The spatial availability of soil nutrients and their status is an important primary factor that determines sound nutrient management practices by using an appropriate method to identify all soil fertility constraints. In India, rubber cultivation spreads over varied agro-climatic conditions with spatial variability in various soil fertility parameters. In the present study, a survey on soil phosphorus availability, classification of soil available P (Av. P) and preparation of soil fertility maps which delineate soil phosphorus status were conducted for the traditional rubber-growing soils of South India including Goa and Maharashtra. Geo- referenced soil samples were collected from rubber-growing regions and soil Av. P was analyzed using standard analytical protocol. The soil Av. P status was mapped geostatistically following the kriging interpolation technique. From the results it was inferred that higher Av. P status was observed in Kerala and Kanyakumari district of Tamil Nadu compared to the entire rubber growing areas of Karnataka, Goa and Maharashtra which showed low Av. P status. Rubber growing soils of Kanyakumari in Tamil Nadu, Alleppey, Idukki, Ernakulam, Thrissur and Palakkad districts in Kerala were adequate in Av. P whereas Thiruvananthapuram, Kottayam, Malappuram, Kozhikode, Wayanad, Kannur and Kasaragod districts were low in Av. P status. Kollam and Pathanamthitta districts in Kerala showed an equal proportion of low and adequate status of Av. P. All districts in Karnataka and the entire rubber growing areas in Goa and Maharashtra were low in Av. P. The study emphasized the need for external input of phosphorus fertilizer with due consideration of the leaf P status of rubber plants in Av. P deficient areas especially in Karnataka and rubber growing areas in Goa and Maharashtra.

One set of four hybrid progeny families and four sets of polycross progenies were evaluated for girth and yield in terms of test tap at the age of three years. Wide range of values was observed for girth and yield among both types of the population studied. However, the hybrid progenies exhibited greater mean values for both growth and yield than polycross progenies. Higher CV for girth and yield in both types of populations indicated greater variability among the progenies of the populations, thereby revealing greater extent of heterozygosity and heterogeneity in the constituent progenies of both types of population. The number of superior progenies identified was less in both the type of populations. Hence, it could be observed that in general, lesser the strength of the population, lower would be the chances of recovering superior progenies. However, the number of selections recovered from the hybrid population was relatively more than that of the polycross progeny population. This might be due to the fact that controlled mating was exercised in case of hybrid population, whereas, random mating was allowed for generation of polycross progeny population. Hence, the study suggested strengthening of the breeding gardens and polyclonal seed gardens by incorporating more pre-potent and divergent parents for the generation of promising hybrids and polycross progenies to realize considerable improvement in primary traits.

The drought tolerance potential of clones of Hevea (RRII 400 series) was assessed by examining the effect of progressive water stress imposition on photosynthesis related to water stress. Seven-month-old polybag plants of five modern Hevea clones and three check clones growing under natural condition were used as experimental material for the study. Stress was imposed by withholding irrigation. Water stress limited plant growth and induced a significant reduction in assimilation rate (A). Decline in the rate of photosynthetic CO2 assimilation was lesser in RRIM 600 (46%) followed by RRII 430 (73%) while RRII 414 was severely affected. The initial response to water stress was the drop in stomatal conductance (gs) and it was found to decrease as a function of leaf water potential in all clones. RRIM 600 showed 75% reduction followed by RRII 430 (88%) and maximum reduction was observed in RRII 105 and RRII 414 (100%). The clones RRIM 600 and RRII 430 had relatively high A per unit of gs. There was an increase in intrinsic water use efficiency (iWUE) indicating efficient CO2 utilization in RRIM 600 and RRII 430 which were physiologically better adapted (in terms of WUE) to drought conditions. The present study indicated that a better WUE and ability to maintain stable photosynthesis under stress condition is a desirable character for selecting clones with drought tolerance.

In many plants, both monocots and dicots, picloram has been successfully used for induction of somatic embryogenesis. However, the effect of picloram on the somatic embryogenesis of rubber has not been studied so far. In the present study, immature anther explants were cultured on a modified MS medium supplemented with varying concentrations of picloram (1.0, 2.0 and 3.0 mg L-1) in combination with BA (1.0 mg L-1). Embryogenic calli were subsequently sub-cultured in embryo differentiation medium which composed of modified MS with BA and picloram (0.5 mg L-1 each). Friable embryogenic callus could be effectively induced on medium containing 1.0 and 2.0 mg L-1 picloram. This combination gave the highest percentage of callus induction (100%), proliferation and callus fresh weight (1.07 and 0.76 g) without significant difference. Moreover, the differentiation of globular and heart-staged somatic embryos was also observed. A double staining test with acetocarmine and Evan’s blue showed positive reaction to both dyes, indicating the existence of both embryogenic and non-embryogenic cells in the friable primary callus. After transfer to the embryo induction phase, a larger percentage of produced calli was heavily stained with acetocarmine, which were identified as embryogenic calli. However, in the friable translucent primary callus, cell mass reacting more strongly to Evan’s blue detected the presence of more non-embryogenic cells. Additionally, PCR amplification using genomic DNA revealed presence of SERK gene in both embryogenic and non-embryogenic calli.

There are direct and indirect methods for determining the shelf life of polymer products. Direct method requires the product to be under real room temperature conditions for a long period while the indirect method predicts shelf life after exposing the product to accelerated temperature within a short period. This research aimed to identify the most prominent properties that can reliably predict shelf life of natural rubber gloves using the Arrhenius model. Accordingly, surgical gloves were subjected to accelerated ageing tests and predicted properties of the same from Arrhenius plots were compared with real-time storage properties of the gloves stored for five years. Properties such as tensile strength, elongation at break and force at break were found to be the most suitable properties for predicting shelf life of glove using the Arrhenius model.

The superior processing rubber (PA80) can be blended with synthetic rubbers to achieve the desired degree of processing advantages in extrusion applications. In the present study, PA80 in different proportions was blended with a medium viscosity grade styrene butadiene rubber (SBR) and their processability and physicomechanical properties were evaluated to identify an ideal blend proportion with optimum properties suitable for extrusion. In the proposed PA80/SBR blends, the optimum crosslinking was achieved with a semi- efficient vulcanization system and the cure rate was found to increase proportionally with PA80 content. Moreover, the Mooney viscosity, tensile strength, 100 per cent modulus, hardness, crosslink density and carbon black dispersion also improved with PA80 content. In contrast, the retention in tensile properties after thermal ageing, abrasion resistance index and compression set properties were found to be better with blends having higher SBR content. However, the appearance and contours of the extrudate shapes produced from the blends had a smoother surface with a lower die swell than the control. Therefore, in extruded products, 30-50 per cent replacement of SBR with PA80 is recommended without significant property reduction.