Studies on variability of Exserohilum turcicum causing Northern corn leaf blight
| dc.contributor.advisor | Anwer, Arshad | |
| dc.contributor.author | Niwas, Ram | |
| dc.date.accessioned | 2023-04-09T09:40:36Z | |
| dc.date.available | 2023-04-09T09:40:36Z | |
| dc.date.issued | 2022 | |
| dc.description.abstract | Maize is considered as one of the most important staple food crops in the world. This crop has been taken into cultivation after the difficulty and interrelated relationship development; hence these crops have the most established record of cultivation by humanity. In current scenario maize cultivation is facing many challenges by several biotic and abiotic factors. Among all diseases, Northern corn leaf blight (NCLB) caused by Exserohilum turcicum (Passerini) (Leonard and Suggs.) accounts for significant damage to this crop and ultimately responsible for maximum loss in terms of quality and quantity. Disease symptoms first appear on the leaves at any stage of plant growth, but usually at or after anthesis. NCLB is an endemic disease in cooler (18-27 oC) maize growing regions, and potential to bring loss in grain yield ranges from 24 to 91%. In India, NCLB is found to be prevalent in Rabi growing season and one of the major factors in reduction of maize production. The state, Bihar also faces a major problem through NCLB because the area of Rabi maize is highest in all over India. Although being a virulent pathogen, no efficient and reliable measures for race identification as well as differential lines are available for NCLB in India. A study was conducted to assess the disease incidence and per cent disease index of NCLB in major maize growing districts (Bhagalpur, Begusarai, Khagaria, Katihar and Samastipur) of Bihar in 2020-21 and 2021-22. At the same time geographical distribution of the NCLB disease was also observed. From each representative district, 3 blocks were surveyed based on the production of maize crop and yield losses due to NCLB disease. Out of 3 blocks, 3 villages were selected at the interval of 3-10 km along road side. Such fields were randomly selected on both sides of the road. Each sampling point was marked with the global positioning system (GPS) using GPS receiver for altitude and longitude. Twenty plants in middle of each field were randomly selected and leaf samples were collected from infected maize fields and assessed for DI and PDI. The study was also done to evaluate initially 120 maize genotypes in field condition for NCLB resistance. These genotypes were also screened resistance to NCLB at molecular level by using specific primers of Ht1, Ht2, Ht3 and HtN1 genes. In this way differential lines of maize for E. turcicum were identified, and used in race identification of this pathogen. Virulence and distribution of races were also observed against Ht resistance genes and also identified the E. turcicum race population distribution in Bihar. These isolates were screened on maize differential lines containing Ht1, Ht2, Ht3 and or HtN1 resistance genes. Survey results revealed the DI and PDI of NCLB across all the districts even though at different blocks level. Mean of DI ranged from 35.0% (2020-21) to 51.6% (2021-22) in Bhagalpur to 86.6% (2020-21) to 90.0% (2021-22) in Samastipur and mean PDI varied between 19.0% (2020-21) to 37.0% (2021-22) in Bhagalpur and 63.6% (2020-21) to 70.0% (2021-22) in Samastipur district. Tmax ranged 23.2-35.4 °C, Tmin ranged 9.3-20.1 °C, RH ranged 52.0-78.0 % and rainfall ranged 6.6 mm-17.4 mm were found suitable for the disease development. The results indicate the severity of the disease in the surveyed area of Bihar. To get a clear picture of the disease significance across geographic regions to identify sources of resistant genotypes and the pathotypes/available in Bihar, and to link weather factors with the development of NCLB, it is necessary to conduct successive surveys for NCLB in all the maize growing regions. Among the 45 fungal isolates, cultural, morphological and molecular characterization were done and identified as E. turcicum. These isolates were grouped into four groups based on colony colour i.e. olivaceous brown, blackish brown, whitish black and greyish and into 2 groups based on regular and irregular margin. The conidial shapes were observed to be elongated and spindle with protruding hilum with conidial septa ranged from 2-12. Similarly, conidial length varied from 52.94 μm to 144.12 μm. β-tubulin gene sequences analysis made it possible to verify the identity of fungal strains and phylogenetic relationship of all isolates, were clustered in the same clade. β-tubulin gene sequences of all the isolates showed high level of similarity (100%) with reference isolate from GenBank accession number KU670342.1, KU670344.1, KU670343.1, KU670341.1, KU670340.1. In the study of genotypes for resistance, results showed that genotype ‘98’ had maximum yield 11.93 t/ha followed by genotype ‘118’ with 11.86 t/ha among 120 selected genotypes. The maximum DI 100%, PDI 89% and AUDPC 1844.5%-dsu (percent development stage unit) were recorded in the genotype ‘67’ having no resistant gene and minimum DI 25%, PDI 8% and AUDPC 42%-dsu were recorded in the genotype ‘115’ having all resistant genes. In addition, those genotypes showed the presence of all resistant genes Ht1, Ht2, Ht3 and HtN1 that could be involved in resistance to NCLB. Among the genotypes, three were moderately susceptible, six were moderately resistant, thirty were resistance, sixty nine were highly resistant and twelve were susceptible out of 120 to NCLB, found on the basis of presence/absence of resistant genes and disease parameter under field condition. The molecular based screening used in this study would utilize in other plants that are sensitive to NCLB, particularly using Ht1, Ht2, Ht3 and HtN1 genes. Studies on variability of E. turcicum, five different physiological races were observed based on the symptoms response of the differential maize lines. These races are race 0, race 1, race 3, race 23N and race 123N. E. turcicum race 3 was the most prevalent race having 26.6% frequency followed by race 0 having 24.4% and race 1 having 22.2% and least prevalent races were race 23N and 123N having 13.3% each. Varied resistance response of different isolates was observed on differential lines having different resistant genes. Despite the fact that virulence was seen against all Ht resistance genes, NCLB control might be increased by combining qualitative Ht resistance genes with quantitative resistance. | en_US |
| dc.identifier.uri | https://krishikosh.egranth.ac.in/handle/1/5810196172 | |
| dc.language.iso | English | en_US |
| dc.pages | 209 | en_US |
| dc.publisher | Department of Plant Pathology, BAU, Sabour | en_US |
| dc.sub | Plant Pathology | en_US |
| dc.theme | Entomology | en_US |
| dc.these.type | Ph.D | en_US |
| dc.title | Studies on variability of Exserohilum turcicum causing Northern corn leaf blight | en_US |
| dc.type | Thesis | en_US |