Rubber is an important industrial commodity for the world.  Hevea brasiliensis is the only commercial source of natural rubber and more than 90 per cent of cultivation is limited to South and South East Asia due to its limited geographic and climatic range. History of Hevea cultivation in Sri Lanka dates back to the year 1876. Starting from unselected Wickham genetic material, progressive breeding and selection over a century incorporating also non-Wickham material, great strides in breeding have been made in the field. Until 1920’s, no significant progress had been made in genetic improvement of preliminary material.  But with the introduction of successful bud grafting techniques in 1918, selection of clones became possible and the clones Mil 3/2, Hil 28 and Wag 6278 were developed from selected  seedlings in commercial estates by the early 1930’s.  Their yield potential ranged from 300-440 kg ha-1 yr-1.  With development of Hevea hybridization techniques by this time, the breeding programme progressed significantly.  Today, genetically improved planting material has resulted in the development of clones with a yield potential of 3,500 kg ha-1 yr-1 under commercial conditions. This is more than a ten-fold increase in rubber yield, since the introduction of Hevea breeding programme in Sri Lanka. The approaches breeding with multiple breeding objectives are discussed in six phases. The clone recommendation has been revised from time to time with achievements in development of new clones over the years. 

Four exotic rubber clones from Prang Besar (PB) estate, Malaysia viz. PB 255, PB 280, PB 312 and PB 314 were introduced to India in 1985. Their suitability for cultivation in the country was under evaluation in various field trials initiated during the period 1988-1996. Six on-station trials were laid out across the traditional rubber growing tract of India including three field trials in Kerala state, two in Hevea Breeding Sub Station (HBSS), Nettana, in South Karnataka and one in Hevea Breeding Sub Station, Keeriparai, in Kanyakumari district of Tamil Nadu. On-Farm Trial (OFT) of these clones were also undertaken in large estates in four locations. Based on the superiority in early performance over the high yielding check clone RRII 105, all the four clones were upgraded to the Category II of the planting recommendation during 2009. The present paper reports the long term performance from 10 field trials over a period of 25 years with a view to upgrading these clones to Category I and to reveal their region specificity before release to the farmers.

The smallholding sector of Kerala which is still the prime contributor to the national rubber production is under severe crisis due to shortage of rubber tappers and declining profitability.  The sector has become incapable to attract new entrants for tapping as wage income of tappers is much lower than their counterparts in the rural labour market. In the present scenario, the sector is incapacitated to augment wage income of the tappers for the existence of structural bottlenecks such as smaller size of holdings, less number of trees available for tapping, piece rate wage payment system and prevalence of single grower dependence.  To attract more tappers into the sector by increasing the wage income of tappers by circumventing these structural bottlenecks, collective farming following the principles of collectivism is proposed.  Collectivism will not only help the tappers to get regular employment, sufficient tapping task and remunerative wage income, it would also have the added advantage of bringing down the cost of production and increasing profitability of natural rubber cultivation as it would facilitate large scale adoption of cost saving technologies like low frequency tapping. 

Hybrid clones evolved from specific cross combinations were evaluated in a small scale trial in the traditional rubber growing region of Kerala. Girth attained by the hybrid clones in the early immature period, girth at the opening of the trial and girth during tapping were analysed.  Hybrids such as 94/23, 94/44, 94/50, 94/90 were high girthing clones.  Yield of clones in the BO-1 panel, BO-2 panel and the overall yield over nine years of tapping were estimated.  The highest yield was recorded in 94/50 (69.8 g t-1 t-1) followed by 94/23 and 94/44 (69.1 g t-1 t-1 each) and 94/101 (64.1 g t-1 t-1). Three of these hybrids also showed high girth at opening (94/23, 94/44, 94/50). Girth at opening exhibited significant positive correlation with yield in different panels and with yield over nine years whereas the early immature girth did not show significant correlation with the later yield of the clones. Four clones viz. 94/50, 94/23, 94/44 and 94/101 were selected for their yield performance. Two of the high yielding clones (94/44 and 94/50) were evolved from the family RRIM 600 x RRIC 52 meanwhile the highest girthing clone (94/23) was from the family RRII 105 x PB 86, and this clone was also one of the clones selected for yield.  Distinct seasonal yield difference was recorded.  February to May stood for the lean yield season and June to January represented the peak yield season. August to October could sustain the longest period of higher yields at the rate of 60.0 g t-1 t-1. July to December was the season with the highest production potential. High variability and heritability was recorded for yield, whereas, low variability and moderate to high heritability was recorded for girth.  Hybrid clones 94/23, 94/44, 94/50 and 94/101 are potential clones for further evaluations. 

A cropping system experiment was conducted with variety of annual and short duration intercrops (upland rice, okra, cowpea, maize, amaranthus, colocasia, elephant foot yam, pineapple and banana) under rubber for entire immaturity period. Two different planting geometries were employed in such a way that the number of rubber per ha remained almost similar (440 and 445 ha-1) In the first model, rubber was planted in paired rows of 9.0 m apart. The distance within the paired row was 5.0 m.  In the second model, rectangular system of planting (6.7 m x 3.4 m) was followed.  Among the annual vegetable intercrops tried, cowpea performed better with an average Benefit Cost Ratio (BCR) of 2.02.  Upland rice/Jhum rice also performed well with a BCR of 1.82 in the first year of intercropping under immature rubber. Maize also yielded well with a BCR of 1.89.  Among all the annual intercrops, the average BCR proved to be highest (3.29) for colocasia. Among the short term crops, the average BCR for banana was 2.69 and for pineapple it was 2.20. Among the forest species planted in the boundary the girth of acacia (44.3 cm) was significantly higher than gamhari (34.7 cm) eight years after planting of rubber.  Fodder grass (signal grass) grown in a single row along the boundary also performed well and the total yield was 252 kg in two cuttings from 300 m row.  It was also found that modified paired row system of planting is a workable alternative for the grower who wants to cultivate intercrops for the entire immaturity period.  An assessment of the system also indicated sustainability in terms of soil fertility maintenance. Moreover, the mean girth of rubber was found statistically comparable for monocropping and intercropping area in both the Models. 

Ten hybrid clones, including five new generation clones of RRII 400 series were evaluated in a large scale trial in the Dooars area of Sub–Himalayan West Bengal over a period of 24 years.  Overall performance in terms of growth during 23 years after planting and dry rubber yield over 16 years of tapping was assessed. RRII 176 recorded the highest girth (84.1cm) and biomass (591 kg tree-1). RRII 429 and RRII 203 were the second best clones with a girth of more than 80cm indicating the growth adaptability of these three clones under the cold stress conditions of Northern West Bengal. Highly significant clonal variation was observed for dry rubber yield. RRII 429 was the highest yielder during the entire tapping duration of 16 years with a mean yield of 61.1 g t-1 t-1 followed by RRII 417 (54.2 g t-1 t-1) and the yields of these two clones were significantly superior to the check clone RRIM 600 (40.5 g t-1 t-1). The pre-winter yield of these two clones was 123.8 g t-1 t-1 and 110.1 g t-1 t-1, respectively. RRII 422 and RRII 430 were the other two clones with annual yield more than 50 gt-1 t-1 and comparable to RRIM 600. RRII 414 showed the lowest yield in the trial. RRII 429 which recorded high tree stand, sustainable growth and 50 per cent yield improvement over RRIM 600 under the prevailing chilling stress conditions is the best suited clone for the region.