PhD

ABSTRACT
Melia dubia commonly known as Malabar neem is a fast growing indigenous
species. It is considered as a major wood in plywood and paper industries and the
plant is put into various medicinal uses, preferred for use in packing cases, cigar
planks etc. There are no identified genotypes of melia, suitable for Kerala. This is
one of the reasons which has made a dearth in the availability of good planting
material. Hence, a study was conducted to determine the genetic diversity of the
trees and select plus trees from the forests of Kerala. Fifteen locations spread over
eighteen localities where the species is common were identified from secondary
data and reconnaissance survey. In total 281 trees were selected for the survey. The
important quantitative and qualitative characters of the trees were determined.
Based on baseline selection system, a regression analysis was done between the
(DBH)2 x height and (crown width)2 x crown length separately for each location
and the trees above the regression line having highest score for the qualitative
characters were selected. This was to ensure that a minimum of one tree got selected
from a locality to ensure diversity in selection. The study showed that variability
existed for all the qualitative characters and it was more within the localities when
compared to between localities. In total twenty five trees were selected. Clustering
done for the twenty five plus showed that Melia dubia genetic resources resolved
the trees into seven clusters and it was found that grouping were independent to the
geographic locations. Inter and intra cluster divergence were also studied.
The evaluation of the seedling progenies from the twenty five plus trees were done
in the nursery for five months. Significant differences among the progenies of the
selected trees were observed for various morphological and physiological
characters studied. The performance of the progenies of two trees from Tholpetty
(FCV-MD-03 and FCV-MD-04) were the best in most of the parameters studied.
The genetic analysis of the causes of variation for the morphological and
physiological traits were studied. The values for the phenotypic coefficient of
variations ranged from 12.62 per cent for height to 24.53 per cent for biovolume.
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The result indicated that the values for genotypic coefficient of variation was less
than the phenotypic coefficient of variations for all the traits studied, indicating
existence of environmental effect on these characters. Heritability estimates in
broad sense were observed higher than 50 per cent for the quantitative characters
such as height, collar diameter, number of leaves, AGR and biovolume. Heritability
was also higher for all the physiological characters studied. The genetic gain was
also high indicating possibilities of using selections for further breeding. The
correlation studies on the morphological and physiological characters showed that
the height was positively correlated with all the morphological and physiological
characters studied except leaf temperature. Photosynthetic rate was positively
correlated with the height, chlorophyll and relative water content of the leaves.
For standardization of clonal progenies, cuttings from the seedlings, semi hardwood
cuttings from mature trees and root suckers by damaging the roots were taken to
develop a method for mass multiplication of the Melia dubia. Three different auxins
IBA, NAA, IAA at different concentrations were administered. The result showed
that the best treatment for the cuttings and rootsuckers were IBA at 1000 ppm. For
the semihardwood cuttings, miniclonal technology was used and the best treatment
observed was IBA at 6000 ppm.