M. K. Rajesh

Development of a SCoT-derived SCAR marker associated with tall-type palm trait in arecanut and its utilization in hybrid (dwarf x tall) authentication

Arecanut cultivars are generally tall, which is a major constraint in arecanut cultivation. High yielding tall cultivars have been crossed with natural dwarf mutant, Hirehalli Dwarf (HD) and hybrids have been developed and released for commercial cultivation. It is very difficult to distinguish selfed progenies of the female mother palm in the nursery stage using morphological traits. Start Codon Targeted (SCoT) primers were used to screen tall cultivars of arecanut and HD. One of the primers, SCoT11, produced an amplicon of around 1300 bp band, which was present in all the tall cultivars, but was absent in the dwarf accession. A SCAR marker, capable of distinguishing tall/dwarf trait in arecanut, was also developed and validated, which could ensure supply of genuine hybrid planting material to the farming community.

Cloning, characterization and expression analysis of NBS-LRR-type resistance gene analogues (RGAs) in coconut

Abstract Coconut palms are highly susceptible to diseases caused by different pathogens, and replanting with resistant varieties is the best way to manage them. Obtaining a collection of resistance gene analogues (RGAs) is an effective strategy to identify genomic regions linked to disease resistance. We have successfully used a comparative genomics approach to amplify putative RGAs from the coconut root (wilt) disease resistant cultivar Chowghat Green Dwarf (CGD) by using primers designed based on conserved motifs of the NBS-LRR domain of the date palm. The amplified sequences were cloned, sequenced and characterized. The coconut RGAs had high identity to monocot NBS-LRRs. A complete structural analysis and 3-D modeling of the NBS domain of coconut RGA was also undertaken. Real-time quantitative polymerase chain reaction analysis indicated that the isolated coconut NBS-LRR class RGAs was expressed more in root (wilt) disease resistant genotypes than in susceptible ones. This study would provide a base for future efforts to map disease resistant traits in coconut.

Characterization of Annur and Bedakam Ecotypes of Coconut from Kerala State, India, Using Microsatellite Markers

The coconut palm is versatile in its adaptability to a wide range of soil and climatic conditions. A long history of its cultivation has resulted in development of many ecotypes, which are adapted to various agro-eco factors prevalent in a particular region. These ecotypes usually are known by the location where they are grown. It is important to explore such adaptation in the coconut population for better utilization of these ecotypes in coconut breeding programs. The aim of the present study was to identify the genetic diversity of the Bedakam and Annur ecotypes of coconut and compare these ecotypes with predominant West Coast Tall (WCT) populations, from which they are presumed to have been derived, using microsatellite markers. All the 17 microsatellite markers used in the study revealed 100% polymorphism. The clustering analysis showed that Annur and Bedakam ecotypes were two separate and distinct populations compared to WCT. It was also evident from the clustering that Annur ecotype was closer to WCT than Bedakam ecotype.

Potential of start codon targeted (SCoT) markers for assessment of genetic diversity of arecanut (Areca catechu L.)

Gene-targeted markers constitute recent and novel marker systems, which are based on polymorphic sites existing within gene targeting regions. One among these marker systems is the Start Codon Targeted (SCoT), which is based on the short conserved region of plant genes, which neighbours the ATG start codon. SCoT markers, by virtue of both their higher length of the primers and annealing temperatures, are generally reproducible and have been reported to be highly polymorphic, compared to other dominant markers. In this study, analysis of genetic diversity among six arecanut accessions, viz., Mangala, Sumangala, Sreemangala, Mohitnagar, Swarnamangala and a natural dwarf mutant (Hirehalli Dwarf) was carried out using SCoT markers to evaluate the applicability of these markers in genetic diversity studies in arecanut. Using 10 SCoT primers, 82 band were produced among the accessions, of which 58 (70.73%) were found to be polymorphic. The highest genetic similarity value of 0.89 was found between the Swarnamangala and Mohitnagar and the lowest value of 0.63 was noticed between the Hirehalli Dwarf and Mohitnagar. The similarity coefficient values were then utilized to construct a dendrogram utilizing the unweighted pair group of arithmetic means (UPGMA). The cultivars were grouped depending on their geographical origins. The results obtained in this study indicate the suitability of SCoT marker system for genetic diversity analysis in arecanut.