Journal of the Rubber Research Institute of Sri Lanka

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Clonal differences in growth parameters of young Hevea buddings and their relation to field performance
(Rubber Research Institute. Agalawatta, 1986) Nugawela, A.; Aluthhewage, R.K.
Hevea trees when tapped exhibited a depression of girth increment and canopy growth. Hence a high growth rate is required to maintain the growth whilst giving a high yield. Growth parameters of 5 Hevea clonal buddings were determined after different growth intervals viz., 3, 6 , 9, and 12 months to study the correlation they show with the field performance of the same clones. Clonal differences were significant, but did not necessarily correlate with the field performance. Growth rates gradually increased with age during the peeriod of investigatiion. Thepossibility of using growth parameters together with gas exchange capacities determinedin earlier studies in predicting later field performance are discussed.
The effect of tapping on the assimilation rates of Hevea brasiliensis Muell. Arg. leaves
(Rubber Research Institute. Agalawatta, 1990) Nugawela, A.; Aluthhewage, R.K.
The CO2 assimilation rates at leaf level were compared in tapped and untaped trees of two Hevea brasiliensis genotypes. In both genotypes, the CO2 assimilation rates of the leaves in the upper stratum were lower in tapped trees. Simmilary, in young microtapped plants the CO2 assimilation rates were lower than in the untapped plants. The decrease in CO2 assimilation rates due to tapping cannot be attributed to an increase in either stomatal or mesophyll limitations. Tapping increases the sink demand for photo assimilates, but it also results in the loss of water, inorganic nutrients and proteins from the plant. Loss of water, inorganic nutrients may results in lower CO2 assimilation rates of the tapped trees. In the long-term this could result in lower sucrose content in the latex. This may be a probable cause for the physiological disorder, tapping panel dryness in rubber.
Field performance of young coffee seedlings and cuttings intercropped with rubber
(Rubber Research Institute. Agalawatta, 1988) Rodrigo, V.H.L.; Nugawela, A.; Kariyawasam, L.S.; Aluthhewage, R.K.
Coffee may be planted either using seedlings or cuttings. Anyhow, a comparative study of their field establishment and performance has not been made. Iin this study seedlings and cuttings of Coffea canephora intercropped with rubber were compared for their field stablishment and growth. It is evident that there is no difference in the success of their field establishment. The dry matter yield determinants of plants, i. e. light intercept ion, conversion efficiency and rate of loss of dry matter, estimated by total leaf area, CO2 assimilation rate and dark respiratory rate respectively, are also similar in both seedlings and cuttings. This is confirmed by the similar mean total dry weight of a seedlings and a cuttings. The partitioning of assimilates is more towards root development in the cuttings and is evident by the significantly high root dry weight and the root/shoot ratio. The percentage of assimilates partitioning towards the growth of aerial parts is less in the cuttings, i. e. 52 and 67perc. for cuttings and seedlings respectively. Despite of similar light levels, the CO2 assimilation rates are lower in the afternoon in both seedlings and cuttings. The perc. deeline is 23.5 and 18.6perc. for seedlings and cuttings respectively.
Gas exchange parameters for early selection of Hevea brasiliensis Muell. Arg
(Rubber Research Institute. Agalawatte, 1985) Nugawela, A.; Aluthhewage, R.K.
Selecting high yielding progeny from Hevea breeding programmes is a money and time consuming approach and limits the progress of breeding, Girth, bark thickness, numberof lates vessel rings, latex vessel density and first few years yield of 7-8 year old Hevea budding are reported to be correlated to the yield potential. These parameters are used by some breeeders for a primary selection using smalle scale clone trials. Latex is biosythesised from sucrose in latex vessels and the potential of sucrose supply to latex vessels depends on CO2 assimilatory capacity of the canopy and the partitioning of assimilates. Attempts were made to estimate the mean CO2 assimilatory capacity of a healthy and a matur eleaf whole in year old Hevea clonal buddings. Preliminary studies show the mean CO2 assimilatory capacity of a whole and its ratio with water use efficiency value to be correlated qith yield potential. These observation suggest that effective selection of clones for further testing in large scale clone trials could be done on this basis, when buddings are around a year old.
Variations involved in field measurements of transpiration rates and stomatal diffusive resistance of Hevea brasiliensis Muell. Arg. clones and the relationship of the latter with net photosynthetic rates
(Rubber research Institute. Agalawatte, 1984) Nugawela, A.; Wickremasinghe, W.N.; Aluthhewage, R.K.
Variance components and their percentage contribution to total variation during field measurements of stomatal diffusive resistance (DR) and transpiration rates (TR) were studied for Hevea clones. Variance from the plant component was much higher than other components viz., leaves of the same plant and determinations of the same leaf. DR, TRand coefficient of varian for DR and TR varied significantly with leaf age and time of the day. The three leaflets in a leaf were similar in respects to DR and TR. Within a whorl, the comparatively smalle leaves at the top of differed significantly withrespect to DR and TR from the rest. DR and Tr of clones RRIC 100, RRIC 103, RRIC 45, PB 86 and IAN 710 were significantly different at 0.1perc. level. Initial studies show stomatal diffusive resistance to have a tendancy to be correlated with net photosynthetic rates (NPR). Other possible factors that might bring about clonal differences in NPR are discussed.