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.

Advances in breeding techniques for durable resistance to spot blotch in cereals

This chapter reviews advances in breeding techniques for durable resistance to spot blotch in cereals. It starts by highlighting the spread, economic importance and the disease cycle of spot blotch. The chapter then goes on to examine the diversity of the pathogen and physiological specialization. This is then followed by a discussion on the identification of resistance sources, as well as the histological, biochemical and morphological components of resistance. The chapter also reviews molecular approaches for resistance breeding, specifically focusing on quantitative trait loci (QTL and genome-wide association mapping (GWAS) studies. Resistance genes and their possible deployment are also discussed, along with a section on low molecular weight toxins and their possible role in pathogenicity. The chapter also examines necrotrophic effector triggered susceptibility and associated genes and breeding for spot blotch resistance in wheat. Breeding for spot blotch resistance in barley is also discussed, before concluding with a discussion on farmers participatory research in the release of spot blotch resistant varieties.

Genetic Evaluation and Screening of Diverse Wheat Genotypes for Spot Blotch Resistance

Production of wheat (Triticum aestivum L.) the main food source of South Asian countries including India faces several constraints including spot blotch caused by Bipolaris sorokiniana resulting in yield loss of 25–43 % depending upon the stage of infection. Fifty genotypes were evaluated for nine quantitative characters and area under disease progress curve (AUDPC) to identify superior genotype with spot blotch resistance. High heritability coupled with moderate to high genetic advance as percent of mean was registered for grains per spike, tillers per square meter, days to 50% heading and days to 50% flowering indicating the characters to be governed by additive genes. Correlation and path coefficient analysis favored days to 50% heading, days to 50% flowering and grains per spike since they had significant positive correlation with yield and simultaneous negative correlation with AUDPC and also conferring highest positive direct effect towards yield. Multiple linear regression (MLR) analysis indicated days to 50% heading to be most sensitive with negative influence on AUDPC. D2 analysis grouped the 50 genotypes into 10 clusters suggesting presence of diversity among the genotypes. Frequency distribution of AUDPC among the genotypes showed more or less normal distribution of the character. Low AUDPC score with acceptable level of yield performance were recorded for the genotypes 29882, 29610, 29473, 29940, 29477, 29748 and 30081. Identification of high yielding and less susceptible genotypes for spot blotch disease in the present investigation offered an opportunity for wheat improvement through selective breeding.

Whole Genome Sequencing and Expression Analysis of ToxA in Bipolaris Sorokiniana Provides Discernment of Pathogenicity Causing Spot Blotch of Wheat

Background: Spot blotch disease of wheat caused by Bipolaris sorokiniana Boerma (Sacc.) is an emerging problem in South Asian countries. In this study, whole genome of highly virulent isolate of Bipolaris sorokiniana (BS112) was sequenced, pathogenicity related gene(s) were identified and role of ToxA gene in spot blotch disease development was established.Results: Bipolaris sorokiniana isolate BS112 infecting wheat was sequenced using hybrid assembly approach. The assembly size of the genome was 35.64Mb (GenBank accession number RCTM00000000) with GC content of 50.2%, providing coverage of 97.6% on reference ND90Pr genome. Average gene density predicted was 250-300 genes/Mb. A total of 235 scaffolds were obtained using pyScaf assembler with N50 of 16,54,800 bp. In addition, 152 transcription factors involved in various biological processes were identified and a total of 682 secretory proteins were predicted using secretome analysis. ToxA gene (535bp) was analyzed and identified in the genome of B. sorokiniana which revealed 100% homology with ToxA gene of Pyrenophora tritici repentis. Further, ToxA gene was amplified, sequenced and validated in the 39 isolates of B. sorokiniana which confirmed the presence of ToxA gene in all the isolates of B. sorokiniana. All these ToxA sequences were submitted in NCBI database (MN601358-MN601396). As ToxA gene interacts with Tsn1 gene of host, 13 wheat genotypes were evaluated for the Tsn1 gene and five genotypes (38.4%) were found to be Tsn1 positive with more severe necrotic lesions compared to Tsn1 negative wheat genotypes. In vitro expression analysis of ToxA gene in B. sorokiniana isolate (BS112) using qPCR revealed maximum upregulation (14.67 fold) at 1st day after inoculation (DAI). Further, in planta expression analysis of ToxA gene in Tsn1 positive and Tsn1 negative genotypes, Agra local and Chiriya 7 respectively was also conducted. Results revealed maximum expression (7.89 fold) of ToxA gene in Tsn1 positive genotype, Agra local at 5th DAI compared to Tsn1 negative genotype Chiriya 7 which showed minimum expression (0.048 fold) at 5th DAI. Conclusions: Full genome of B. sorokiniana was sequenced; secreted proteins and virulence genes were identified in the genome. ToxA gene was validated in thirty nine isolates of B. sorokiniana. In planta ToxA-Tsn1 interaction studies established that spot blotch disease is more severe in Tsn1 positive genotypes. This genomic resource will provide a new insight into better understanding and management of spot blotch disease and B. sorokiniana of wheat.