Browsing by Author "Chandrasekhar, A."

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    Assessment of the genetic diversity of Indian coconut accessions and their relationship to other cultivars, using microsatellite markers
    (No. 145 Plant Genetic Resources Newsletter, 2006) Devakumar, K.; Jayadev, K.; Rajesh, M.K.; Chandrasekhar, A.; Manimekalai, R.; Kumaran, P.M.; Parthasarathy, V.A.
    Coconut cultivation in the Indian subcontinent over many centuries has given rise to diverse cultivar types, identi- fied based on discernible morphological traits, geographical locations and farmers’ choice. The Indian coconut germplasm base has also been enriched through introductions from other major coconut growing regions of the world. This study assessed the genetic diversity in a range of coconut accessions, and their relationship to other major coconut cultivars, using microsatellite markers. Microsatellite assay was used for 23 Indian accessions (15 Talls and 6 Dwarfs) and for 21 exotic accessions (18 Talls and 6 Dwarfs). A total of 48 alleles were detected in the Indian accessions by using 8 microsatellite primers (average 6 alleles per locus). More alleles were detected in the Indian accessions than in the exotics, indicating the presence of a wide allelic spectrum in the Indian accessions. Mean gene diversity ranged from 0.00 for ‘Chowghat Green Dwarf’ to 0.59 for ‘Lakshadweep Ordinary Tall’, with an overall mean of 0.32. The within-population variation was slightly higher (53%) than the betweenpopulation variation (47%), suggesting recent local adaptation and subsequent divergence among Indian cultivars. An UPGMA dendrogram separated the Indian accessions into two groups, one clustering with South-east Asian cultivars, which are introgressed types, and another clustering with African and Sri Lankan cultivars. The results are discussed in terms of diversity of Indian coconut accessions and relationships to other major coconut cultivars.
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    COCOS-SATDB: A microsatellite databse for coconut (Cocos nucifera L.)
    (Indian Society for Plantation Crops, 2008) Praseeda, B.; Chandrasekhar, A.; Rajesh, M.K.; Anitha Karun; George V. Thomas
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    Improved protocol for AFLP analysis as a base for tagging root (wilt) resistance genes in coconut
    (2002) Rajesh, M.K.; Jayadev, K.; Chandrasekhar, A.; Anuradha Upadhyay; Devakumar, K.; Manimekalai, R.; Nair, R.V.; Parthasarathy, V.A.
    The root (wilt) disease of coconut is endemic in Southern districts of Kerala and the adjoining areas of Tamilnadu causing enonnous loss of nuts. Integrated management practice is the only suggested method to reduce its effect to some extent while development of resistant varieties will offer permanent solution, for which concrete breeding efforts are required. Considering Ute long life cycle of coconut, selection of resistant varieties through conventional methods will be time consuming and laborious. Molecular markers offer numerous advantages over markers traditionally used in plant mapping and selective breeding. AFLP (Amplified Fragment Length Polymorphism) is a versatile DNA fingerprinting technique for marker assisted selection which combines universal applicability with high powers of discrimination and reproducibility. In this preliminary ttudy for tagging root(wh6 resistkce genesiicoconut, AFLP parameters, geirunning a& silver staining conditions were optimized. Also, primer pairs detecting variations between resistant and susceptible palms were selected.
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    Mining of expressed sequence tag libraries of cacao for microsatellite markers using five computational tools
    (2009) Aikkal Riju; Rajesh, M.K.; Fasila Sherin, P.T.P.; Chandrasekhar, A.; Elain Apshara, S.; Vadivel Arunachalam
    Expressed sequence tags (ESTs) provide researchers with a quick and inexpensive route for discovering new genes, data on gene expression and regulation, and also provide genic markers that help in constructing genome maps. Cacao is an important perennial crop of humid tropics. Cacao EST sequences, as available in the public domain, were downloaded and made into contigs. Microsatellites were located in these ESTs and contigs using five softwares (MISA, TRA, TROLL, SSRIT and SSR primer). MISA gave maximum coverage of SSRs in cacao ESTs and contigs, although TRA was able to detect higher order (>5-mer) repeats. The frequency of SSRs was one per 26.9 kb in the known set of ESTs. One-third of the repeats in ESTcontigs were found to be trimeric. A few rare repeats like 21-mer repeat were also located. A/T repeats were most abundant among the mononucleotide repeats and the AG/GA/TC/CT type was the most frequent among dimerics. Flanking primers were designed using Primer3 program and verified experimentally for PCR amplification. The results of the study are made available freely online database (http://riju.byethost31.com/cocoa/). Seven primer pairs amplified genomic DNA isolated from leaves were used to screen a representative set of 12 accessions of cacao.
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    Optimising DNA Amplification Parameters for RAPD Analysis in Cocoa (Theobroma cacao L.)
    (2010) Anuradha Sane; Chandrasekhar, A.; Manimekalai, R.