The Rubber Board of India has evolved clone recommendations for the traditional and non-traditional regions and updating of these recommendations is done periodically based on data that is made available from the clonal evaluation trials in various regions. In addition to these recommendations, the formulation of a regionspecific clone advisory based on agroclimatic zoning was a long felt need of the rubber plantation sector, so as to enable maximisation of rubber yield from each region and thereby improve rubber production per se.Based on results of 29 long term field evaluation trials of rubber clones in the traditional regions as well as studies on disease reaction, genotype x environment interaction studies and yield from nine large scale and on farm evaluation trials of these clones in Tripura, Assam and northern part of Bengal, region specificity in performance of the clones was determined. This paper details the specificity in performance of clones in the planting recommendations across the various agroclimatic zones where rubber is presently cultivated. A new region-specific advisory of clones suited to each of the nine agroclimatically distinct zones in the traditional region and the non-traditional regions of rubber cultivation in India is formulated for the first time.

Abnormal leaf fall (ALF) disease caused by Phytophthora spp. is one of the most destructive diseases of rubber causing extensive defoliation leading to a reduction in the yield of natural rubber. Shoot rot and die back occur on young rubber plants due to infection with Phytophthora spp. Panel diseases viz. black stripe and patch canker are also caused by Phytophthora spp. on mature rubber trees. As a molecular tool for species identification,DNA barcodes offer significant potential using a short, unique, standardized portion of the DNA. This study aimed at presenting a molecular phylogeny of the four major Phytophthora species viz. P. meadii, P. botryosa,P. colocasiae and P. citrophthora predominantly infecting rubber trees in India. Two nuclear DNA regions:Internal Transcribed Spacer region of the nuclear ribosomal DNA and the microtubule constituent protein β-tubulin, and the mitochondrial gene cytochrome c oxidase subunit II were used in this study to get a more resolved phylogeny of the four Phytophthora species of rubber, providing better interpretation of the overall evolutionary history of the genus. Sequence information suggests that P. meadii has a hybrid origin with P. colocasiae as a parent and it is also possible that P. citrophthora is an asexual derivative of P. colocasiae. The study also demonstrates significant diversity in the population of Phytophthora spp. isolated from rubber plantations in India.

Climate-resilient smart rubber clones need to be developed for expansion of rubber cultivation to regions where environmental stresses are a limiting factor. In this context physiological responses of young plants belonging to ten clones of Hevea brasiliensis were analyzed under soil moisture deficit condition. The relative drought tolerance potential of these clones were evaluated using key physiological parameters such as leaf water potential, photosyntic oxygen evolution rate of leaf, quantum yield of PS II and CO2 assimilation rates. Clones viz. RRIM 600, RRII 208 and RRII 430 were more drought tolerant even as they recorded comparatively less decline in photosynthesis and PS II activity. On the other hand, clones PB 260, RRII 105, RRII 414 and RRII 417 were relatively more drought susceptible in terms of severe inhibition of various photosynthetic activities under moisture stress. Western blot analysis of a low molecular weight (23.8 kDa) chloroplast stress protein indicated its consistent over-expression in the relatively drought tolerant clones when these plants were subjected to water deficit stress. Abundance of this protein was associted with relatively lesser inhibitions in photosynthetic activity in drought stressed young rubber plants. The relative expression level of this protein together with other crucial physiological parameters such as photosynthetic activity can be used as potential screening tools for selection of drought tolerant clones at a young stage.

Although Indian economy is growing rapidly, however there has been widening of income disparity in the society. The present study highlights the relevance of comprehensive policy approaches in transformation of the economically and socially marginalized groups engaged in Jhumming to commercial cultivation of natural rubber (NR) in Tripura. The better livelihood pattern of the NR growers has been reflected in terms of selfsustaining occupational shift. The previous land use pattern of the surveyed NR cultivators revealed that majority of the area presently under NR cultivation was previously barren land (66 %). The study suggests replication of the NR model in North and Dahalai districts of Tripura. This success model of Tripura could also be replicated in other regions of the country having similar socio-economic and agro-climatic conditions to ensure rural upliftment and livelihood security of rural peasantry.

Sixteen ortets selected from different agro-climatic regions of India were tested for their initial performance along with seven check clones in the field under two extreme stress situations, viz. drought stress at Dapchari in Maharashtra and low temperature stress at Nagrakata in West Bengal. Under severe soil moisture deficit stress conditions, ortets RRSA 98, DAP 35 and GH 1 had better photochemical efficiency in terms of gas exchange and chlorophyll fluorescence. The photosynthetic activities declined sharply during low temperature stress (winter) at Nagrakata. Low temperature stress was found more detrimental to photosynthetic apparatus of young rubber plants than soil moisture deficit together with high temperature. Ortets, DAP 1, RRST 24, GH 1 and GH 9, showed relatively better CO2 assimilation under low temperature stress. Ortets DAP 1, NGK 1 and GH 9 that had better CO2 assimilation under low temperature condition did not perform equally well under drought conditions. The PS II activity of ortets and check clones did not vary significantly under drought conditions, however, it declined sharply in clones tested at Nagrakata during low temperature conditions, indicating the adverse effect of low temperature on photosystem II. Ortets GH 1, GH 9 and RRSA 585 showed better PS II activity during winter season. Soluble leaf protein content decreased in most of the plants tested under low temperature while it increased under drought. Malondialdehyde (MDA), a major lipid peroxidation product was less under low temperature conditions compared to drought in these plants. Among the ortets, GH 1 and GH 3 recorded comparatively high magnitude of reduction in sucrose content under stress in both the locations. Ortets GH 1, GH 3, DAP 1, NGK 1, DAP 35 and RRSA 98 recorded better adaptive traits under abiotic stress conditions in the early stages of growth and may be further shortlisted as potential clones suitable for extreme climatic conditions, which may also yield better, as their selection was primarily based on term performance of yield and other secondary traits in the fields.

The impact of rubber cultivation on soil can be assessed precisely if the changes are monitored in the same field itself at different stages of growth. Accordingly two fields in the second cycle of rubber cultivation in the farm of Rubber Research Institute of India, Kottayam, were selected and monitored for soil organic carbon, pH and available nutrients at the beginning of the cycle, after eight years and at the end of the cycle. A decline in soil organic carbon status was observed in both the fields after eight years. However, after 25 years, in both the fields a significant increase was noted. Available phosphorus and potassium improved towards the end of the cycle. It is observed that the available calcium was maintained at the end of the cycle, though an increase was noted in between. The changes in available magnesium status in soil was different in the two fields, however, both the fields maintained the ‘medium’ status throughout the period of cultivation. Soil pH changes were also slightly different in the two fields. In one field, a slight decrease was noted compared to the initial status while in the other a reverse trend was recorded. In general, in both the fields an increase in organic carbon and available form of nutrients in soil was observed towards the end of the cultivation cycle