Mathematical models developed earlier showed that maximum and minimum temperatures were the two most important weather parameters that determined rubber productivity and both had a negative impact on rubber yield in the traditional rubber growing areas (Satheesh and Jacob, 2011; Satheesh, 2014). In the present study, we made use of these models on the influence of climate warming on natural rubber yield to estimate past productivity of natural rubber in parts of the traditional heartland of rubber cultivation in India (based on the then existing temperatures) and compared the same with actual commercial productivity as obtained from growers’ fields and published by Rubber Board. Commercial productivity of natural rubber from growers’ fields registered a steady increase over the years even as the local climate continued to warm, apparently contradicting the model prediction. Increase in the area under the high yielding clone, RRII 105 that came into tapping over the years was responsible for masking the adverse impact of climate warming on productivity until recently. Our results show that there existed a gap between estimated productivity based on temperature sensitivity models and the actually realized productivity in field. The differences were more pronounced in the past than in the more recent years when yielding area under the high yielding clone did not continue to register any marked increase and the warming effect started to have an overriding adverse effect on productivity as compared to the past. The difference between estimated productivity and actual productivity became zero in 2010 and since then productivity must have started to decline, contrary to the general perception. Projecting future yields without taking the impact of weather variables into consideration will not be correct. Our analyses clearly show that rising temperatures (warming effect) have now become strong enough to make a dent in productivity of natural rubber in India, overriding the positive influence of clone (clone effect). Since there has been no expansion in highly productive young area under tapping (compensating for the decline in productivity) it is concluded that total production of natural rubber in the country must have taken a beating since early this decade. This can explain the increased import of natural rubber and increased use and production base of synthetic rubbers in the country in recent times which is certain to have serious implications for the sustainability of the natural rubber sector the country.

The impact of six different land use systems on soil properties were examined in a tropical region. Three systems based on natural rubber (Hevea brasiliensis), teak (Tectona grandis), cassava (Manihot esculenta) and nearby natural forest located between 76o 52' and 77o E longitude and 9o 25' to 9o 30' N latitude, in Kerala, India were investigated. Representative soil samples were collected and analyzed for organic carbon (OC), water soluble organic carbon (WSOC), hot water extractable carbon (HWEC), permanganate oxidizable carbon (POSC), available nutrients (K, Ca, Mg, P, Cu, Zn, Fe, Mn) and pH. In situ field soil respiration measurements were also taken from representative sites in the different systems. Carbon management indices (CMI) were worked out in terms of OC, WSOC, HWEC and POSC of different systems with respect to forest system. Soil organic matter quantity and quality were found to be declining in all cultivated systems compared to forest. Nitrogen and available cations such as K, Ca and Mg also had declined in cultivated systems. Microbial activity indicated by soil respiration rate also had declined in all the land use systems compared to forest. The declining trends in soil properties were more in the regularly tilled cassava soil where the crop residue inputs were also negligible. The rubber-Mucuna system had conserved more organic matter, quantity wise while teak system had conserved more organic matter, quality wise. The teak system had higher soil respiration rate than all other cultivated systems. The forest and teak systems where multi-species flora existed had less soil acidity than rubber based land use systems. In rubber based systems, av.Cu status was found to be higher, probably due to the regularly applied Cu based fungicides. Soil respiration rate was found to be having significant and positive correlation with soil organic matter quantity and quality and pH while negative correlation with available Cu status.

This study was carried out to investigate the effect of paclobutrazol, a gibberellin synthesis inhibitor in young rubber plants and standardise its optimum concentration to develop better root system. Paclobutrazol treatment in young rubber (Hevea brasiliensis) plants resulted in short and compact plants having dark green leaves, with more fibrous root development and improved root-to-shoot ratio. Plants of Hevea clone RRII 429 were treated with 0, 50, 100, 250, 500 and 750 mg active ingredient of paclobutrazol per plant as soil application. Three months after treatment the leaves showed increased chlorophyll (25.9%) and carotenoid (33.6%) contents over control. The height increment in paclobutrazol (50 mg) treated plants was significantly lower than control plants of same age, whereas, the girth increment was significantly higher (10.9%) in the treated plants. Paclobutrazol treatment remarkably increased root dry weight (maximum of 132 per cent with 50 mg) and root-to-shoot ratio. The results indicated that paclobutrazol at a concentration of 50 mg was optimum for more fibrous root development without any significant changes in stem girth and leaf number. The modified root system may likely be an advantage to young Hevea plants during drought.

The increasing demand of natural rubber and land unavailability in traditional regions has been resulted the cultivation of rubber in non-traditional regions. However, the severe agro-climatic conditions in nontraditional regions adversely affected growth and yield of rubber. In this context, scope for the introduction of genes conferring tolerance to abiotic stresses is of paramount importance and hence the study was undertaken. Embryogenic callus derived from immature anther of Hevea brasiliensis, clone RRII 105 was used as the target tissue for genetic transformation. Kanamycin sensitivity to embryogenic callus was examined by kill curve test and medium with 100 mgL-1 kanamycin completely suppressed the growth of untransformed callus and was selected as the suitable concentration for selection of transformants. Addition of ABA was found to be beneficial for embryogenesis and maximum embryo induction was obtained with 2.0 mgL-1. Among various levels of sucrose (2-10%), 4 per cent sucrose enhanced embryo induction efficiency and gradually decreased by higher levels. Mature embryos get germinated and converted into plantlets. GUS histochemical assay revealed expression of uidA gene in transformed callus and embryos which was evidenced by the intense blue colour. Polymerase chain reaction confirmed the presence of S6PDH, uidA and nptII genes in transformed callus and embryos. The transgenes were also detected in plasmid DNA (positive control), but absent in untransformed callus (negative control).

A large-scale clone evaluation trial incorporating 12 popular clones including the new RRII 400 series clones was laid out in Padiyoor, in Kannur district of North Kerala. Overall performance in terms of growth during immature and mature phase, dry rubber yield over seven years of tapping, disease incidence and secondary traits was studied. The highest percentage of tappable trees was recorded in PB 217 (82%) followed by RRII 430 (76%). Growth performance of RRII 400 series clones was superior to RRII 105 in the immature phase and comparable to RRII 105 in the mature phase. RRII 430 was the highest yielder during the entire tapping period of seven years with a mean yield of 60.98 gt-1 t-1 and was significantly superior to that of RRII 105. The yield of RRII 414, RRII 417 and RRII 422 was comparable to that of RRII 105 which recorded 51.14 g t-1 t-1. RRII 422 recorded the maximum summer yield (41.11 g t-1 t-1). Seasonal yield behaviour of RRII 430 was very distinct from other clones. RRII 430 and RRII 417 recorded relatively high drc (39%). Observations on abnormal leaf fall disease under sprayed conditions, the RRII 400 series clones showed high leaf retention above 80 per cent of which the lowest retension was observed in RRII 422. Pink disease incidence was the lowest in RRII 430, while disease incidence in RRII 414, RRII 417 and RRII 422 was comparable to that of RRII 105. The suitability of RRII 400 series clones to the prevailing dry sub-humid climatic conditions of the region is discussed.

Somatic embryo induction was achieved earlier with a high frequency (>70%) from leaf explants of glass house grown, bud grafted plants of Hevea brasiliensis (clone RRII 105). Experiments were carried out to improve quality of germinating embryos, enhance rooting and improve embryo-plant conversion. White, opaque embryos at the cotyledonary stage were cultured for two weeks in maturation medium after which they were given different desiccation treatments. Three desiccation treatments such as slow and fast desiccation in empty petri dishes and water stress by PEG (10, 15 and 20 g L-1) were provided. Embryos after desiccation were cultured in maturation medium where the IAA/GA3 ratio was optimized. The effect of phloroglucinol (0-200 mg L-1), in the germination medium containing the optimized level of phytohormones was also studied. Among the desiccation treatments tried, slow desiccation of embryos in sealed Petri dishes for 3 days, after an initial two week culture in maturation medium, improved embryo quality and rate of germination. It was observed that optimizing the ratio of IAA/GA3 in presence of ABA (0.1 mg L-1) in the germination medium, favoured embryo germination after the desiccation treatment. Phloroglucinol (100 mg L-1) enhanced rooting by lateral root induction in 40 per cent of germinating somatic embryos. Germination response was evaluated in terms of both root-shoot apex induction and conversion to plantlets. The effect of embryo desiccation and phloroglucinol in presence of phytohormones, on somatic embryo germination and embryo-plant conversion in Hevea is discussed.