Hevea brasiliensis is the most important commercial source of natural rubber. Its cultivation is being extended to drought prone non traditional areas to meet the increasing global demand. The wild germplasm accessions of Hevea collected from its primary centre of origin, the Amazon forests, are valuable source of genes conferring tolerance to various biotic and abiotic stresses. Identifying suitable germplasm accessions with stress tolerance and yield sustainability would be important to enhance crop productivity. In the present study, a set of 18 Hevea germplasm accessions (14 relatively drought tolerant and 4 relatively drought susceptible), short listed based on previous observations were further evaluated for their drought tolerance potential using physiological and biochemical parameters such as photosynthetic rate, chlorophyll fluorescence, leaf wax content and pigments. The data revealed wide genetic variability among the accessions as indicated by a wide range obtained for these characters in the ranking. The accessions were ranked for their pooled performance using the rank sum method and the results indicated that accessions RO 3261, AC 612 and RO 3157 are the top three drought tolerant accessions among the lines studied.

In rubber (Hevea brasiliensis), seedling plants are raised either in the ground nursery or in polythene bags for producing good quality stock plants for bud grafting. Field experiment in rubber seedling nursery was conducted during 2009-2010 and 2010-11 planting season to study the possibility of reducing the dose of nitrogen and phosphorus fertilizers by incorporating bio-inoculants. The treatments were (T1) control, (T2) standard practice (SP), (T3) standard practice (SP) + bio-inoculants (BI), (T4) 50 per cent N and P and recommended dose of K and Mg + bio inoculants (BI) and (T5) bio- inoculants (BI) alone. The consortia of bio-inoculants were one isolate of N fixing bacteria (Azotobacter sp.), two strains of P solubilizing bacteria (Bacillus spp.) and two strains of plant growth promoting rhizobacteria (Pseudomonas spp.) isolated from the rubber growing soils and multiplied at RRII and arbuscular mycorrhizal fungi (AMF) from The Energy and Resources Institute (TERI) , New Delhi. Growth of the plants in T5, viz., BI alone was on par with reduced dose of N and P with BI(T4) or full dose of chemical fertilizers (T2) indicating the possibility of reducing the dose of N and P fertilizers. Pseudomonas population was significantly different among the treatments and was higher in all treatments with BI viz., T3, T4 and T5. AMF in the root indicated 70 to 80 per cent infection in all the plants irrespective of the treatments. The results need to be reconfirmed through on-farm trials in different locations with varying soil fertility status.

Two polybag nursery experiments were conducted at the Central Experiment Station of the Rubber Research Institute of India, Chethackal during 2008-2009 with the objective of comparing the growth performance of two types of planting materials viz., direct-seeded and budded stump rubber (Hevea brasiliensis) plants under inorganic fertilizers and integrated nutrient management with different organic sources. The experiments were laid out in a completely randomized design with eight treatments and four replications. The treatments comprised of chemical fertilizers alone and in combinations with cow dung slurry, groundnut cake, neem cake and plant growth promoting rhizobacteria (PGPR). Significant difference was observed in growth of the two planting materials to the application of inorganic fertilizers alone and in combination with different organic sources. Integrated application of chemical fertilizers with cow dung slurry, groundnut cake, neem cake or PGPR produced significantly higher dry matter than standard practice of chemical fertilizers alone in direct-seeded and budded stump polybag plants. Planting materials produced through direct-seeding was significantly superior in diameter, height, number of whorls, fibrous root and dry matter compared to the budded stump plants.

The article presents the first part of the review on the current status of sulphur vulcanization and devulcanization chemistry. The purpose of presenting a review of the chemistry of sulphur vulcanization and devulcanization was to develop a devulcanization process and also to address the issue of very low scorch during revulcanization. Accelerated sulphur vulcanization is a very complex chemical process. Although consensus on various reaction mechanisms are yet to reach, there is widespread agreement about three basic steps involved. These are: (i) accelerator chemistry in which the reactions of accelerator, activator and sulphur leading to the formation of an active sulphurating agent (ii) crosslinking chemistry which involves the reactions of the active sulphurating agent leading to the formation of crosslink precursors and subsequent reactions of these precursors to form polysulphidic crosslinks and (iii) postcrosslinking chemistry leading to chain shortening and degradation of the polysulphidic crosslinks and other main chain modifications. The current understanding of the chemical reactions and the underlying mechanism involved in these basic steps, both in accelerator, activator and sulphur as well as accelerator- cum- sulphur donor and activator cure systems are reviewed. Reaction mechanisms leading to scorch delay inherent to sulphenamide accelerators and those involved by the addition of prevulcanization inhibitors are also presented.