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Item Secondary characters and their association with latex yield in Hevea brasiliensis(Mull Arg.)(Rubber Research Institute. Agalawatta, 1988) Olapade, E.O.Ten Hevea clones developed at the Rubber Research Institute Of Nigeria (RRIN) and a control clone RRIM 600 were evaluated for their latex yield after six months of tapping. The mean dry latex yield recorded for each clone was correlated with their Juvenile secondary characters i. e Height, Girth and Plant Vigour at 18 months. Significant variability was exhibited by the clones in terms of yield with clone C 83 having the highest mean latex yield of 42.15 g/t/t/ while clone C 202 had the least mean yield of 22.73 g/t/t. The secondary characters i. e Hewight, Girth and Vigour were significantly positively correlated to themselves but all negatively correlasted to latex yield. However a spurious correlation was established between latex yield and the secondary characters. The implication of the results are discussedItem Effect of potassium and magnesium on growth of young Hevea brasiliensis(Rubber Research Institute. Agalawatta, 1988) Weerasuriya, S.M.; Yogaratnam, N.The effect of potassium and magnisium fertilisers on growth of young Hevea brasiliensis were studied using clones PB 86, RRIC 100, RRIC 103, and RRIC 121 with the objective of determining the requirement of these elements during the early phase of establishment of these clones. Three commercial fertilisers were evaluated as of magnesium. Potassium requirement of clone PB 86 during the first year was found to be approsimately 33g K/plant/year. It was found that clones. RRIC 100 and RRIC 121 needed higher amount of K than PB 86 for normal growth. Potassium application caused an overall reduction in growth of clone RRIC 103 where the soil K level was 0.07 me./100g suggesting that this level is adequate for this clone during its first year of growth. Total dry weight was significantly increased when Mg application was increased from 11 to 22g/plant/year in clone RRIC 103 but such effects were not seen in clones PB 86, RRIC 100 and RRIC 121Item An analysis of growth patterns of Hevea clones(Rubber Research Institute. Agalawatta, 1988) Margret, H.A.W.; Abeyasekera, S.; Jayasekera, N.E.M.Four girth measurements collected over four years, before tapping from ten Hevea clones grown in two sites have been analysed to study the growth pattern. Year to year variation in both sites was mainly due t linear component of growth. Growth of individual clones too was mainly due to linear effect. But some clones in one site showed significant quadratic and or cubic component. This was due to non linear growth of plants in some plots. Ten clones have been groued (a) according to the when averaged over four years so that clones within a group have the same average girth and (b) on the gradient of the regression fitted to the girth measurement increasing over the four years. RRIC 52 had the fastest growth in both sites. RRIC 103 had the same growth rates in both sites suggesting that it has a greater stability to local environmental changes.Item Shoot tip culture as a method of micropropagation of Hevea(Rubber Research Institute. Agalawatta, 1988) Gunatilleke, I.D.; Samaranayake, C.Shoot tips of Hevea from aseptically grown seeedlings were established in culture on Murashige and Skoog (MS) liquid medium with half strenth salts, supplimented with BAP +IBA or MS solid medium, with full strenth salts with and without BAP + IBA. BAP was found to be better for axillary bud proliferation and growth than the other cytokinines. Proliferation of buds improved with successive subcultures. A multiplication rate of 30 + 2 shoots per explant was obtained with threee subcultures in 165 daysItem 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.Item Virgin bark tapping of some RRIC 100 series clones(Rubber Research Institute. Agalawatta, 1987) Samaranayake, C.; Waidyanatha, U.P. De S.; Pathiratne, L.S.S.; De Soysa, A.G.A.All RRIC 100 series clones reached tappability much earlier than the two control clones viz. RRIM 600 and PB 86. Significantly higher yield per tree per tapping was obtained in the first year on a 1/2 S d/3 system compared to 1/2S d/2 tappings in many of the clones tested. However, during the second year there was no significant differences in yields obtained on both frequencies indicating that the tree was able to replenish the latex removed in a tapping, much faster than in the first year of tapping. The data presented indicate the possibility of tapping all recommended clones on 1/2S d/32 system of tapping from the second year, without any adverse effects.Item Reaction of oriental Hevea clones to isolates of Microcyclus ulei and the response of isolates to fungicides(Rubber Research Institute. Agalawatta, 1986) Fernando, E.B.; Hashim, I.Hevea clones from Sri Lanka, Malasia and India were assessed in vitro for their resistance to four isolates of microcyclus ulei. Clones SL 26, R-14, 5B/17/4, and 1/2/56/77 were infected by all isolates of M. ulei tested. However, they were found to have some resistance to M. ulei. Propiconazole was more effective than Triforine and Triadimefon in inhibiting germination of conidia of M.ulei. These fungicides were also effective in inhibiting lesion formation. Triadimefon (Bayleton 50 w.p.) had a better curative effect than propiconazole (Tilt 25 EC) and Triforine (Saprol). The effect of Triadimefon on germination of conidia varied between isolate while the effect varied little between isolates for propiconazole and triforine. The effect of the fungicides on the number of lessios on leaf discs did not show major differences between iaolates.Item Accumulation of free proline in bark and latex of Hevea brasiliensis affected by brown bast(Rubber Research Institute. Agalawatta, 1986) Wickramasinghe, S.I.; Yapa, P.A.J.; De Soysa, T.V.W.Free proline accumulation in clone RRIC 101 of Hevea brasiliensis was investigated. The bark and the latex samples collected from both healthy and brown bast effected trees were analysed for free prline content. The average bark proline concentration/unit present in the brown bast trees was found to be considerable higher (P = 0.10) than that of healthy trees. The accumulation of free proline in latex was found to be significant in brown bast trees.Item Effect of vesicular-arbuscular mycorrhizae on seedling of Hevea and Pueraria phaseoloides(Rubber research Institute. Agalawatte, 1984) Jayaratne, A.H.R.; Peries, O.S.; Waidyanatha, U.P. De S.Hevea seedlings showed a slight growth responce when inculated with Gigaspora margarita out of four species, tested in sterilised soil. There were no significant differences in the uptake of nutrient by mycorrhizal Hevea plants. Non-mycorrhizal Pueraria plants grew very poorly unless they were given liberal quantities of phosphate fertilizer, confirming previous reparts. All mycorrhizal plants took up more nutrients from soil than non-mycorrhizal plants. Effective nodule formation wassignificantly grater in mycorrhizal plants when phosphorus was added.Item Effect of moisture on the processability and physical properties of natural rubber(Rubber Research Institute. Agalawatte, 1985) Perera, M.C.S.; Siriwardena, T.A.S.The natural rubber absorbs moisture when exposed to high humuditiess. The presence of moisture is found to reduce the mastication efficiency of rubbers resulting in stocks with high Mooney viscosities. The green strenth and the die swell increases as a result. It has also been found that this affects the milling efficiency resulting in heterodlsperse stocks. These effects could be climinated by further milling. The presence of moisture, however, affects directly, the Mooney scorch time of conventional mixes, the tensile strength, resilience and heat build - up