Reduction of rolling resistance by tyre-sizing. Natural Rubber Research, 22(1 & 2): 1-9. Rolling resistance of tyres and the consequent increase in fuel consumption are of concern in automotive and tyre industries. As rolling resistance directly contributes to high fuel consumption, tyre industry has focused on the development of tyres with low rolling resistance. The objective of the present study is to develop a method to reduce the rolling resistance by tyre-sizing. The basic expression for rolling loss (R = h . L. d. W / A) has been modified to express R in terms of tyre diameter and wheel size. These revised expressions indicate that increasing tyre diameter or wheel size can reduce R. These equations form the basis of two tyre-sizing methods: one method is to substitute with next bigger size tyre, having same aspect ratio and wheel diameter. The second method involves selection of bigger wheel size tyre with low aspect ratio but of same tyre diameter. The results showed that by adopting tyre-sizing method, the rolling resistance decreased by about 5 - 8 per cent for passenger tyres and 6 - 12 per cent for truck tyres. This rolling resistance reduction has been explained by applying simple scientific principles. It is concluded that tyre-sizing method reduces rolling loss and thereby improves fuel economy. 

The quality and decomposition pattern of litter from three different sources viz. rubber (Hevea brasiliensis), Pueraria phaseoloides and Mucuna bracteata and the nutrient release from that in a rubber plantation were studied in situ in the central part of the traditional rubber growing tract in India by litter bag technique. Among the three species, rubber litter had significantly higher content of lignin and polyphenol and lower content of nitrogen, phosphorus and potassium than Pueraria and Mucuna. Pueraria litter had significantly higher cellulose, phosphorus and magnesium and lower lignin and polyphenol than the litter from the other two species. Significantly higher carbon, nitrogen and calcium and lower cellulose were recorded in Mucuna litter. The rate of decomposition of litter decreased in the order Pueraria > Mucuna> rubber. The decomposition half life values were 2.7, 3.3 and 3.6 months for Pueraria, Mucuna and rubber respectively. For 95 per cent decay, Pueraria took less time (11.5 months) than Mucuna (14.3 months) and rubber (15.8 months) litter. The nutrients remaining in the residual rubber litter were significantly higher than that of Pueraria and Mucuna. After one year, nitrogen, phosphorus, potassium, calcium and magnesium remained in the residual rubber litter were 13.2,19.6,3.3,7.9 and 7.5 per cent respectively. The corresponding values for Pueraria litter were 2.2, 3.1,1.0,2.1 and 1.7 per cent and for Mucuna litter were 8.8,7.4,2.7,4.1 and 3.9 per cent. 

The performance of 34 hybrid clones of rubber, Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg., evolved from the 1989 hand pollination programme, was evaluated in a small-scale trial over a period of 12 years (seven years before tapping and five years under tapping). Yield over a period of five years, summer yield depression, girth increment before tapping and on tapping, mean girth at opening and in the fifth year of tapping, bark thickness and number of latex vessel rows at the time of opening the trees for tapping, incidence of major diseases, wind damage and tapping panel dryness were recorded. Five clones recorded significantly higher yield than the control RRII 105 in the first five years of tapping. The mean yield ranged from 10.22 to 62.00 g/t/t. The hybrid clone 89/ 95 recorded the highest yield (62.00 g/t/t) followed by the clone 89/7 (60.89 g/t/t). Girth at opening ranged from 37.25 cm (89/287) to 62.83 cm (89/27). Girth increment before opening was high in 89/27 and in the mature phase it was high in clone 89/88. Bark thickness was high in 89/27 and the number of latex vessel rows was high in 89/95. Incidence of major diseases and damage caused by wind were comparatively less. Thirteen clones viz. 89/7, 89/27, 89/63, 89/64, 89/79, 89/95, 89/102, 89/124, 89/243, 89/308, 89/309, 89/349 and 89/356 showing high yield and good secondary attributes were selected for the next phase of evaluation. 

The properties of rubber produced are influenced by the climatic conditions of North East India where these variations are more pronounced than in the traditional regions. The seasonal effect on the properties of rubber from seven clones was studied. The impact of season and clone on different physical and technological parameters of rubber is discussed. Season was found to have a strong influence on dry rubber content (DRC) and total solids content (TSC) in North East India. The DRC and TSC levels decreased from summer to winter. Most of the clones under study gave medium to hard rubbers in terms of plasticity, Mooney viscosity and gel content. The lowest initial Wallace plasticity (P_o) and Mooney viscosity were shown by RRII 430 and the highest by RRII 417. All the clones under study produced relatively low viscosity rubber with low Po during winter season. The best processing properties in terms of Mooney viscosity (in the range of 60-70 units) and low P_o were obtained in winter season. Good correlation was observed between Mooney viscosity and P_o for all the clones. Correlation between P_o and accelerated storage hardening test (ASHT) was also significant. The study revealed that in North East India, low winter temperature had profound influence on the properties of latex. 

Five newly evolved RRII 400 series clones were biochemically characterised and compared with the popular clone RRII 105. Characterisation was done based on biochemical parameters associated with latex flow, flow cessation and latex regeneration. During the peak yielding season, clones RRII 422 and RRII 430 recorded significantly higher dry rubber yield than RRII 105. Biochemical parameters such as latex ATP, content, amount of thiols in C-serum and lutoid membrane ATPase were significantly higher in these clones than in RRII 105 while SOD levels were on par in these three clones. The highest ATP content was observed in clone RRII 429 followed by clones RRII 414, 422 and 430. Clones RRII 417 and 429 were characterised by low SOD in C-serum, and low ATPase and pyrophosphatase activities in the lutoid membrane. Sucrose, glutathione reductase activity, protein profiles of C-serum, hevein content and N-acetyl glucosaminidase activity in lutoids of all the 400 series clones were comparable to RRII 105. The significance of these biochemical parameters is discussed in relation to general metabolic activity of these clones

Plant genetic transformation offers a potential tool for crop improvement in Hevea brasiliensis by the integration of agronomically useful genes with stable expression. The objectives of the present study were to develop a method for rapid regeneration of transgenic plants via somatic embryogenesis using root explants and validation of stable foreign gene integration. Actively growing root explants were collected from germinating in vitro-derived MnSOD transgenic somatic embryos (RRII 105), sliced into thin segments and placed on callus induction medium. Callus induction and proliferation were observed within four weeks of explant inoculation. Half-strength Murashige and Skoog (MS) basal medium containing B5 vitamins and growth regulators (1.4 µM each of 2, 4-D and Kin, 1.0 µM each of NAA, BA and GA3) showed the highest embryo induction frequency of 42 per cent. Maximum conversion of pro-embryos into heart, torpedo and cotyledonary stage was achieved by incorporating 40 g/L sucrose and 4 g/L phytagel in the embryo induction medium. The highest percentage of fully developed plantlets was obtained in half-strength modified MS basal medium containing 1.3 µM BA, 1.5 µM GA₃ and 2.5 µM IBA, Molecular confirmation of the presence of the transgene was performed by polymerase chain reaction with nptII and MnSOD gene-­specific primers and Southern hybridization with nptII gene-specific probe. Regeneration of transgenic plants could be achieved within eight months using this protocol.