A pathogen-inducible isoform of β-1, 3-glucanase gene(β- glu) from the Para rubber tree (Hevea brasiliensis Muell. Arg.) is reported for the first time. In order to induce the production of β- glu, two-week-old leaves of H. brasiliensis (clone RRII 105) were inoculated with abnormal leaf fall-causing pathogen, Phytophthora meadii. RNA was isolated from the near necrotic zones of the infected samples by LiCl precipitation. First strand cDNA was synthesized and sequence coding for the final mature β-glu (EC 3.2.1.39) was amplified. A functional cDNA clone was constructed using the pET 32a+ expression system. The major difference of the new basic isoform with a predicted pI of 9.26 is the absence of a glycosylation site at Asn-27, which is present in all the reported cDNA sequences of Hevea β-glu. Conditions were optimized for IPTG- induced over-expression of the gene in the E. coli strain BL21 (DE3), in soluble form. The column purified recombinant protein retained its functionality as proved by its ability to hydrolyze its natural substrate, laminarin. The purified recombinant Hevea β-glu was assayed for its antifungal activity against Phytophthora. When the fungus was grown on PDA plates, clear inhibition zones were observed around the filter paper discs soaked with 10µg of the purified protein, indicating the inhibitory action of the purified enzyme. 

The growth and yield performance of 13 Hevea clones were evaluated in Tripura in North East India which experiences a non-traditional environment for rubber cultivation. Analysis of growth performance of the clones revealed that RRII 429 had the highest girth and girth increment during immature phase. Clone RRII 176 recorded significantly higher girth increment under tapping than the check clone, RRIM 600 and attained the highest girth after six years of tapping. Yield analysis showed that RRII 422, RRII 429 and RRII 417 had significantly superior yield compared to RRIM 600 after six years of tapping. Among the clones tested, RRIM 600 had the lowest yield reduction during both summer and winter periods indicating the adaptability of the clone to the climatic conditions of Tripura. The results of the present study will aid in the identification of potential clones for commercial cultivation in this region. 

Genetic stability of somatic plants developed through somatic embryogenesis from immature anther-derived callus cultures of Hevea brasiliensis (clone RRII 105) was examined using random amplified polymorphic DNA (RAPD) analysis. Ten somatic plants along with their mother tree and 10 monoclonal seedlings were subjected for RAPD analysis and compared. Fifteen arbitrary decamers displayed monomorphic banding profile within all somatic plants and their mother plant. However, polymorphism was detected among monoclonal seedlings with all the five primers tested. UPGMA-based dendrogram showed that all the somatic plants along with the source plant clustered together and no variation was observed among these plants. Absence of polymorphism displayed in the RAPD profile indicated a stable genome in plants developed through somatic embryogenesis. 

A field experiment was conducted to study the response of rubber to NPK fertilizers in the Lower Brahamaputra Valley Zone (LBVZ) of Assam. The treatments consisted of four levels of N and three levels each of P and K in factorial randomized block design. Nitrogen and K significantly influenced the girth and girth increment. Optimum level of N, P and K for achieving good growth in immature phase and improving the soil fertility was found to be 50:20:40 kg/ha/year. The interactions of N, P and K were non significant. Nitrogen, P and K application significantly improved the rubber yield. Positive linear response to N, P and K on rubber yield was observed. The highest yield was recorded by 60:40:40 kg NPK/ha/year. Continuous application of N, P and K fertilizers improved the fertility status of the soil. 

The extent of natural damage and crop loss in rubber plantations in the estate sector was studied and the economic loss was estimated based on a life cycle approach. The results highlighted the contradictions between popular perceptions and field-level data on the nature of natural damage which was dominated by wind (66%) across different age groups and regions. The dominance of weather-related damage (79%) indicates limited role of policy interventions targeted towards preventive mechanisms. However, identification of phasewise sources of damage during the entire life cycle assumes significance since the generation of reliable annual database on the natural damage in rubber plantations is an essential prerequisite for the adoption of policy initiatives for minimising loss through the coverage of comprehensive insurance schemes. 

Genetic improvement of Hevea brasiliensis by conventional breeding is difficult due to its perennial nature, long breeding cycle, seasonal flowering and asynchronous flowering among clones. The major bottleneck in Hevea breeding through conventional methods is the low recovery of fruits after artificial pollination and fruit loss due to fungal diseases. The average fruit set after hand pollination is usually less than 5%. In this context, the present work was undertaken with an objective to develop a protocol for the rescue of immature embryos of H. brasiliensis, thereby improving the recovery of hybrid seeds. Open-pollinated fruits of different maturity (1-8 weeks) were collected from the field-grown trees and inoculated in nutrient medium. Different basal media, various combinations and concentrations of growth regulators and two sterilization techniques were tried. Embryos could be rescued from 5-week-old immature fruits in Nitsch basal medium supplemented with the growth regulators kinetin, zeatin and GA₃ The highest frequency of embryo recovery (42%) was obtained with 3.0 mg/L zeatin coupled with 1.0 mg/L GA₃. Plantlets were developed, hardened and established in the field.