BSc - MSc (Int.)

Stylosanthes is a dominant pasture legume growing in tropical and subtropical regions of
India and is extensively applied as forage and cover crop in agricultural systems. The fundamental
concern with Stylosanthes is the restricted number of superior varieties. The genus Stylosanthes
under the family Fabaceae comprises approximately 50 spp. distributed worldwide in the tropics
among which S. scabra, S. seabrana, S. hamata and S. guianensis are predominant. The current
study entitled “Population structure analysis in Stylo [Stylosanthes sp.] using SSR markers” was
undertaken at College of Agriculture, Vellayani, Thiruvananthapuram to assess the genetic
variability among Stylosanthes accessions using SSR markers and to construct the population
structure of Stylosanthes genotypes thereby delimiting these species.
In this study, 19 accessions of Stylosanthes which belong to the genotypes S. scabra,
S. seabrana, S. hamata and S. guianensis were collected from IGFRI, Jhansi, Kerala Livestock
Development Board and centres under AICRP on Forage Crops and Utilisation. The 19 accessions
were characterized using fifty seven molecular markers and correlated with the available
phenotypic data.
The purity and concentration of DNA ranged from 1.63 to 1.96 and 525 ng/µl to 3024 ng/µl
respectively, indicates that a good quality DNA obtained from the Stylosanthes species. Forty nine
markers showed amplification and produced a total of 120 alleles among the 19 Stylosanthes
accessions. Forty one showed polymorphic bands and they produced a total of 101 polymorphic
alleles. The highest number of alleles was produced by gSsb-16 (6 alleles) and the polymorphism
information content (PIC) for these markers revealed that gSsb-11, eSgu-29 and eScap-24 (0.48)
have the highest PIC followed by gSsb-16 (0.477). S. hamata (T5) and S. seabrana (T18) showed
more than one allelic band in a maximum number while S. seabrana Phule Kranti (T9) showed
only one allelic band with the entire set of polymorphic markers
A Bayesian model population structure study of these 19 Stylosanthes accessions using
STRUCTURE v2.3.4 showed the existence of three gene pools (number of sub-population, k = 3).
Also, the dendrogram generated using NTSYSpc v2.02e, based on 41 markers distinctively
demarcated Stylosanthes accessions into five clusters indicating its vast genetic diversity in the
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population. A maximum genetic similarity of 85.37% was shown by two pairs of accessions
namely S. scabra ILCA140 (T1) with S. seabrana (T19) and S. scabra Fitzroy (T7) with S. seabrana
(T13). A minimum genetic similarity of 48.78% was shown by S. guianensis CIAT (T10) with
S. hamata (T11).
Variance components analysis of seven phenotypic characteristics showed that the values of
PCV and GCV was higher for leaf breadth, green fodder yield per plot and dry fodder yield per
plot; high heritability coupled with high genetic advance was noted for green fodder yield per plot
and dry fodder yield per plot. Cluster analysis based on phenotypic data divided the 19
Stylosanthes accessions into five clusters. The highest similarity was observed in S. scabra DRSS4-RRR94197 (T4) with S. seabrana (T14) at a similarity coefficient of 0.71. In the study, S. scabra
with S. seabrana showed the highest genetic similarity within the genotypes in terms of molecular
and phenotypic cluster analysis and the grouping was performed irrespective of the origin of
genotypes. A better performance in phenotypic traits and molecular analysis was noticed in
S. guianensis Reyan (T8) and S. guianensis CIAT (T10) showing their suitability in fodder
improvement programmes of Stylosanthes species.
Overall, the level of genetic variability and 76.9 per cent average polymorphism indicated
by the primers in the current study suggests that SSR markers can be utilized for fodder
improvement and genetic resource management and utilization. For proper validation of the
results obtained, cytological studies of the Stylosanthes accessions, increasing the number of
accessions in the different species and evaluation of more SSR markers need to be done.