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Authors: ROHINI M.R.
Advisor: Rekha Chaudhury
Title: Genetic Diversity Assessment and Cryopreservation Studies in Indian Rough lemon (Citrus jambhiri Lush., Rutaceae)
Language: en_US
Type: Thesis
Agrotags: null
Abstract: Citrus is one of the economically important fruit crops of India, belonging to the family Rutaceae. South-east Asia is recognised as one of the centres of origin of Citrus and related genera. Citrus genetic diversity of India represented by several wild and cultivated species has great potential for improvement of Citrus industry. Rough lemon (Citrus jambhiri Lush.) is one of the interspecific hybrids originated in India which is found throughout the country up to an altitude of 1000 m. Rough lemon is largely used as a rootstock for commercial plantations of citrus and the studies showed that trees on these stocks are vigorous, high yielding, tolerant to tristeza virus and adaptable to drought, salinity, high pH and deep soil conditions. These diverse genotypes constitute a very important germplasm source to be utilized for future rootstock breeding programmes especially for abiotic stress tolerance traits. Therefore, collection, characterization and conservation of this important rootstock species is of prime importance. In the present study, thirty eight accessions of C. jambhiri collected from different geographical regions of India (North east, Foothills of Himalayas and South India) were taken for investigation of various aspects of germplasm management including diversity assessment, population genetic analysis, studies on seed physiology, storage behaviour and cryopreservation of embryonic axes. Morphological characterization of 28 qualitative and 14 quantitative leaf, fruit and seed characters using IPGRI descriptors indicated the existence of wide morphological variability (64%) between the accessions. This variability could be attributed to the fact that this species is reported as a hybrid of mandarin and citron. Molecular diversity analysis using 23 RAPD and 17 ISSR markers detected only 20-23% polymorphism indicating narrow genetic base of the accessions. However, analysis with 17 SSR markers detected high polymorphism (85.29%) in C. jambhiri accessions showing that SSRs are more efficient for diversity analysis in C. jambhiri. Although the correlation between the morphological and molecular data was low in the analysed accessions of C. jambhiri, both methods allowed fare clustering of accessions based on the analysed traits. Population genetic analysis by SSR markers revealed that accessions collected from North Eastern India were most diverse in terms of genetic diversity parameters. Genetic distance analysis of populations revealed that the accessions from Himachal Pradesh and North east were most similar genetically probably owing to their similar ecological conditions of adaptation while population collected from Punjab and North east were the most distinct genetically. Molecular analysis of population showed that population structure is not significant as only two sub-populations were formed. High gene flow value (4.69) and low Fst (0.23) value also indicated less genetic differentiation occurring among the regions of collection. Two RAPD, two ISSR and two SSR primers produced unique and specific bands in 114 C. jambhiri which can be used for the authentic identification of this rootstock species at an earlier stage. Seeds of this species exhibited intermediate seed storage behaviour and had moderate seed longevity. Seeds are desiccation and freezing sensitive which further confirmed the intermediate seed storage behaviour of the species. The cryopreservation of embryonic axes of C. jambhiri was attempted using three different cryopreservation techniques viz., air desiccation-freezing, vitrification and encapsulation-dehydration. Cryopreservation was efficient for the axes desiccated to 12-15% moisture content. Among the three cryo-techniques, in terms of higher recovery after LN exposure, encapsulation-dehydration using 0.5M sucrose (recovery 60%) was found superior followed by air desiccation-freezing (recovery 45%) and vitrification (recovery 25%).
Description: T-10099
Subject: Tree Improvement and Genetic Resources
Theme: Genetic Diversity Assessment and Cryopreservation Studies in Indian Rough lemon (Citrus jambhiri Lush., Rutaceae)
These Type: Ph.D
Issue Date: 2019
Appears in Collections:Theses

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