Twenty-two potential wild Hevea accessions along with three modern clones viz. RRII 105, RRIM 600 and RRII 208 were evaluated in the seventh to eleventh years of growth in the traditional rubber growing region of Kerala, India. Highly significant clonal differences were observed for yield and growth traits, except bole height. RO 2629 had the highest yield of 29.4 g t-1 t-1 followed by AC 716 (24.9 g t-1 t-1) and AC 4149 (23.6 g t-1 t-1), respectively. RO 2629 also had the highest girth, girth increment per year over four years and bole volume. The girth in the seventh year ranged from 26.9 cm (RO 287) to 47.8 cm (RO 2629); girth increment from 3.6 cm (RO 3804) to 6.7 cm (RO 2629); branching height from 2.2 m (RO 3804) to 3.1 m (MT 2233); wood quantity from 0.03 m3 (RO 3804) to 0.10 m3 (RO 2629). PCV was higher than the GCV for all the characters and the highest PCV was recorded for mean yield over two years. Heritability was also high for mean yield. Girth was significantly correlated with girth increment and wood quantity. RO 2629, MT 2233, AC 4149 and AC 626 ranked top with the maximum number of desirable traits. Having a different genetic background from the traditional Wickham clones, these accessions will serve to broaden the genetic base of present-day cultivated Hevea by introgression into the elite cultivars.

Twenty five phosphofungal isolates from rubber (Hevea brasiliensis) plantations were evaluated for solubilzation of ferric phosphate, aluminium phosphate, tricalcium phosphate fertilizer grade rock phosphate and acid phosphatase activity. Among the twenty five, seven isolates showed solubilization of phosphates and fertilizer grade rock phosphate and belonged to Aspergillus spp. and Penicillium spp. and was selected for further studies. These selected isolates were further evaluated for its beneficial effect on growth of rubber seedlings raised in root trainer cups. Among the seven, one isolate, Penicillium spp. (Pf 11) was further evaluated for growth improvement in root trainer plants in combination with 25, 50 and 100 per cent of the recommended dose of fertilizer and compared with uninoculated plants with 25, 50 and 100 per cent of fertilizer. The plants inoculated with Pf 11 at 50 per cent fertilizer showed higher girth, height and root development followed by inoculation with Pf 11 at 25 per cent fertilizer level. Girth of plants in treatment with Pf 11 at full fertilizer was lower than the treatment with 25 and 50 per cent fertilizer application in combination with inoculation. Highest population of inoculated phospho fungi was at 25 per cent fertilizer application and was reduced as the fertilizer levels increased. An efficient phosphofungus (Pencillium spp.) could be isolated from the rubber plantations and upon inoculation in rubber seedlings recorded better growth at 50 per cent of the recommended level of fertiliser.

Yield components like total volume and dry rubber content (DRC) of latex were analyzed in summer and peak yielding seasons in the renewed bark to assess the performance of RRII 400 series clones. Significant variations were observed among the clones under evaluation with regard to the parameters. RRII 414 and RRII 430 showed the highest total latex volume as well as dry rubber yield both in summer and peak yielding seasons when tapped in the renewed bark. Total latex volume was less irrespective of the clone during summer compared to peak season. Clones responded differently to summer stress. The drop in total latex volume during summer ranged from 39.5 to 64 per cent and 36.6 to 60.9 per cent in LST I and LST II,respectively. The highest drop in summer latex volume was recorded in clone RRII 430. When virgin and renewed panels were compared, the total volume of latex was less in renewed panel compared to virgin panel in both the LST’s barring very few exceptions. Status of clones with regard to latex volume, DRC and dry rubber yield in virgin panel (BO-1) and renewed panel (BI-1) were comparable in majority of the clones. The present study proved the superiority of RRII 430, RRII 417 and RRII 414 in the long run as well.

Devulcanisation of filled rubber vulcanisates through mechanical/ mechano-chemical processes in a tworoll mill is a well-established technique. The general mechanism of mechano-chemical devulcanisation suggests blocking of possible reunion of free radicals produced via crosslink scission. Hence the efficiency of shear induced devulcanisation processes can be improved significantly by the effective utilization of a chemical /process that can instantaneously block the reunion of the radicals formed by bond scission. A new concept of blocking the reunion free radicals formed by shear breaking of crosslinks using a stable free radical and thereby increasing the efficiency of devulcanisation is presented. A cyclic nitroxide stable free radical viz. 4-hydroxy 2, 2, 6, 6-tetramethylpiperidine 1-oxyl free radical (4-Hydroxy TEMPO abbreviated as 4HT) assisted mechanical devulcanisation of carbon black filled NR vulcanisates (un-aged and aged) in which 4HT was used to block the recombination of the radicals formed by bond scission.

Stable free radical increased the per cent devulcanisation and revulcanisate properties of devulcanised rubber in all cases under consideration. The recombining capacity of different type of cleaved crosslinks (mono-, di- and poly- sulphidic) were found to decisively influence the per cent devulcanisation of samples under shear induced devulcanisation. The influence of factors like cure system, crosslink density, the extent of ageing etc. of the original sample on the devulcanisation efficiency and the subsequent revulcanisate properties are discussed in detail.