Evaluation of ten ortet clones was carried out in a clonal nursery trial under dry sub-humid conditions of Odisha state in eastern region of India. The ortet clones were assessed for yield based on test tapping, girth and girth increment, bark thickness, first branching height and number of primary branches. Ortet clones O 3 and O 4 recorded high annual yield of 114.8 g t-1 10t-1 and 116.4 g t-1 10t-1 respectively over three years. On the basis of pooled yield, two ortet clones viz. O 3 and O 4 were found superior to RRIM 600, IRCA 111, SCATC 93-114 and comparable with RRII 208, the clone recommended for eastern India.  Five ortet clones viz. O 3, O 4, O 5, O 8 and O 10 had better girth and girth increment. Clones O 3, O 4 and O 10 recorded high bark thickness. Clones O 3, O 4 and O 8 recorded high branching height. Four ortet clones viz. O 3, O 4, O 7 and O 10 were found superior in terms of yield and growth.  These selections will be subjected to further large scale evaluation. 

Natural rubber cultivation in India faces adverse effects of drought and cold stresses in the non-traditional rubber growing areas. As genetically divergent germplasm accessions are an excellent repository of various stress tolerance traits, their systematic screening can help to identify potential accessions with intrinsic tolerance to abiotic stresses such as drought, temperature extremes etc. With this objective, a field evaluation of 33 Hevea clones comprising of wild Amazonian accessions and Wickham clones was initiated at Regional Research Station (RRS), Dapchari located in Maharashtra, experiencing high temperature, high light intensity and very low soil moisture during the summer months.  The check clones in the experiment were RRII 105, RRII 430, RRII 414, RRII 208, RRIM 600 and Tjir 1. Growth parameters such as annual girth and girth increment were recorded from the third year onwards. Based on empirical visual scoring on leaf yellowing and drying during summer period, potential drought tolerant clones were identified and they were further evaluated for in vivo leaf chlorophyll stability during the following summer. Based on per cent reduction in chlorophyll content the accessions were ranked for intrinsic tolerance.  Among the 20 tested, five tolerant and three susceptible accessions were again evaluated in polybags under controlled moisture stress condition and various drought related physiological parameters were monitored. A structural parameter viz. quantification of intra xylary phloem (IXP) from one-year-old twig samples was also evaluated for its usefulness to identify the potential accessions. These physiological and structural parameters were utilized to compare the actual field performance of these clones. Results indicated significant clonal differences leading to the selection of potential candidates towards the development of drought tolerant rubber clones.

Somatic embryogenesis and plant regeneration was achieved using leaf explants of Hevea brasiliensis clone RRII 105. Modified MS medium containing calcium nitrate [Ca(NO3)2.4H2O] and phytohormones was used for callus induction. The concentration of calcium nitrate was optimized for enhanced callus induction. Callus proliferation was carried out by sequential subculture (2-3 times) at an interval of 50 days in solidified proliferation medium. The combined effect of different concentrations of Ca(NO3)2.4H2O and sucrose in enhancing callus proliferation and texture improvement was studied. After proliferation, the callus was sub-cultured in embryo induction medium containing phytohormones and devoid of charcoal. Polyethylene glycol (MW 6000) was added to the above medium for providing osmotic stress. Compact friable calli, which developed in the medium containing PEG (5.0 g L-1) solidified with phytagel (3.5 g L-1), were transferred to the medium fortified with activated charcoal (2.0 g L-1) for embryogenic callus initiation. Osmotic stress was induced through addition of different concentrations of sucrose (30-80 g L-1) and PEG (5-10 g L-1). Induction of osmotic stress by addition of sucrose at 60 g L-1 and PEG at 8.0 g L-1 in the embryo induction medium containing phytohormones led to embryogenic calli initiation. Concentration of the solidifying agent phytagel (0.5%) for enhanced induction of embyogenic callus and somatic embryogenesis was also optimized. The present study reports embryogenic callus initiation induced by osmotic stress provided in the medium aiding somatic embryogenesis from leaf explants of Hevea brasiliensis. 

Effect of variable frequencies of yield stimulation on natural rubber (NR) yield under controlled upward tapping (CUT) system was evaluated using aged trees of clone RRIM 600.  The study was conducted in the Regional Research Station, Rubber Board, Dhenkanal, Odisha, located in a dry sub-humid region in India. The CUT system of tapping in panel HO-1 was compared with the downward normal tapping system S/2 d2 in base panel BI-1. A good response to stimulation on rubber yield was observed under CUT.  Yield in CUT was significantly higher than normal tapping under S/2 d2 tapping system with 70 to 110 per cent increase in CUT system. The highest rubber yield of 83.1 g t-1 t-1 was recorded in S/3.d2.6d/7.ET.5.0 % La 12/y following monthly stimulation. There was 39.5 to 64.0 per cent yield increase under CUT system in HO-1 panel when compared to BI-1 panel. The present study showed that CUT can be adopted to get higher rubber yield from aged rubber trees under dry sub-humid regions of Odisha.

Colletotrichum Leaf Disease (CLD) caused by Colletotrichum acutatum and C. gloeosporioides adversely affect commercial production of natural rubber. Repeated spraying with chemical fungicides to manage the disease pollutes the environment. Bioprospecting of fungal endophytes and their use as biocontrol agents is an effective alternative. Trichoderma spp. is a most promising biocontrol agent that produce antagonistic compounds effective in managing plant diseases. In this study, four sporulating Trichoderma spp. [T. koningii (R12), T. harzianum (L8), T. inhamatum (FX-T) and T. piluliferum (T1)] and a non-sporulating basidiomycete Rigidoporous vinctus (R17) were isolated from leaves and roots of two rubber clones viz. FX 516 and RRII 105 for evaluation of their potential as biocontrol agents against Colletotrichum spp. In the dual culture study, isolate L8 showed 90 and 84 per cent inhibition of radial growth (PIRG) against C. acutatum and C. gloeosporioides respectively followed by T1 which showed 88 PIRG with both C. acutatum and C. gloeosporioides. The isolate R12 showed 89 and 82 PIRG against C. acutatum and C. gloeosporioides respectively. As microbial consortia are more effective than the use of single organism, compatibility tests were conducted for isolate L8 with the other fungal isolates. L8 was compatible with T1, R12 and R17 and incompatible with FX-T. All five fungal isolates were fast growers and were identified based on morphological features.

The present study attempted preparation and evaluation of natural rubber (NR) samples from NR field latex with varying non-rubber compositions, derived through four different approaches. The approaches were designed in such a way that stage wise removal of different non-rubber constituents from the rubber phase could be achieved. The study assessed the role of fragmented and non-fragmented protein components and other non-proteinaceous non-rubber components both under complete retention and partial retention within the rubber phase and its effect on various technological properties of the rubber composites. Nitrogen content of the rubber samples subjected to the four different approaches varied from 0.57 to 0.90 per cent. The preparation of NR-HAF carbon black composites with the above rubber samples and evaluation of its cure behavior and technological properties were carried out. The thermo-oxidative ageing behavior of the corresponding NR composites was also evaluated. This study showed that the content of non-rubber constituents in NR has a significant role in improving the processability, determining the cure rate and cure state of the rubber compounds and influencing technological properties of rubber vulcanizates. Most remarkably, ageing resistance of the vulcanizates improved significantly with increasing content of proteins, both in its fragmented and non-fragmented states in NR.