ANNOUNCEMENTS
As the first objective, I assessed the genetic diversity of different Capsicum landraces grown in Northeast India. For this purpose, 171 accessions of Capsicum spp. were used. Out of these, 131 accessions were collected from NE states of India. A total of 420 bands were obtained with six primer combination of which 254 (60.48 %) were polymorphic across the dataset. The neighbor joining tree grouped all accessions into two major clusters each of which further divided into two sub-groups. Principal coordinate analysis (PCoA) displayed groupings which were consistent with neighbour joining analysis. Structure results indicated that the sampled accessions belonged to two distinct populations designated as Pop A and Pop B. This study revealed the presence of high diversity in the accessions of NE India which may be due to natural interspecific hybridization and selection pressure due to environmental and anthropogenic factors.
As the second objective, I estimated the variation in the level of capsaicinoids in 139 accessions from the above dataset. The total capsaicinoids content in the accessions varied from 0.02 to 72.05 mg/g whereas the pungency varied from 317 to 1152832 SHU. Within NE accessions, the capsaicinoids content varied from 0.39 to 72.05 mg/g. The capsaicinoid content among 92 accessions of Bhut Jolokia varied from 11.95 to 72.05 mg/g with corresponding pungency levels of 191135 to 1152832 SHU. Hierarchical cluster analysis based on total capsaicinoid content of 139 accessions produced a dendrogram consisting of 4 major clusters. The capsaicin: dihydrocapsaicin ratio varied from 0.33 to 4.92. In the current study, we observed a greater variability in pungency in BhutJolokia accessions as compared to previously published reports.
As the third objective, an interspecific mapping population was created and used to construct a genetic linkage map and identify QTLs for pungency. A total of 146 BC1 plants, derived from the inter-specific cross between C. annuum (CC063) and C. chinense (CC015) using CC063 as the recurrent parent were used for this analysis. A total of 599 markers were scored using three marker techniques, namely, TE-AFLP, AFLP and microsatellites. A total of 424 markers could be assigned into 12 linkage groups covering a total span of 1197.73 cM. The mean marker intervals within each LG ranged from 1.18 cM to 7.67 cM with an overall mean marker interval of 3.36 cM. The number of markers per linkage group varied from 51 to 11 with a mean of 35.33.
For QTLs analysis, capsaicinoid content for two parents, six F1 plants and one hundred thirty three (133) BC1 individuals was estimated. The BC1 individuals showed an extremely high range of variability in terms of capsaicin, dihydrocapsaicin, capsaicinoid content and cap/dhc ratio. Out of 133 BC1 individuals, two genotypes, CBC1-018 and CBC1-034 were found to be completely non-pungent and no capsaicinoids could be detected by HPLC. The total capsaicinoid content in BC1 varied from 0 to 11.12 mg/g. The mean capsaicinoid content in BC1 was 3.59 mg/g which was comparable to the expected value of 3.85 mg/g (the mean capsaicinoid content of F1 plants and the recurrent parent). This indicated that the mean capsaicinoid content of BC1 population was further reduced as compared to F1 as was expected and shifted towards that of the recurrent parent. The mean of cap/dhc ratio in BC1 was 1.51 which was slightly greater than 1.29 (the mean of F1 and recurrent parent).
QTL analysis using QTL Icimapping software identified a total of 8 QTLs on four linkage groups for the four traits. Two QTLs were detected for capsaicin, of which one was on LG4 and the other was on LG5. Two QTLs were identified for dihydrocapsaicin one each on LG4 and LG11. Similarly, two QTLS were identified for total capsaicinoids, located on LG4 and LG9. For cap/dhc ratio, two QTLs were identified on LG4 and LG11.
This is the first study using a BC1 population derived from Bhut Jolokia and C. annuum. This population and its derivatives can be further used for future studies on mapping and gene identification for a number of agronomically important traits. The study has laid the foundation for the improvement of the landrace, Bhut Jolokia, through molecular breeding to make it an economically attractive variety for farmers.
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