MULTIVARIATE ANALYSIS OF YOUNG AND MATURE :CLONES IN PARA RUBBER (Hevea brasiliensis Muell. Arg.) By. - JAY ASHREE MACHA VAN -. THESI~. SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE DOCTOR OF PHILOSOPHY FACUL TV OF AGRICULTURE KERALA AGRICULTURAL UNIVERSITY DEPARTMENT OF PLANT BREEDING AND GENETICS. " COLLEGE OF AGRICULTURE VELLA YANI. THIRUV ANANTHAPURAM 2001
CERTIFICATE.. Certified that this thesis entitled "Multivariate analysis of young and mature clones in para rubber (Hevea brasiliensis Muell.Arg.)" is a record of research work done independently by Smt. JAYASHREE MADHAVAN under my guidance and supervision and that it has not previously formed the basis for the award of any degree, fellowship or associateship to her. Vellayani, 11.06.2001. Dr. S. G. SREEKUMAR (Chairman, Advisory Committee) Associate Professor, Department of Plant Breeding and Genetics College of Agriculture, Vellayani,Thiruvananthapuram.
ABSTRACT A study on young and mature clones of rubber (Hevea brasiliensis) was undertaken with the objectives of estimating the variabilit)\ correlations, direct and indirect effects of various traits influencing yield, estimating the genetic divergence and the factors contributing to divergence, identifying those variables that remain stable in both stages of the crop, and to examine the extent to which mature yield could be predicted using immature attributes. A number of morphological, structural, physiological and biochemical parameters were observed at the two stages of growth. Significant clonal differences at both stages were observed for almost all the traits. There was high genetic variability at the mature stage for most traits, especially girth increment, laticifer area index, initial flow rate, final volume of latex, latex biochemical parameters (except for total solids content) and yield.. However number of stomata per unit area, density of latex vessels, diameter of latex vessels, total solids content and chlorophyll a:b ratio had very low variability as indicated by their genotypic coefficients of variation. It was shown that the traits yield, girth, laticifer area index, initial flow rate, final volume of latex, plugging index, latex thiols, inorganic phosphorous, sucrose, magnesium, chlorophyll band total chlorophyll were most likely to respond to selection since there was a preponderance of additive gene action in the inheritance of these traits, as indicated
by their moderate to high estimates of heritability coupled with high genetic advance. High heritability coupled with low genetic advance observed for stomatal density, bark thickness, leaf midrib lamina and palisade layer thickness indicate that these are governed by non additive gene action. Among the immature plants, high genetic variability was observed for immature yield, time taken to sprout, number of flushes shed by the end of the first year (W3), diameter increment, number of new flushes produced and those. retained on the entire plant in the second year (W5 and 7), number of latex vessel rows, laticifer area index, latex thiols, inorganic phosphorous, sucrose and magnesium and juvenile yield. Leaf size, specific leaf weight, density and diameter of latex vessels and chlorophyll a:b ratio showed extremely low estimates of genotypic coefficient of variation. Higher heritability estimates were recorded for all the anatomical and biochemical traits except density of latex vessels, than for the morphological traits, indicating the greater influence of environment on the latter. High heritability combined with high genetic advance was recorded for most of the anatomical and biochemical parameters and yield (except density and diameter oflatex vessels and chlorophyll a:b ratio which had very low genetic advance estimates) indicating the preponderance of additive gene action in these traits. Moderate to high heritability followed by low genetic advance were seen for the traits height, first year scion diameter bark thickness, diameter of latex vessels, which implies the inheritance of these traits is governed mainly by non additive gene action, and hence will not respond to selection. At the mature phase, strong genotypic correlations of average annual yield were observed with final volume of latex and initiaulow rate, girth, girth increment, number of latex vessel rows, laticifer area index, bark thickness and inorganic
phosphorous content, while at the immature stage, laticifer area index, scion diameter in the second year, number of latex vessel rows, bark thickness, inorganic phosphorous, thiol content, girth increment, number of new flushes produced and those retained on the main stem in the second year, latex magnesium, chlorophyll ( a, chlorophyll b, total chlorophyll, leaf size, and number of flushes produced on the main stem in the two years (W8), were positively associated with testap yield at both the phenotypic and genotypic levels. Biochemical parameters at both stages contributed relatively less than the other characters to variation in yield, except. for inorganic phosphorous in the immature stage which showed moderate association with yield. "" Path analysis at the mature phase revealed that initial flow rate and bark thickness could be used effectively as selection parameters for yield, as their direct effects were the highest. Inspite of the moderate to high correlations of girth, girth increment, number of latex vessel rows, final volume of latex, density and diameter of latex vessels, selection for these traits per se will not effectively improve yield, as their direct effects are low. A negligible residue was obtained in the present study, implying that almost all the variation in mature yield in the present study could be accounted for by these variables. At the immature stage, number of latex vessel rows was found to exert the highest positive direct effect on yield, while bark thickness had a very high negative direct effect on yield. A residue of 0.33 indicates that other variables contributing to variability in yield at this stage have not been included. These could be the physiological parameters initial flow rate and final volume of latex, which had strong correlations with mature yield.
Genetic divergence was assessed using the D2 statistic and Tocher's method of clustering was employed to group the clones in the two stages. Seven and five clusters respectively were formed for the mature and immature groups of clones. A great deal of similarity was found in the clustering pattern of the clones at the two stages, inspite of the difference in age and the variables used to compute the genetic distance. Most of the clones fell into one major group (Cluster I) with 18 and 19 clones respectively, of which 16 clones were in common. The clustering patterns of the remaining clones were also similar, with many of them being independent or forming two clone clusters. This indicates that though most of the clones were genetically close as they fell into one cluster, the remaining clones included in different clusters having diverg~ce can be exploited in hybridization programmes. Factor analysis carried out in the two stages identified 10 factors at the mature stage which were principally associated with yield, stomatal density, latex biochemical components, initial flow rate, bark structural traits and chlorophyll content. The nine factors identified at the immature stage were mainly associated with vigour, yield, chlorophyll content and leaf structural traits. The perfomance of the 25 clones at the two stages of growth was evaluated on the basis of indices formulated using discriminant function analysis. There was no correlation between the performance of the clones at the two stages. Correlations between immature attributes and corresponding mature attributes reveal that latex biochemical traits thiols, inorganic phosphorous, sucrose and magnesium, bark structural traits number of latex vessel rows, laticifer area
index, stomatal density, density and diameter of latex vessels were relatively stable over the years, while morphological traits and yield appear to be the most affected with increase in age. Correlations between mature yield in the BI 2 panel and immature attributes of two year old plants revealed that the association with immature bark thickness and number of latex vessel rows were still retained at this age. Step wise regression of mature yield on immature attributes showed that number of latex vessel rows could explain only 21 per cent of the variability in mature yield. As no good fit was obtained, yield at this stage cannot be predicted using the first two years' attributes included in this study. ~