Browsing by Author "Debnath, Ashim"
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ThesisItem Open Access Genetic analysis of leaf and neck blast resistance in rice.(College of Post Graduate Studies in Agricultural Sciences, CAU-Imphal, Umiam, 2018-11) Debnath, Ashim; Rai, MayankRice blast is one of the most devastating biotic stresses that limits rice productivity in NE region and causes yield loss from 40 to 46 %. The NEH region is considered to be the centre of diversity for both rice and Magnaporthe grisea. Here, host resistance is short-lived in the disease-prone environments because of high level of variability in the pathogen population. Therefore, the present study was carried out to elucidate the genetic basis of leaf and neck blast resistance under Meghalaya conditions in terms of genes and loci associated with resistance to the local patho types, and intra and inter allelic interactions, if any, that play a role in the expression of the resistance pathotype and other related yield contributing traits. The field experiments involved a set of 80 genotypes and six generations of a cross between LR-5 (Lal Jangali) and Sambha mahsuri SUB 1. The study involved association analysis of reported major gene linked markers with leaf and neck blast resistance in natural and F2 populations to identify effective genes under local conditions; and generation mean analysis to understand the genetic components of mean and variance for resistance and other yield related traits. A set of 80 genotypes were screened across two seasons, under two different rice ecosystems (upland and lowland) and a panel of 43 tolerant and susceptible genotypes was identified for marker trait association study. Marker trait association studies revealed seven different loci to be associated with blast resistance. These genes/loci were Pi54, Pi2, Pib, Pi2/9 locus, Pi5, Pb1/qPbm locus and Pi20(t). Genes Pi5 and Pi54 were found to be associated with leaf blast resistance in both, natural population and biparental F2 population. Pib and qPbm showed some degree of association with neck blast resistance in natural population. Generation mean analysis revealed that dominance genetic variance was higher than additive variance for majority of the traits under study. It also suggested that the epistatic interaction model was found adequate to explain the gene action in the blast resistant related traits like Leaf Blast Score, Percent Infected Leaf, Neck Blast Percentage and Spikelet Fertility Percentage. Narrow sense heritability was found to be moderate for Leaf Blast Score and Neck Blast Percentage indicating that marker assisted selection would be an effective way to augment phenotypic selection for blast resistance. The study indicates that leaf and neck blast resistance is primarily governed by dominant alleles of multiple genes that interact with each other to impart resistance. The markers and genes identified in this study can be used for marker assisted selection of breeding material to increase the frequency of favourable alleles at these loci in the elite rice breeding populations so that varieties with durable resistance can be developed.ThesisItem Open Access Genetic Analysis of Yield Contributing Traits in Lowland Rice Genotypes and NILs Under Acidic Soil(College of Post Graduate Studies, CAU, Imphal, 2014-06) Debnath, Ashim; Rai, MayankRice (Oryza sativa) farming is the largest single use of land for producing food. India is the largest rice growing country and 2nd in terms of production. Rice belongs to the genus Oryza of the family Gramineae and forms the staple food of 2.7 billion people. Various abiotic stresses limit rice production in acidic soil environments. Among these various abiotic stresses Iron (Fe) and Aluminium (Al) toxicity affect the rice production under low and upland conditions respectively. The present study was conducted on a set of promising genotypes, their F1s, and a set of NILs (Near isogenic Lines) to determine the combining ability of parents adapted to acidic soil conditions through L X T analysis and also for evaluation of parents and NILs under acidic soil, aluminium and iron toxic hydroponics conditions. A relationship between seedling stage aluminium and iron toxicity tolerance under hydroponics condition and field performance under acidic soil was also made in this study. In the genetic analysis, among the lines, L1 and L5 (Priya and Sahbhagi Dhan), while among the testers T1 and T3 (IR 24 and Kasalath) showed the best general combining ability while the crosses Sahbhagi Dhan X Kasalath (L5 X T3), Shahsarang X Sambamasuri (L4 X T2), Priya X IR 24 (L1 X T1) showed the best specific combining ability. Also, Sahbhagi Dhan X Kasalath (L5XT3) showed maximum heterosis for seven of the ten traits studied when compared to the best commercial cultivar of the region, Shahsarang. Field level screening of NILs in acidic soil was done in augmented design along with three checks Swarna, Shahsarang, Sahbhagi Dhan. Based on nine different traits superior, average and inferior performing lines were selected. By means of hydroponic experiment conducted using Magnavaca’s nutrient solution (for Al toxicity screening) and Yoshida‘s solution (for iron toxicity screening), different superior and inferior lines were identified based on parameters like root growth, root/shoot biomass. It may however be mentioned that there were no significant correlation between superior and inferior lines in field and hydroponics but some lines were identified which perform well in both condition and perform poor in field as well as hydroponics condition. The information generated would help identify suitable parents for breeding programme under acidic soils and the phenotypic data on the NILs may serve as a base for future mapping of loci responsible for yield under acidic soils, aluminium and iron toxic conditions.