Exchange properties of the soils from five locations in the traditional rubber growing tract in South India with distinct variation in average annual rainfall were compared. The base saturation per cent and exchangeable bases showed wide variation between soils with variation in average annual rainfall. Soils of the high rainfall areas were showing very low base saturation with extremely low status of potassium, calcium and magnesium. Extractable acidity values were also high in two locations experiencing high rainfall. Though natural rubber is adapted to acidic, low base environment, studies are required to assess the growth and yield performance in soils with extremely low base status.

Twenty years weather data taken at RES, Nagrakata was analyzed to estimate whether there was any change in weather attributes in this part of India. Successive averages of ten years data (moving average) over a stretch of twenty years meteorological attributes indicated an increasing trend in minimum (T_min) and maximum (T_max) temperature and relative humidity (RH) in the morning. This may make this region more suitable for rubber cultivation. A clone trial was initiated in 1991 in this region with ten clones along with a check clone RRIM 600. The girth increment (GI) and weather data were grouped into non-winter (NW - April to September) and winter (W - October to March) periods in order to understand the effect of two contrasting weather on growth of rubber. In general, the T_max during NW period was higher than the W period. Similarly, T_min during NW was almost double the temperature during W period indicating a cooler weather during W period than that of the NW period. The girth increment (GI) during NW was significantly higher than the W period at immature (3-5 yr), juvenile (6-8 yr) and early mature stage (9-11 yr) stage indicating effect of weather on growth of rubber. Data on the dry rubber yield showed that none of the clones was superior to the check clone RRIM 600. In terms of yield, coefficient of variance over years, incidence of tapping panel dryness and wind damage, only one clone i.e. RRII 208 was found to be suitable for the region along with RRIM 600. Study on correlation between yield and weather parameters showed that in post-W (May to September) and pre-W (October to December) periods, there was a positive correlation between yield and T_max. During post-W period when T_max was high, T_min showed negative correlation; during pre-W period, when environment dominated with cool weather, increasing trend of T_min would be appreciable which reflected on correlation study with yield showing positive trend. Therefore, with changing climate in the sub-Himalayan West Bengal, rubber production responded positively.

Variation in yield and associated biochemical changes were studied in five newly evolved RRII 400 series clones during peak yielding and low yielding stress (summer) seasons and compared with the popular check clone RRII 105. A significant reduction in dry rubber yield was observed in all the clones during the stress period compared to peak yielding season. Metabolism of carbohydrates and activities of antioxidant enzymes showed significant variation between seasons. Significant clonal variations were also observed in the case of latex ATP, C-serum thiols and SOD during the stress season. Clones RRII 422, RRII 430 and RRII 414 showed higher ATP concentration in latex, C-serum thiols, invertase and SOD during stress season. RRII 429, RRII 417 and RRII 105 showed very low SOD, thiols and invertase activity in C-serum during this period. The present study indicates that among the clones studied for yield attributes, RRII 422 followed by RRII 430 and RRII 414 may be more tolerant to stress situation than other clones. The significance of these biochemical parameters are discussed in relation to yield obtained during the peak yielding and stress seasons.

Recent incidences of attack of the pathogen, Corynespora cassiicola on rubber trees in North Kerala and South Karnataka necessitated the study of critical weather conditions which trigger the onset of the disease. Daily leaf fall due to Corynespora infection during the January-February period was studied in relation to the prevailing weather parameters at five different locations. A new index, termed the Humid Minimum Temperature Index (HT_nI) was found to be related to disease incidence and severity of leaf fall in all the locations in the traditional rubber growing belt. A value of HT_nI > 5.5 for seven consecutive days was found to be the critical limit for severe leaf fall and HT_nI > 4.0 for consecutive 3 to 4 days for the onset of the disease. Similar results were obtained when leaf fall was studied in relation to spore count per unit area within the canopy. Forecasts during the refoliation period based on the critical values of HT_nI could be utilised to wisely adopt prophylactic measures to combat this disease, a major biotic constraint of rubber productivity.

Abnormal leaf fall (ALF) disease caused by Phytophthora spp. is one of the most destructive diseases of rubber (Hevea brasiliensis) in South India. High incidence of pod rot and ALF disease caused by P. botryosa was observed in Tripura (North East India) during 1988 and 1989 but not during the subsequent years although a Phytophthora-susceptible rubber clone RRIM 600 is widely cultivated in this area. Therefore, a possible threat of Phytophthora exists in the rubber plantations of North East India. In this study Phytophthora was isolated from soil and litter collected from rubber plantations in Agartala, Tripura and Kottayam in India. It was found that Phytophthora inoculum density was low in Tripura and they were less virulent. As weather plays an important role in development and spread of Phytophthora disease, a comparison of weather parameters between Tripura and Kottayam during May to August 1988 to 2009 was made. A hot weather with low relative humidity coupled with less number of continuous rain spells may be some of the important factors preventing inoculum build up for initiating Phytophthora infection in rubber plantations of Tripura. Low virulence of Phytophthora would also have contributed to near complete absence of ALF in NE India.

During the processing of block rubber, a major share of energy is required in drying. The power and fuel used together constitute around half of the direct cost of production of block rubber. This forced the processor to explore alternate and cost effective sources of heat energy which led to the introduction of biomass gasifiers in the block rubber sector. The utilization of biomass gasification technology is found to reduce the drying cost of block rubber by 50 per cent when compared to diesel fired driers. It would also result in considerable reduction in the emission of CO₂ in addition to avoiding the use of fossil fuels. This technology has further scope for contributing towards CO₂ emission reduction in natural rubber processing as very little quantity of block rubber is now being dried with this technology.