Corynespora cassiicola causing leaf diseases of Hevea is considered to be a serious problem in most of the rubber growing countries. Production of a pathogenesis related [PR]protein β-1,3-glucanase upon infection  was tested  in four clones of Hevea. Considerable variability in the β-1,3-glucanase activity  of enzyme was observed among different clones during pathogenesis. Increased enzyme activity was found in the tolerant clone (GT.1), while a decrease was observed in the susceptible (RRII 105). Three prominent  β-1,3-glucanase isozyme  bands were detected by 17.5 per cent PAGE in the tolerant clone.

An attempt was made to produce low protein natural rubber latex suitable for making dipped goods with  low extractable  protein  content.   A laboratory process was standardized for the deproteinization of natural rubber latex using a proteolytic enzyme. Using the standardized process deproteinized latex was prepared on a pilot plant scale and its processing and technological properties were assessed.

Tapping panel dryness (TPD) affects the ability of Hevea trees to synthesise rubber (cis-poly isoprene) and thus decreases the yield.  The present study conducted in Hevea clones RRIM 600 and RRII 105 showed that  concomitant with  an  increase  in the  total  sugars and  starch  contents in the  bark, respiration rate also increased but  the ATP concentration in the cytosol  markedly decreased in TPD affected  bark  compared to healthy  bark  from  normal trees. This appears to be due  to an increase  in the non-phosphorylating cyanide resistant  alternative respiration in the TPD affected trees.

Culture conditions and other parameters for improving the efficiency of somatic embryo induction and germination were investigated.  Explants precultured in liquid medium for 10 days followed by 25 days culture in solid medium was most suitable for primary callus induction.  Fifteen day old primary callus was found to be ideal for first subculture onto embryo induction medium. Histological analysis confirmed the relationship of callus age and its morphogenetic potential. Polyamines had no significant effect on somatic embryogenesis except for a slight enhancement with 0.5 mg/1 spermidine.   Embryo induction efficiency was promoted by supplementing 200 mg/l glutamine and 400 mg/l casein hydrolysate in embryo induction medium.  Dark incubation favoured  induction  and proliferation of callus as well as induction  of embryogenesis whereas plantlet regeneration was found to be light-dependent. From these results, an efficient method for proliferation of callus, induction of embryos and their maturation is proposed.

Wide variations have been observed in dirt content values from identical raw natural rubber samples in different laboratories using similar test procedures.  Factors investigated in this study ranged from the physical nature and concentration of the peptiser employed to heat transfer during dissolution of raw natural rubber in the solvent. Rubbers of latex grade, as against those of cuplump, required longer heating before the formation of clear homogeneous solutions.  After a critical duration of dissolution, prolonged heating led to the formation of a macrogel that remained insoluble in most nonpolar hydrocarbon solvents.  This macrogel seemed to have been in part responsible for the poor repeatability of dirt values.  The duration of swelling in white spirit, before heating, affected the formation of insoluble fractions, though this seemed to vary with the time of introduction of the rubber into the mixture.

A study was carried out in ten oriental clones of Hevea brasiliensis, planted in a clone evaluation trial in Tripura (North East India) to understand the clonal variation and environmental influence on phenotypic expression of yield and related traits during two peak yielding seasons.  Pheno­typic coefficient of variation for plugging index (PI), inorganic phosphorus  (Pi), sucrose content (SC), total volume (TV) and dry rubber yield (RY) was high when compared to that for initial flow (IF), dry rubber content (DRC) and total solids content (TSC). Mean performance of clones RRII 105, RRIM 600 and PB 235 was better for yield and related traits. These clones had less outflow of sucrose indicating better efficiency of metabolism. Stability of clones decreased with better yielding nature, except for RRIM 600, which showed better stability. GT 1 and RRII 118 showed higher stability for most of the traits. The 10 clones were grouped into three clusters using non-hierarchical Euclidean cluster analysis.  Cluster I included high yielding clones RRII 105, RRM 600 and PB 235, cluster II consisted of RRII 118, RRII 203, PB 86 and GT 1 which were medium yielding clones and cluster III comprised the low yielding clones RRIC 105, GI 1 and Herbel 1. Average inter cluster distance showed that cluster III was more divergent from clusters I and II. Phenotypic variation in the character expression for yield of clones was considerably influenced by factors, which were associated with senescence and low temperature reaction. The clones, which were stable and high yielding like RRM 600 would be more desirable for this region.