Complex resistance of spring and winter bread wheat lines to biotic and abiotic stresses

An original initial material of spring and winter bread wheat with group resistance to stem and leaf rust was developed using new donors of resistance to stem rust: winter soft wheat GT 96/90 (Bulgaria) and accession 119/4-06rw with genetic material of the species Triticum migushovae and (Aegilops speltoides and Secale cereale), respectively, a line of spring wheat 113/00i-4 obtained using the species Ae. triuncialis and T. kiharae, as well as spring accession 145/00i with genetic material of the species Ae. speltoides resistant to leaf rust. The transfer of effective Sr-genes to progeny was monitored using molecular markers. New lines underwent a field assessment of resistance to leaf and stem rust in the epiphytotic development of diseases in the Central Region of the Russian Federation, as well as in the North Caucasus and Western Siberia, and showed high resistance to these pathogens. Fourteen genotypes of spring wheat with group resistance to these diseases and parental forms that participated in the origin of the lines were evaluated for resistance to spot blotch (Cochliobolus sativus) and tan spot (Pyrenophora tritici-repentis) using isolates from Kazakhstan and Omsk in laboratory conditions. A highly resistant parental form of winter soft wheat from “Arsenal” collection 119/4-06rw (wheat-Ae. speltoides-rye hybrid 2n = 42) with group resistance to two spots, four medium-resistant genotypes to both isolates of tan spot from Kazakhstan and Omsk populations of the pathogen, as well as genotypes resistant to the Omsk isolate of P. triticirepentis (parental form 113/00i-4 and lines 1-16i, 6-16i, 9-16i) were isolated. Among the lines of winter wheat, four were identified with group resistance to spot blotch and tan spot. Additionally, the stress resistance of the lines to NaCl salinization and prolonged flooding of seeds with water was evaluated at the early stages of ontogenesis in laboratory conditions. Lines 33-16i, 37-16i, 32-16i and 9-16i showed a high ability to withstand excess moisture. Lines 33-16i, 37-16i, 32-16i and 3-16i were characterized by high salt tolerance, exceeding the average of 49.7 %. Among the winter genotypes, lines were identified with increased resistance to hypoxia (37-19w, 32-19w, 16-19w, 90-19w) and with increased salt tolerance (20-19w, 9-19w, 37-19w, 90-19w), significantly exceeding the standard cv. Moskovskaya 39. The listed lines are of interest as sources of resistance to anaerobic and salt stress, as well as donors of resistance to a group of fungal diseases: leaf and stem rust and tan spot. We attribute the increased level of resistance of the new initial material to the presence of alien translocations in the original parental forms involved in the origin of the lines.

Tan spot disease under the lenses of plant pathologists

Necrotrophic plant pathogens pose an important threat to crop production, and many fungi in the Pleosporales have caused the sudden emergence of major epidemics on cereal crops. Tan spot of wheat, caused by Pyrenophora tritici-repentis, is one example, and since its emergence in the 1970s, scientists have explored its virulence and interactions with the host. In this chapter, our aim is to provide a comprehensive review of the most significant landmarks in tan spot research over the past 50 years from a plant pathology perspective.

MAJOR DISEASES OF WHEAT AND THEIR MANAGEMENT: A REVIEW

Wheat is the staple crop throughout the world and a great source of nutrition. Sometimes the wheat plant gets attacked by pathogens like fungi, bacteria and virus. Some of the common disease their symptoms and management are studied. The complexity of the interaction between a pathogen and its host, influenced by biotic and abiotic factors of the environment, make the control of these disease. Fungi is the most common causative agent in case of wheat. Some of the common disease caused by fungi are leaf rust, stem rest, stripe rust, loose smut, tan spot, powdery mildew, ergot and common bunt. Virus and bacteria also cause diseases in wheat. Wheat strike mosaic virus one of the diseases is bacterial blight of leaf. These diseases can be controlled by using disease resistant varieties. Due to the infection of these diseases there can be loss of 40-50% but sometimes it may be more. These diseases can be controlled by using some control measures. There are several chemical and herbal methods are used for the control of these diseases.

Immunological characteristics of winter wheat varieties to the main pathogens in the right-bank Forest Steppe

Aim. To determine the resistance of winter wheat varieties to the main pathogens, to establish their stability and plasticity, to identify perspective sources of resistance. Methods. Laboratory – production of inoculum of pathogens; field – artificial inoculation,, assessment of variety stability; statistical calculation of disease severity, indicators of stability and plasticity. Results. In 2015–2017, the resistance of 43 varieties of winter wheat to the main pathogens of leaf diseases, common bunt and root rots was assessed. Resistance to powdery mildew was found in 32 varieties, tan spot – in 2, root rot – in 3, hard smut – in 2 varieties. Six varieties of winter wheat were characterized by group resistance. Varieties that combine high plasticity and stability of the sign of disease resistance have been identified. Conclusions. Valuable sources of resistance are winter wheat varieties with group resistance to common bunt and powdery mildew – Tradytsiia Odeska and Kurs; powdery mildew and tan spot – Nasnaga and Zolotonozhka; powdery mildew and root rot – Nezabudka and Shchedrist kyivska.Keywords: resistance, winter wheat, diseases, plasticity, stability.

The first genome assembly of fungal pathogen Pyrenophora tritici-repentis race 1 isolate using Oxford Nanopore MinION sequencing

Objectives The assembly of fungal genomes using short-reads is challenged by long repetitive and low GC regions. However, long-read sequencing technologies, such as PacBio and Oxford Nanopore, are able to overcome many problematic regions, thereby providing an opportunity to improve fragmented genome assemblies derived from short reads only. Here, a necrotrophic fungal pathogen Pyrenophora tritici-repentis (Ptr) isolate 134 (Ptr134), which causes tan spot disease on wheat, was sequenced on a MinION using Oxford Nanopore Technologies (ONT), to improve on a previous Illumina short-read genome assembly and provide a more complete genome resource for pan-genomic analyses of Ptr. Results The genome of Ptr134 sequenced on a MinION using ONT was assembled into 28 contiguous sequences with a total length of 40.79 Mb and GC content of 50.81%. The long-read assembly provided 6.79 Mb of new sequence and 2846 extra annotated protein coding genes as compared to the previous short-read assembly. This improved genome sequence represents near complete chromosomes, an important resource for large scale and pan genomic comparative analyses.

Isolate Virulence and Cultivar Response in the Winter Wheat: Pyrenophora tritici-repentis (Tan Spot) Pathosystem in Oklahoma

Prevalence of tan spot of wheat caused by the fungus Pyrenophora tritici-repentis has become more prevalent in Oklahoma as no-till cultivation in wheat has increased. Hence, developing wheat varieties resistant to tan spot has been emphasized, and selecting pathogen isolates to screen for resistance to this disease is critical. Twelve isolates of P. tritici-repentis were used to inoculate 11 wheat cultivars in a greenhouse study in splitplot experiments. Virulence of isolates and cultivar resistance were measured in percent leaf area infection for all possible isolate x cultivar interactions. Isolates differed significantly (P < 0.01) in virulence on wheat cultivars, and cultivars differed significantly in disease reaction to isolates. Increased virulence of isolates detected increased variability in cultivar response (percent leaf area infection) (r = 0.56, P < 0.05) while increased susceptibility in cultivars detected increased variance in virulence of the isolates (r = 0.76, P < 0.01). A significant isolate × cultivar interaction indicated specificity between isolates and cultivars, however, cluster analysis indicated low to moderate physiological specialization. Similarity in wheat cultivars in response to pathogen isolates also was determined by cluster analysis. The use of diverse isolates of the fungus would facilitate evaluation of resistance in wheat cultivars to tan spot.

Impact of Crop Rotation and Soil Tillage on the Severity of Winter Wheat Leaf Blotches

Reduced tillage is considered as one of the main tools to save biological diversity; however, it increases pressure of diseases, including wheat leaf blotches. The aim of present study was to clarify the impact of reduced soil tillage on the development of winter wheat leaf blotches in different schemes of crop rotation. The impact of different growing technologies on the severity of winter wheat disease was evaluated in a two-factorial experiment: A – soil tillage system, and B – different combinations of wheat pre-pre-crop and pre-crop (wheat, oilseed rape, barley and faba beans). Diseases were assessed every 10 days approximately and total impact of diseases was evaluated by calculating AUDPC (Area under Diseases Progress Curve). Tan spot, caused by Pyrenophora tritici-repentis was dominated disease over the long period, regardless of meteorological conditions. Development of Septoria leaf blotch was not influenced by neither crop rotation nor soil tillage. The level of tan spot was essentially higher after wheat, regardless of the pre-pre-crop. Reduced soil tillage promoted severity of tan spot. Ploughing mitigated effect of previous crops and differences in tan spot level were insignificant. Despite many positive effects of conservation tillage, increasing of fungicide treatment could be necessary, in conditions, when the tan spot is most devastating and widespread wheat disease.

Genetic Protection of Soft Wheat from Diseases in the Southern Ural of Russia and Virulence Variability of Foliar Pathogens

The southern Ural is consistently among the 10 best regions in Russia for agricultural production, including wheat. Breeding in the Chelyabinsk Research Institute of Agriculture aims to develop wheat cultivars genetically protected from the main diseases (leaf and stem rust, septoria leaf blotch and tan spot). The genes for resistance to leaf rust, Lr1, Lr9, Lr10 and Lr26/Sr31, alone or in combination, are widespread in cultivars grown in the southern Ural. In 2012, a new wheat cultivar, Chelyaba 75, was proposed for commercial production in the southern Ural, being highly resistant to leaf rust with the highly effective genes LrSp and SrSp transferred from the cuckoo line with the genetic material Aegilops speltoides. Isolates virulent to cv. Chelyaba 75 were not found in Russian populations of Puccinia triticina. Additionally, for a long period, genes Lr29, Lr 41, Lr42, Lr45, Lr47, Lr50, Lr51, Lr53 and Lr57 were characterized by high efficiency. Virulence frequencies to other Lr genes vary annually, but no races with new virulence have been identified. The resistance of lines with the Sr31 and Sr24 genes indicates that the Puccinia graminis population does not contain genotypes with the potentially damaging race Ug99. Mixed septoria and tan spot infections occurred in the southern Ural, with the latter dominating. Races producing the exotoxin ToxA are widely distributed in Pyrenophora tritici-repentis populations. Two causal agents of septoria leaf blotch (Parastagonospora nodorum and P. avenae f. sp. tritici) occur in the region, with the first dominating. Aggressiveness of P. nodorum isolates to wheat cultivars was higher than that of P. avenae f. sp. tritici. All Parastagonospora isolates showed the presence of the SnTox3 marker. SnToxA and SnTox1 markers were found in P. nodorum isolates, usually separately, but in one isolate, these genes were found together. The analysis of the genetic diversity of wheat cultivars grown in the southern Ural, and the pathogenic complex present, indicate that pathogens continuously evolve under the influence of the host plant.

Measuring plant disease severity in R: introducing and evaluating the pliman package

Image analysis based on color thresholding is the reference method for measuring severity as percent area affected. It is deemed to produce accurate results, usually considered the "true" severity value. More than a dozen applications have been used for the task in phytopathometry studies, but none was coded in R language. Here we introduced and evaluated pliman, a suite for the analysis of plant images. In particular, we show functions for computing percent severity based on RGB information contained in image palettes prepared by the user. Six image collections, totaling 249 images, from different diseases (wheat tan spot, soybean rust, olive leaf spot, rice brown spot, bean angular spot, and Xyllela fastidiosa on tobacco) exhibiting a range of symptomatic patterns and severity were used to evaluate the agreement of pliman predictions with APS Assess, LeafDoctor and ImageJ. Three users independently prepared three image palettes (each representing leaf background, symptomatic or healthy leaf tissue) by manually inspecting and subsetting these target areas in the images. Pliman predictions by a joint palette (by joining images by the three users into one) were highly concordant (ρc &gt; 0.98) with measures by the other software for all but Xylella fastidiosa on Tobacco (ρc = 0.49). The error for the latter may be due to the low contrast between symptomatic and healthy tobacco tissues. Users showed to be a source of variation in the overall concordance depending on the disease. Reduction in the image resolution (&lt; 1 megapixel) did not impact the results. Combined with parallel processing, the use of low image resolution sped up the processing time resulting in pliman being ~170 to ~430 times faster than existing tools for disease quantification. Pliman showed great potential to produce accurate measures and accelerate studies involving plant disease severity measurements, especially for the batch processing of large sets of image collections.