Yield of Hevea brasiliensis Muell. Arg. (clone RRII 105) over a period of three years under  third daily (d/3),  fourth daily (d/4)  and weekly (d/7)  frequencies of tapping of half spiral cuts with different frequencies of ethephon application (stimulation) were  compared with  that  of unstimulated trees under alternate daily tapping (d/2). Tapping under d/2 frequency was injurious and resulted in yield depression in the third year. Tapping under d/3 frequency with stimulation resulted in high yield of 7382 kg/ha for three years.  Comparable yield could be achieved under d/ 4 frequency of tapping with appropriate stimulation. There was yield depression under weekly tapping  in the first two years.   In the third year, yield responses under weekly tapping  were comparable to those of d /3 and d /4 frequencies of tapping. The low yield under d/7 frequency of tapping in the newly opened trees can be overcome by increased frequency of stimulation.  Under d/7 frequency of tapping, maximum  response to stimulation  was observed when it was done between 48 - 72 h before tapping.   Thus the low frequency tapping systems including weekly tapping can be successfully adopted  in India without compromising production.

Field screening of 25 indigenous and exotic clones against powdery mildew(Oidium  heveae) was carried out for four consecutive years relying on natural disease incidence.  The phenotypic expression of symptom severity in terms of percent disease intensity (PDI) was used to compare the clones. The disease incidence of clones varied significantly in different years as evidenced by the significant clone x year interaction. Two methods viz., mean and CV of genotypes and Huhn's rank sum were used to identify the comparatively stable genotypes. The clones RRII 208 and PB 310 were found to have less disease intensity with greater stability over the years based on mean and CV. As per Huhn's  rank sum method, clones SCATC 93-114, RRIM 703, Hai Ken 1, RRII 208, RRII 5 and PB 310 were identified as stable sources of resistance.

The study analyses  the commercial realisation of the experimentally  proven  difference in the duration  of immature phase between polybagged plants and budded stumps of Hevea brasiliensis under smallholding conditions and its variations under different cultural practices. The database consisted of secondary information obtained from Rubber Plantation Development(RPD) files related to 1814 polybagged plant and 471 budded stump planted fields, collected from 23 regional offices of the Rubber Board located in Kerala, Tamil Nadu and Karnataka in India. The pattern of the adoption  of major cultural  practices in both categories was comparatively  assessed. On an average, polybagged  plant and budded  stump  planted fields reported a duration of immature phase of 6.99 and 7.19 years respectively and the difference (73 days) was statistically significant. However, it was found that the difference in duration of immature phase was not economically significant as fields of polybagged plants required an advantage of at least 150 days to realise an annuity  equivalent to that of budded  stump  planted fields. But an assumed 2.6 per cent higher yield in the former gave an annuity equivalent to that of the latter fields.  Hence the economic advantage of fields with polybagged plants may have to originate from the cumulative economic impact of shorter immature phase, lower vacancy, uniform establishment; higher tappability and higher yield rather than from shorter immaturity period alone.

The effect of titanium dioxide and its combinations with fillers such as china clay, precipitated calcium carbonate and barium sulphate at a low dosage on the physical properties and degradation resistance of latex thread prepared using conventional and efficient vulcanization systems were investigated.   Though titanium dioxide had little effect, its combination with fillers attributed better modulus and tensile strength to the thread samples.  Addition of titanium dioxide did not improve the degradation resistance of thread to heat and UV light. The combination of titanium dioxide with precipitated calcium carbonate showed better performance under photo oxidative ageing.

Effect of gibberellic acid(GA₃) on embryo induction and germination during somatic embryogenesis of Hevea brasiliensis with respect to clone RRII 105 was studied.  Immature anthers were inoculated on callus induction medium supplemented with 2, 4-dichlorophenoxyacetic acid (2,4-D) and kinetin(KIN) and the induced calli were then transferred to the embryo induction medium.  Incorporation of GA₃ up to 2.0 mg/l increased the embryo induction. Germination percentage was significantly enhanced by higher concentrations, however, further plant development was affected by increasing GA₃ levels. A reduction in response to both embryo induction and germination was observed by co-autoclaving of GA₃

New oil-dispersible fungicide formulations, mancozeb and its combination with copper oxychloride(COC) and  metalaxyl in combination with COC were field - tested  in different  locations  for the control  of abnormal leaf fall disease  of rubber  (Hevea brasiliensis) caused  by Phytophthora spp.  by aerial and  ground spraying. A powder formulation of mancozeb and a combination product of COC and metalaxyl (5 kg/ha) were found  to be as effective as COC (8 kg/ha). The new fungicides are useful alternatives for COC which has been continuously in use for about  four decades.