PhD

ABSTRACT
The present study investigated standardization of the Miniclonal propagation
technique, assessing genetic diversity among accessions using ISSR markers, screening
plus trees for drought stress and recovery, and discovering Single Nucleotide
Polymorphisms (SNPs) through Genotyping by Sequencing in plus trees of Tectona
grandis L. f. The study attempted to map the QTLs associated with drought tolerance,
providing valuable insights into the genetic basis of this trait in teak.
The effects of auxins on epicormic shoot production and rooting were evaluated
to select the best hormone combination. The shoot production varied among the auxins
and their concentrations. Indole-3-butyric acid (IBA) at 4000 mg L-1 showed optimal
shoot production, enhancing rooting potential, with the highest rooting percentages
observed at 49.19% for 4000 mg L-1 IBA and 41.71% for 3000 mg L-1 IBA. The cuttings
treated with 1-Naphthaleneacetic acid (NAA) showed only 5.61 to 14.01% rooting,
whereas a combination of IBA and NAA encouraged the callusing. The size of the
cuttings affected the rooting potential, and the rooting percentage showed a
significantly positive correlation with shoot diameter (r=0.89). Further, epicormic shoot
and root production was observed to vary significantly among the accessions.
Aravallikkavu (10.67) and Top slip-6 (8.33) exhibited the highest epicormic shoot
numbers, while Nedumkayam-1 displayed minimal shoot production. Nellikutha-6
showed the highest rooting percentage (57.11%), contrasting with Nellikutha-2
(22.50%). Subsequently, ten accessions were successfully propagated for further
investigations.
Genomic DNA from ten accessions was extracted using the modified CTAB
protocol, yielding DNA concentrations ranging from 166.7 to 269.4 ng μL-1, with
OD260/280 values between 1.86 and 2.08. Amplified bands resulted in 212 observed
alleles, of which 199 were polymorphic, demonstrating genetic diversity, while 13 were
monomorphic. The Jaccard similarity coefficient between Topslip-6 and Topslip-10
was 0.361, suggesting their genetic similarity. Accessions 6, 4, 10, 8, and 7 displayed
coefficients of 0.504, 0.476, 0.465, and 0.440, respectively, indicating close
relationships.
Morpho-physiological and biochemical responses of teak ramets to drought
stress were evaluated, indicating varying tolerance levels among accessions. Based on
morphological indicator (percent leaf retained), accessions Topslip-6, Topslip-10, and
Shankaramthode-1 were classified as "Highly Tolerant," whereas Nellikutha-2 was
"Highly Susceptible". Photosynthesis varied, with Topslip-6 maintaining the highest
2 m-2 s-1) and Nellikutha-2 exhibiting the lowest (1.200) under
drought. Accessions displayed diverse responses under drought for Fv/Fm (0.819-
Topslip-10 to 0.309-TC11) and chlorophyll content (1.573- Nedumkayam-1 to 4.342
- TC4). Maximum proline was produced by Topslip-6 -1), whereas
-1 -1) produced minimal proline. Similarly,
Accession 8 produced lower glycine content -1), and Topslip-10 exhibited
-1. Cluster analysis revealed distinct groupings, with PCA
aiding accession selection based on performance indices, categorizing teak accessions
into Highly Susceptible (Nellikutha-2), Susceptible (Nedumkayam-2 and Nellikutha-
1), Moderately Tolerant (Topslip-6, TC4, Nedumkayam-1, and Shankaramthode-1),
and Highly Tolerant (Topslip-10, TC11, and Topslip-6) categories.
Genotyping based on Illumina-assembled genomic sequences for diverse
accessions was carried out. Variant calling on ten genomes yielded 7,518,960 variants
and filtered down to 3,665 SNPs. GWAS identified 19 significant SNPs linked to
drought tolerance, supported by QQ and Manhattan plots. BLASTX and UniProt
annotations unveiled genes associated with stress resistance, organ formation, and
metabolic processes. QTLs on Chromosome_1 (BLH9, POX), Chromosome_4 (DXS,
TKL), and Chromosome_11 (MFS, MIK2) were implicated in diverse physiological
functions. BLH9 is implicated in plant organ and shoot formation, xylem development,
morphogenesis, and meristem activity. DXS is involved in chlorophyll biosynthesis and
terpenoid biosynthesis. MFS regulates stomatal closure, while MIK2 is associated with
various cellular responses, including cellular and root activity.
The study enhances understanding of the genetic basis of drought tolerance in teak,
contributing valuable information for breeding programs and sustainable forest
management. The multidisciplinary approach integrating physiological, biochemical,
and genomic analyses offers a comprehensive framework for understanding and
improving teak cultivation, ensuring sustainable production in the face of
environmental challenges