Two hundred and ten soil samples were collected from the rubber growing areas of Assam, Meghalaya and Tripura. DTPA extractable cations were estimated and their relations with different physico-chemical properties of the soils were studied. Soils varied from sandy loam to clay loam in texture, extreme to moderately acidic in reaction (pH: 3.9 to 6.1) and medium to high organic carbon content (5.50 to 22.50 mg kg-1). Cation exchange capacity of the soil samples ranged from 4.52 to 17.45 cmol (p+) kg-1. DTPA extractable Fe, Mn, Zn and Cu content of the soil samples ranged from 41 to 308 (mean 160.5), 6.1 to 72.0 (mean 29.1), 0.13 to 2.86 (mean 0.84) and 0.50 to 2.46 (mean 1.47) mg kg-1 of soil, respectively. Based on the prescribed critical limit, all the samples were sufficient in DTPA-Fe and Mn. Cu deficiency was observed in 4.11 per cent of the total soil samples collected. About 29 per cent of the soil samples were deficient in DTPA-Zn. Hill Zone of Assam recorded the highest (33.6%) and Garo Hills of Meghalaya recorded the lowest (21.65%) number of Zn-deficient samples. Organic carbon and clay content of the soils were positively and significantly correlated with the DTPA-extractable micronutrients and contributed significant variations towards their availability.

Forty two ortets selected from a large estate in Central Kerala were evaluated during the first five years under tapping in a smallscale trial. The parameters evaluated include yield, girth and timber attributes. Eight promising primary clones were selected from the estate. Three top ranking clones viz. Cy O 48, Cy O 41 and Cy O 35 recorded a mean yield of 67.7, 64.3 and 60.4 g t-1t-1, respectively and they were significantly superior in yield to that of RRII 105 with above average bole volume. Among these, Cy O 48 was the most promising selection in terms of yield, vigour and bole volume. Three ortets noted for high yield and high girth increment rate on tapping were Cy O 31, Cy O 43 and Cy O 48. The superiority of ortets with respect to yield and secondary characters is discussed in detail, giving emphasis to the eight final selections based on rubber yield.

Soil samples collected at two depths (0-30 and 30-60 cm) from the rubber growing areas of Meghalaya were analysed for available nutrient status. The organic carbon (OC) content ranged from 5.7 to 21.6 g kg-1 and the mean value was 11.7 g kg-1. Highest OC content was recorded in West Garo Hills and lowest in South Garo Hills. In the entire Meghalaya state, 79.40 per cent of soil samples were recorded OC content in the medium range. The nutrient index value for organic carbon for the state as a whole was 1.99 indicating medium range of organic carbon status. Available phosphorus (P) was very low for all the districts and the lowest in South Garo Hills (1.79 kg ha-1). Majority of the samples from all the districts where rubber is cultivated have shown low available and nutrient index values ranged from 1.00 to 1.02 and the fertility rating for available was low for the entire rubber growing areas of Meghalaya state. Wide variation in available potassium (K) content of the rubber growing soils of Meghalaya was observed. The available K ranged from 91.8 to 318.1 kg ha-1 and the mean available K was 167.8 kg ha-1. Nutrient index values for available K ranged from 1.92 to 2.10. Fertility rating for available K content was found to be medium for the entire rubber growing soils of Meghalaya. The soil pH ranged from extremely acidic (3.97) to moderately acid (pH 5.41) and 64 per cent soil samples recorded pH between 4.5 to 5.0.

Growth performance of high yielding RRII 400 series clones of rubber (Hevea brasiliensis) viz. RRII 417, RRII 429 and RRII 430 with RRIM 600 as the check clone, was studied during 2004-2011 under the agro-climatic conditions of Tripura. Influence of higher doses of NPK fertilizers on growth of these clones during immature phase of plantation was also investigated. At the end of the seventh year of planting, the clone RRII 429 registered highest girth (51.5 cm) followed by RRIM 600 (49.6 cm) and the clone RRII 417 (47 cm) was the lowest. Highest tappability was observed for the clone RRII 429 (67.1%), while on other three clones it ranged from 47.7 to 60.1 per cent. The clone RRII 429 showed significant response towards application of NPK fertilizers. At the end of sixth year of planting, the clone RRII 429 registered a mean girth of 50.6 cm and 73.3 per cent plants attained tappable girth when 150 per cent of recommended NPK doses were applied. The other three clones required seven years or more to attain a mean girth of 50 cm and 70 per cent tappability. The result showed that immaturity period of RRII 429 could be reduced by six months to one year by applying higher doses of NPK. Application of higher doses of NPK fertilizers in soils showed a significant improvement in organic carbon (OC) and available phosphorus, particularly in the surface layer; however a gradual decline in available potassium-balance was recorded in rubber soils indicating potassium vulnerability of soils under rubber in Tripura.

In Hevea brasiliensis, latex is produced in the laticiferous tissue present in the secondary phloem or bark. Sieve tubes and companion cells are the other two important components of secondary phloem tissue with the main function of sap conduction. In this context the transportation of metabolites through the sieve elements have great significance in terms of latex synthesis taking place in the laticifers. Ten different clones of H. brasiliensis were selected to study the clonal variability in the distribution pattern of sieve tubes, companion cells and dimensional variation of sieve tubes. The sieve elements were identified as enucleated elongated cells placed end to end in the longitudinal axis of the stem. Sieve plates were obliquely arranged at the end of the sieve elements. Occurrence of one or two companion cells, in close association with sieve tubes, implies its functional relationship with the counterpart. Sharing common companion cells among two sieve elements within a row was noteworthy. Considerable clonal variation in sieve tube length was noticed. The maximum length of sieve tube was recorded in the clone PB 235 and minimum in RRIM 703. The maximum diameter of sieve tube was recorded in PB 86. The analysis of variance indicated that the length of sieve tubes exhibited considerable variation between Hevea clones but less variability within clones. Characteristically PB clones showed superiority of over other clones under study for the dimension of sieve tubes. The dimensional variation of sieve tubes in the bark tissue can be considered as a marker for the identification of clonal variability and yield potential of Hevea clones.

Phytophthora meadii and Corynespora cassiicola cause severe leaf infection leading to leaf fall in Hevea brasiliensis. At present, growers resort to spraying of chemical fungicides to control these pathogens in rubber plantations. Biocontrol measures are not yet practiced for the management of these diseases in rubber plantations as they were not proved effective. In this study, isolation and selection of endophytic bacteria ware made from rubber that exhibit significant antifungal activity against these two fungal pathogens. A total of 154 bacterial isolates were collected from leaves, petioles, barks and tender stems of three Hevea clones, viz. RRII 105, GT 1 and RRIM 600. These isolates were screened for in vitro antagonistic activity against the two pathogens. Isolates showing more than 3 cm inhibition zone on the growth of pathogens in dual culturing were selected. These antagonists produced antipathogenic volatile compounds and siderophores. In vitro salicylic acid production by the antagonistic bacteria was also estimated. Seven isolates showing more antagonism and production of antifungal metabolites were selected for further studies. Bioassay using the detached leaves of endophyte treated plants showed reduction in lesion size upon inoculation with the pathogens. The inoculated plants also showed increase in PR proteins - chitinase, peroxidase and phenylalanine ammonia lyase activity that give systemic resistance to plants. Antagonistic isolates were identified as Bacillus spp. by 16S rDNA sequencing.