Somatic embryogenesis (SE) is an illustration of cellular totipotency, given that a single plant cell can regenerate into a complete and functional plant. Unlike organogenesis, SE is the most important in vitro pathway, having wide applications both in basic and applied research.  Among various stages, the developmental transition from somatic cell to embryogenic cell is the key step in SE.  This transitional reprogramming is influenced by various external and internal factors.  Although substantial progress has been made in understanding these factors for many plant species, the molecular mechanisms behind SE remain largely unknown. This review provides information on various factors influencing SE.  Moreover, a few embryogenesis specific genes, gene encoded proteins and enzymes and other stress factors recently identified have been discussed briefly. An overview of current progress made in woody plants SE mainly on potential genes is also highlighted. Research developments on SE in rubber with a focus on molecular innovations are also summarized. 

Global rubber cultivation is facing significant challenges due to root diseases that affect Hevea brasiliensis, commonly known as the rubber tree. Despite the negative impact of root diseases on tree health and latex yield, they often receive less attention than above-ground pests and diseases.  Fungal pathogens such as Rigidoporus lignosus, Ganoderma pseudoferreum and Phellinus noxius are major contributors to root diseases in rubber trees, causing white root rot, red root disease and brown root disease respectively. Managing these diseases is a difficult task due to the lack of disease-resistant plant varieties, the ability of pathogens to remain in the soil for long periods, environmental factors and limited effectiveness of control methods. To tackle these challenges, it is suggested to adopt integrated disease management strategies that combine cultural, biological and chemical approaches. Cultural practices such as optimal site selection and sanitation, biological control using beneficial microorganisms and botanical control utilizing plant extracts offer sustainable alternatives to chemical fungicides.  Although chemical control is commonly used, it should be integrated with other methods to minimize environmental impact and reduce the risk of resistance development.  Moreover, the adoption of integrated approaches, early disease detection and resistant cultivars are essential for long-term disease management and sustainable rubber cultivation. Policymakers play a crucial role in promoting sustainable practices through funding support, extension services and regulations that incentivize environmentally friendly approaches. Collaboration among stakeholders is crucial for knowledge exchange, innovation and collective action towards a resilient rubber industry.  Urgent action and collaboration are imperative to effectively manage root diseases, safeguard livelihoods and ensure sustainability of rubber cultivation.

Experimental clones in a central large scale trial (CLST, 2014) at Kottayam (Kerala, India) showed highly significant variation for leaf retention (LR) following incidence of abnormal leaf fall (ALF) disease caused by Phytophthora. Clone P 129 had the highest LR (88%) while P 073 showed the lowest LR (44%).  Investigation on leaf cuticle thickness of clones in the above trial showed that clones with very low ALF incidence had thicker leaf cuticle and vice versa. Another set of twenty five genotypes of Hevea spp. comprised of popular clones and pipeline clones of H. brasiliensis along with two other species viz. H. benthamiana and H. spruceana, which were assessed for leaf retention after ALF and their corresponding leaf cuticle thickness.  It was observed that genotypes with thicker leaf cuticle had low level of ALF disease incidence and vice versa conforming to the results obtained for clones in the CLST.  Regression analysis indicated a strong relationship between ALF disease and leaf cuticle thickness (R2=0.57). The above study indicated that thicker leaf cuticle possibly play a critical role in imparting high tolerance to ALF disease in Hevea which needs further confirmation using larger population of clones.

Developing drought tolerant high yielding clones is the way forward for expanding rubber cultivation to non-traditional areas, including dry sub-humid areas of India. The present study attempted to explore and utilize genetic variability among selected hybrid progenies of the 1996 HP (cross between high yielding (RRII 105) and drought tolerant (PB 280) clones and its reciprocal cross) and thereby to identify drought tolerant high yielding hybrid clones. Performance of the progenies was evaluated under a Clonal Nursery Experiment in a dry sub-humid area in Maharashtra, India. Forty trial clones along with nine control clones were evaluated both in the field as well as in the polybag grown plants.  Clones were evaluated for its growth and dry rubber yield during the peak yielding as well as summer seasons.  Chlorophyll index and other morphological parameters were also recorded and analyzed.  The study identified clones with superior yield as well as drought tolerance. Clones 114, 66, 117, 98, 59, 69, 29 and 78 were found to be promising and were selected for further evaluation. 

Twenty one clones of natural rubber (Hevea brasiliensis), RRII 105, RRII 208, RRII 300, RRII 351, RRII 352, RRII 357, RRII 51, RRII 5, RRIM 600, RRIM 701, GT 1, PB 310, PB 28/59, PR 255, PR 261, SCATC 88/13, SCATC 93/14, Haiken 1, RRIC 102, IRCA 109, IRCA 111 and polyclonal seedlings under different trial plantations at Kadalipal, Dhenkanal in Odisha state of eastern India were evaluated for wind damage and endurance. Parameters assessed were uprooting, trunk snapping and branch breakage.  The study indicated that periodic winds in the region caused higher number of branch breakage followed by uprooting and trunk snaping. Periodic winds usually occurred in April-May and resulted in visible damages.  Study showed that wind endurance varied among the clones.  Clones SCATC 93/14, Haiken 1, PB 310, PR 261, RRIC 102, IRCA 111, RRII 351, RRII 352 and polyclonal seedlings were broadly categorized as most wind-fast clones. Clones RRII 105, SCATC 88/13, IRCA 109, RRII 300, GT 1 and PR 255 were moderately tolerant clones. Clones PB 28/59, RRII 51, RRII 5, RRII 208, RRIM 600 and RRIM 701 were comparatively more susceptible to wind damage in the region. Initial plant vacancies, gaps in plantations, tall trees, heavy canopy, poor anchorage of trees in soil and strong winds coupled with rains seemed to be the major causes of wind damage. Form of wind damages and remedial measures to mitigate the damages is discussed in this paper. The present study found that wind damage is not of serious consequence and rubber can be cultivated successfully dry sub-humid region of Odisha.

Effect of conservation pits on growth and yield of natural rubber (Hevea brasiliensis) was examined for five consecutive years (2017-22) in the slopy lands of Tripura.  Influence of silt pits on soil properties was also studied. The experiment was carried out in a block design with 150 plants per block with 200 pits per ha. Pits were set in between row of plants in a staggered manner.  In an adjacent plot, a control block (without pits) was also maintained for comparison.  Trunk girth of the plants was measured periodically and annual yield data (kg ha-1 yr-1) of the plants were recorded.  The soils that were deposited in pits were excavated; their chemical properties were determined and compared with that of bulk soil.  Results showed a positive but non-significant improvement in mean trunk girth of the plants during the study period. However, a positive and significant increase in mean yield from second year of recording was observed due to construction of conservation pits.  It was also observed that about 3.98 to 5.42 mt soil ha-1 yr-1 was conserved in the pits, which prevented the loss through surface run off from the slopy lands. The study revealed that a considerable amount of nutrients was conserved, ranging from 21.6 to 31.5, 3.1 to 4.5 and 30.6 to 35.5 kg N, P and K ha-1 yr-1 respectively.  Similarly, an amount of 29.14 kg organic carbon and  216.2 kg clay ha-1 could be protected per annum from these slopy lands. Intercepting the surface water run­off into the pits could raise the soil moisture, particularly in the subsurface layer, which could prolong the moisture availability to plants for a longer period resulting in an increased latex flow from the plants in the block with conservation pits.