Blast Disease of Millets: Present Status and Future Perspectives

Millet crops are affected by various biotic and abiotic stresses. Among biotic stresses, blast disease caused by Pyricularia grisea (finger, pearl and proso millets) and Pyricularia setariae (foxtail millet) is the most devastating and widespread disease that causes substantial grain and forage yield losses and is a key constraint to pearl millet, finger millet and foxtail millet production in most of finger millet growing areas, and recently, it is also reported in barnyard millet in few locations. This book chapter emphasizes mainly on occurrence, distribution, symptoms, yield loss, etiology, genetic diversity, mode of spread of the pathogen and survival and integrated disease management approaches for mitigating of disease. This information will be highly helpful for better understanding of the disease. Further, it will be useful to enhance production and productivity of millets and to reinforce the food and nutritional security in the developing countries of Asia and Africa continents where the millets are mainly grown as staple food crops

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Not AvailableA new leaf blight disease of browntop millet (Brachiaria ramosa) was noticed during rainy season (Kharif) 2018 at small millet experimental field, University of Agricultural Sciences, Gandhi Krishi Vignana Kendra (GKVK), Bengaluru, India. To assess the disease severity, an intensive roving survey was conducted during the 2019 cropping season. Based on the morphological characterization, the causal agent of leaf blight disease was identified as Bipolaris spp. Further sequencing and combined gene analysis of ITS (internal transcribed spacer of rDNA), GAPDH (glyceraldehyde 3-phosphate dehydrogenase) and LSU (large subunit) of all the nine isolates confirmed the pathogen as B. setariae. Pathogenicity study showed that all the isolates were pathogenic and caused leaf blight symptoms on browntop millet. The B. setariae isolates showed marked variability with respect to disease incidence on browntop millet (cv. Dundu korale) under artificial inoculation conditions. However, the host range was limited only to browntop millet and found non-pathogenic to other six small millets examined. To our knowledge, this is the first completely described study on characterization of B. setariae causing leaf blight disease of browntop millet in India.Not Availabl

Phenotypic and Genotypic screening of fifty-two rice (Oryza sativa L.) genotypes for desirable cultivars against blast disease.

Magnaporthe oryzae, the rice blast fungus, is one of the most dangerous rice pathogens, causing considerable crop losses around the world. In order to explore the rice blast-resistant sources, initially performed a large-scale screening of 277 rice accessions. In parallel with field evaluations, fifty-two rice accessions were genotyped for 25 major blast resistance genes utilizing functional/gene-based markers based on their reactivity against rice blast disease. According to the phenotypic examination, 29 (58%) and 22 (42%) entries were found to be highly resistant, 18 (36%) and 29 (57%) showed moderate resistance, and 05 (6%) and 01 (1%), respectively, were highly susceptible to leaf and neck blast. The genetic frequency of 25 major blast resistance genes ranged from 32 to 60%, with two genotypes having a maximum of 16 R-genes each. The 52 rice accessions were divided into two groups based on cluster and population structure analysis. The highly resistant and moderately resistant accessions are divided into different groups using the principal coordinate analysis. According to the analysis of molecular variance, the maximum diversity was found within the population, while the minimum diversity was found between the populations. Two markers (RM5647 and K39512), which correspond to the blast-resistant genes Pi36 and Pik, respectively, showed a significant association to the neck blast disease, whereas three markers (Pi2-i, Pita3, and k2167), which correspond to the blast-resistant genes Pi2, Pita/Pita2, and Pikm, respectively, showed a significant association to the leaf blast disease. The associated R-genes might be utilized in rice breeding programmes through marker-assisted breeding, and the identified resistant rice accessions could be used as prospective donors for the production of new resistant varieties in India and around the world

Exploring the diversity of virulence genes in the Magnaporthe population infecting millets and rice in India

Blast pathogen, Magnaporthe spp., that infects ancient millet crops such pearl millet, finger millet, foxtail millet, barnyard millet, and rice was isolated from different locations of blast hotspots in India using single spore isolation technique and 136 pure isolates were established. Numerous growth characteristics were captured via morphogenesis analysis. Among the 10 investigated virulent genes, we could amplify MPS1 (TTK Protein Kinase) and Mlc (Myosin Regulatory Light Chain edc4) in majority of tested isolates, regardless of the crop and region where they were collected, indicating that these may be crucial for their virulence. Additionally, among the four avirulence (Avr) genes studied, Avr-Pizt had the highest frequency of occurrence, followed by Avr-Pia. It is noteworthy to mention that Avr-Pik was present in the least number of isolates (9) and was completely absent from the blast isolates from finger millet, foxtail millet, and barnyard millet. A comparison at the molecular level between virulent and avirulent isolates indicated observably large variation both across (44%) and within (56%) them. The 136 Magnaporthe spp isolates were divided into four groups using molecular markers. Regardless of their geographic distribution, host plants, or tissues affected, the data indicate that the prevalence of numerous pathotypes and virulence factors at the field level, which may lead to a high degree of pathogenic variation. This research could be used for the strategic deployment of resistant genes to develop blast disease-resistant cultivars in rice, pearl millet, finger millet, foxtail millet, and barnyard millet

Genome expansion and gene loss in powdery mildew fungi reveal tradeoffs in extreme parasitism

Powdery mildews are phytopathogens whose growth and reproduction are entirely dependent on living plant cells. The molecular basis of this life-style, obligate biotrophy, remains unknown. We present the genome analysis of barley powdery mildew, Blumeria graminis f.sp. hordei (Blumeria), as well as a comparison with the analysis of two powdery mildews pathogenic on dicotyledonous plants. These genomes display massive retrotransposon proliferation, genome-size expansion, and gene losses. The missing genes encode enzymes of primary and secondary metabolism, carbohydrate-active enzymes, and transporters, probably reflecting their redundancy in an exclusively biotrophic life-style. Among the 248 candidate effectors of pathogenesis identified in the Blumeria genome, very few (less than 10) define a core set conserved in all three mildews, suggesting thatmost effectors represent species-specific adaptations