An efficient plant regeneration pathway through somatic embryo induction has been established in Hevea brasiliensis using root explants. In this experiment, actively growing roots of germinating somatic embryos were used as the initial explants. Different basal media viz. modified MS, white’s low salt base, N6 basal and woody plant medium fortified with growth regulators 2, 4-D, NAA, IBA and BA were tried at various stages of the pathway. Compact calli could be induced at a high frequency (80%) when root explants were cultured over modified MS containing 2.0 μM 2, 4, D and 1.0 μM Kinetin. Modified MS and WPM were found to be effective for induction of friable embryogenic calli. A combination of 4.35 μM GA3 and 8.8 μM BA was optimum for embryogenesis (50%). A plant regeneration frequency of 60 per cent could be achieved on modified WPM medium fortified with 2.9 μM GA3 and 8.8 μM BA. Regenerated plants were successfully hardened. This system is reproducible and efficient in terms of frequency of embryogenesis and plant development and can provide a constant supply of target tissues for genetic transformation, which now depend upon the seasonal availability of floral explants. Moreover, after appropriate modifications, this pathway can be utilized for propagation of elite root stocks identified for specific desirable characters.

In India, attempts are being made to expand rubber cultivation to agro-climatically less favourable regions also, where drought is the major constraint. Climate uncertainty and increasing drought are adversely affecting the establishment and growth of plants even in traditional regions. Objective of the present study was to develop a viable technology for mitigating adverse effects of drought in young rubber plants in dry areas. The effectiveness of super absorbent polymer, tillage and potassium (K) supplement was tested in a field experiment conducted at Puthukkad Estate, Trichur, which is a drought prone area during 2010-12. Three types of planting materials viz. polybag plants raised from green budded stumps, polybag plants raised through direct seeding and root trainer plants were evaluated. Observations on chlorophyll content index (CCI), soil moisture and plant growth were recorded. Plants which received super absorbent polymer, tillage and K supplement retained significantly higher CCI compared to control during dry period in January. Soil moisture status during dry period in January was significantly higher in the treatments with super absorbent polymer and tillage. Tillage and super absorbent polymer improved growth of plants during 2012. Polybag plants raised through direct seeding were significantly superior to polybag plants raised from budded stumps with respect to CCI and growth during both years and were superior to root trainer plants after two years. The results showed that tillage and super absorbent polymer are effective in mitigating adverse effects of drought in young rubber plants and polybag plants raised through direct seeding have a better performance in dry areas compared to the other two planting materials.

Canopy and tree architecture are important features determining both the tree-level and stand-level productivity of rubber and susceptibility towards wind damage in plantations. However, genetic base of crown architecture is less studied and is rarely utilized in tree improvement programmes. A natural mutant of Hevea brasiliensis showing distinct morphological variation in the crown was reported earlier. In the present study, genetic improvement of the compact canopy morphotypes was attempted through half-sib approach and selected progenies were subjected to field evaluation adopting recommended spacing. Girth and yield of four morphotypes (Compact: 12 cm, 5.5 g t-1t-1; intermediate: 81.0 cm, 28.3 g t-1t-1; semi compact: 46 cm, 17.2 g t-1t-1; normal: 76 cm, 25 g t-1t-1 and RRII 105-control: 64.2 cm, 45 g t-1t-1) showed significant variability while original natural mutant (compact) showed stunted growth and less yield. The mean canopy spread/width in the 5th year in RRII 105 and the normal type ranged from 4.6 to 5.5 m; whereas, the intermediate type had a canopy spread of 2.2 m only. The intermediate crown type can be considered more promising than the check clone in terms of extent of crown width though rubber yield (28 g t-1t-1) is less. Increase in plant density can compensate for lower yield and can also reduce the damage/tree loss in wind prone areas. This type could be subjected to further density cum clone evaluations to arrive at an optimum tree stand for profitable yield. Compact canopy genotypes not only avoid wind damage but also help the planters in getting enough room for optimal utilization of land.

Conventionally, cured coir pith is used as the potting medium to raise advanced planting materials of rubber in root trainers. An alternative potting medium suitable to fill root trainers was needed in areas where coir pith is not available. Top soil, which is the commonly used potting medium, was found not suitable for root trainer planting technique. However, properties of top soil as a potting medium was considerably improved when mixed with powdered cow dung up to 25 per cent by volume of the potting mixture. It was also found that fertility of coir pith could be improved by adding powdered cow dung up to 25 per cent by volume of the potting mixture, without much adverse impact on the consistency and compactness of the soil core.

Tapping panel dryness (TPD) is a serious problem of Para rubber tree (Hevea brasiliensis) causing significant losses in latex yield. The present study was conducted to assess heritability of TPD using a full-sib population planted in a small scale trial at Central Experimental Station, Chethackal (Pathanamthitta, Kerala). Symptom of TPD among the full-sibs was confirmed through tapping for two consecutive years. Narrow-sense heritability of TPD was estimated based on parent-offspring regression. There was considerable variation for TPD in the population. Incidence of TPD ranged from 3.6 per cent in clone PB 5/51 to 46.4 per cent in PB 235. Clone RRII 33 did not show any incidence of TPD. Progenies of PB 5/51 x RRII 208 showed minimum TPD incidence (3.6%) while those of RRIM 600 x PB 235 exhibited maximum incidence (29.6%). Progenies of RRIM 600 x RRII 33 did not exhibit TPD symptoms. The study showed high narrow-sense heritability (h2=0.50) for TPD. Progenies from hybridization between clones with very low TPD incidences (e.g. RRII 33) exhibited very low TPD incidences. Similarly, progenies from hybridization between clones with very high TPD (e.g. PB 235) possessed more TPD incidences. Overall, the study indicated that TPD may be governed by heritable gene action, which may possibly imply scope for achieving appreciable genetic gain through breeding for TPD tolerance.

under pineapple intercropping were compared with cover crop established plantations and natural forest. A total of 82 and 21 soil samples from rubber-pineapple intercropping system and rubber-cover crop system respectively were collected from surface layer (0-30 cm) of selected fields, including estates and small holdings in the central region of Kerala. Soil samples (15 nos.) were also collected from natural forest within the region of the study. Processed samples were analysed for pH, OC (%), available nutrients and phyto-available heavy metals such as Pb, Cd, Cr, Cu, Zn, Mn and Fe. Compared to soil under rubber-cover crop system, significant decrease in soil pH, available calcium and magnesium, and significant increase in available P and K were observed in soil under rubber-pineapple intercropping system. Phyto-available heavy metal status of the soils showed significantly higher cadmium and iron contents, and significantly lower lead, chromium, copper and manganese contents in rubber-pineapple intercropping system, compared to rubber-cover crop system. Comparison with soil under natural forest showed significantly lower pH and available calcium and magnesium, significantly higher copper content, and a build of available P in both the rubber based systems. Arsenic and mercury contents in soils of all the three systems were below detection limit.