A protocol was developed for long term maintenance of embryogenic callus aggregates induced from immature anther of Hevea brasiliensis, clone RRII 105. In H. brasiliensis, establishment of embryogenic callus is a long term process coupled with low frequency.  Maintenance of embryogenic callus cultures for prolonged duration in regenerable state is one of the important requirements for adopting the technique in genetic improvement of rubber.  In this study, factors influencing long term somatic embryogenesis including subculture interval and effects of proline and activated charcoal were examined.  Results showed that somatic embryo induction from embryogenic calli subcultured at an interval of 50 days was better than that at intervals of 25 and 75 days indicating that 50 day subculture cycle was more suitable for long term establishment. Addition of proline and activated charcoal at 100 mg L-1 and 0.1 per cent respectively improved embryo induction.  Genetic stability analysis did not reveal any variation in the RAPD banding pattern in short and long term cultures (eight and 36-months-old). Embryogenic callus aggregates maintained in the above medium retained their embryogenic potential even after 36 months.

Mapping the recent pattern of rubber area expansion in North East India through earth observation satellite data.  Rubber Science, 36(1): 14-27. Physiography, climate and soil play a crucial role in the growth and yield of natural rubber (Hevea brasiliensis). Tripura and Assam are the two major rubber producing states, which account for 88 per cent of total natural rubber production in North East India. In this study, the recent pattern of expansion of rubber area in Tripura and Assam according to elevation was monitored using Sentinel 2 satellite data as of 2021-2022 and high-resolution Cartosat I satellite data as of 2010-2011. In the last decade, rubber area had expanded substantially in both the states. Satellite derived spatial extent of rubber area in Tripura was estimated to be around 1,12,455 ha in 2021-2022. From 2010 to 2021, about 64,084 ha of rubber area were expanded in the state at a rate of 5826 ha year-1. In 2021-2022, there was 41,414 ha of rubber area in Assam, an expansion of about 24,544 ha compared to high-resolution estimates from 2010-2011, at 2231 ha year-1. Rubber area in these states expanded substantially to higher elevations between 2010 and 2021; around 77 per cent of the area expansion occurred between 50 and 100 m in Tripura and 55 per cent of area above 100 m in Assam. Assam showed considerable expansion of rubber area to higher elevations than Tripura.  Delineating the area by elevation is vital in order to select  rubber clones suitable for higher elevations as well as to predict yield in the newly expanded regions. Monitoring spatial and temporal expansion of the rubber area would also help to assess and develop plans for sustainable management of rubber plantations and monitoring land use changes. Rubber plantation expansion is promoted in the North-eastern states of India to increase domestic natural rubber production and enhance socio-economic status of people in the region. Geospatial datasets derived from the current study can help to monitor future changes in rubber plantation expansion in the North-eastern part of India. 

Corynespora leaf fall disease (CLFD) caused by the fungus Corynespora cassiicola is a major leaf disease of Hevea brasiliensis that severely affects its growth and yield.  The pathogen is genetically highly diverse, but there is no clear understanding regarding its pathogenicity.  A small glycosylated secreted protein called cassiicolin is thought to be an effector involved in the disease development process in most of the virulent isolates. The present study was aimed at identifying the virulence factors involved in CLFD in Hevea. 

The genome of a highly virulent C. cassiicola isolate (HV) from the rubber tree was sequenced and assembled. Sequence data was generated and gene prediction was performed.  The predicted genes were searched against the Database of Fungal Virulence Factors (DFVF).  One thousand and twenty six proteins of the organism matched against the database and two hundred and twenty nine proteins were classified as leaf spot-associated virulence factors. The genes predicted from the assembled whole genome were validated by RNA sequencing and transcriptome analysis.  The de novo transcriptome was assembled, and the transcripts were searched for homology against DFVF using Diamond tool with an e-value threshold of 0.00001. One thousand four hundred and twenty eight genes were annotated as virulence factors, of which five hundred and sixty five were classified as plant pathogen related.  The genomic and transcriptomic analysis revealed that the major virulence proteins were classified as leaf spot-associated virulence factors of the mapped genes, which are predominant in Corynespora leaf fall disease of rubber. 

The COVID-19 pandemic wreaked many threats to sustainability of both the global and Indian agricultural sectors. To assess the impact of COVID-19 pandemic on plantation management activities related to natural rubber production in Kerala, an online/telephonic survey was conducted among the rubber growers through a well-structured questionnaire with a series of questions related to agricultural practices adopted during the period 2020-2021. A total of 300 rubber growers were interviewed based on stratified sampling with Neyman allocation method. Results of the survey indicated that restrictions imposed during the pandemic induced lockdown and the resultant shortage of labourers affected the functioning of agricultural activities in rubber plantations. Substantial heterogeneity in the impact of lockdown was found in small and large holdings with regional variations.  During the initial few months of the pandemic, tapping was hindered in about 58 per cent of the smallholdings and in the entire large estates due to the unavailability of tappers.  The delay in other plantation management activities like rainguarding, weeding and spraying also contributed to considerable reduction in production. Huge hike in expenditure due to delayed replanting operations of rubber was also observed.  In order to overcome the negative impacts and to reduce the yield gap, both the small and the large growers modified agricultural operations in  their own rubber plantations. This study gives a valuable insight to the resilience of rubber growers in the state, amid disruptions and adversities. 

A polycross progeny population was evaluated in the drought-prone non-traditional region of Dapchari in Maharashtra. Initially, 4500 progenies were established, however, only 1853 progenies survived the successive drought seasons. The population was test-tapped when the progenies were three years old.  Based on test-tap yield and girth, promising progenies were identified.  The range of test-tap yield of the population varied from 0.00 to 42.5 g t-1 10 t-1 with a mean yield of 4 g t-1 10 t-1. Coefficient of variation for yield was 101.4 per cent, showing high heterogeneity for population yield. The population yield showed an R2 value of  0.441 on the population girth, showing a high dependency of population yield on the population girth, in the drought climate. Selected progenies from the population exhibited a high yield potential (0.9), low coefficient of variation (32%) and a less R2 value (0.252), which indicated that heterogeneity was less among the selections with high yield potential. Growth parameters such as girth, height and the number of leaves showed a normal distribution of the traits in the population.  However, the yield of the population revealed a highly skewed distribution of the trait.  Majority of the yield data points (1274 progenies) were oriented to the left and represented the low yielders and a few data points were distributed to the extreme right representing the high yielders. Hence, unlike the growth parameters, yield is a distinct quantitative trait, which warrants specific approaches for improvement.  Selection based on a large population is therefore one of the most important approaches in Hevea population improvement.  The selected progenies from the trial would be subjected to clonal multiplication and evaluation for identifying drought tolerant selections for the region.

Abnormal leaf fall (ALF) disease caused by Phytophthora spp. is considered to be the most destructive disease of rubber in India. Phenotypic and molecular methods were used for characterizing 30 Phytophthora isolates obtained from different geographical locations in Kerala over a period of three years.  Phenotypic parameters such as colony morphology, virulence, sporangial characteristics and metalaxyl fungicide sensitivity were studied. Phytophthora colony morphology revealed eight different types of mycelial growth patterns.  There was substantial variation in the sporangial morphology of the isolates.  The isolates were sensitive to metalaxyl fungicide. Among the RRII 400 series clones assessed, clone RRII 414 was found to be tolerant and RRII 429 susceptible. Amplification and sequencing of the internal transcribed spacer (ITS) regions of the Phytophthora isolates confirmed the pathogen as P. meadii. The isolates of P. meadii were clustered together in the phylogenetic tree, regardless of their geographic origins.