Journal of the Rubber Research Institute of Sri Lanka
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Item 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.Item An economic evaluation of the use of rainguards(Rubber Research Institute. Agalawatta, 1993) Rodrigo, V.H.L.; Herath, P.H.M.U.; Nugawela, A.Use of rainguards can minimize the loss of tappping days and hence the loss in rubber crop. A simple model was developed to study different components determinig the profitability of using rainguard is discussed. Price of rubber, yield potential of a plant and tapping wage rate were identified as most important factors which determine the worthiness of the use of rainguards. Sealent price is also a major factor in deciding profitability. If the price of scalent is less than Rs. 20/= per kg, the profilability from both the apron and the gutter types is sameItem Seed production of clones PB 86, RRIC 100 and RRIC 121 in three rubber growing areas of Sri Lanka(Rubber Research Institute. Agalawatta, 1997) Seneviratne, P.; Nugawela, A.; Amaratunge, K.A.G.B.; Karunasena, R.P.; Wilbert, S.The rubber seed production in wet rubber growing areas in Sri Lanka has gone to very low levels in the recent past affecting the culling process that should be adopted in establishing rootstock nurseries.From the three rubber growing areas studied satisfacton seed production irrespective of the clone was observed only in Kegalle region.Regional differences may be due to direct or influences of the climate and weather during flowering and pod set. Clonal differences seems to be existing in regions where climate or the weather is favourable for spread of diseases.Further RRIC 100 being a resistant clone for oidum and phytopthora.produced a higher percemage of good quality seeds compared with the other two clones.PB 86 and RRIC 121 which have below average tolerance to these two diseases.However currently country as a whole produces enough seeds to fulfill country's annual seed requirement for the production of rootstocks provided the seeds are collected and transported without delayItem Factors affecting the budgrafting success and the scion growth of young budding of Hevea(Rubber Research Institute. Agalawatta, 1994) Seneviratne, P.; Nugawela, A.; Samarakoon, S.M.A.The size of the bag in which the stock plant is grown seems to have an effect on the growth of the seedling; from the three bag sizes tested, ie 15 x33 cm, 18 x 38 cm, 23 x 45 cm, it was found that the diameter the number of leaf whorls of the seedling increased with the increase of the bag size.Though the differences are not statistically significant, the budding success too increased in the same pattern. There was no effect of the bag size on the growth of the scion. The two types of buds, axillary scale, showed no difference either on bud grafting success or on the growth of the scion. The growth stage of the top most leaf whorl of the stock plant, either mature or immature, had no effect on the peeling qualities budgrafting success though a little higher budgrafting success was seen when the top flush was immature. There was an effect of the snag, on the scion growth; when the snag was shorter the sprouting took place earlier but, the scion growth was slightly poor as was evident by the diameter the length of the scion. Long snags delayed the sprouting , but the scion growth was better. The best growth of the scion was obtained when the snag was long with a few leaves attached to it.Item Diurnal variation in gas exchange characters of leaves of Hevea brasiliensis exposed to sun light at different canopy levels and their contribution to dry matter production(Rubber Research Institute of Sri Lanka. Agalawatte, 1995) Nugawela, A.; Abeysinghe, D.C.A.; Samarasekera, R.K.As in many other crops a significant percentage of leaves in the canopy of a rubber plantation are found under limiting light levels. The photosynthetic capacity of these shaded leaves may play an important role in determining the productivity of the rubber plants. The dry matter production capacity of shade leaves was srudied using polybag plants of Hevea brasiliensis and grown under different light regimes. The CO2 assimilation rates and related parameters were monitored through-out the day using a portable photosynthesis system. The diurnal variation pattern of CO2 assimilation rates and the internal leaf CO2 concentration to ambient CO2 concentration ratio (ci/ca) were different in plants grown under different light regimes. Though peak CO2 assimilation rates are shown at around 0930h in all treatments, the assimilation rates tend to decline very early in plants grown under full light. During the early and latter parts of the day, plants grown under full light showed significantly higher CO2 assimilation rates than in plants grown under 40 per cent and 25 per cent of incident light. However, stomatal conductance declined with time of the day and it was similar in all treatments. Low CO2 assimilation rates later in the day could be either due to accumulation of abscisic acid or due to end product inhibition. It is apparent that photosynthesis is only marginally high during the major part of the day, ie 0930h - 1430h in plants grown in full light. Therfore, sun and shde leves may be comparable as the daily photosynthetic integral and hence the dry matter production is concerned. Thus, shaded leaves in rubber plantations may significantly contribute to the total dry matter production of the plant.Item The role of snag on the growth of scion in bud grafted plants of Hevea with special reference to young buddings(Rubber Research Institute of Sri Lanka. Agalawatte, 1995) Senaviratne, P.; Nugawela, A.; Samarakoon, S.M.A.Item Physiological yield determinants of sun and shade leaves of Hevea brasiliensis Muell. Arg(Rubber Research Institute of Sri Lanka. Agalawatte, 1995) Nugawela, A.; Ariyawansa, P.; Samarasekera, R.K.Item The correlation between branching and the tree growth of Hevea brasiliensis (Muell.Arg.)(Rubber Research Institute of Sri Lanka. Agalawatte, 1996) Seneviratne, P.; Nugawela, A.; Ramawickrama, D.The main objective of the present study was to see whether there is a correlation between the number of branches and the tree grwoth in hevea brasiliensis. Considerable variation in brancing habits is observed among the trees of different clones. Also, some clones such as RRIC 121 show less brancing when compared to other clones such as RRIC 100 indicating brancing is also a clonal characteristic. Canopy architecture too, shows differences among trees within a clone. Highly significant positive correlation was observed between the number of branches and the tree girth for all clones tested for trees aged from one year to seven years. The correlation between the canopy distribution (grouped as very good, good or poor) and the tree girth was also positive.Item Rubber cum sugarcane intercropping. a sustainable cropping system for farmers in the intermediate zone of Sri Lanka(Rubber Research Institute. Agalawatta, 2000) Rodrigo, V.H.L.; Nugawela, A.; Sivanathan, A.; Witharama, W.R.G.; Jayasinghe, W.K.Item The effect of girth at opening on yield and growth of modern Hevea brasiliensis Muell Arg. clones(Rubber Research Institute. Agalawatta, 2002) Nugawela, A.; Samarasekera, R.K.; Wilbert, S.