Hevea brasiliensis trees grown in two distinct agroclimatic regions (one experiencing drought and high temperature stress in summer and the other experiencing cold stress in winter, both concomi­tant with high PPFD) showed severe inhibition of photosynthesis during the unfavourable sea­sons. The degree of inhibition was so large at high light intensity that the upper canopy leaves of the stressed plants exposed to high PPFD fixed little carbon for most of the day. Photosynthesis rates were higher at lower PPFD, suggesting that the shaded leaves present inside the canopy were important in the overall carbon budget of the stressed plants. 
Inhibition of photosynthesis due to high PPFD was also evident in the decreased quantum yield of CO₂ assimilation and in vivo PSII activity in the stressed leaves. Pot culture studies showed that the inhibition in PSII activity was higher in the drought and cold stressed leaves than in their respective control leaves as indicated by the reductions in the maximum potential quantum yield (measured as the ratio of variable to maximum chlorophyll fluorescence, Fv /Fm in the dark adapted state) and the effective quantum yield of PSII, (ϕ_PSII' measured at a PPFD of 500 µmol/m²/s). This corroborated the high PPFD-dependent inhibition of photosynthesis observed in mature Hevea trees experiencing drought and cold stresses in the field. The activities of several anti-oxidant enzymes such as superoxide dismutase, peroxidase, catalase, ascorbate peroxidase and concentrations of antioxidants like total glutathione in the leaves indicated possible oxidative stress in mature Hevea trees experiencing drought and cold temperature stresses concomitant with high PPFD in the field. 

The use of silt pits (conservation pits) to conserve soil and water is a common practice in rubber plantations. The results of a field experiment to evaluate the effect of such pits on soil and moisture conservation and growth and yield of rubber are discussed. The experimental area was well drained with an average slope of 17-22 %. The treatments were conservation pits taken at the rate of 100, 150, 200 and 250 per ha with a no pit control. It was found that about 5-13 t/ha/year of soil was conserved and thus prevented from being eroded when the number of silt pits was increased from 100 to 250 per ha. The quantity of nutrients conserved ranged from 13-34, 7-18 and 9-25 kg/ha of N, P and K respectively. The data on quantity of soil deposited in the observation pits taken at the lower most part of the field indicated that when the number of pits was increased, the quantity of soil lost was considerably reduced. The plant response in terms of growth and yield for a period of 18 months did not indicate any significant difference between the treatments. The effect of silt pits on soil and leaf nutrient status is also discussed. 

A study was conducted to understand the yield performance of trees grown from polycross seeds of rubber in the North Konkan region of Western India, which has a subhumid type climate with high temperature and soil moisture deficits in summer as the major constraints for the growth and productivity of the crop. Data on rubber yields collected on each tapping day from two blocks of trees formed the basic data from which monthly, seasonal and annual yields were calculated. Popu­lation characteristics like frequency distribution of various yield classes and the yield contribu­tions of tree groups categorized on the basis of yield levels were worked out. Monthly block yields increased gradually with the onset of monsoon, peaked after the monsoon, sustained up to Decem­ber and declined thereafter. Contribution of post-monsoon season to total yield was about 52 to 58% while that of monsoon and dry seasons were almost similar with 21 to 24%. Yield level cat­egory tallying classified 68% of the trees as low, 20% as medium and 6% as high yielders. Contri­bution in yield of the trees to the total was 49, 24, 11 and 16% respectively. Mean annual yield of about 800 kg/ha/annum (with a range of 610 to 998 kg) over seven years of tapping was compa­rable with that in the traditional region. The study indicated that though North Konkan experi­ences a long rainless period with more than three months of high temperature and drought condi­tions, rubber cultivation may be viable under judicious agromanagement practices. 

The available information on intraclonal variations of Hevea clones is based on CV alone, which is not sufficient to attribute such variations to the heterogeneity of root stock. A study was conducted to examine the magnitude of intraclonal variations in 13 Hevea clones with respect to juvenile yield and girth and 'b' values computed to examine the influence of heterogeneous root stock on such variations. Variability was low for girth while it was comparatively higher for test tap yield. High 'b' values for girth and yield indicated high genetic involvement for the intraclonal variations, which should be due to stock-scion interaction. The study revealed differential sensitivity of the clones to foreign stock. The scope of identification and utilization of stock sensitivity of clones for generating desirable variability, within a clone, for the improvement in growth and productivity is discussed. The advantages of stock sensitivity in reducing the detrimental effect of monoculture and its influence on character associations are also discussed. The need for more work to compare the magnitude of variability among seedling populations and the variability generated by stock­-scion interaction in clonal populations of rubber is suggested. 

Thonningia sanguinea Vahl. was observed to develop tyloses internally, as a result of intrusion of the host Hevea brasiliensis into its tissues. The tissues were also squeezed and xylem cells split off into strands. At the point of contact between T. sanguinea and the host plant, enlarged tissues (galls) developed. Ecologically, the plant is hazardous to rubber as it dominates the plantation floor. 

Clonal variations were observed in pollen germination studies of six clones of Hevea Brasiliensis viz. RRII 118, RRIM 600, PB 235, PB 255, PB 280 and KRS 128 for pollen size, stainability, germination percentage, mode of germination, pollen tube length and breadth. Largest pollen was observed in PB 255 (40.63 x 31.82 µm) and smallest in KRS 128 (37.35 x 30.75 µm). The highest pollen stainabil­ity (92.74%) and germination (51.19%) was recorded in RRII 118. The lowest germination was noticed in PB 280 (25.73%), which also registered the maximum pollen tube length (165.23 µm). The highest pollen tube breadth was observed in PB 255 (13.24 µm). Several abnormalities such as de­formed pollen tube growth, development of more than one tube from a single pore and pollen tube branching were noticed in the clones PB 280 and KRS 128.