FACTORS AFFECTING RICE-TORIA DOUBLE CROPPING IN UPPER BRAHMAPUTRA VALLEY ZONE OF ASSAM – AN ANALYSIS THROUGH AGRICULTURAL KNOWLEDGE INFORMATION SYSTEM
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Date
2018-01
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AAU, Jorhat
Abstract
The Northeast region of India including Assam is considered as original home of the world’s hottest chilli, Bhut Jolokia (Capsicum chinense). In recent years several varietal types of Bhut Jolokia exhibiting considerable variation in plant, fruit and pungency traits has been observed in the farmers’ field. Therefore, an attempt was made to characterise a few accessions of Bhut Jolokia at morphological, biochemical and DNA level to elucidate the extent and nature of genetic variation. Expression profile of few pungency related genes in Bhut Jolokia was also attempted to detect their possible allelic variation in the Bhut Jolokia accessions. A set of 20 Bhut Jolokia (C. chinense) accessions, three Capsicum annum accessions (Krishna Jolokia, bell pepper and Cherry type) and one C. frutescens accession (Mem Jolokia) were analysed using 35 morphological and biochemical characters. Analysis of variance (ANOVA) for quantitative characters revealed considerable genetic variation among the genotypes. Variability and path analysis identified fruits/ plant, fresh fruit weight and photosynthetic rate as important parameters for improvement. Principal component analysis (PCA) isolated eight principal components each comprising of several characters and accounting for 78.36% of the total variability among the accessions. Several seedling, fruit and physiological characters contributed towards total variability of the population. The PCA plots failed to distinguish Bhut Jolokia accessions into distinct clusters despite sufficient diversity among them. Sixteen characters were identified based on their contribution to PCA, as minimum morphological descriptors for preliminary characterization of Bhut Jolokia genotypes. Population structure analysis separated the accessions into Bhut Jolokia and non Bhut Jolokia populations. Majority of the genotypes had > 80% membership coefficients for each specific group. Only Acc-21 (Cherry type) showed genomic admixture indicating gene flow between Bhut Jolokia and non Bhut Jolokia populations. The genetic diversity studies conducted with the use of 51 SSR markers and 40 gene specific markers exhibited a low inbreeding coefficient (FIS=0.147), thereby indicating high heterozygosity among the genotypes. The overall FST value of 0.432 indicated large genetic differentiation between the populations. AMOVA performed
between all lines grouped according to structure indicated 43% variation between populations, 20% variation among individuals within populations and 37% variation was due to variation within individuals. Gene expression analysis of 6 genes of the capsaicinoid biosynthetic pathway exhibited that the Capsaicinoid pathway genes studied showed significantly higher expression in Bhut Jolokia (C. chinense) genotypes while very low expression levels were observed in Bell pepper genotype (low-pungent). Amongst these candidate genes, AMT, Pun1, PAL from Phenylpropanoid pathway and BCAT, KAS and ACL from Fatty acid biosynthetic pathway were found to be up-regulated in pungent genotypes especially in the breaker stage (25-35 DAF) of the fruit development. The variations in the pungency level were found to be associated with changes in the expression level of the genes of the biosynthetic pathway.