Most parts of the traditional natural rubber growing regions of India, extending from Kanyakumari district in the south to Kasaragod district in the north received excess and prolonged rains during 2013. This led to severe incidence of Abnormal Leaf Fall (ALF) disease caused by the fungus, Phytophthora sp. We demonstrate here for the first time the use of satellite-based remote sensing technique to monitor LAI in natural rubber holdings in real time. Leaf retention was monitored every month between April and December 2013 using real time satellite-based remote sensing measurements from rubber holdings spread across all districts in the traditional rubber growing region of the country that were earlier mapped using satellite imageries. Corresponding LAI data for 2012 was also similarly estimated from satellite data. It was found that as the monsoon advanced, LAI decreased substantially in both years, but the reduction was much more substantial and prolonged in many districts during 2013 than 2012, reflecting increased leaf fall due to ALF disease in 2013. The decline was more pronounced in central and northern Kerala than in the south. Kanyakumari district is generally known to be free from ALF disease, but there was considerable leaf loss due to ALF in June 2012 and June and July 2013 even as the monsoon was unusually severe in 2013. Weighted mean LAI for the entire period of April to December was estimated based on LAI and per cent of total area under rubber in each district for the two years. This was markedly less in 2013 than 2012. The implications of poor leaf retention for biomass production (net primary productivity), carbon sequestration and rubber yield are discussed.

Drought assessment and monitoring are important in the management of a crop particularly in the context of global warming and climate change. Rubber being a perennial crop goes through periods of moisture deficits during different phases of its growth. Real or near real time drought monitoring is required for adopting proper management strategies to mitigate the adverse effects of drought. Satellite-based remote sensing techniques are increasingly becoming handy in assessing and monitoring drought in many crops. Severe drought during the summer season results in appreciable reduction in growth and yield in natural rubber. In the present study, an attempt has been made to identify the spatial extent of agricultural drought stress in natural rubber plantations of Kerala and Kanyakumari district of Tamil Nadu using satellite based remote sensing data and GIS. By combining remotely sensed land surface reflectance and thermal properties from Terra MODIS, changes in land surface temperature (LST) and Normalized Difference Vegetation Index (NDVI) over a region is estimated. Vegetation Temperature Condition Index (VTCI), derived from the association between NDVI and LST gives an estimate of the temperature status of the vegetation for a given NDVI which is an indirect reflection of the soil moisture status. Our results indicate that VTCI is a powerful proxy estimate of the drought stress rubber plantations experience during peak summer season in Kerala and Kanyakumari district of Tamil Nadu.

The presently cultivated clones of Hevea brasiliensis represent only a very small gene pool. Considering the urgent need for broadening the narrow genetic base of Hevea, the wild germplasm collected through the 1981 IRRDB expedition from the three states of Acre, Rondonia and Mato Grosso of Brazil needs to be utilized for further improvement of the crop. Eighty seven accessions belonging to the 1981 IRRDB collections were evaluated in two trials in the experimental farm in Tripura, North East India. The present study revealed that certain accessions had superior growth character compared to the check clone, RRIM 600. Two accessions viz. MT 4713 (74.4 cm) and MT 4874 (72.7 cm) showed significantly higher girth than RRIM 600 (63.5 cm) in trial I. In trial II, the accessions RO 5449 (46.8 g t-1t-1) and MT 4788 (22 g t-1t-1) recorded high dry rubber yield and RRIM 600 yield 55.1 g t-1t-1. The accession MT 4713 also recorded the highest clear bole volume (0.11 m3) at the age of 13 years growth. Anatomical studies revealed that MT 4796 had the highest bark thickness (5.8 mm) and number of latex vessel rows (7.5) among the accessions evaluated. The accessions from Mato Grosso provenance revealed superiority for dry rubber yield in comparison with the accessions from Acre and Rondonia. The superior wild accessions identified for growth and yield in this study can be utilized as parents in future breeding programmes to enrich the available gene pool of Hevea.

A large scale trial, which is the second stage of clone evaluation in Hevea, was laid out at Central Experiment Station of Rubber Research Institute of India during 1994. Twelve clones consisting of three exotic hybrid clones introduced from Malaysia in 1993 and three indigenous hybrid clones and four ortets developed by RRII were evaluated along with RRII 105 and RRIM 600 as controls. Among the 12 clones, indigenous hybrid clone 86/44 recorded the highest yield of 67.17 g t-1t-1 in the BO-1 panel over six years of tapping. The yield performance of introduced clone RRIM 712 (59.87 g t-1t-1) and hybrid clone 86/120 (54.68 g t-1t-1) were on par with that of RRII 105 (54.0 g t-1t-1). The highest summer yield was recorded in 86/120 (38.31 g t-1t-1) which was significantly superior to that of RRII 105 (29.64 g t-1t-1). Indigenous hybrid clone 86/120 showed significantly better girth over both the controls with a mean girth of 60.93 cm and maximum tappability of 88. 63 per cent. 86/44 recorded 75 per cent tappability as against 70 per cent recorded for RRII 105. Incidence of wind damage and tapping panel dryness was comparatively low in the clone 86/44. 86/120 exhibited less incidence of pink disease. RRIM 712 was not affected by any forms of wind damage. The present investigation shows the superior performance of the hybrid clone 86/44.

A study was undertaken to compare the performance of plants having single rootstock (single root system) and twin rootstock (double root system) in terms of growth and yield in Hevea. Planting materials with single root system were produced as per the standard technique while plants with two root systems were produced by twin-grafting two stock plants at one whorl stage. Clone RRII 105 was used for the study. The plants were evaluated in the field. The design was RBD with three replications having a plot size of nine plants. Seven treatments were included; twin stocks and single stocks raised in polybags, twin stocks and single stocks raised directly in field by seed-at-stake planting, twin stocks and single stocks raised in seedling nursery and transplanted to the field as budded stumps and polybag plants as control. Annual girth was measured for 13 years and monthly dry rubber yield for four years. The mean girth of plants having single rootstock and twin rootstock was found to be statistically comparable during immature phase as well as at the time of opening and after tapping for four years. The mean yield of plants having single rootstock and twin rootstock was also found to be comparable. On excavation after 17 years, only less than 27 per cent of the twin rootstock plants were found to have two separate fully developed root systems and in the other cases, either the two roots united or one root had become aborted. The present study showed that twin rootstock plants and single rootstock plants do not differ significantly in growth and yield indicating that twin grafting may not have an added advantage in Hevea.

India introduced five hybrid clones of Hevea brasiliensis in 1991 from the Institut de Recherches sur le Caoutchouc (IRCA), Cote d’Ivoire. A field evaluation trial comprising of these clones and a popular Indian clone, RRII 105 was laid out during 1992 in a randomized block design with five replications and a plot size of eight plants. The trial was opened for regular tapping at the age of nine years and the growth performance and monthly dry rubber yield trend were evaluated. Significant clonal differences were observed for all the characters studied. At the time of opening, IRCA 111 and IRCA 130 were superior to all other clones in terms of vigour, while RRII 105 had the least girth. The remaining three IRCA clones were on par with RRII 105. IRCA 111 and IRCA 130 maintained their superiority over the next 10 years of tapping too. In the 10th year of tapping, IRCA 111 and IRCA 130 continued to show the highest girth, followed by IRCA 18 and RRII 105. Clonal differences for yield were highly significant every year. In the first year of tapping, IRCA 130 had the highest yield (52.0 g t-1t-1). IRCA 111 (47.2 g t-1t-1) was on par with it, followed by IRCA 18 (39.7 g t-1t-1), while the check clone RRII 105 recorded 36.2 g t-1t-1. Yield in the 10th year continued to be the highest in the clone IRCA 130 (93.0 g t-1t-1) followed by RRII 105 (72.1 g t-1t-1) and IRCA 111 (64.8 g t-1t-1). IRCA 130 had the highest mean yield over ten years of tapping (76.0 g t-1t-1), followed by RRII 105 (56.8 g t-1t-1) and IRCA 111 (55.9 g t-1t-1) which were on par. Yield components such as plugging index (PI) and dry rubber content were recorded in the 19th year of growth. Lowest PI was recorded in the clones IRCA 130 and IRCA 111. The clone IRCA 109 had the highest dry rubber content, while RRII 105 and IRCA 230 were on par with IRCA 130. IRCA 111 had the lowest dry rubber content. IRCA 130 remained in the top for timber volume followed by IRCA 111, IRCA 109 and IRCA 18. These four clones had significantly higher bole volume than RRII 105. Two clones (IRCA 130 and IRCA 111) with good dry rubber yield and timber yield can be considered as potential latex- timber clones.