Spot Blotch Research Articles

Seed Priming Through Fungicides, Biocontrol Agents and Botanicals as Effective Method for Controlling Spot Blotch Pathogen, Bipolaris sorokiniana in Barley

Seed Priming Through Fungicides, Biocontrol Agents and Botanicals as Effective Method for Controlling Spot Blotch Pathogen, Bipolaris sorokiniana in Barley

Spot blotch: A journey from minor to major threat of wheat

In the recent times, the rapidly changing climate has transformed the host-pathogen-environment interactions considerably, leading to minor pathogens, such as Bipolaris sorokiniana, emerging as a major threat. B. sorokiniana attacks leaves, stem, sheath, root and grains of wheat which causes significant yield loss. However, lack of precise forecasting models, limited resistant cultivars and inadequate knowledge of new technologies for disease management serves as limitations in the proper management of the disease. In this article, we discuss the pathogen biology, its host range, host pathogen interactions, trend of severity, prevalence area, changing weather condition, newly reported resistant line/germplasm, gene and some other ecological sound approaches of the management

Use of Crop Wild Relatives (CWRs) of Wheat in Disease Resistance Breeding

Wheat (Triticum aestivum L.) is one of the three major cereal crops contributing 20% calories to the world population. The most serious constraints to wheat production are biotic stresses like rusts, blights, powdery mildew, bunts and smuts. Genetic or host plant resistance is the best way to control these diseases than use of chemical pesticides. Continuous search for novel genes is indispensable to counter the dynamic and rapidly evolving pathogen population. In case of some diseases like spot blotch, Karnal Bunt and Fusarium head blight development of resistant cultivars is not an easy task as the resistance to them found in the germplasm is not satisfactory and none of the commercial cultivars showed resistance. Hence, underutilized crop wild relatives prove to be valuable resource in the search for new disease resistance genes to combat wheat diseases.

STUDY ON RESEARCH WORKS AND FUTURE RESEARCH DIRECTIONS OF POST-GRADUATE PROGRAM AT PATHOLOGY DEPARTMENT, IAAS, RAMPUR, CHITWAN, NEPAL

The Institute of Agriculture and Animal Science (IAAS) under Tribhuwan University (TU) has been carrying out various disciplinary and system research works through post-graduate students' research and publishing their findings through the M.Sc.Ag and Ph.D. thesis dissertations. Various thesis written by researchers under IAAS were collected and the appraisal of pathological research works on major cereals, vegetable crops, legume crops, oilseed crops and high-value crops along with ideas on management practices was done with the help of a thorough literature review. Data were gathered from IAAS/TU libraries, Rampur Library, Kritipur library, GAASC library and IAAS journals. A total of 68 types of research were conducted at IAAS. It is revealed that major diseases associated with cereals area brown spot of rice, rice blast, yellow rust of wheat, helminthosporium leaf blight of wheat, spot blotch of wheat and leaf blast of finger millet. Similarly, diseases of vegetables include late blight of potato, a white mold of french beans. The major diseases of legumes are wilt of lentil & chickpea, powdery mildew of pea, anthracnose of soybean and those of oilseeds are mainly leaf blights. Large cardamom, greatly known as high- value crop, is found to be suffered from Chirkey Foorkey and leaf blight diseases. Fungal pathogens cause most of the diseases in almost all crops. The management practices at their best results included the use of biological agents along with commonly available fungicides. The study found out a research gap in agricultural pathology as well. It also luminated the future area of research works that is lacking in current research works

DUAL CULTURE APPROACH FOR THE EVALUATION OF ANTAGONISTIC ACTIVITY OF NATIVE TRICHODERMA ISOLATES AGAINST BIPOLARIS SOROKINIANA

Spot blotch disease caused by Bipolaris sorokiniana (Sacc.) shoem. is one of the most destructive diseases of wheat (Triticum aestivum L.) in plain areas of Nepal. A laboratory experiment was conducted to evaluate the antagonistic activity of seven test Trichoderma isolates obtained from the soil sample by employing dual culture method against spot blotch pathogen of wheat Bipolaris sorokiniana at Plant Pathology Division, Nepal Agriculture Research Council, Khumaltar, Nepal. The experiment was laid out in a Completely Randomized Design (CRD). The result revealed that all Trichoderma isolates showed control over the pathogen. Isolate T517 stands out to be the most effective one giving 67.81% mycelial growth inhibition but isolate T528 was the least effective. Native Trichoderma can have significant biocontrol potential and may provide an effective solution against plant fungal diseases.

Expression analysis of hormonal pathways and defense associated genes in gamma-rays mutagenized wheat genotypes against combined stresses of spot blotch and terminal heat

Wheat (Tritium aestivum L.) productivity is severely hampered by various pathogens and changing climatic conditions. Spot blotch and terminal heat stress are the major constraints of wheat production in the eastern Gangetic plains of India. To identify novel breeding sources and to understand underlying resistance mechanisms, forty-four gamma rays mutagenized wheat genotypes, derived from three different parents were screened under favourable agro-ecological conditions for spot blotch and terminal heat stress. Ten mutants showed reduced spot blotch infection calculated based on Area Under Disease Progress Curve (AUDPC), than their respective parents. The mutant TAW41 had the least infection (AUDPC: 354.32), significantly lower than its parent HD2967 (AUDPC: 675.51) and other checks. TAW41 also had a higher Normalized Difference Vegetation Index (NDVI) and chlorophyll content than the parent. Gene expression analysis of TAW41 showed differential accumulation of transcripts involved in hormonal pathways (Salicylic acid, Jasmonic acid, and ethylene) and other defense-associated genes, indicating that TAW41 might have unique resistance mechanism that facilitates this genotype to perform better against the combined stress of spot blotch and terminal heat. Hence, mutant TAW41 has been identified as a novel source of resistance that could be exploited in wheat improvement programmes to enhance tolerance to spot blotch and terminal heat stress.

Resistance of modern spring barley cultivars to harmful organisms

Background. Diseases and pests cause great damage to barley stands and harvests. Harvest losses from harmful organisms reach 25–30%.Materials and methods. During 2017–2020, 46 spring barley cultivars from the VIR collection, listed in the State Register for Selection Achievements, were studied for their resistance to fritfly, net and spot blotches, brown rust, and powdery mildew. The tests were carried out in the field with provocative colonization by fritfly and under natural infection pressure of leaf pathogens.Results and conclusions. In 2017, net blotch predominated over other diseases. In 2018, there was an epyphytotic outburst of spot blotch, and cultivars with weak development of this disease were identified. In 2019 and 2020, the incidence of brown rust and powdery mildew was significant, and the virulence of fritfly increased greatly in the same years. Field tests resulted in identification of 3 barley accessions resistant to fritfly: ‘Odon’ (k-31118, Buryatia), ‘Miar’ (k-31203, Orenburg Province), and ‘Omsky 99’ (k-31230, Omsk Province). Cv. ‘Posada’ (k-31245, Germany) was weakly affected by fritfly, brown rust and powdery mildew. Cultivars were selected for their low susceptibility to powdery mildew (up to 5%): ‘Chiraz’ (k-31131, Denmark), ‘Cheerio’ (k-31297, Denmark), and ‘Odyssey’ (k-31333, England), and brown rust: ‘Chiraz’ (k-31131, Denmark), ‘Eifel’ (k-31249, France), ‘Ursa’ (k-31339), and ‘Sunshine’ (k-31129, Germany). Such long-term assessment results can be used in breeding programs to develop cultivars with group or complex resistance to harmful organisms.

Mutations in a barley cytochrome P450 gene enhances pathogen induced programmed cell death and cutin layer instability.

Disease lesion mimic mutants (DLMMs) are characterized by the spontaneous development of necrotic spots with various phenotypes designated as necrotic (nec) mutants in barley. The nec mutants were traditionally considered to have aberrant regulation of programmed cell death (PCD) pathways, which have roles in plant immunity and development. Most barley nec3 mutants express cream to orange necrotic lesions contrasting them from typical spontaneous DLMMs that develop dark pigmented lesions indicative of serotonin/phenolics deposition. Barley nec3 mutants grown under sterile conditions did not exhibit necrotic phenotypes until inoculated with adapted pathogens, suggesting that they are not typical DLMMs. The F2 progeny of a cross between nec3-γ1 and variety Quest segregated as a single recessive susceptibility gene post-inoculation with Bipolaris sorokiniana, the causal agent of the disease spot blotch. Nec3 was genetically delimited to 0.14 cM representing 16.5 megabases of physical sequence containing 149 annotated high confidence genes. RNAseq and comparative analysis of the wild type and five independent nec3 mutants identified a single candidate cytochrome P450 gene (HORVU.MOREX.r2.6HG0460850) that was validated as nec3 by independent mutations that result in predicted nonfunctional proteins. Histology studies determined that nec3 mutants had an unstable cutin layer that disrupted normal Bipolaris sorokiniana germ tube development.

Spot blotch disease of wheat as influenced by foliar trichome and stomata density

Spot blotch, caused by Bipolaris sorokiniana, is a potent biotic constraint to wheat crop leading to substantial yield abatement in warm humid South Asia (e.g. India, Nepal and Bangladesh) and other major wheat-growing countries such as Canada, the United States, Brazil and Australia. A set of 98 bread wheat genotypes were evaluated over two growing seasons to investigate the relationship among foliar trichome, stomata density, and susceptibility to the spot blotch pathogen. The higher density of trichomes (90-140 mm −2 ) on the adaxial surface of flag leaves entrapped 32-74 mm −2 pathogen spores. It restricted the dew droplets size (0.15–0.3 mm 2 ) on the flag leaves and thus prevented direct contact between the spores and the leaf epidermis. Trichome density was negatively associated with the disease development and spore germination but positively associated with grain size and the number of spores entrapped on trichomes per mm 2 . Conversely, stomata density was positively associated with the development of the disease. Cluster and principal component analyses divided trichome density, the number of spores trapped on trichome per mm 2 , and thousand grain weight into one group and stomata density, the area under disease progress curve, percent spore germination, and dew scale into another group. The results from this study provided a novel insight to breeders where the selection of bread wheat genotypes with high trichome (90-140 mm −2 ) and low stomata density (72-90 mm −2 ) on foliage could enhance spot blotch resistance in wheat. • Spot blotch of wheat reduces up to 30% yield in the Indian subcontinent. • The relationship among foliar trichome, stomata density, and susceptibility to the spot blotch pathogen was studied. • The higher density of trichomes (90-140 mm −2 ) entrapped 32-74 mm −2 spores prevented direct contact between the spores and the leaf epidermis. • This study assists breeders for the selection of bread wheat genotypes with high trichomes and low stomata density on foliage could enhance spot blotch resistance.

First Report of Spot Blotch Caused by Bipolaris sorokiniana on Winter Rye in Kentucky.

The Kentucky distilling industry ranks as one of the state's largest industries and continues to expand. In 2017, the Kentucky distilling industry was responsible for approximately $235 million in state and local tax revenues (Coomes and Kornstein, 2019). Rye (Secale cereale L.) grains are a vital component for production of some distilled spirits. Although winter rye is produced on relatively few hectares in Kentucky currently, a recent initiative has supported expanding production to help meet the growing demand of local distilleries. University of Kentucky winter rye research field trials were visited in Caldwell and Logan Counties, KY in May 2018, and in Fayette County, KY in May 2019. Leaves were collected that had dark brown, oval to irregular-shaped lesions with definite margins and yellow halos. Symptoms were present on approximately 50% to 80% of the flag leaves, with severity ranging from 5% to 30% of the flag leaf area affected. Leaves were surface-disinfested by soaking in a 2% NaOCl solution for 1 min and rinsed twice in sterilized water and then placed in a humidity chamber (plastic bag with moist paper towels) at room temperature (approximately 24°C) to induce fungal sporulation. Seventeen single-spore isolates were obtained and stored at -80°C in 15% glycerol solution. Isolates were grown on potato dextrose agar under 12 h cycles of white light/darkness for 5 days. Colonies were gray to black. Conidia that formed were mostly straight or slightly curved, dark olivaceous brown, 3-7 septate, and 41.0-90.4 × 15.2-29.3 µm. Based on the symptoms observed on the collected leaves and these morphological characteristics similar to those described by Chang and Hwang (2000) and Manamgoda et al. (2014), the fungus was tentatively identified as Bipolaris sorokiniana (Sorokin) Shoemaker. The sequence of internal transcribed spacer regions (ITS) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were used to identify three isolates (18Bs004, 18Bs111 and 19Bs064) using primer ITS1/ITS4 (White et al. 1990) and GPD1/GPD2 (Berbee et al. 1999), respectively. The sequences were deposited in GenBank with accession numbers MT457817, MT457818 and MZ066635 for ITS sequences and MZ073644 to MZ073646 for GAPDH sequences. BLAST searches with ITS and GAPDH sequences matched 100% identity (344/344 bp and 515/515 bp for ITS and GAPDH sequences, respectively) to B. sorokiniana (GenBank accession No. MT254731 and MH844813, respectively). To prove pathogenicity, a conidial suspension (1 × 105 conidia/ml) was used to inoculate 15-day-old cultivar 'Serafino' winter rye plants in the greenhouse. Leaves of 8 plants were inoculated with 50 ml of the conidial suspension using a spray bottle. Plants were covered with a transparent plastic bag for 48 h, and symptoms were observed 10 days after inoculation. Leaf lesions, similar to those described above, were present on all inoculated plants, but no symptoms were observed on non-inoculated control plants. Bipolaris sorokiniana was reisolated from symptomatic leaves and the identity of the pathogen was confirmed based on the morphology previously described. To our knowledge, this is the first report of spot blotch caused by B. sorokiniana on winter rye in Kentucky, but B. sorokiniana has been reported on rye in the neighboring state of Virginia (Roane 2009). Kentucky produces approximately 150,000 and 4,000 ha of winter wheat (Triticum aestivum) and winter barley (Hordeum vulgare) annually, respectively, which are both known hosts of B. sorokiniana (Kumar et al. 2002). An isolate of B. sorokiniana from rye was reported by Ghazvini and Tekauz (2007) to be less virulent on barley differential lines. Further research is needed to better understand spot blotch distribution, susceptibility in winter rye cultivars, and potential yield and quality loss implications in winter rye production and end use. It is unknown how susceptible various winter rye cultivars grown in Kentucky are to spot blotch.

Functional analysis of SCD1 gene involved in pathogenicity of spot blotch disease of wheat causing fungus Bipolaris sorokiniana

Functional analysis of SCD1 gene involved in pathogenicity of spot blotch disease of wheat causing fungus Bipolaris sorokiniana

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 f ield 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. tritici-repentis (parental form 113/00i-4 and lines 1-16i, 6-16i, 9-16i) were isolated. Among the lines of winter wheat, four were identif ied with group resistance to spot blotch and tan spot. Additionally, the stress resistance of the lines to NaCl salinization and prolonged f looding 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 identif ied 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), signif icantly 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.

Weather-based models to forecast spot blotch disease (Bipolaris sorokiniana) of wheat (Triticum aestivum) in North Bengal

Experiment was laid with wheat (Triticum aestivum L.) genotypes Sonalika (susceptible check) and HD 2967 (popular variety) at Pundibari, Coochbehar, India (26o23’52”N, 89o23’26”E) on two dates of post-rainy (rabi) seasons of 2018 and 2019 at one-year interval. Data of experiments conducted previously at Pundibari were also used. Correlation values indicated that percent disease severity and Area under Disease Progress Curve on cv. Sonalika and HD 2967 had significant (P<0.1) correlations with maximum temperature and morning relative humidity. Weighted interactions between maximum temperature and morning relative humidity, maximum temperature and rainfall, minimum temperature and afternoon relative humidity, minimum temperature and rainfall, morning and afternoon relative humidity were also significant (P<0.1). Cultivar-specific models were developed to predict the severity of the spot blotch disease (Bipolaris sorokiniana) on the crop. This will allow the growers to make need-based timely effective application of fungicides prior to inception of the disease. Here we report only the models that were found effective based on validation in the two years. As per available literature, this report seems to be the first of its kind for forecasting spot blotch of wheat.

Gain from genomic selection for a selection index in two-row spring barley.

New breeding programs are faced with many challenges including evaluation of unknown germplasm, initiation of breeding populations that will satisfy short- and long-term breeding goals, and implementation of efficient phenotyping strategies for multiple traits. Genomic selection (GS) is a potentially valuable tool for recently established breeding programs to quickly accelerate genetic gain. Genomic selection on selection index (SI) values may increase gain over phenotypic selection but empirical studies remain limited. We compared gain in overall SI value for height, heading date, preharvest sprouting (PHS) resistance, and spot blotch resistance and component traits in two cycles of GS with one round of phenotypic selection (PS) in two-row spring malting barley (Hordeum vulgare L.). Higher realized gain for SI value, height, and PHS was observed with GS compared with PS but GS did not result in significant gain for heading date and spot blotch. Genetic variances for height and heading date, which had small index weights, were not reduced with GS but variances were substantially reduced for heavily weighted PHS and correlated seed germination traits. Inbreeding was increased by GS compared with PS but restricted mating of high breeding value individuals limited potential inbreeding. Our results indicate GS is a useful method to improve selection on index values with different weights.

Comparative Evaluation of Different Fungicides and Bio-agents for Management of Spot Blotch of Barley Caused by Bipolaris sorokiniana (Sace. Ex Sorok)

Among the fungicides Propiconazole, Tebuconazole, Azoxystrobin and Azxoxystrobin + Difenconazole completely inhibited the mycelia growth of pathogen at 200 ppm concentration under in-vitro condition. Among bio control agents, T. harzianum-1 (77.90 per cent) was found most effective antagonist against pathogen followed by T. harzianum-2 (74.80per cent) and T. viride-1 (74.41per cent).

Biochemical Profiling of Seedling and Adult Plant and Its Association with Spot Blotch Resistance in Bread Wheat

Biochemical Profiling of Seedling and Adult Plant and Its Association with Spot Blotch Resistance in Bread Wheat

Integrated omics approaches for deciphering antifungal metabolites produced by a novel Bacillus species, B. cabrialesii TE3T, against the spot blotch disease of wheat (Triticum turgidum L. subsp. durum)

Bipolaris sorokiniana is an important biotic constraint for global wheat production, causing spot blotch disease. In this work, we present a comprehensive characterization of the cell-free culture filtrate (CF) and precipitated fraction (PF) of Bacillus cabrialesii TE3T showing an effective inhibition of spot blotch. Our results indicated that CF produced by B. cabrialesii TE3T inhibits the growth of B. sorokiniana through stable metabolites (after autoclaving and proteinase K treatment). Antifungal metabolites in CF and PF were explored by an integrated genomic-metabolomic approach. Genome-mining revealed that strain TE3T contains the biosynthetic potential to produce wide spectrum antifungal (surfactin, fengycin, and rhizocticin A) and antibacterial metabolites (bacillaene, bacilysin, bacillibactin, and subtilosin A), and through bioactivity-guided LC-ESI-MS/MS approach we determined that a lipopeptide complex of surfactin and fengycin homologs was responsible for antifungal activity exhibited by B. cabrialesii TE3T against the studied phytopathogen. In addition, our results demonstrate that i) a lipopeptide complex inhibits B. sorokiniana by disrupting its cytoplasmatic membrane and ii) reduced spot blotch disease by 93 %. These findings show the potential application of metabolites produced by strain TE3T against B. sorokiniana and provide the first insight into antifungal metabolites produced by the novel Bacillus species, Bacillus cabrialesii.

Genetics of Resistance to Common Root Rot (Spot Blotch), Fusarium Crown Rot, and Sharp Eyespot in Wheat.

Due to soil changes, high density planting, and the use of straw-returning methods, wheat common root rot (spot blotch), Fusarium crown rot (FCR), and sharp eyespot (sheath blight) have become severe threats to global wheat production. Only a few wheat genotypes show moderate resistance to these root and crown rot fungal diseases, and the genetic determinants of wheat resistance to these devastating diseases are poorly understood. This review summarizes recent results of genetic studies of wheat resistance to common root rot, Fusarium crown rot, and sharp eyespot. Wheat germplasm with relatively higher resistance are highlighted and genetic loci controlling the resistance to each disease are summarized.

Analysis of Cultural and Pathogenic Diversity in Bipolaris sorokiniana Causing Spot Blotch of Bread Wheat in North India

Present study was conducted to analyse the cultural and pathogenic diversity in different isolates of Bipolaris sorokiniana the causal organism of spot blotch in bread wheat. Six isolates of Biplorais sorokiniana (BS-F-5, BS-D-2, BS-K,4, BS-DWR-K-1, BS-V-6, and BS-P-3) were evaluated simultaneously for cultural and pathogenic variability on the basis of diverse characteristics against seven different genotypes of wheat grown in the region viz: BOW’S’, HS 375, HUW 234, PBW 343, PBW 443, K9107 and A9-30-1. The results indicated that isolates varied significantly among themselves for all the characters analysed. The isolate BS-F-5 exhibited the maximum colony diameter, maximum average dimension (length and width) of conidiophore, maximum number of septa in conidiophore and conidia. Variations were also observed in texture of the colony. Among the seven genotypes tested against six isolates, BOW’S’ showed resistance against three isolates (BS-D-2, BS-K,4, BS-DWR-K-1) and genotype A-9-30-1 showed high susceptibility against all isolates except BS-D-2. The isolates BS-F-5 and BS-P-3 exhibited maximum pathogenic virulence among the isolates analysed in the present investigation.

Sensitivity of Bipolaris sorokiniana to strobilurin, triazole, and carboxamide premixes

Spot blotch of barley, caused by Bipolaris sorokiniana, has increased its intensity during the last growing seasons in Argentina. The in vitro inhibitory effect of different fungicide premixes on the mycelial radial growth of 10 B. sorokiniana isolates from different locations was assessed. Effective fungicide concentration that caused 50% inhibition of mycelial growth (EC50) was determined using a linear log analysis. The EC50 values varied from 0.05 to 0.37 µg mL−1 among fungicides. The lower EC50 values were obtained with premixes containing carboxamides. An additional in vivo experiment was performed to test the SB control when fluxapyroxad + pyraclostrobin + epoxiconazole was applied preventively or curatively. The fungicide significantly reduced the SB intensity (incidence, severity, number and size of lesions) when applied preventively. To our knowledge, this is the first report of sensitivity of B. sorokiniana and EC50 estimation to fungicides worldwide.