Lignins are phenolic polymers of the plant cell wall associated with mechanical strength, sap conduction, defense mechanisms and imperviousness to biodegradation. Cinnamyl alcohol dehydrogenase (CAD) is the key enzyme involved in the synthesis of lignin monomers. A study was conducted in stems of 18 wild germplasm accessions and five Wickham clones of Hevea brasiliensis to localize and correlate CAD activity and lignification at various stages of xylogenesis. CAD activity was maximum during the early stages of stem development and minimum during the mature stage of xylogenesis whereas the pattern of lignification showed a reverse trend. The quantity of lignin also increased in association with the progress of secondary thickening. The lignin percentage in the wild accessions ranged from 21.0 - 27.4 per cent and it was 20.0 - 23.0 per cent in the Wickham clones. Nine wild accessions showed significantly higher percentage of lignin over the Wickham clones. The localization of CAD activity and quantification of lignin in the juvenile growth phase can be used as early selection parameters for wood quality in Hevea brasiliensis. 

The physical and chemical properties of rubber growing soils in south-eastern Nigeria were studied using soil samples collected from three rubber plantations. The soil texture varied greatly from sand to sandy clay depending on the parent rocks. The soils were gravel-free on the surface and highly eroded when devoid of vegetative cover. The soils were acidic in nature (pH 4.09 - 5.50), low in organic carbon (0.12 -2.87%), total nitrogen (0.01 - 0.25%) effective cation exchange capacity (2.22 - 9.45 cmol/kg) , base saturation (14.00 - 65.69%) and low to high in available phosphorus (0.55-80.0mg/kg). The low nutrients content is partly attributable to the parent materials and partly to the high rainfall experienced in the region. 

The breakdown properties of sheet rubber from twelve exotic clones and RRII 105 did not show significant differences. Compounds prepared from ACS 1 as well as HAF filled mixes showed comparable cure characteristics and technological properties. Similar retention of strength and modulus when subjected to thermal ageing were observed for samples of both the mix types using rubber from all the clones studied. 

In an experiment to study the growth response of young rubber during the initial three years to varying levels of irrigation, plant girth and girth increment were on par with irrigation at 1.2, 0.9 and 0.6 IW/CPE ratio and significantly superior to that of the control and irrigation at IW/CPE of 0.3. Growth showed a peak in April and August for the irrigated plants. Seasonal girth increments showed that growth during the period from June to November was higher than that during December to May. Irrigation at IW/CPE ratio of 1.2, 0.9, 0.6 and 0.3 during the period from December to May exhibited a girth increment that was 84, 67, 49 and 46 per cent higher than that of the corresponding girth increment observed during the monsoon season. In the unirrigated treatment this was only 38 per cent. A significant increase in RGR was observed for the treatments irrigated at IW /CPE ratio of 1.2 and 0.9 over that of the other treatments. Consumptive use and the ratio of consumptive use to pan evaporation were also worked out. 

The yield potential of 18 Hevea brasiliensis clones were evaluated over the first ten years of tapping under continuous tapping system (without rest) in Assam, North East India. Secondary attributes like TPD, clear bole volume, wind damage and tolerance to powdery mildew disease of these clones were also evaluated. RRIC 102 showed the highest girth in immature stage, closely followed by RRlC 105, while the lowest girth was observed in GI1. RRIC 102 exhibited the highest girth increment after the commencement of tapping and during mature stage. RRIM 600 had the highest yield (33.91 g) over the first ten years of tapping followed by PB 311 (31.08 g). Yield was less for all the eighteen clones during winter months (December to March) characterized by low temperature, combined with wintering and refoliation stresses. High dry rubber content (DRC) of latex was observed in all the clones from May to August, while it was low in December and January. Yield got stabilized by six years of tapping. The projected commercial yield (kg/ha/year) over the first ten years of tapping indicated that RRIM 600 ranked first (2034 kg) followed by PB 311 (1864 kg). The potential yield of RRlI 105, (the popular clone in the traditional tract) was only 1680 kg/ha/year in the experimental location. 

Twenty clones comprising 15 of the RRII 400 series, one introduced (Prang Besar) clone, one tetraploid and three clones with normal morphotype (derived from the progeny of the compact canopy type variant) were evaluated in large scale evaluation trials. Mean yield and growth parameters over four years of tapping, clear bole volume, monthly yield trends and early tappability were used as selection parameters. Clones with an overall superior performance were identified based on performance indices. The response to selection for yield was estimated to assess the improvement in yield of selected clones over the high yielding check, RRI! 105. Significant variability for the parameters and high heritability for yield helped in identifying four precocious high yielding hybrid clones viz., RRII 430, RRII 422, RRII 414 and RRII 402 of parentage RRII 105 x RRIC 100.