CHARACTERIZATION OF WILD JUTE SPECIES THROUGH MOLECULAR CYTOGENETICS

Abstract

Characterization of six wild species of Corchorus L viz. C. brevicornatus, C. septentrionalis, C. urticifolius, C. hirtus, C. siliquosus and C. pinnatipartitus was carried out cytogenetically following orcein, CMA-, DAPI- staining. Moreover, molecular characterization of these species was conducted using RAPD-, SSR-and barcode primers. This study has helped to understand the relationship as well as evolutionary trends among these wild species of jute. The interphase nuclei and prophase chromosomes of these species exibited variation in heterochromatin distribution using orcein-staining. Chromosomes with 2n = 2x = 14 were observed in case of C. brevicornatus, C. septentrionalis and C. urticifolius whereas C. hirtus and C. siliquosus were found to possess 2n = 4x = 28 somatic chromosome with basic chromosome number of x = 7. On the other hand, 2n = 78 chromosomes were observed in somatic cells of C. pinnatipartitus with different basic chromosome number except x = 7. This is the first report of the existence of 2n chromosome number for C. pinnatipartitus. These species also found to be different in respect of other karyotypic features including total length of 2n chromosome complements, number of satellites, range of relative length, centromeric index etc. The centromeric formula was 14m in C. brevicornatus, C. septentrionalis and C. urticifolius, while 28m in C. hirtus and C. siliquosus and 74m + 4sm in case of C. pinnatipartitus. A wide range of CMA-positive bands (4 - 23) and DAPI-positive bands (3 - 25) was found in the metaphase chromosomes of these six wild jute species. The number, location and distributions of GC- and AT-rich repeats are different for each species. DNA from six wild Corchorus species was investigated with 13 oligonucleotide primers, 8 microsatellite primer pairs and 3 barcode primer pairs for RAPD, SSR and Phylogenetic analysis, respectively. The thirteen RAPD primers generated 69 loci with 100% polymorphism. Corchorus septentrionalis was distantly related from other 5 wild species and thus formed a separate cluster at highest genetic distance with C. pinnatipartitus (1.1431) whereas C. hirtus and C. pinnatipartitus were close to each other at lowest genetic distance 0.2638 in case of RAPD analysis. With SSR analysis, a total number of 27 loci were generated from eight primer pair combinations which resulted in 96.30% polymorphism for six wild Corchorus species. These results indicated diverse genetic variability among six wild Corchorus species. Moreover, unique RAPD and SSR bands were obtained through this investigation could be utilized as a useful tool for characterization of the studied six wild Corchorus species. With Maximum Likelihood analysis of combined (ITS, MatK and rbcL) data matrices, a well defined clade were constructed for six wild Corchorus species with strong bootstrap support (98%). C. pinnatipartitus and C. siliquosus were found to be distant from rest of the species with 98% and 100% bootstrap significance and make a different sub-clade. The phylogenetic tree generated from barcode primers made C. pinnatipartitus distinct from the rest of the studied Corchorus species and placed alone in a separate cluster that correlated with its phenotypic and cytogenetical features. Therefore, through this investigation wild species of Corchorus could be characterized authentically by cytogenetical as well as molecular analysis.