Ten clones were evaluated in a large scale trial in Meghalaya, India. Parameters such as immature girth, girth at opening, mature girth, immature and mature girth increments, biomass, clear bole volume, survival and annual attrition rates of the trees, and the rubber yield were utilized to analyse the performance of clones in the trial. Opening girth was highest in PB 235 followed by RRIM 600, RRII 203 and RRII 118. After 35 years of the plantation establishment, among clonal trees that survived the long duration, the highest girth was exhibited in RRII 203 followed by PB 235, RRIM 600, RRII 118 and GT 1. Estimated biomass accumulation was also highest in RRII 203 followed by PB 235 and RRIM 600. High timber yield was also recorded in these clones. The average reduction in girth increment due to tapping was 39 per cent, and the minimum and the maximum were recorded in RRII 203 (35%) and RRII 105 (44%) respectively. The average girth increment of the clones over a period of 35 years was 3.1 cm annually, and the minimum and maximum values were recorded in RRII 105 (2.7 cm) and RRII 203 (3.6 cm) respectively. The survival rate was highest in RRIM 600 followed by RRII 203, PB 86, PB 235 and GT 1. The popular clone from the traditional region, RRII 105 showed poor performance with regard to growth and survival rate, although the yield was on par with RRIM 600. High attrition rate observed in the plantation showed that retaining a plantation for such a long duration as 35 years was not economically viable, although there were clonal variations. Based on reports from other regions including both the traditional and the non-traditional regions, RRII 203 is a clone well adapted to the stressful marginal climatic conditions in India showing performance comparable to the Malaysian clones RRIM 600 and PB 235 which are known for their performance in the marginal areas all over the rubber growing regions in the world. Adaptability of clones RRIM 600, RRII 203 and PB 235 coupled with better yield performance make them suitable for the marginal Indian conditions.

Establishment of vegetative hedges/biological bunds is one of the alternative measures to conserve soil and water. A field experiment to assess the effectiveness of different vegetative hedges for soil conservation in rubber plantation was initiated at Mundakayam Estate, Mundakayam, Kottayam district, Kerala (90 30’N latitude and 760 53’ E longitude) during the year 2009.  The average slope of the area was around 20 per cent and the average annual rain fall was 3000 mm.  The vegetative hedges evaluated were vetiver (Vetiveria zizanioides), guinea grass (Panicum maximum), pineapple (Ananas comosus) and Strobilanthes sp. in comparison with a control without hedge. A continuous terrace of width 150 cm was constructed for rubber plants and a single row of vegetative hedges was planted along the edge of the terrace across the slope.  The hedges were planted immediately after the planting of rubber and height of the hedges was maintained by regular pruning. Results of the study indicated that establishment of different types of hedges significantly reduced soil erosion up to the 4th year of the plantation.  Among the hedges, performance of vetiver was significantly superior and reduced 50 per cent of soil loss compared to control plots. Significant difference in growth of rubber was not observed in plots with and without vegetative hedges over a period of five years. Establishment of vegetative hedges provided a very effective means of terrace stabilization and retention. In control plots, 10 to 30 per cent reduction in width of the terrace was observed.  Comparative study on the initial establishment of hedges showed that the success rate of establishment was the highest in vetiver and pineapple followed by guinea grass and Strobilanthes sp. The comparative evaluation of soil organic carbon (SOC) stock of different conservation systems showed that vetiver was the only system which possessed significantly higher SOC stock (62 t ha-1) compared to all other systems. Considering the effectiveness of controlling soil erosion, terrace stabilization, success rate of establishment and soil carbon storage potential, vetiver was the best soil conservation measure in immature rubber plantations for sustaining soil and crop productivity.

Natural rubber (NR) plantation industry in India is facing constraints due to low rubber prices, spiraling cost of production and shortage of skilled tappers. Practice of Controlled Upward Tapping (CUT), is ideal under Indian conditions for assured sustainable rubber production from old and senile rubber trees. An experiment was conducted in the Experimental Farm Unit of Rubber Research Institute of India, Kottayam, Kerala to compare yield response of clone RRII 105 to Low Frequency Controlled Upward Tapping (LFCUT) under different panel change systems for eight years in the virgin bark of high panel above the renewed panels. Mean dry rubber yield over eight year’s period under d4 and d7 frequencies of LFCUT with periodic panel change was comparable to third daily tapping (d3).  Yield increase of 38 per cent was observed in the first year under d3 and d4 frequencies of high panel tapping over the basal renewed panel tapping.  However, considering the overall mean of eight years, yield increase of 11 per cent could be obtained under LFCUT over the basal panel tapping.  By adopting d4 and d7 frequencies of tapping, requirement of tapper can be reduced by 25 and 49 per cent respectively, compared to third daily tapping (d3), with the additional benefits of long term sustainable yield and longer economic life at reduced cost.

Natural rubber, with its center of origin in the Amazon rain forests of Brazil, is a strategic industrial crop cultivated mainly in the Southeast Asian countries.  To broaden the narrow genetic base of cultivated rubber in this region, a huge collection of wild germplasm was made from three states in Brazil viz. Acre (AC), Rondonia (RO) and Mato Grosso (MT) by the IRRDB in 1981, and distributed to member countries including India. Around 4500 accessions are now being conserved in nurseries in India and are under different stages of evaluation. In the present study, a set of thirty potential wild accessions and six modern clones viz. RRII 105, RRII 118, RRII 208, PB 260, GT 1 and Gl 1 were evaluated in detail in a replicated trial planted in 1996 in the non-traditional rubber growing region of Chhattisgarh state, India. The design adopted was simple lattice with two replications at the standard spacing of 4.9 x 4.9 m and plot size of 10.  The trial was located on plain land with similar soil nutrient status at Regional Research Sation at Sukma, Chhattisgarh state, India. Girth was recorded annually from the fourth year onwards.  Performance of these genotypes in terms of girth (9th year to 13th year), girth increment (GI) per year over five years, crotch height, bole volume, number of laticifer rows and yield (peak, summer, average of two seasons) was assessed.  Highly significant variability was observed for all these traits.  Yield was positively correlated with other growth traits. Based on this study, the wild accessions RO 5363 and RO 5430 were found to be superior for yield and growth in the drought stress region, which could be of use in future crop improvement programmes, particularly for stress-prone regions. 

In order to augment the narrow genetic base of cultivated rubber clones, IRRDB has made a collection of wild Hevea germplasm and distributed to its member countries after germplasm exploration in Brazilian rain forests during 1980s. Fifty-five wild accessions from three provenances of Brazil viz. Acre (AC), Rondonia (RO) and Mato Grosso (MT), were evaluated along with RRII 105 and RRIM 600 as nursery trial in the traditional rubber growing region of Kerala state, India. The genotypes exhibited highly significant clonal differences for all the growth and yield traits. The highest mean values noted for the traits at 6th year after planting were, girth of plant - 35.60 cm (RO 5432); annual girth increment (cm yr-1) over three years ­

5.47 cm (RO 5432); bark thickness - 5.30 mm (MT 4771); crotch height - 5.14 m (MT 4690); single leaf area ­

150.40 cm2 (RO 5365) and yield - 11.19 g t-1 t-1 (RO 5018). The genotypes were grouped into six clusters, indicating considerable genetic diversity in the population.  Clusters I, VI, II and III had highly potential genotypes which can be used for the development of high yielding clones and broadening the genetic base of the cultivated rubber. 

Mapping the distribution of weeds at local/regional levels help to monitor and assess changes in their distribution over decades and relate with changes in ecology of the region.  The data on the distribution of major weeds in rubber plantations of South India was collected through visual scoring in 10760 geo-referenced holdings and was mapped in GIS.  Axonopus compressus was the major weed in rubber plantations though regional variations were observed in occurrence.  Chromolaena odorata was also a major weed in the northern districts of Kerala viz. Trissur, Kannur, Kozhikode, Malappuram and Kasaragod, Dakshin Kannada district of Karnataka and Sindhudurg district of Maharashtra. Association between soil fertility status and weed distribution was observed and available calcium and magnesium status of the soil influenced weed distribution. The data gives an overall picture of the distribution of major weeds in rubber plantations of South India.