Indian rubber industry is a major contributor to the country’s manufacturing GDP and national economy, including earning significant foreign exchange through export of rubber products that was close to US$ 2.5 billion during 2016-17. Natural rubber (NR) has a dominant role in the Indian rubber industry as it constitutes nearly 65 per cent of the total amount of rubber the industry consumes. In recent years, NR production has been declining in the country largly as a result of growers abstaining from tapping the trees because of nonremunerative price. Despite its declining domestic production, NR consumption continued to grow, albeit at lower rates, with substantial imports of NR. There are indications that Indian rubber industry may be losing its momentum and its contributions to the economy are on the decline in recent years even as the industry started to become overly dependent on imported NR. There are structural changes happening to the rubber sectors of major NR exporting countries and seamless availability of cheap NR in the international market cannot be taken for granted forever. Indian rubber industry is too important for the country to be left to the uncertainties and vagaries of NR supply in the global market in the long run. With the current per capita NR consumption in India one of the lowest in similar economies, the country will require unhindered supply of this critical raw material in increasing amounts for the continued growth of Indian rubber industry. Over-dependence of the Indian rubber industry on imported NR may pose serious challenges to its sustainable growth and competitiveness. The longer the present decline in domestic NR production continues, the more difficult it will be to reverse the trend because of the long gestation period and the perennial nature of this tree crop. Therefore, proactive steps to consolidate the domestic NR production base with adequate public investments are urgently required to ensure sustained domestic supply of NR to the Indian rubber industry.

Hundred and ten hybrid clones evolved from the 1983 hybridization programme and five ortets which were selections from GG1 polyclonal seedlings planted at the Central Experimental Station of Rubber Research Institute of India (RRII) were evaluated over five years of tapping in seven small scale trials laid out in the farms of Kerala Agricultural University, Vellanikkara campus, Thrissur. The performance of these clones with respect to rubber yield, timber yield, summer yield depression, girth at opening and girth increment rate at immaturity and under tapping in comparison to the high yielding check clone RRII 105 is presented. A total of 22 promising clones could be identified from this population. Of these, 11 clones exhibited high rubber yield of which nine were dual purpose latex-timber clones (83/24, 83/35, 83/29, 83/173, 2/372, 83/191, 83/17, 83/224 and 83/234). Four of the latex-timber clones were from the cross RRIM 600 x Gl 1, two belonged to the cross GT 1 x RRII 105, two were ortets selected from GG1 polycross trees and one belong to the cross PB 5/51 x RRII 105. Based on the criterion of timber yield, 11 clones exhibited very good timber yield of > 0.2 m3 tree-1 at the age of 20 years (83/31, 83/8, 83/12, 83/60, 83/111, 83/117, 83/120, 2/185, 83/19, 83/11 and 83/37) of which two clones had rubber yield on par with RRII 105, eligible to be designated as timber-latex clones (83/37 and 83/11). Among the 115 clones evaluated, the recovery of high rubber yielders was 10 per cent and high timber yielders was 11 per cent.

Yield data for 12 years was analyzed from a 25 year old polyclonal Hevea brasiliensis population consisting of 284 seedling trees in experiment 1. Based on yield profile, trees were categorized into 10 groups and latex [ATP] was analyzed over two years and its correlation with yield was estimated. High yielding groups showed high yield in all seasons and all the years compared to low yielders. It was observed that mean yield over 12 years was positively correlated with girth (r=0.55**) and crop efficiency (yield per cm of tapping cut) (r= 0.85**). Latex ATP concentration had significant positive correlation with mean seasonal yield and annual yield in the two years in which ATP estimation was done, as well as with the mean yield over twelve years. In the second experiment which was a replicated trial consisting of eleven ortets (selected from experiment 1), latex ATP concentration was positively correlated with the yield of the genotypes, though not significant, possibly due to low coefficient of variation in the selected population. Latex ATP concentration had significant positive correlation with crop efficiency of polyclonal population (r=0.76**) and selected genotypes (r=0.61*). ATP concentration in latex is an indicator of high yield potential of rubber trees and can be utilized as a marker for selection of high yielders in the north- eastern region of India.

The possibility of establishing perennial intercrops like cocoa and coffee in mature rubber plantation and its effects on growth and yield of rubber and physico-chemical properties of the soil were studied in a field experiment conducted in a small holding in Kerala representing the central traditional rubber growing tract in India. The treatments comprised two varieties of coffee (Robusta and C x R) and cocoa inter-planted in mature rubber (clone RRII 105) in combination with two doses of fertilizers viz. 100 and 50 per cent of the recommended dose for the intercrops. Coffee and cocoa were established well and started yielding by the third year. Growth and yield of rubber were not influenced by interplanting coffee and cocoa. Intercropping improved the fertility of the soil by maintaining a higher N and P status compared to monoculture field. The intercropped fields retained higher soil moisture status both at the surface and subsurface layers and recorded low soil bulk density. Yield of coffee ranged from 30-36 per cent of that of monoculture where as that of cocoa ranged from 40-56 per cent. The study suggests that cocoa is a potential intercrop for mature rubber under tapping. Conversion of existing monoculture rubber plantations to such diversified and sustainable cropping systems assumes importance in the current context of sharp decline in rubber prices and environmental challenges.

Evaluation and selection of eighty Amazonian wild germplasm accessions of Hevea brasiliensis was done in the mature growth phase aiming to select potential accessions based on growth, rubber yield, timber yield, latex biochemical parameters pertaining to yield and field tolerance to Phytophthora leaf disease. The accessions represented three provenances of the centre of diversity in Brazil viz. Acre, Rondonia and Mato Grosso. Four accessions (MT 1032, MT 941, MT 1630, MT 915) exhibited significantly high growth performance during three consecutive years of growth (14th, 15th & 16th years) in terms of tree girth. Four accessions (AC 166, AC 2004, RO 2385, and RO 2908) were identified with respect to high dry rubber yield during the 6th, 7th and 8th year of tapping. Ten potential accessions identified for timber yield have been included in the breeding pool for developing timber-latex clones. Estimation of biochemical parameters in latex (ATP, sucrose and thiols) in eight high yielding and five low yielding accessions along with the check clone RRII 105 revealed that two accessions, AC 166 and AC 2004 (high yielders) possessed high ATP content in latex similar to RRII 105 pointing to the role of latex ATP content in determining yield in rubber clones. Thiol content in latex was also high in AC 2004. Per cent leaf retention after the disease season indicated that accession MT 922 had the highest leaf retention (82.9%) followed by MT 999 (76.7%) indicating their disease tolerance potential whereas it was only 60.0 per cent in the susceptible clone RRII 105. The selected accessions have been included in W x A hybridization programme for generating new recombinants in future.

The study comprehensively analyses the recommendation of various natural rubber (NR) clones over the years for the north-eastern region of India. It also evaluates the yield realized by the small NR growers of Tripura state where RRIM 600 occupies more than three-fourth of the area under NR cultivation in Tripura. The average yield of RRIM 600 was 1490 kg ha-1 year-1 over 22 years of tapping in small grovers’ fields in Tripura. This was higher than yields realised by the estate sector for the same clone in the traditional rubber growing region in India.