterial pathogens. For instance, in the plant pathogen Dickeya dadantii, PecS controls a range of virulence genes, including pectinase genes and the divergently oriented gene pecM, which encodes an efflux pump through which the antioxidant indigoidine is exported. In the plant pathogen Agrobacterium fabrum (formerly named Agrobacterium tumefaciens), the pecS-pecM locus is conserved. Using a strain of A. fabrum in which pecS has been disrupted, we show here that PecS controls a range of phenotypes that are associated with bacterial fitness. PecS represses flagellar motility and chemotaxis, which are processes that are important for A. fabrum to reach plant wound sites. Biofilm formation and microaerobic survival are reduced in the pecS disruption strain, whereas the production of acyl homoserine lactone (AHL) and resistance to reactive oxygen species (ROS) are increased when pecS is disrupted. AHL production and resistance to ROS are expected to be particularly relevant in the host environment. We also show that PecS does not participate in the induction of vir genes. The inducing ligands for PecS, urate, and xanthine, may be found in the rhizosphere, and they accumulate within the plant host upon infection. Therefore, our data suggest that PecS mediates A. fabrum fitness during its transition from the rhizosphere to the host plant. IMPORTANCE PecS is a transcription factor that is conserved in several pathogenic bacteria, where it regulates virulence genes. The plant pathogen Agrobacterium fabrum is important not only for its induction of crown galls in susceptible plants but also for its role as a tool in the genetic manipulation of host plants. We show here that A. fabrum PecS controls a range of phenotypes, which would confer the bacteria an advantage while transitioning from the rhizosphere to the host plant. This includes the production of signaling molecules, which are critical for the propagation of the tumor-inducing plasmid. A more complete understanding of the infection process may inform approaches by which to treat infections as well as to facilitate the transformation of recalcitrant plant species.

Antifeedant and insecticidal effects of alfalfa saponins in the management of the Japanese beetle Popillia japonica

AbstractPopillia japonica is a quarantine pest of priority interest for the EU, given its potentially important economic, social and environmental impacts. Alternative strategies to chemical methods are essential to limit its spread in newly infested areas with favourable climatic and environmental conditions. Saponins are biologically active molecules widely distributed in plants, displaying a well‐known repellent activity combined with a mortality effect against insects. In this context, saponins were extracted from alfalfa Medicago sativa, where medicagenic and zanhic acid glycosides and Soyasaponin I were the most abundant compounds and used in the laboratory and semi‐field experiments for treating leaves of susceptible host plants for P. japonica. Under laboratory conditions, a food deterrence effect and a significant mortality rate were observed using Corylus avellana leaves treated at increasing saponin concentrations, ranging from 1% to 5% w/v. Semi‐field condition experiment supported the food deterrence effect, as a significant food preference was observed for untreated plants of Vitis vinifera compared to treated plants. The promising results obtained suggest that alfalfa saponins could represent a potential eco‐friendly approach for Japanese beetle control.

Genomic Analysis Highlights Putative Defective Susceptibility Genes in Tomato Germplasm.

Tomato (Solanum lycopersicum L.) is one of the most widely grown vegetables in the world and is impacted by many diseases which cause yield reduction or even crop failure. Breeding for disease resistance is thus a key objective in tomato improvement. Since disease arises from a compatible interaction between a plant and a pathogen, a mutation which alters a plant susceptibility (S) gene facilitating compatibility may induce broad-spectrum and durable plant resistance. Here, we report on a genome-wide analysis of a set of 360 tomato genotypes, with the goal of identifying defective S-gene alleles as a potential source for the breeding of resistance. A set of 125 gene homologs of 10 S-genes (PMR 4, PMR5, PMR6, MLO, BIK1, DMR1, DMR6, DND1, CPR5, and SR1) were analyzed. Their genomic sequences were examined and SNPs/indels were annotated using the SNPeff pipeline. A total of 54,000 SNPs/indels were identified, among which 1300 were estimated to have a moderate impact (non-synonymous variants), while 120 were estimated to have a high impact (e.g., missense/nonsense/frameshift variants). The latter were then analyzed for their effect on gene functionality. A total of 103 genotypes showed one high-impact mutation in at least one of the scouted genes, while in 10 genotypes, more than 4 high-impact mutations in as many genes were detected. A set of 10 SNPs were validated through Sanger sequencing. Three genotypes carrying high-impact homozygous SNPs in S-genes were infected with Oidium neolycopersici, and two highlighted a significantly reduced susceptibility to the fungus. The existing mutations fall within the scope of a history of safe use and can be useful to guide risk assessment in evaluating the effect of new genomic techniques.

Hormetic Effect of Glyphosate on the Morphology, Physiology and Metabolism of Coffee Plants.

Glyphosate is a nonselective herbicide of systemic action that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, thus compromising amino acid production and consequently the growth and development of susceptible plants. The objective of this study was to evaluate the hormetic effect of glyphosate on the morphology, physiology, and biochemistry of coffee plants. Coffee seedlings (Coffea arabica cv Catuaí Vermelho IAC-144) were transplanted into pots filled with a mixture of soil and substrate and subjected to ten doses of glyphosate: 0, 11.25, 22.5, 45, 90, 180, 360, 720, 1440, and 2880 g acid equivalent (ae) ha-1. Evaluations were performed using the morphological, physiological, and biochemical variables. Data analysis for the confirmation of hormesis occurred with the application of mathematical models. The hormetic effect of glyphosate on coffee plant morphology was determined by the variables plant height, number of leaves, leaf area, and leaf, stem, and total dry mass. Doses from 14.5 to 30 g ae ha-1 caused the highest stimulation. In the physiological analyses, the highest stimulation was observed upon CO2 assimilation, transpiration, stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, electron transport rate, and photochemical efficiency of photosystem II at doses ranging from 4.4 to 55 g ae ha-1. The biochemical analyses revealed significant increases in the concentrations of quinic acid, salicylic acid, caffeic acid, and coumaric acid, with maximum stimulation at doses between 3 and 140 g ae ha-1. Thus, the application of low doses of glyphosate has positive effects on the morphology, physiology, and biochemistry of coffee plants.

The identification of the methylation patterns of tomato curly stunt virus in resistant and susceptible tomato lines.

Tomato curly stunt virus (ToCSV) is a monopartite begomovirus infecting tomatoes in South Africa, with sequence similarity to tomato yellow leaf curl virus (TYLCV). While there are numerous reports on the mechanism of TYLCV resistance in tomato, the underlying mechanisms in the tomato-ToCSV pathosystem is still relatively unknown. The main aim of this study was to investigate and compare the global methylation profile of ToCSV in two near-isogenic tomato lines, one with a tolerant phenotype (T, NIL396) and one with a susceptible phenotype (S, NIL395). Bisulfite conversion and PCR amplification, coupled with a next-generation sequencing approach, were used to elucidate the global pattern of methylation of ToCSV cytosine residues in T and S leave tissue at 35 days post-infection (dpi). The extent of methylation was more pronounced in tolerant plants compared to susceptible plants in all sequence (CG, CHG and CHH) contexts, however, the overall methylation levels were relatively low (<3%). Notably, a significant interaction (p < 0.05) was observed between the viral genomic region and susceptible vs. tolerant status for CG methylated regions where it was observed that the 3'IR CG methylation was significantly (p < 0.05) higher than CG methylation of other genomic regions in tolerant and susceptible plants. Additionally, statistically significant (EdgeR p < 0.05) differentially methylated cytosines were located primarily in the genomic regions V2/V1 and C4/C1 of ToCSV. The relative expression, using RT-qPCR, was also employed in order to quantify the expression of various key methylation-related genes, MET1, CMT2, KYP4/SUVH4, DML2, RDM1, AGO4 and AGO6 in T vs. S plants at 35dpi. The differential expression between T and S was significant for MET1, KYP4/SUVH4 and RDM1 at p<0.05 which further supports more pronounced methylation observed in ToCSV from T plants vs. S plants. While this study provides new insights into the differences in methylation profiles of ToCSV in S vs. T tomato plants, further research is required to link tolerance and susceptibility to ToCSV.

Utilization of primary and secondary biochemical compounds in cotton as diagnostic markers for measuring resistance to cotton leaf curl virus.

Cotton (Gossypium hirsutum L.) is one of the most important staple fibrous crops cultivated in India and globally. However, its production and quality are greatly hampered by cotton leaf curl disease (CLCuD) caused by cotton leaf curl virus (CLCuV). Therefore, the aim of the present study was to investigate the biochemical mechanisms associated with CLCuD resistance in contrasting cotton genotypes. Four commercial cotton varieties with susceptible (HS 6 and RCH-134 BG-II) and resistant (HS 1236 and Bunty) responses were used to analyze the role of primary (sugar, protein, and chlorophyll) and secondary (gossypol, phenol, and tannin) biochemical compounds produced by the plants against infection by CLCuV. The resistant cultivars with increased activity of protein, phenol, and tannin exhibited biochemical barriers against CLCuV infection, imparting resistance in cotton cultivars. Reducing sugar in the healthy plants of the susceptible Bt cultivar RCH 134 BG-II exhibited the highest value of 1.67 mg/g at 90 days. In contrast, the lowest value of 0.07 mg g-1 was observed at 60 DAS in the highly diseased plants of the susceptible hybrid HS 6. Higher phenol content (0.70 mg g-1) was observed at 90 DAS in resistant cultivars, whereas highly susceptible plants exhibited the least phenol (0.25 mg g-1) at 90 DAS. The lowest protein activity was observed at 120 DAS in susceptible cultivars HS 6 (9.4 mg g-1) followed by RCH 134 BG-II (10.5 mg g-1). However, other biochemical compounds, including chlorophyll, sugar, and gossypol, did not show a significant role in resistance against CLCuV. The disease progression analysis in susceptible cultivars revealed non-significant differences between the two susceptible varieties. Nevertheless, these compounds are virtually associated with the basic physiological and metabolic mechanisms of cotton plants. Among the primary biochemical compounds, only protein activity was proposed as the first line of defense in cotton against CLCuV. The secondary level of defense line in resistance showed the activity of secondary biochemical compounds phenol and tannins, which displayed a significant increase in their levels while imparting resistance against CLCuV in cotton.

Metal Micronutrient and Silicon Concentration Effects on Growth and Susceptibility to Pythium Root Rot for Hydroponic Lettuce (Lactuca sativa)

The objectives were to evaluate the effects of increasing metal micronutrient concentrations and silicon (Si) concentrations on plant growth and susceptibility to Pythium root rot with hydroponically grown lettuce (Lactuca sativa). In the first experiment, lettuce was grown in hydroponic solutions with metal micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) supplied at either 0, 2.5, 5, or 10 mg∙L−1. A standard commercial hydroponic solution was also included as a control, with metal micronutrients supplied at 2 Fe, 1 Mn, 0.5 Cu, and 0.5 Zn mg∙L−1. In the second experiment, hydroponic lettuce was grown with Si at 0, 7, 14, 28, and 56 mg∙L−1. Hydroponic treatment solutions for both experiments were either dosed with Pythium myriotylum (Pythium treatment) at 1.80 × 104 oospores per L or deionized water as a non-Pythium control. Data were collected on leaf SPAD chlorophyll content, shoot height and width, total plant fresh mass, and root disease severity. Increasing the Cu concentration in solution decreased Pythium disease severity but reduced lettuce growth and yield. Increasing the concentration of the other metal micronutrients also tended to reduce lettuce growth but had no significant influence on root disease. Supplementing the hydroponic solution with Si had no effect on Pythium root disease severity and slightly decreased lettuce growth at 56 mg∙L−1 Si. Results of this study suggest that the management of micronutrients and Si nutrition is not an effective strategy and, at best, a risky strategy for controlling Pythium in hydroponic lettuce. Growers would likely benefit from maintaining metal micronutrient and Si concentrations within the ranges of (in mg∙L−1) 0.5 to 5.5 for Fe, 0.1 to 2.0 for Mn, 0.1 to 0.6 for Cu, 0.1 to 0.6 for Zn, and 0 to 28 for Si for many hydroponic crops. Supplementing Si has the potential to negatively influence plant growth and quality for certain plant species, and testing is necessary to evaluate phytotoxicity risks prior to implementing in commercial practice. Overall, successful mitigation of root rot pathogens in commercial hydroponic production requires the combination of proper sanitation, best management and cultural practices, appropriate hydroponic system design, and the implementation of a water treatment system with proper design and a multi-barrier approach.

A bacterial type III effector targets plant vesicle-associated membrane proteins.

The soilborne bacterial pathogen Ralstonia solanacearum is one of the most destructive plant pathogens worldwide, and its infection process involves the manipulation of numerous plant cellular functions. In this work, we found that the R. solanacearum effector protein RipD partially suppressed different levels of plant immunity triggered by R. solanacearum elicitors, including specific responses triggered by pathogen-associated molecular patterns and secreted effectors. RipD localized in different subcellular compartments in plant cells, including vesicles, and its vesicular localization was enriched in cells undergoing R. solanacearum infection, suggesting that this specific localization may be particularly relevant during infection. Among RipD-interacting proteins, we identified plant vesicle-associated membrane proteins (VAMPs). We also found that overexpression of Arabidopsis thaliana VAMP721 and VAMP722 in Nicotiana benthamiana leaves promoted resistance to R. solanacearum, and this was abolished by the simultaneous expression of RipD, suggesting that RipD targets VAMPs to contribute to R. solanacearum virulence. Among proteins secreted in VAMP721/722-containing vesicles, CCOAOMT1 is an enzyme required for lignin biosynthesis, and mutation of CCOAOMT1 enhanced plant susceptibility to R. solanacearum. Altogether our results reveal the contribution of VAMPs to plant resistance against R. solanacearum and their targeting by a bacterial effector as a pathogen virulence strategy.

Chitin synthases containing myosin motor-like domain are required for cell wall integrity and virulence of vascular wilt pathogen Verticillium dahliae

Verticillium wilt (VW) of cotton poses a serious threat to the quality and yield of cotton. Verticillium dahliae is the primary causal agent of cotton VW. Moreover, V. dahliae can infect more than 200 species of dicotyledonous plants. The fungal cell wall plays a crucial role in its growth, development and pathogenicity. However, the mechanism of cell wall synthesis in V. dahliae and its role in pathogenesis remains unclear. In this study, we identified two chitin synthase (CHS) genes VdChs5 and VdChs7 containing myosin motor-like domain (MMD) and characterized their role in virulence of V. dahliae. The results showed that the functions of VdChs5 and VdChs7 were largely redundant, and target deletion of both VdChs5 and VdChs7 in V. dahliae did not affect vegetative growth, but reduced conidial production. ΔVdChs5Chs7 deletion mutant failed to colonize and proliferate in cotton vascular tissue, and exhibited significantly reduced virulence on cotton, suggesting that VdChs5 and VdChs7 are necessary for pathogenesis. In addition, the thickness of the cell wall in ΔVdChs5Chs7 showed significantly decreased, and ΔVdChs5Chs7 mutant exhibited hypersensitivity to cell wall perturbing agents and reactive oxygen species (ROS), indicating that VdChs5 and VdChs7 play key roles in cell wall integrity. Further, host-induced gene silencing (HIGS) silenced transcripts of VdChs5 and VdChs7 in susceptible cotton (Gossypium hirsutum L. acc. TM-1) enhanced resistance to cotton VW. Taken together, our data demonstrated that VdChs5 and VdChs7 play pivotal roles in proliferation, cell wall integrity, and pathogenicity, and provided a novel strategy to improve Verticillium wilt resistance in cotton and other susceptible host plants.

FIRE Mimics a 14-3-3-Binding Motif to Promote Phytophthora palmivora Infection.

The oomycete Phytophthora palmivora infects a wide range of tropical crops worldwide. Like other filamentous plant pathogens, it secretes effectors to colonize plant tissues. Here, we characterize FIRE, an RXLR effector that contains a canonical mode I 14-3-3 phospho-sensor-binding motif that is conserved in effectors of several Phytophthora species. FIRE is phosphorylated in planta and interacts with multiple 14-3-3 proteins. Binding is sensitive to the R18 14-3-3 inhibitor. FIRE promotes plant susceptibility and co-localizes with its target around haustoria. This work uncovers a new type of oomycete effector target mechanism. It demonstrates that substrate mimicry for 14-3-3 proteins is a cross-kingdom effector strategy used by both prokaryotic and eukaryotic plant pathogens to suppress host immunity. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Antifungal Potential of Melaleuca alternifolia against Fungal Pathogen Fusarium oxysporum f. sp. cubense Tropical Race 4.

Fusarium wilt of bananas caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4) poses the most serious threat to banana production globally. The disease has been managed using chemical fungicides, yet the control levels are still unsatisfactory. This study investigated the antifungal activities of tea tree (Melaleuca alternifolia) essential oil (TTO) and hydrosol (TTH) against Foc TR4 and their bioactive components. The potential of TTO and TTH in inhibiting the growth of Foc TR4 was evaluated in vitro using agar well diffusion and spore germination assays. Compared to the chemical fungicide, TTO effectively suppressed the mycelial growth of Foc TR4 at 69%. Both the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of TTO and TTH were established at 0.2 µg/µL and 50% v/v, respectively, suggesting the fungicidal nature of the plant extracts. The disease control efficacies were also demonstrated by a (p ≤ 0.05) delayed Fusarium wilt symptom development in the susceptible banana plants with reduced LSI dan RDI scores from 70% to around 20-30%. A GC/MS analysis of TTO identified terpinen-4-ol, eucalyptol, and α-terpineol as the major components. In contrast, an LC/MS analysis of TTH identified different compounds, including dihydro-jasmonic acid and methyl ester. Our findings indicate the potential of tea tree extracts as natural alternatives to chemical fungicides to control Foc TR4.

Nontarget-site resistance due to rapid physiological response in 2,4-D resistant Conyza sumatrensis: reduced 2,4-D translocation and auxin-induced gene expression.

Resistance to 2,4-Dichlorophenoxyacetic acid (2,4-D) has been reported in several weed species since the 1950s; however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4-D herbicide. Differences were found in 2,4-D absorption between the resistant and susceptible biotypes. Herbicide translocation was reduced in the resistant biotype compared to the susceptible. In resistant plants 98.8% of [14 C] 2,4-D was found in the treated leaf, whereas ≈13% translocated to other plant parts in the susceptible biotype at 96 h after treatment. Resistant plants did not metabolize [14 C] 2,4-D and had only intact [14 C] 2,4-D at 96 h after application, whereas susceptible plants metabolized [14 C] 2,4-D into four detected metabolites, consistent with reversible conjugation metabolites found in other 2,4-D sensitive plant species. Pre-treatment with the cytochrome P450 inhibitor malathion did not enhance 2,4-D sensitivity in either biotype. Following treatment with 2,4-D, resistant plants showed increased expression of transcripts within plant defense response and hypersensitivity pathways, whereas both sensitive and resistant plants showed increased expression of auxin-response transcripts. Our results demonstrate that reduced 2,4-D translocation contributes to resistance in the C. sumatrensis biotype. The reduction in 2,4-D transport is likely to be a consequence of the rapid physiological response to 2,4-D in resistant C. sumatrensis. Resistant plants had increased expression of auxin-responsive transcripts, indicating that a target-site mechanism is unlikely. © 2023 Society of Chemical Industry.

Application of Associative Rhizobacteria for Increasing the Soft Wheat Productivity and Reducing the Diseases Harmfulness

Background: The search for environmentally friendly biological approaches to increase the productivity and resistance to phytopathogens of wheat is an urgent task for agriculture. For this purpose, the effect of plant growth-promoting rhizobacteria on yield and disease development of soft wheat was studied. Methods: Two soft wheat varieties (Trizo and Sudarynya) were inoculated with Bacillus subtilis 124-11, Pseudomonas fluorescens SPB2137 and Sphingomonas sp. K1B under field conditions during 2017-2021 years. Wheat development was monitored at different stages using a set of indicators characterizing morphological traits and yield structure. Susceptibility of plants to root rot pathogens and leaf diseases (brown and yellow wheat rust, powdery mildew, septoria-pyrenophorous spotting) was analyzed using a number of phytopathological indicators. Result: The maximal increase in yield by 1,14 g plant-1 and 0,87 g plant-1 was revealed after treatments with B. subtilis 124-11 and Ps. fluorescens SPB2137. The minimal ecological variation in wheat productivity elements was observed when B. subtilis 124-11 was used. The bacteria reduced plant damage caused by helminthosporiotic root rot, leaf-stem infections, yellow and brown rust and septoria-pyrenophorous spotting. The effects of bacteria on wheat growth and biocontrol of phytopathogens significantly varied depending on meteorological conditions and plant cultivar.

Chitosan oligomers (COS) trigger a coordinated biochemical response of lemongrass (Cymbopogon flexuosus) plants to palliate salinity-induced oxidative stress

Plant susceptibility to salt depends on several factors from its genetic makeup to modifiable physiological and biochemical status. We used lemongrass (Cymbopogon flexuosus) plants as a relevant medicinal and aromatic cash crop to assess the potential benefits of chitosan oligomers (COS) on plant growth and essential oil productivity during salinity stress (160 and 240 mM NaCl). Five foliar sprays of 120 mg L−1 of COS were applied weekly. Several aspects of photosynthesis, gas exchange, cellular defence, and essential oil productivity of lemongrass were traced. The obtained data indicated that 120 mg L−1 COS alleviated photosynthetic constraints and raised the enzymatic antioxidant defence including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities that minimised salt-induced oxidative damage. Further, stomatal conductance (gs) and photosynthetic CO2 assimilation (A) were improved to support overall plant development. The same treatment increased geraniol dehydrogenase (GeDH) activity and lemongrass essential oil production. COS-induced salt resilience suggests that COS could become a useful biotechnological tool in reclaiming saline soil for improved crop productivity, especially when such soil is unfit for leading food crops. Considering its additional economic value in the essential oil industry, we propose COS-treated lemongrass as an excellent alternative crop for saline lands.

Evaluation of Host Plant Susceptibility Indices and Screening of Sugarcane Promising Lines for Resistance Potential Against Whitefly, Aleurolobus barodensis (Maskell) in Sindh, Pakistan.

The whiteflies are polyphagous, host, and feed on the sap of sugarcane leaves may cause a loss in yield production. This study was designed to screen out the fifteen sugarcane genotypes to recognize their comparative resistance/susceptibility during 2014-15 and 2015-16. The whitefly attack was first found in June, rapidly increased in August, and reached its maximum population in October. After that, the population gradually declined from November to December. The highest 1.80 per cm2 leaf-1 population of whitefly (nymph + puparia) was recorded on YT-53, followed by 1.56 per cm2 leaf-1 in S-2007-AUS-384, which showed moderate susceptibility. The genotypes Hoth-127, NARC-1, and CP-TJ-349, exhibited less susceptible responses with an average range of 1.01-1.50 per cm2 leaf-1. The other genotypes, i.e., CP-TJ-349, Hoth-326, Th-910, S-2005-CSSG-33, S-2007-AUS-384, Hoth-2109, LAM-76/TJ-803, Th-1201, S-2009-CPSG-06, S-1996-NSG-197, NARC-2, and Th-1210 showed resistance response with an average range of 0.01-1.00 per cm2 leaf-1. The maximum Host Plant Susceptibility Indices (HPSIs) during 2015 (16% and 15%), 2016 (13% and 14%), and cumulative (16% and 14%) were recorded in YT-53 and S-2007-AUS-384, respectively. Based on the cumulative result of HPSIs, these genotypes keep in the moderately susceptible category. Similarly, the genotypes Hoth-127, NARC-1, and CP-TJ-349 showed intermediate HPSIs (12, 11, and 9% respectively, found to be less susceptible. While the genotypes, i.e., Hoth-326, Th-910, S-2005-CSSG-33, LAM-76/TJ-803, Hoth-2109, Th-1201, S-1996-NSG-197, S-2009-CPSG-06, NARC-2, and Th-1210 were recorded minimum HPSIs in the range of 1-8% possibly found to be resistant.

Influence of Plant Growth Retardants and Nitrogen Doses on the Content of Plant Secondary Metabolites in Wheat, the Presence of Pests, and Soil Quality Parameters

Wheat is the cereal most susceptible to lodging, particularly during the flowering period and at the early ripening stage. The use of plant growth retardants (PGRs) is especially recommended when intensive nitrogen (N) fertilisation is applied, which increases the susceptibility of plants to lodging. This paper presents the results of tests into the effects of PGRs (PGR0—control; PGR1—chlormequat chloride (CCC) + trinexapac-ethyl (TE); PGR2—chlormequat chloride (CCC) + ethephon (ET)), and N dose—N0, N20, N40, and N60 [0, 20, 40, and 60 kg N ha−1] on the content of selected plant secondary metabolites (PSM) in the Indian dwarf wheat (Triticum sphaerococcum Percival) of the Trispa cultivar, and on the abundance of insect pests. In the developmental stage of wheat (BBCH 39), insects were collected with an entomological net. The study also investigated the effect of experimental factors on the physicobiochemical properties of the soil (pH in KC, granulometric composition, total organic carbon TOC, total nitrogen TN, fractional composition of humus, and the activity of enzymes). An increase in the plant secondary metabolite (PSM) and FRAP (ferring reducing ability of plasma) contents following the application of PGRs and N fertilisation already from as low a rate as 20 kg ha−1 was demonstrated. A significant positive correlation was noted between the abundance of Oulema spp. and the contents of total polyphenols, chlorogenic acid, and FRAP. No such relationship was noted for Aphididae or Thysanoptera. TOC content was higher on the plots on which N fertilisation was applied at the highest rate and after the application of PGRs. The factor determining the TN content was N fertilisation. Soil samples of the PGR0 N0 treatment were characterised by the greatest proportion of carbon in the humic and fulvic acid fractions and by the smallest proportion of carbon in the humin fraction. N fertilisation increased the proportion of carbon in the humin fraction on the plots on which no PGRs were applied. The study demonstrated an increase in the activity of oxidoreductive enzymes following the application of higher N rates. The application of PGRs resulted in no inhibition of enzymes in the soil compared to the control (PGRs0).

Eggsplorer: a rapid plant–insect resistance determination tool using an automated whitefly egg quantification algorithm

BackgroundA well-known method for evaluating plant resistance to insects is by measuring insect reproduction or oviposition. Whiteflies are vectors of economically important viral diseases and are, therefore, widely studied. In a common experiment, whiteflies are placed on plants using clip-on-cages, where they can lay hundreds of eggs on susceptible plants in a few days. When quantifying whitefly eggs, most researchers perform manual eye measurements using a stereomicroscope. Compared to other insect eggs, whitefly eggs are many and very tiny, usually 0.2 mm in length and 0.08 mm in width; therefore, this process takes a lot of time and effort with and without prior expert knowledge. Plant insect resistance experiments require multiple replicates from different plant accessions; therefore, an automated and rapid method for quantifying insect eggs can save time and human resources.ResultsIn this work, a novel automated tool for fast quantification of whitefly eggs is presented to accelerate the determination of plant insect resistance and susceptibility. Leaf images with whitefly eggs were collected from a commercial microscope and a custom-built imaging system. A deep learning-based object detection model was trained using the collected images. The model was incorporated into an automated whitefly egg quantification algorithm, deployed in a web-based application called Eggsplorer. Upon evaluation on a testing dataset, the algorithm was able to achieve a counting accuracy as high as 0.94, r2 of 0.99, and a counting error of ± 3 eggs relative to the actual number of eggs counted by eye. The automatically collected counting results were used to determine the resistance and susceptibility of several plant accessions and were found to yield significantly comparable results as when using the manually collected counts for analysis.ConclusionThis is the first work that presents a comprehensive step-by-step method for fast determination of plant insect resistance and susceptibility with the assistance of an automated quantification tool.

Genome-wide identification of xylan glucuronosyltransferase family in cotton and function characterization of GhGUX5 in regulating Verticillium wilt resistance

Xylan glucuronosyltransferase (GUX) is widely involved in a variety of physiological processes in plants, including plant development, growth and the defense response to pathogens. However, the function of GUX regulators in Verticillium dahliae (V. dahliae) infection has not been considered previously in cotton. Overall, 119 GUX genes were identified from multiple species and were phylogenetically categorized into seven classes. Duplication event analysis indicated that GUXs in Gossypium hirsutum primarily originated from segmental duplication. GhGUXs promoter analysis indicated cis-regulatory elements capable of reacting to several different stresses. RNA-Seq data and qRT-PCR analysis both indicated that most GhGUXs were associated with V. dahliae infection. Gene interaction network analysis showed that GhGUX5 interacted with 11 proteins, and the relative expression of these 11 proteins changed significantly following V. dahliae infection. In addition, silencing and overexpression of GhGUX5 results to enhance and reduce plant's susceptibility to V. dahliae. Further study showed that TRV:GhGUX5 silenced cotton plants exhibited a decrease in the degree of lignification, total lignin content, gene expression levels involved in lignin biosynthesis, and enzyme activity compared with TRV:00. The above results indicate that GhGUX5 enhances Verticillium wilt resistance through the lignin biosynthesis pathway.

Exotic tree species have consistently lower herbivore load in a cross-Atlantic tree biodiversity experiment.

It is commonly expected that exotic plants experience reduced herbivory, but experimental evidence for such enemy release is still controversial. One reason for conflicting results might be that community context has rarely been accounted for, although the surrounding plant diversity may moderate enemy release. Here, we tested the effects of focal tree origin and surrounding tree diversity on herbivore abundance and leaf damage in a cross-Atlantic tree-diversity experiment in Canada and Germany. We evaluated six European tree species paired with six North American congeners in both their native and exotic range, expecting lower herbivory for the exotic tree species in each pair at each site. Such reciprocal experiments have long been called for, but have not been realized thus far. In addition to a thorough evaluation of overall enemy release effects, we tested whether enemy release effects changed with the surrounding tree diversity. Herbivore abundance was indeed consistently lower on exotics across all six tree genera (12 comparisons). This effect of exotic status was independent of the continent, phylogenetic relatedness, and surrounding tree diversity. In contrast, leaf damage associated with generalist leaf chewers was consistently higher on North American tree species. Interestingly, several species of European weevils were the most abundant leaf chewers on both continents and the dominant herbivores at the Canadian site. Thus, most observed leaf damage is likely to reflect the effect of generalist herbivores that feed heavily on plant species with which they have not evolved. At the German site, sap suckers were the dominant herbivores and showed a pattern consistent with enemy release. Taken together, the consistently lower herbivory on exotics on both continents is not purely a pattern of enemy release in the strictest sense, but to some degree additionally reflects the susceptibility of native plants to invasive herbivores. In conclusion, our cross-Atlantic study is consistent with the idea that nonnative trees have generally reduced herbivory, regardless of tree community diversity and species identity, but for different reasons depending on the dominant herbivore guild.