Resistant Wheat Cultivars Research Articles

Myb10-D confers PHS-3D resistance to pre-harvest sprouting by regulating NCED in ABA biosynthesis pathway of wheat.

Summary Pre‐harvest sprouting (PHS), the germination of grain before harvest, is a serious problem resulting in wheat yield and quality losses.Here, we mapped the PHS resistance gene PHS‐3D from synthetic hexaploid wheat to a 2.4 Mb presence–absence variation (PAV) region and found that its resistance effect was attributed to the pleiotropic Myb10‐D by integrated omics and functional analyses.Three haplotypes were detected in this PAV region among 262 worldwide wheat lines and 16 Aegilops tauschii, and the germination percentages of wheat lines containing Myb10‐D was approximately 40% lower than that of the other lines. Transcriptome and metabolome profiling indicated that Myb10‐D affected the transcription of genes in both the flavonoid and abscisic acid (ABA) biosynthesis pathways, which resulted in increases in flavonoids and ABA in transgenic wheat lines. Myb10‐D activates 9‐cis‐epoxycarotenoid dioxygenase (NCED) by biding the secondary wall MYB‐responsive element (SMRE) to promote ABA biosynthesis in early wheat seed development stages.We revealed that the newly discovered function of Myb10‐D confers PHS resistance by enhancing ABA biosynthesis to delay germination in wheat. The PAV harboring Myb10‐D associated with grain color and PHS will be useful for understanding and selecting white grained PHS resistant wheat cultivars.

Take-All Disease: New Insights into an Important Wheat Root Pathogen.

Take-all disease, caused by the fungal root pathogen Gaeumannomyces tritici, is considered to be the most important root disease of wheat worldwide. Here we review the advances in take-all research over the last 15 years, focusing on the identification of new sources of genetic resistance in wheat relatives and the role of the microbiome in disease development. We also highlight recent breakthroughs in the molecular interactions between G. tritici and wheat, including genome and transcriptome analyses. These new findings will aid the development of novel control strategies against take-all disease. In light of this growing understanding, the G. tritici-wheat interaction could provide a model study system for root-infecting fungal pathogens of cereals.

QTL Analysis of Adult Plant Resistance to Stripe Rust in a Winter Wheat Recombinant Inbred Population

Stripe rust, caused by the fungus Puccinia striiformis f. sp. tritici, is a worldwide disease of wheat that causes devastating crop losses. Resistant cultivars have been developed over the last 40 years that have significantly reduced the economic impact of the disease on growers, but in heavy infection years it is mostly controlled through the intensive application of fungicides. The Pacific Northwest of the United States has an ideal climate for stripe rust and has one of the most diverse race compositions in the country. This has resulted in many waves of epidemics that have overcome most of the resistance genes traditionally used in elite germplasm. The best way to prevent high yield losses, reduce production costs to growers, and reduce the heavy application of fungicides is to pyramid multiple stripe rust resistance genes into new cultivars. Using genotyping-by-sequencing, we identified 4662 high quality variant positions in a recombinant inbred line population of 196 individuals derived from a cross between Skiles, a highly resistant winter wheat cultivar, and Goetze, a moderately to highly susceptible winter wheat cultivar, both developed at Oregon State University. A subsequent genome wide association study identified two quantitative trait loci (QTL) on chromosomes 3B and 3D within the predicted locations of stripe rust resistance genes. Resistance QTL, when combined together, conferred high levels of stripe rust resistance above the level of Skiles in some locations, indicating that these QTL would be important additions to future breeding efforts of Pacific Northwest winter wheat cultivars.

Population Genetic Structure and Chemotype Diversity of Fusarium graminearum Populations from Wheat in Canada and North Eastern United States.

Fusarium head blight (FHB) is a major disease in wheat causing severe economic losses globally by reducing yield and contaminating grain with mycotoxins. In Canada, Fusarium graminearum is the principal etiological agent of FHB in wheat, producing mainly the trichothecene mycotoxin, deoxynivalenol (DON) and its acetyl derivatives (15-acetyl deoxynivalenol (15ADON) and 3-acetyl deoxynivalenol (3ADON)). Understanding the population biology of F. graminearum such as the genetic variability, as well as mycotoxin chemotype diversity among isolates is important in developing sustainable disease management tools. In this study, 570 F. graminearum isolates collected from commercial wheat crops in five geographic regions in three provinces in Canada in 2018 and 2019 were analyzed for population diversity and structure using 10 variable number of tandem repeats (VNTR) markers. A subset of isolates collected from the north-eastern United States was also included for comparative analysis. About 75% of the isolates collected in the Canadian provinces of Saskatchewan and Manitoba were 3ADON indicating a 6-fold increase in Saskatchewan and a 2.5-fold increase in Manitoba within the past 15 years. All isolates from Ontario and those collected from the United States were 15ADON and isolates had a similar population structure. There was high gene diversity (H = 0.803–0.893) in the F. graminearum populations in all regions. Gene flow was high between Saskatchewan and Manitoba (Nm = 4.971–21.750), indicating no genetic differentiation between these regions. In contrast, less gene flow was observed among the western provinces and Ontario (Nm = 3.829–9.756) and USA isolates ((Nm = 2.803–6.150). However, Bayesian clustering model analyses of trichothecene chemotype subpopulations divided the populations into two clusters, which was correlated with trichothecene types. Additionally, population cluster analysis revealed there was more admixture of isolates among isolates of the 3ADON chemotypes than among the 15ADON chemotype, an observation that could play a role in the increased virulence of F. graminearum. Understanding the population genetic structure and mycotoxin chemotype variations of the pathogen will assist in developing FHB resistant wheat cultivars and in mycotoxin risk assessment in Canada.

Mayetiola destructor (Diptera: Cecidomyiidae) host preference and survival on small grains with respect to leaf reflectance and phytohormone concentrations

The Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae) is a major pest of wheat, globally. We conducted a series of laboratory choice and no-choice assays to quantify Hessian fly host preference for barley (cv. Champion), oat (cv. Cayuse), susceptible (cv. Alturas), and resistant (cv. Hollis) wheat. In addition, larval survivorship and adult emergence were compared among the evaluated host plants. We then examined whether insect preference for a host can be explained by differences in plant spectral reflectance. Further, larval survivorship and adult emergence were compared among host plants in relation to phytohormone concentrations. Hessian flies laid more eggs on wheat compared to either oat or barley. Spectral reflectance measurements of leaves were similar between susceptible and resistant wheat cultivars but different from those of barley and oat. Our results suggested that higher reflectance in the near-infrared range and lower reflectance in the visible range may be used by females for host selection. Hessian fly larvae were unable to develop into the pupal stage on resistant wheat and oat. No significant difference in larval survivorship was detected between the susceptible wheat and barley. However, adult emergence was significantly higher on barley than the susceptible wheat. Phytohormonal evaluations revealed that salicylic acid (SA) may be an important contributor to plant defense response to larval feeding as relatively higher concentrations of SA were present in oat and resistant wheat. While resistance in the resistant wheat is achieved only through antibiosis, both antibiosis and antixenosis were in effect rendering oat as a non-host for Hessian flies.

Changes in defense-related enzymes and phenolics in resistant and susceptible common wheat cultivars under aphid stress

The cereal aphids Rhopalosiphum padi L. are serious pests on grain crops, reducing the quality and yield by direct feeding damage and virus transmission. The changes in the physiological and biochemical parameters of two wheat cultivars under aphid stress were investigated to understand aphid-resistance mechanisms. The activity levels of phenylalanine ammonia-lyase (PAL), peroxidase (POD), tyrosine ammonia-lyase (TAL), Ca2+-ATPase and Mg2+-ATPase in resistant cultivar W0923 increased during aphid feeding, and most of them were significantly higher than those in the susceptible cultivar GN21. However, these enzyme activities increased and then decreased in GN21. The polyphenol oxidase (PPO) activity in W0923 was maintained longer than in GN21. The total phenol contents of the two cultivars exhibited significant increases on the 15th day compared with the untreated controls, and the content in W0923 was significantly higher than in GN21 by the 30th day. Most of the POD, PPO, PAL, TAL and Ca2+-ATPase activities and phenolic metabolite contents were higher in W0923 than in GN21 under the untreated control conditions. The Ca2+-ATPase and PAL activities positively correlated with POD, PPO and Mg2+-ATPase activities. Ca2+-ATPase and PAL may be key biochemical markers for evaluating aphid resistance. W0923 had a strong ability to maintain higher enzyme activities and synthesize more phenols and tannins than GN21, which contributed to aphid resistance.

Characterization of histological changes at the tillering stage (Z21) in resistant and susceptible wheat plants infected by Tilletia controversa K\xfchn

BackgroundDwarf bunt, which is caused by Tilletia controversa Kühn, is a soilborne and seedborne disease that occurs worldwide and can lead to 70% or even total losses of wheat crops. However, very little information is available about the histological changes that occur in dwarf bunt-resistant and dwarf bunt-susceptible wheat plants at the tillering stage (Z21). In this study, we used scanning electron microscopy and transmission electron microscopy to characterize the histological changes at this stage in resistant and susceptible wheat cultivars infected by T. controversa.ResultsUsing scanning electron microscopy, the root, stem, and leaf structures of resistant and susceptible cultivars were examined after T. controversa infection. The root epidermal and vascular bundles were more severely damaged in the susceptible T. controversa-infected plants than in the resistant plants. The stem cell and longitudinal sections were much more extensively affected in susceptible plants than in resistant plants after pathogen infection. However, slightly deformed mesophyll cells were observed in the leaves of susceptible plants. With transmission electron microscopy, we found that the cortical bundle cells and the cell contents and nuclei in the roots were more severely affected in the susceptible plants than in the resistant plants; in the stems and leaves, the nuclei, chloroplasts, and mesophyll cells changed significantly in the susceptible plants after fungal infection. Moreover, we found that infected susceptible and resistant plants were affected much more severely at the tillering stage (Z21) than at the seedling growth stage (Z13).ConclusionHistological changes in the wheat roots, stems and leaves were much more severe in T. controversa-infected susceptible plants than in infected resistant plants at the tillering stage (Z21).

QTL mapping of adult plant resistance to stripe rust in the Fundulea 900 × Thatcher RIL population

Wheat stripe rust, caused by Puccinia striiformis Westend. f.sp. tritici Eriks (Pst), is one of the most important diseases of bread wheat worldwide. Breeding resistant wheat cultivars is the most economical, effective and environmentally friendly way for controlling wheat stripe rust in China. The Romanian wheat line Fundulea 900 showed good resistance to wheat stripe rust at the adult stage. The present study aimed to map the quantitative trait loci (QTLs) for stripe rust resistance in 176 F<sub>2:6</sub> recombinant inbred lines (RIL) derived from the cross of Fundulea 900 × Thatcher. The RIL population was phenotyped for stripe rust (YR) severity at Mianyang in the Sichuan province and Baoding in the Hebei province in the 2016/2017 and 2017/2018 cropping seasons. SSR markers combined with a preferred screened group (PSG) analysis were used to identify the QTLs for stripe rust in the population. Three QTLs for stripe rust resistance were mapped on chromosomes 1AL, 7BL and 7DS, respectively. All three QTLs originated from Fundulea 900 and were detected in all the environments. The QTL on 7DS was provided by the known resistance gene Yr18/Lr34. The two QTLs on chromosomes 1AL and 7BL were explained by 9.2 to 21.5% and 5.1 to 10.1% of the phenotypic variance, respectively and might be new QTLs. The QTLs identified in the study and their closely linked markers can be used for marker-assisted selection (MAS) in wheat breeding programmes.

Effect of temperature on the expression of resistance to Hessian fly (Diptera: Cecidomyiidae) in durum wheat cultivars

Hessian fly, Mayetiola destructor (Say) is a destructive insect pest occurring in many wheat growing areas of the world. The most effective management option for controlling Hessian fly is the use of resistant wheat cultivars carrying specific resistance genes. However, wheat resistance genes to Hessian fly are affected by temperature. Two Moroccan cultivars ‘Chaoui’ and ‘Marouane’ and three ICARDA elites DWHF01, DWHF02 and Icamoram7 all carrying resistance to Moroccan Hessian fly populations were evaluated at three different temperatures (20, 25 and 30 °C). Results showed that the elite DWHF01 and DWHF02 resistance was less affected by higher temperatures with percentage of resistant plants remaining above 60% at 30 °C. However, ‘Marouane’, ‘Icamoram7’ and ‘Chaoui’ lost more than 50% of their resistance at 30 °C. Resistance in all these genotypes was expressed only as antibiosis with presence of dead first instars on resistant plants. The number of live larvae on susceptible plants was counted and larval density decreased with increasing temperature. Moreover, length measurements of live larvae showed significant differences across different temperatures, the size of larvae increased as temperature increased and ranged between 3.23 and 4.13 mm. In light of the warming climates and increase occurrence of days above 30 °C during the first months of the Moroccan wheat season, the data presented here are meant to help breeders recommend cultivars better adapted to the raising temperatures.

Effect of wheat powdery mildew on grain nitrogen metabolism

AbstractGlutamine synthetase (GS) and glutamate synthase (GOGAT) play a central role in plant nitrogen (N) metabolism. In order to study the effect of powdery mildew (Blumeria graminis f. sp. tritici, Bgt) on N metabolism, field experiments were carried out to evaluate GS and GOGAT activity, GS expression and grain protein content (GPC) in susceptible (Xi'nong 979) and resistant (Zhengmai 103) wheat cultivars under three treatments. The three treatments were no inoculation (CK), inoculated once with Bgt (MP) and inoculated nine times with Bgt (HP). For Xi'nong 979, the activities of GS and GOGAT in grains as well as GS activity in flag leaves increased at 10–15 days after anthesis (DAA), and decreased significantly at 15 or 20–30 DAA in HP and MP. However, GS activity in grains decreased from 20 DAA, which was later than that of flag leaves (15 DAA). At the same time, GS expression in grains was up-regulated at early stage, with GS1 at 10 DAA and GS2 at 15 DAA, followed by a continuous down-regulation. This result indicated that GS and GOGAT activity as well as GS expression were inhibited by powdery mildew, indicating that N metabolism in grains was inhibited at 20–30 DAA. The current study also found out that the yield of the susceptible cultivar decreased significantly, while its GPC increased obviously in HP. It was shown that the increase of GPC was not due to the enhancement of N metabolism, but due to the passive increase caused by yield reduction.

Performance and transcriptomic response of the English grain aphid, Sitobion avenae, feeding on resistant and susceptible wheat cultivars

Plant resistance against insects mainly depends on nutrient restriction and toxic metabolites, but the relative importance of nutrition and toxins remains elusive. We examined performance, nutrition ingestion, and transcriptome response of the English grain aphid, Sitobion avenae, feeding on resistant Xiaoyan 22 (XY22) and susceptible Xinong 979 (XN979) wheat cultivars. Aphids had lower body weight and fecundity when feeding on XY22 than on XN979, although the phloem sap of XY22 had a higher nutritive quality (in terms of amino acid:sucrose ratio). Aphids feeding on XY22 also had a lower honeydew excretion rate than those on XN979, suggesting that aphids ingested less phloem sap from XY22. The transcriptome data showed 600 differentially expressed genes (DEGs), and 11 of the top 20 KEGG pathways significantly enriched in DEGs were involved in nutrient metabolism. We found 81 DEGs associated with the metabolism of sugars, lipids, and amino acids, 59 of which were significantly downregulated in aphids feeding on XY22. In contrast, there were 18 DEGs related to detoxifying metabolism, namely eight UDP-glucuronosyltransferases, six cytochromes P450 monooxygenases, one glutathione S-transferase, two ATP-binding cassette transporters, and one major facilitator superfamily transporter; 12 of these were upregulated in the aphids feeding on XY22. Our results indicated that both the quantity and quality of phloem nutrition available to aphids are critical for the growth and development of aphids, and the higher resistance of XY22 is mainly due to the reduction in phloem sap ingested by aphids, rather than toxic metabolites.

Identification of QTLs/Defense Genes Effective at Seedling Stage Against Prevailing Races of Wheat Stripe Rust in India.

Resistance in modern wheat cultivars for stripe rust is not long lasting due to the narrow genetic base and periodical evolution of new pathogenic races. Though nearly 83 Yr genes conferring resistance to stripe rust have been cataloged so far, few of them have been mapped and utilized in breeding programs. Characterization of wheat germplasm for novel sources of resistance and their incorporation into elite cultivars is required to achieve durable resistance and thus to minimize the yield losses. Here, a genome-wide association study (GWAS) was performed on a set of 391 germplasm lines with the aim to identify quantitative trait loci (QTL) using 35K Axiom® array. Phenotypic evaluation disease severity against four stripe rust pathotypes, i.e., 46S119, 110S119, 238S119, and 47S103 (T) at the seedling stage in a greenhouse providing optimal conditions was carried out consecutively for 2 years (2018 and 2019 winter season). We identified, a total of 17 promising QTl which passed FDR criteria. Moreover these 17 QTL identified in the current study were mapped at different genomic locations i.e. 1B, 2A, 2B, 2D, 3A, 3B, 3D, 4B, 5B and 6B. These 17 QTLs identified in the present study might play a key role in marker-assisted breeding for developing stripe rust resistant wheat cultivars.

Progress in the management of Fusarium head blight of wheat: An overview

Fusarium head blight (FHB), also known as head scab, is a devastating fungal disease that affects small grain cereal crops such as wheat (Triticum aestivum L.). The predominant causal agent, Fusarium graminearum Schwabe (teleomorph: Gibberella zeae (Schwein.) Petch), is ranked the fourth most important fungal plant pathogen worldwide. Apart from yield and quality losses, mycotoxin production can occur from FHB infection, resulting in harmful effects on human and animal health. Some level of disease control may be achieved by using certain fungicides and agronomic practices plus host resistance. In South Africa, there are currently no registered fungicides or bio-fungicides, no resistant wheat cultivars and only limited control is achieved by cultural practices. Because effective disease reduction cannot be achieved by using a single strategy, the integration of multiple management strategies can enhance disease control. We review possible strategies for reducing the risk for FHB infections that are relevant to the context of South Africa and other wheat growing areas in Africa.
 Significance:
 
 The importance of the effect of FHB on wheat cannot be overemphasised. This review highlights and describes the various control options and their efficacies. It also describes the current state of research in an effort to control FHB and its associated mycotoxins.
 Wheat is one of the most produced crops worldwide and in South Africa, hence this review could promote and intensify research towards the development of more effective management strategies for FHB of wheat.

Identification and validation of Fusarium head blight resistance QTL in the U.S. soft red winter wheat cultivar ‘Jamestown’

AbstractUse of genetic resistance is one of the most important strategies to manage the devastating disease Fusarium head blight (FHB) in wheat. Numerous quantitative trait loci (QTL) having varying effects on reducing FHB and the mycotoxin deoxynivalenol (DON) accumulation have been reported from Asian, European, or distant sources such as wild relatives of wheat (Triticum aestivum L.). However, coming from nonadapted backgrounds, the incorporation of such QTL into regional breeding programs has often resulted in the simultaneous transfer of other undesirable traits. Therefore, it is important to identify, characterize, and deploy sources of genetic resistance that do not suffer from poor adaptability and/or linkage drag. In the present work, QTL associated with FHB resistance in a high‐yielding, moderately resistant soft red winter wheat cultivar ‘Jamestown’ were mapped and validated. The QTL mapping was done using a recombinant inbred line (RIL) population of Pioneer ‘25R47’ × Jamestown having 186 individuals. Phenotyping over 2 yr at three locations, and genotyping using the 90K single nucleotide polymorphism (SNP) platform identified two new QTL, named QFHB.vt‐1B.1 and QFHB.vt‐1B.2, on the chromosome 1B long arm. The QTL contributed to FHB incidence, FHB severity, Fusarium‐damaged kernels, and DON content. Independent mapping of these QTL using two additional RIL populations of FG95195 × Jamestown (170 RILs) and Jamestown × LA97113UC‐124 (77 RILs) validated their stability and effectiveness in different genetic backgrounds. Kompetitive allele specific polymerase chain reaction (KASP) assays were developed using linked SNPs for marker‐assisted selection of the QTL. These QTL are being used in breeding programs to develop FHB‐resistant, high‐yielding varieties.

Pathotype, Resistance Classification, and Seed-Coating Control of Heterodera avenae and H. filipjevi in the North China Plain.

Heterodera avenae and H. filipjevi are cereal cyst nematodes (CCNs) that infect cereals in 16 provinces of China. CCN populations from Xuchang, Tangyin, Qihe, and Juye were tested using 23 barley, oat, and wheat entries of the International Test Assortment for Defining Cereal Cyst Nematode Pathotypes. H. avenae populations from Tangyin, Qihe, and Juye were classified as pathotype Ha91, and H. filipjevi from Xuchang was classified as a new pathotype similar to pathotype West. Among 42 other winter wheat cultivars, 29 and 30 were differentially susceptible, 13 and 12 were differentially resistant to H. avenae and H. filipjevi, respectively. Three entries were resistant to both species, and three other entries were resistant to H. avenae and moderately resistant to H. filipjevi. Coating wheat seed with abamectin + isopycnic imidacloprid or methylene (bis) thiocyanate + thiamethoxam reduced the number of H. avenae and H. filipjevi cysts by 46 to 56%, increased wheat yield by 9 to 27%, and improved net income by 660 to 2,640 Chinese Yuan ha-1, respectively. Resistant wheat cultivars are scarce in China, and seed coating is considered the most suitable method for controlling CCNs in the North China Plain, where crop rotation cannot be practiced.

The wheat receptor-like cytoplasmic kinase TaRLCK1B is required for host immune response to the necrotrophic pathogen Rhizoctonia cerealis

Receptor-like cytoplasmic kinases (RLCKs) represent a large family of proteins in plants. In Arabidopsis and rice, several RLCKs in subfamily VII (RLCKs-VII) have been implicated in pathogen-associated molecular pattern-triggered immunity and basal resistance against bacterial and fungal pathogens. However, little is known about roles of RLCKs-VII of the important crop common wheat (Triticum aestivum) in immune responses. Here, we isolated a RLCK-VII-encoding gene from wheat, designated as TaRLCK1B, and investigated its role in host immune response to infection of a necrotrophic fungus Rhizoctonia cerealis that is a major pathogen of sharp eyespot, a destructive disease of wheat. RNA-sequencing and RT-qPCR analyses showed that transcriptional level of TaRLCK1B was significantly higher in sharp eyespot-resistant wheat cultivars than in susceptible wheat cultivars. The gene transcription was rapidly and markedly elevated in the resistant wheat cultivars by R. cerealis infection. The TaRLCK1B protein was closely related to OsRLCK176, a rice resistance-related RLCKs-VII, with 84.03% identity. Virus-induced gene silencing plus wheat response to R. cerealis assay results indicated that silencing of TaRLCK1 impaired resistance to R. cerealis. Meantime, silencing of TaRLCK1 significantly elevated both the content of H2O2 (a major kind of reactive oxygen species, ROS) and the transcriptional level of the ROS-generating enzyme-encoding gene RBOH, but repressed the expression of the ROS-scavenging enzyme-encoding gene CAT1 at 18 hours after inoculation (hai) with R. cerealis. Taken together, these data suggested that TaRLCK1B was required for the early immune response of wheat to R. cerealis through modulating ROS signaling in wheat.

Proteomic Analysis of UV-B-Induced Virulence-Mutant Strains of Puccinia striiformis f. sp. tritici Based on iTRAQ Technology.

The emergence of new physiological races of Puccinia striiformis f. sp. tritici (Pst) causing wheat stripe rust can lead to the loss of resistance of wheat cultivars to stripe rust, thus resulting in severe losses in wheat yield. In this study, after the germination of urediospores of three Pst strains including the original strain (CYR32, a dominant physiological race of Pst in China) and two virulence-mutant strains (CYR32-5 and CYR32-61) acquired from CYR32 via UV-B radiation, proteomic analysis based on isobaric tags for relative and absolute quantification (iTRAQ) technology was performed on the strains. A total of 2,271 proteins were identified, and 59, 74, and 64 differentially expressed proteins (DEPs) were acquired in CYR32-5 vs. CYR32, CYR32-61 vs. CYR32, and CYR32-61 vs. CYR32-5, respectively. The acquired DEPs were mainly involved in energy metabolism, carbon metabolism, and cellular substance synthesis. Furthermore, quantitative reverse transcription PCR assays were used to determine the relative expression of the 6, 7, and 1 DEPs of CYR32-5 vs. CYR32, CYR32-61 vs. CYR32, and CYR32-61 vs. CYR32-5, respectively, at the transcriptional level. The relative expression levels of one, five, and one gene, respectively, encoding the DEPs, were consistent with the corresponding protein abundance determined by iTRAQ technology. Compared with CYR32, the DEPs associated with energy metabolism and stress—including E3JWK6, F4S0Z3, and A8N2Q4—were up-regulated in the mutant strains. The results indicated that the virulence-mutant strains CYR32-5 and CYR32-61 had more tolerance to stress than the original strain CYR32. The results obtained in this study are of great significance for exploring the virulence variation mechanisms of Pst, monitoring the changes in Pst populations, breeding new disease-resistant wheat cultivars, and managing wheat stripe rust sustainably.

Karnal Bunt: A Re-Emerging Old Foe of Wheat.

Wheat (Triticum aestivum L.) crop health assumes unprecedented significance in being the second most important staple crop of the world. It is host to an array of fungal pathogens attacking the plant at different developmental stages and accrues various degrees of yield losses owing to these. Tilletia indica that causes Karnal bunt (KB) disease in wheat is one such fungal pathogen of high quarantine importance restricting the free global trade of wheat besides the loss of grain yield as well as quality. With global climate change, the disease appears to be shifting from its traditional areas of occurrence with reports of increased vulnerabilities of new areas across the continents. This KB vulnerability of new geographies is of serious concern because once established, the disease is extremely difficult to eradicate and no known instance of its complete eradication using any management strategy has been reported yet. The host resistance to KB is the most successful as well as preferred strategy for its mitigation and control. However, breeding of KB resistant wheat cultivars has proven to be not so easy, and the low success rate owes to the scarcity of resistance sources, extremely laborious and regulated field screening protocols delaying identification/validation of putative resistance sources, and complex quantitative nature of resistance with multiple genes conferring only partial resistance. Moreover, given a lack of comprehensive understanding of the KB disease epidemiology, host-pathogen interaction, and pathogen evolution. Here, in this review, we attempt to summarize the progress made and efforts underway toward a holistic understanding of the disease itself with a specific focus on the host-pathogen interaction between T. indica and wheat as key elements in the development of resistant germplasm. In this context, we emphasize the tools and techniques being utilized in development of KB resistant germplasm by illuminating upon the genetics concerning the host responses to the KB pathogen including a future course. As such, this article could act as a one stop information primer on this economically important and re-emerging old foe threatening to cause devastating impacts on food security and well-being of communities that rely on wheat.

AN OVERVIEW OF COMPARISON BETWEEN WHEAT RUSTS MYCOFLORA IN INDIA WITH GLOBAL SCENARIO

Wheat rusts are the oldest plant disease known to human and caused by Puccinia species. Puccinia species are the main constraints in wheat production wherever wheat is grown. Early literatures mention these devastating diseases and their ability to destroy entire wheat crops. These wheat rust pathogens are highly transmissible through air current in both cases, primary and secondary infections. Primary infection occur through alternate host developing spore (Aeciospores) and secondary infection caused by wheat (primary host) developing spore (Uredospores). Secondary infection results epidemics, several time as globally occurrence. Ecologically, the persistence of rusts as a significant disease in wheat can be attributed to specific characteristics of the rust mycoflora. Their ability to spread aerially over the large distance, production of urediospores in enormous number and evolving new pathotypes, makes the management of wheat rusts a very daunting task. These characteristics include a capacity to produce a large number of spores which can be wind disseminated over long distances and infect wheat under favorable environmental conditions and the ability to change genetically, thereby producing new races with increased aggressiveness on resistant wheat cultivars. KEY WORDS: Wheat Rust, Puccinia, Rust Mycoflora, Stem Rust, Leaf Rust, Stripe Rust

The potential of cultivar mixtures to reduce fungicide input and mitigate fungicide resistance development

The potential of cultivar mixtures to reduce disease severity and increase yields in cereals across the globe is well established. The effect of cultivar mixtures on the selection for pathogen strains resistant to specific fungicides has, however, not previously been investigated. In this study, the case of the pathogen Zymoseptoria tritici causing Septoria tritici blotch in wheat (Triticum aestivum) and resistance development to azole fungicides by single mutations in CYP51 was explored. Cultivar mixtures composed of a range of resistant and susceptible winter wheat cultivars were grown across a total of seven field trial sites and three growing seasons. The treatments consisted of untreated plots and plots with one, two, or three fungicide applications. From the trials, the economically optimal fungicide input was calculated and the level of fungicide resistance was measured as the frequency of key CYP51 mutations. The study demonstrates for the first time how cultivar mixtures can reduce the selection for fungicide resistance and can reduce the need for fungicide input. Based on four trial sites in two growing seasons, the majority of cultivar mixtures reduced the frequency of a CYP51 mutation compared with the component cultivars in pure stand. The highest significant reduction in mutation frequency by a cultivar mixture was 73%. Conditions with high fungicide input and low disease severity resulted in the most pronounced reductions in mutation frequency by cultivar mixtures. The economical need for using fungicides was also impacted by cultivar mixtures when compared with pure stand. Based on six trial sites across two growing seasons, the majority (67%) of cultivar mixtures had the potential to reduce the number of fungicide applications compared with their pure stand counterparts. These findings could have notable implications for intensive crop production. Within-field diversity can reduce the threat from diseases that have become resistant to fungicides and contribute to creating a more sustainable production where lower chemical inputs can sustain high yields.