Wheat Leaf Research Articles

INFLUENCE OF THE OZONATED WATER APPLICATION ON THE OCCURRENCE OF SOME PESTS AND DISEASES IN SPRING WHEAT CROP

Investigations were carried out in the production fields of agricultural company Linas in Ringaudai eldership, Kaunas district. Spring wheat variety 'Koksa' was grown on non-damp, light loamy soil with a mobile phosphorus content of 173 mg kg-1 and a potassium content of 139 mg kg-1. Soil acidity - pH 6.9-7.0. The ozonator was attached on the trailing sprayer JARMET. During the studies, the concentration of ozone-saturated water and the spray rate were determined so as not to damage the crop, pollute the environment, or harm humans or animals. The speed of the sprayer was 6 km h-1. The application was performed 2 or 4 times. It was determined that treatment of spring wheat with ozonated water, although not always statistically significantly, however, reduced the occurrence of powdery mildew (Blumeria graminis), brown rust (Puccinia recondita), and inhibited the spread of aphids. A tendency for tan spot (Pyrenophora tritici repentis) and thrips decrease in the crop was observed. The aim of the study was to determine the effect of ozonated water application on the spread of spring wheat pests and leaf diseases.

Long-Read-Based de novo Genome Assembly and Comparative Genomics of the Wheat Leaf Rust Pathogen Puccinia triticina Identifies Candidates for Three Avirulence Genes.

Leaf rust, caused by Puccinia triticina (Pt), is one of the most devastating diseases of wheat, affecting production in nearly all wheat-growing regions worldwide. Despite its economic importance, genomic resources for Pt are very limited. In the present study, we have used long-read sequencing (LRS) and the pipeline of FALCON and FALCON-Unzip (v4.1.0) to carry out the first LRS-based de novo genome assembly for Pt. Using 22.4-Gb data with an average read length of 11.6 kb and average coverage of 150-fold, we generated a genome assembly for Pt104 [strain 104-2,3,(6),(7),11; isolate S423], considered to be the founding isolate of a clonal lineage of Pt in Australia. The Pt104 genome contains 162 contigs with a total length of 140.5 Mb and N50 of 2 Mb, with the associated haplotigs providing haplotype information for 91% of the genome. This represents the best quality of Pt genome assembly to date, which reduces the contig number by 91-fold and improves the N50 by 4-fold as compared to the previous Pt race1 assembly. An annotation pipeline that combined multiple lines of evidence including the transcriptome assemblies derived from RNA-Seq, previously identified expressed sequence tags and Pt race 1 protein sequences predicted 29,043 genes for Pt104 genome. Based on the presence of a signal peptide, no transmembrane segment, and no target location to mitochondria, 2,178 genes were identified as secreted proteins (SPs). Whole-genome sequencing (Illumina paired-end) was performed for Pt104 and six additional strains with differential virulence profile on the wheat leaf rust resistance genes Lr26, Lr2a, and Lr3ka. To identify candidates for the corresponding avirulence genes AvrLr26, AvrLr2a, and AvrLr3ka, genetic variation within each strain was first identified by mapping to the Pt104 genome. Variants within predicted SP genes between the strains were then correlated to the virulence profiles, identifying 38, 31, and 37 candidates for AvrLr26, AvrLr2a, and AvrLr3ka, respectively. The identification of these candidate genes lays a good foundation for future studies on isolating these avirulence genes, investigating the molecular mechanisms underlying host–pathogen interactions, and the development of new diagnostic tools for pathogen monitoring.

Genome-Wide Association Studies in Diverse Spring Wheat Panel for Stripe, Stem, and Leaf Rust Resistance.

Among several important wheat foliar diseases, Stripe rust (YR), Leaf rust (LR), and Stem rust (SR) have always been an issue of concern to the farmers and wheat breeders. Evolution of virulent pathotypes of these rusts has posed frequent threats to an epidemic. Pyramiding rust-resistant genes are the most economical and environment-friendly approach in postponing this inevitable threat. To achieve durable long term resistance against the three rusts, an attempt in this study was made searching for novel sources of resistant alleles in a panel of 483 spring wheat genotypes. This is a unique and comprehensive study where evaluation of a diverse panel comprising wheat germplasm from various categories and adapted to different wheat agro-climatic zones was challenged with 18 pathotypes of the three rusts with simultaneous screening in field conditions. The panel was genotyped using 35K SNP array and evaluated for each rust at two locations for two consecutive crop seasons. High heritability estimates of disease response were observed between environments for each rust type. A significant effect of population structure in the panel was visible in the disease response. Using a compressed mixed linear model approach, 25 genomic regions were found associated with resistance for at least two rusts. Out of these, seven were associated with all the three rusts on chromosome groups 1 and 6 along with 2B. For resistance against YR, LR, and SR, there were 16, 18, and 27 QTL (quantitative trait loci) identified respectively, associated at least in two out of four environments. Several of these regions got annotated with resistance associated genes viz. NB-LRR, E3-ubiquitin protein ligase, ABC transporter protein, etc. Alien introgressed (on 1B and 3D) and pleiotropic (on 7D) resistance genes were captured in seedling and adult plant disease responses, respectively. The present study demonstrates the use of genome-wide association for identification of a large number of favorable alleles for leaf, stripe, and stem rust resistance for broadening the genetic base. Quick conversion of these QTL into user-friendly markers will accelerate the deployment of these resistance loci in wheat breeding programs.

Genome-Wide Identification of Effector Candidates With Conserved Motifs From the Wheat Leaf Rust Fungus Puccinia triticina.

Rust fungi secrete various specialized effectors into host cells to manipulate the plant defense response. Conserved motifs, including RXLR, LFLAK-HVLVxxP (CRN), Y/F/WxC, CFEM, LysM, EAR, [SG]-P-C-[KR]-P, DPBB_1 (PNPi), and ToxA, have been identified in various oomycete and fungal effectors and are reported to be crucial for effector translocation or function. However, little is known about potential effectors containing any of these conserved motifs in the wheat leaf rust fungus (Puccinia triticina, Pt). In this study, sequencing was performed on RNA samples collected from the germ tubes (GT) of uredospores of an epidemic Pt pathotype PHTT(P) and Pt-infected leaves of a susceptible wheat cultivar “Chinese Spring” at 4, 6, and 8 days post-inoculation (dpi). The assembled transcriptome data were compared to the reference genome of “Pt 1-1 BBBD Race 1.” A total of 17,976 genes, including 2,284 “novel” transcripts, were annotated. Among all these genes, we identified 3,149 upregulated genes upon Pt infection at all time points compared to GT, whereas 1,613 genes were more highly expressed in GT. A total of 464 secreted proteins were encoded by those upregulated genes, with 79 of them also predicted as possible effectors by EffectorP. Using hmmsearch and Regex, we identified 719 RXLR-like, 19 PNPi-like, 19 CRN-like, 138 Y/F/WxC, and 9 CFEM effector candidates from the deduced protein database including data based on the “Pt 1-1 BBBD Race 1” genome and the transcriptome data collected here. Four of the PNPi-like effector candidates with DPBB_1 conserved domain showed physical interactions with wheat NPR1 protein in yeast two-hybrid assay. Nine Y/F/WxC and seven CFEM effector candidates were transiently expressed in Nicotiana benthamiana. None of these effector candidates showed induction or suppression of cell death triggered by BAX protein, but the expression of one CFEM effector candidate, PTTG_08198, accelerated the progress of cell death and promoted the accumulation of reactive oxygen species (ROS). In conclusion, we profiled genes associated with the infection process of the Pt pathotype PHTT(P). The identified effector candidates with conserved motifs will help guide the investigation of virulent mechanisms of leaf rust fungus.

The role of reactive oxygen species in the virulence of wheat leaf rust fungus Puccinia triticina.

SummaryReactive oxygen species (ROS) play an important role during host–pathogen interactions and are often an indication of induced host defence responses. In this study, we demonstrate for the first time that Puccinia triticina (Pt) generates ROS, including superoxide, H2O2 and hydroxyl radicals, during wheat infection. Through pharmacological inhibition, we found that ROS are critical for both Pt urediniospore germination and pathogenic development on wheat. A comparative RNA‐Seq analysis of different stages of Pt infection process revealed 291 putative Pt genes associated with the oxidation–reduction process. Thirty‐seven of these genes encode known proteins. The expressions of five Pt genes, including PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod, were subsequently verified using RT‐qPCR analysis. The results show that the expressions of PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod are up‐regulated during urediniospore germination. In comparison, the expressions of PtNoxA, PtNoxB, PtNoxR and PtCat are down‐regulated during wheat infection from 12 to 120 h after inoculation (HAI), whereas the expression of PtSod is up‐regulated with a peak of expression at 120 HAI. We conclude that ROS are critical for the full virulence of Pt and a coordinate down‐regulation of PtNox genes may be important for successful infection in wheat.

Contribution of Parastagonospora nodorum to the leaf and glume blotch of durum wheat in Bulgaria

Abstract. Parastagonospora nodorum is an important necrotrophic fungal pathogen causing leaf and glume blotch of wheat worldwide. The disease can result in significant losses in grain yield and quality. The purpose of the current investigation was to estimate the occurrence of P. nodorum as a foliar and ear pathogen of durum wheat and disease severity on a set of cultivars under natural infection. Field experiments were performed at two locations (Sofia and Chirpan) in the period 2010-2017. Twelve winter cultivars of durum wheat were involved in the study. P. nodorum was not found at both locations in 2010 and 2011. Thereafter the pathogen was recorded on the leaves of durum wheat in Sofia every year except 2013. Symptoms included chlorosis and necrosis of the leaf tissue. The strongest manifestation of the disease was observed in 2016 and especially in 2017. In Chirpan leaf blotch was noticed only in 2 out of 8 growing seasons. The ear infection led to development of dark brown patches on the glumes, which later became purple-brown. These symptoms were noted in Sofia in 2014, 2016 and 2017. In Chirpan, glume blotch of studied cultivars was recorded in 2017 but in the previous year the symptoms were widely observed on some genotypes among the initial breeding material of durum wheat. In the present investigation P. nodorum caused leaf and glume blotch only. Symptoms on stems, nodes and leaf sheaths were not noted at both locations. The 12 cultivars under study differed in their susceptibility to leaf and glume blotch. The leaf symptoms caused by P. nodorum were recorded on all cultivars, but were more pronounced on Zvezditsa, Deyana and GK Bétadur. The glume blotch was more noticeable on Vazhod. The results of this multiyear research showed that although P. nodorum did not appear every year, the pathogen could contribute to the leaf and glume blotch of durum wheat under conditions favourable for disease development. The evaluation of cultivars demonstrated encouraging preliminary results. Several cultivars showed lower disease severity on flag leaf and no or little infection on the ear. They deserve further studies on resistance to P. nodorum.

Estimation of winter wheat leaf area index at different growth stages using optimized red-edge hyperspectral vegetation indices

Leaf area index (LAI), as one of the most important indicators in vegetation growth monitoring, has been widely used in crop growth monitor and yield estimation. Previous studies focused on LAI retrieval for whole growth stages, this study inversed LAI at five main growth stages using widely-acknowledged vegetation indices and their optimized red-edge transformations. We used hyperspectral data to analyse relationships between LAI and vegetation indices. Partial least square discriminant analysis (PLS-DA) was used in this study to distinguish the best indices for distinct growth stages. The results show that LAI retrieval at various growth stages have distinct results. The best fitted indices for different growth stages are not fixed. The best indices for five stages are OSAVIre1, SRre1, SAVIre2, SAVIre2 and OSAVIre1 with R2 value of 0.20, 0.50, 0.49, 0.72 and 0.23, respectively. Most vegetation indices show better performance in milky stage than other four stages this may due to the high vegetation cover in this stage because leaves rise to maximum. Indices composed of red-edge exhibited better relationships with LAI with higher R2 and lower RMSE. Indices combined reflectance at 740 nm are capable of inversing LAI at stem elongation, anthesis and milk development stages. Indices with 705 nm showed better results in jointing and ripening stages. The results indicate that:1) specific vegetation indices for distinct growth stages lead to better estimation than inversing LAI for whole growth stages; 2) indices take advantage of red-edge showed better potentials in estimating high LAI than traditional visible wavelength.

High-Resolution Mapping of the Novel Early Leaf Senescence Gene Els2 in Common Wheat.

Early leaf senescence negatively impacts the grain yield in wheat (Triticum aestivum L.). Induced mutants provide an important resource for mapping and cloning of genes for early leaf senescence. In our previous study, Els2, a single incomplete dominance gene, that caused early leaf senescence phenotype in the wheat mutant LF2099, had been mapped on the long arm of chromosome 2B. The objective of this study was to develop molecular markers tightly linked to the Els2 gene and construct a high-resolution map surrounding the Els2 gene. Three tightly linked single-nucleotide polymorphism (SNP) markers were obtained from the Illumina Wheat 90K iSelect SNP genotyping array and converted to Kompetitive allele-specific polymerase chain reaction (KASP) markers. To saturate the Els2 region, the Axiom® Wheat 660K SNP array was used to screen bulked extreme phenotype DNA pools, and 9 KASP markers were developed. For fine mapping of the Els2 gene, these KASP markers and previously identified polymorphic markers were analyzed in a large F2 population of the LF2099 × Chinese Spring cross. The Els2 gene was located in a 0.24-cM genetic region flanked by the KASP markers AX-111643885 and AX-111128667, which corresponded to a physical interval of 1.61 Mb in the Chinese Spring chromosome 2BL containing 27 predicted genes with high confidence. The study laid a foundation for a map-based clone of the Els2 gene controlling the mutation phenotype and revealing the molecular regulatory mechanism of wheat leaf senescence.

Migration of volatile compounds from natural biomaterials and their safety evaluation as food contact materials

The concern for environmental conservation is increasing, and a very important factor to consider is the search for alternatives to the use of plastics in the food packaging industry. A good option is the manufacture of containers of biodegradable materials, such as the so-called biomaterials made of vegetable fibre such as wheat, wood, bamboo or palm leaf pulp. The migration of compounds from food packaging can cause alterations in food safety and acceptability. Therefore, their control through studies of specific migration is definitely important in the food industry. Specific migration has been studied in two types of dishes (wheat pulp and wood) in contact with three liquid simulants (ethanol 10%, acetic acid 3% and ethanol 95%). The analysis of migration extracts have been carried out by solid-phase microextraction coupled to gas chromatography (SPME-GC-MS) in the most suitable working conditions. In addition, those identified compounds considered of interest according to existing legislation have been quantified in order to assess whether exceed or not the migration limits established for some of them. The results obtained show that the quantified compounds are well below the specific migration limits (SML) set by the legislation, thereby showing the safety in use of this type of biodegradable dishes.

Breeding Wheat for Durable Leaf Rust Resistance in Southern Africa: Variability, Distribution, Current Control Strategies, Challenges and Future Prospects.

Leaf or brown rust of wheat caused by Puccinia triticina (Pt) is one of the most damaging diseases globally. Considerable progress has been made to control leaf rust through crop protection chemicals and host plant resistance breeding in southern Africa. However, frequent changes in the pathogen population still present a major challenge to achieve durable resistance. Disease surveillance and monitoring of the pathogen have revealed the occurrence of similar races across the region, justifying the need for concerted efforts by countries in southern Africa to develop and deploy more efficient and sustainable strategies to manage the disease. Understanding the genetic variability and composition of Pt is a pre-requisite for cultivar release with appropriate resistance gene combinations for sustainable disease management. This review highlights the variability and distribution of the Pt population, and the current control strategies, challenges and future prospects of breeding wheat varieties with durable leaf rust resistance in southern Africa. The importance of regular, collaborative and efficient surveillance of the pathogen and germplasm development across southern Africa is discussed, coupled with the potential of using modern breeding technologies to produce wheat cultivars with durable resistance.

Terminal drought and heat stress alter physiological and biochemical attributes in flag leaf of bread wheat.

Heat stress along with low water availability at reproductive stage (terminal growth phase of wheat crop) is major contributing factor towards less wheat production in tropics and sub-tropics. Flag leaf plays a pivotal role in assimilate partitioning and stress tolerance of wheat during terminal growth phase. However, limited is known about biochemical response of flag leaf to combined and individual heat and drought stress during terminal growth phase. Therefore, current study investigated combined and individual effect of terminal drought and heat stress on water relations, photosynthetic pigments, osmolytes accumulation and antioxidants defense mechanism in flag leaf of bread wheat. Experimental treatments comprised of control, terminal drought stress alone (50% field capacity during reproductive phase), terminal heat stress alone (wheat grown inside plastic tunnel during reproductive phase) and terminal drought stress + terminal heat stress. Individual and combined imposition of drought and heat stresses significantly (p≤0.05) altered water relations, osmolyte contents, soluble proteins and sugars along with activated antioxidant defensive system in terms of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Turgor potential, POD and APX activities were lowest under individual heat stress; however, these were improved when drought stress was combined with heat stress. It is concluded that combined effect of drought and heat stress was more detrimental than individual stresses. The interactive effect of both stresses was hypo-additive in nature, but for some traits (like turgor potential and APX) effect of one stress neutralized the other. To best of our knowledge, this is the first report on physiological and biochemical response of flag leaf of wheat to combine heat and drought stress. These results will help future studies dealing with improved stress tolerance in wheat. However, detailed studies are needed to fully understand the genetic mechanisms behind these physiological and biochemical changes in flag leaf in response to combined heat and drought stress.

Fine Mapping of the Wheat Leaf Rust Resistance Gene LrLC10 (Lr13) and Validation of Its Co-segregation Markers.

Wheat leaf rust, caused by the fungus Puccinia triticina Eriks. (Pt), is a destructive disease found throughout common wheat production areas worldwide. At its adult stage, wheat cultivar Liaochun10 is resistant to leaf rust and the gene for that resistance has been mapped on chromosome 2BS. It was designated LrLC10 and is the same gene as cataloged gene Lr13 by pedigree analysis and allelism test. We fine-mapped it using recessive class analysis (RCA) of the homozygous susceptible F2 plants derived from crosses using Liaochun10 as the resistant, male parent. Taking advantage of the re-sequencing data of Liaochun10 and its counterpart susceptible parent, we converted nucleotide polymorphisms in the LrLC10 interval between the resistant and susceptible parents into molecular markers to saturate the LrLC10 genetic linkage map. Four indel markers were added in the 1.65 cM map of LrLC10 flanked by markers CAUT163 and Lseq22. Thirty-two recombinants were identified by those two markers from the 984 F2 homozygous susceptible plants and were further genotyped with additional ten markers. LrLC10 was finally placed in a 314.3 kb region on the Chinese Spring reference sequence (RefSeq v1.0) that contains three high confidence genes: TraesCS2B01G182800, TraesCS2B01G182900, and TraesCS2B01G183000. Sequence analysis showed several variations in TraesCS2B01G182800 and TraesCS2B01G183000 between resistant and susceptible parents. One KASP marker and an indel marker were designed based on the differences in those two genes, respectively, and were validated to be diagnostic co-segregating markers for LrLC10. Our results both improve marker-assisted selection and help with the map-based cloning of LrLC10.

Genetic diversity of Alternaria species associated with black point in wheat grains.

The genus Alternaria is a widely distributed major plant pathogen that can act as a saprophyte in plant debris. Fungi of this genus frequently infect cereal crops and cause such diseases as black point and wheat leaf blight, which decrease the yield and quality of cereal products. A total of 25 Alternaria sp. isolates were collected from germ grains of various wheat cultivars from different geographic regions in Kazakhstan. We investigated the genetic relationships of the main Alternaria species related to black point disease of wheat in Kazakhstan, using the inter-primer binding site (iPBS) DNA profiling technique. We used 25 retrotransposon-based iPBS primers to identify the differences among and within Alternaria species populations, and analyzed the variation using clustering (UPGMA) and statistical approaches (AMOVA). Isolates of Alternaria species clustered into two main genetic groups, with species of A.alternata and A.tennuissima forming one cluster, and isolates of A. infectoria forming another. The genetic diversity found using retrotransposon profiles was strongly correlated with geographic data. Overall, the iPBS fingerprinting technique is highly informative and useful for the evaluation of genetic diversity and relationships of Alternaria species.

Short communication: Virulence of Puccinia triticina in the North Caucasus region of Russia

Aim of study: To analyze the structure of P. triticina populations by a virulence survey in the North Caucasus region of Russia from 2011 to 2015.Area of study: The North Caucasus region is a leading grain production region in Russia where wheat leaf rust causes losses in yield.Material and methods: Uredinial samples of leaf rust were collected in all agro-climatic zones of the North Caucasus on the production sites of winter wheat and on the plots of official state trials. Single uredinial isolates (a total of 564) were tested for virulence with 41 ˈThatcherˈ near isogenic lines with Lr resistance genes.Main results: Clones virulent to Lr9, Lr42, Lr47 and Lr50 were not found. Isolates virulent to the Lr19, Lr24, Lr29, Lr41, Lr43 + 24, Lr45, Lr52 genes were characterized by low frequencies. The 564 fungal isolates studied were represented by 564 virulence phenotypes, the majority of them with a virulence complexity from 9 to 19. A high level of intrapopulation fungus diversity in virulence was noticed during the whole period of research (Shannon diversity index from 2.994 to 3.314). The differences in the frequencies of virulences in the years of research were small (Rogers distance from 0.001 to 0.160).Research highlights: Due to the fact that the North Caucasus region is a zone of epiphytotic danger and high variability of the P. triticina population, the analysis of the genetics of the fungus population is important for the strategy of varietal distribution in the region and development of rust-resistant varieties.

A fungal pathogen induces systemic susceptibility and systemic shifts in wheat metabolome and microbiome composition

Yield losses caused by fungal pathogens represent a major threat to global food production. One of the most devastating fungal wheat pathogens is Zymoseptoria tritici. Despite the importance of this fungus, the underlying mechanisms of plant–pathogen interactions are poorly understood. Here we present a conceptual framework based on coinfection assays, comparative metabolomics, and microbiome profiling to study the interaction of Z. tritici in susceptible and resistant wheat. We demonstrate that Z. tritici suppresses the production of immune-related metabolites in a susceptible cultivar. Remarkably, this fungus-induced immune suppression spreads within the leaf and even to other leaves, a phenomenon that we term “systemic induced susceptibility”. Using a comparative metabolomics approach, we identify defense-related biosynthetic pathways that are suppressed and induced in susceptible and resistant cultivars, respectively. We show that these fungus-induced changes correlate with changes in the wheat leaf microbiome. Our findings suggest that immune suppression by this hemibiotrophic pathogen impacts specialized plant metabolism, alters its associated microbial communities, and renders wheat vulnerable to further infections.

IDENTIFICATION OF WHEAT GERMPLASM RESISTANT TO LEAF, STRIPE AND STEM RUST USING MOLECULAR MARKERS

Wheat leaf rust, stripe and stem rust are major wheat diseases in Kazakhstan that reduce yield and quality and cause considerable economic damage. This study utilized winter wheat germplasm from different national and international nurseries to evaluate their value for genetic and breeding programs directed towards improvement of wheat rust resistance in Kazakhstan. Based on the data from field experiments, the most valuable sources, combined resistance to both leaf and stripe rust were 16 lines and cultivars (28.6%), including mainly entries from CIMMYT and IWWIP. Nineteen entries (30.6%) had high level of resistance to leaf rust in the field tests. Thirty-three entries (53%) were effective to control stripe rust. In our study 22% wheat accessions studied had polymorphic band linked to leaf rust resistance gene Lr10. Based on rust reactions and data of molecular analysis, 3% entries were found to have Lr19/Sr25, 11% entries – Lr26/Sr31/Yr9/Pm8, 43% entries – Lr34/Yr18, 12% entries – Lr37/Yr17/Sr38, 17% – Lr68 gene and 6% entries – Yr10 gene. Only one line from IWWIP nursery showed presence of Yr15 gene. Out of 38 studied entries, the fragment of DNA associated with Sr22 gene in 13 wheat entries observed. Gene Sr22 was identified in five Kazakhstani and in 8 Belarusian wheat entries. The results obtained used for developing wheat cultivars resistant to rust.

Cultivar, planting date and weather linked to wheat leaf rust development

During four growing seasons (2013–2017), 282 leaf rust progress curves were characterized across experimental plots according to a number of climate-crop-disease variables in Kermanshah province, Iran. Leaf rust severity differed significantly between levels of cultivar, planting date, sampling time and year factors. Area under disease progress curve (AUDPC) based on disease severity was ranked using Kruskal–Wallis one-way ANOVA. H-test comparison between two disease-onset levels indicated lower mean AUDPC value for late disease onset than that for early disease onset. Highest and lowest AUDPC values were obtained in spring 2016 and 2015, respectively. According to principal component analysis, three principal components accounting for 73% of data variance verified dependence of leaf rust intensity on air temperature and wetness, cultivar resistance, date of disease onset, wheat maturity, and planting date. Based on principal component regression model, disease-onset and maturity date, mean 6-monthly temperature, number of days with minimum temperatures within the range of 5–25 °C and maximum RH > 60%, resistance index, and planting date justified 74% of variability in AUDPC dataset. These findings recommend involvement of cultivar resistance, dates of wheat maturity and planting along with weather predictors in wheat-leaf-rust studies to increase prediction value of future models, durability of host resistance to disease, and sustainability of disease control methods.

The Hsp90 Inhibitor, Monorden, Is a Promising Lead Compound for the Development of Novel Fungicides.

Endophytic fungi are great resources for the identification of useful natural products such as antimicrobial agents. In this study, we performed the antifungal screening of various plant endophytic fungi against the dollar spot pathogen Sclerotinia homoeocarpa and finally selected Humicola sp. JS-0112 as a potential biocontrol agent. The bioactive compound produced by the strain JS-0112 was identified as monorden known as an inhibitor of heat shock protein 90 (Hsp90). Monorden exhibited strong antagonistic activity against most tested plant pathogenic fungi particularly against tree pathogens and oomycetes with the minimum inhibitory concentration values less than 2.5 μg mL–1. Extensive in planta assays revealed that monorden effectively suppressed the development of several important plant diseases such as rice blast, rice sheath blight, wheat leaf rust, creeping bentgrass dollar spot, and cucumber damping-off. Especially, it showed much stronger disease control efficacy against cucumber damping-off than a synthetic fungicide chlorothalonil. Subsequent molecular genetic analysis of fission yeast and Fusarium graminearum suggested that Hsp90 is a major inhibitory target of monorden, and sequence variation among fungal Hsp90 is a determinant for the dissimilar monorden sensitivity of fungi. This is the first report dealing with the disease control efficacy and antifungal mechanism of monorden against fungal plant diseases and we believe that monorden can be used as a lead molecule for developing novel fungicides with new action mechanism for the control of plant diseases caused by fungi and oomycetes.

Effects of different fertilizer ratio on senescence of flag leaf in winter wheat

In order to increase the fertilizer use efficiency, the effects of different ratio of slow-release fertilizer, water retention agent and compound fertilizer in wheat production on senescence of flag leaf in winter wheat had been studied. The results showed that, water retaining agent 15 kg/ha with slow-release fertilizer 324 kg/ha and compound fertilizer 324 kg/ha (T2) effectively maintained the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activity and soluble protein content in wheat flag leaves after flowering, and reduced the malondialdehyde (MDA) content which could delay the flag leaves senescence and gain high yield in wheat.

Effects of cuticular wax content and specific leaf area on accumulation and partition of PAHs in different tissues of wheat leaf.

An indoor simulation experiment was conducted to explore the effects of cuticular wax content and specific leaf area (SLA) on accumulation and distribution of PAHs in different tissues of wheat leaf. Three levels (0, 1.25, 6.0mgL-1) of mixed solution of five PAHs (Σ5PAHs) including phenanthrene (PHE), anthracene (ANT), pyrene (PYR), benz[a]anthracene (BaA), and benzo[a]pyrene (BaP) were sprayed on leaves of seven varieties of winter wheat for every other day during 20 consecutive days. Shoot and root biomass of wheat under 6.0mgL-1 Σ5PAHs exposure were 5.87 and 0.33g, which were significantly (p< 0.05) lower than those (7.14 and 0.65g) without spraying Σ5PAHs solution, respectively. Elevated Σ5PAHs concentration in spraying solution significantly (p< 0.0001) decreased cuticular wax content (59.1 and 65.1 vs. 67.8mgg-1) in leaves of wheat but exerted slight effects on SLA. Regardless of spraying Σ5PAHs or not, SLA in leaves of Jiaomai (269-276cm2g-1) and Zhengmai (265-285cm2g-1) and cuticular wax content (104-118mgg-1) in leaves of Zhengmai were significantly higher than other varieties of wheat, respectively. Σ5PAHs concentration in cuticular waxes ranged from 24,616 to 106,353μgkg-1, which was 2~3 orders and 1~2 orders of magnitude higher than that in mesophylls (46.0-535μgkg-1) and leaves (785-5366μgkg-1). There was a significant (r = 0.46, p < 0.05, n = 28) positive correlation between SLA and Σ5PAHs concentration in wheat leaves when spraying 1.25mgL-1 of Σ5PAHs. The present study indicated that cuticular wax content was significantly (p < 0.01) positive correlated with Σ5PAHs concentration in the leaves and the translocation factor (TFw-m) of PHE, ANT, PYR, and Σ5PAHs from cuticular wax to mesophyll. Based on principal component analysis (PCA), cuticular wax content was the main limiting factor for folia uptake of PAHs in winter wheat. The present study suggested that cuticular wax could play significant roles in foliar uptake of PAHs of wheat via affecting their accumulation in cuticular wax and translocation to mesophyll.