Comparative Performance of Natural Rubber (Hevea Brasiliensis) Polyclonal and Multiclonal Bud Grafted Population in Suboptimal Environment of Odisha, India  

B. Krishan
Regional Research Station, Rubber Research Institute of India, Dhenkanal 759 001, Odisha, India
Author    Correspondence author
Tree Genetics and Molecular Breeding, 2015, Vol. 5, No. 1   doi: 10.5376/tgmb.2015.05.0001
Received: 09 Jan., 2015    Accepted: 03 Mar., 2015    Published: 10 Mar., 2015
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Krishan, 2015, Comparative Performance of Natural Rubber (Hevea Brasiliensis) Polyclonal and Multiclonal Bud Grafted Population in Suboptimal Environment of Odisha, India, Tree Genetics and Molecular Breeding, Vol.5, No.1 1-7 (doi: 10.5376/tgmb.2015.05.0001)


The natural rubber (Hevea brasiliensis) yield and growth performance of polyclonal rubber seedlings was evaluated and compared with an adjacent multiclonal population comprising of three clones RRII 105, RRIM 600 and GT1 in the dry sub humid climate of Odisha state, which experiences high temperature and low rainfall as the major environmental constraints for the growth and yield of the crop. The study revealed that seedling population is highly heterogeneous with respect to yield, growth and other secondary characters. Tappable girth was attained earlier in polyclonal population as compared to multiclonal population. The Mean annual girth increment was also higher in polyclonal population (5.95 cm) as compared to multiclonal population (3.90 cm). Mean annual rubber yield of 34.02 gt-1t-1 was recorded in polyclonal population over a five years period as compared to 25.10 gt-1t-1 for multiclonal population. Some polyclonal seedlings genotypes are outstanding performers, which recorded even two to threefold higher rubber yield than the mean of the multiclonal population. Ten elite mother trees with high yield over the five year period were selected for further evaluation. The highest mean dry rubber yield was recorded in OR2 (75.40 gt-1t-1) followed by OR3 (69.04 gt-1t-1) and OR7 (64.18 gt-1t-1) among the ten elite seedling mother trees. Highest yield contribution was recorded during the cold months for polyclonal as well as multiclonal population. The highest annual girth increment before and after tapping was recorded in OR1 (10.16 cm) and OR7 (4.68 cm), respectively. In addition to the yield and growth, the population was assessed for bole volume, bark thickness and incidence of tapping panel dryness and wind damage. Polyclonal population also recorded comparatively less wind damage and tapping panel dryness. Bole volume was significantly higher (0.27 m³/tree) for polyclonal as compared to multiclonal population (0.08 m³/tree). The present study, in a sub-optimal environment of Odisha of eastern India, reveals the large variation among the population and ample scope for selection of promising genotypes from poly cross progeny suited to the sub optimal environment.

Hevea brasiliensis; Multiclonal population; Polyclonal seedlings; Elite mother trees; Suboptimal environment; Selection and yield

The Para rubber tree, Hevea brasiliensis (Willd.ex Juss.) Muell. Arg. is a tropical tree native to Amazon rainforest. More than 90 percent of the world natural rubber is obtained from rubber tree latex (Verheye, 2010). Rubber has been traditionally cultivated in the equatorial region, in a zone lying between 10˚ north and 10˚ south of the equator. Compared to other crops, rubber is relatively new introduction, was brought in to cultivate to India a century ago. In the country the traditional rubber belt (8˚ N to 12˚ N) encompasses the southern tips of the peninsula (Sethuraj, 1989), where it provided appro- priate environmental conditions and has been grown on a plantation scale for nearly a century.

Early rubber plantations were generally raised using polyclonal seedlings as planting material. Selection of promising mother trees from existing polyclonal seedling populations and development of primary clones was one of the most important methods adopted for evolving new clones (Fernando, 1974; Marattukalam et al., 1990). Some of these are still used as planting materials in different rubber growing countries (Tan et al., 1996). The Polycross seedling population has also facilitated the evolvement of high timber yielding clones in India (Mydin et al., 2005). Polyclonal seeds are collected from polyclonal seed gardens where different clones are planted in an area with specific layout. Plantations raised from seeds are considered to have high inherent genetic variability. Therefore elite polycross mother seedling trees offer possibilities in the development of clones with high yield and tolerance to biotic and a biotic stress (Varghese et al., 2006). The potential of poly cross population for outstanding genotypes in any new environment has been widely accepted (RRII, 2002).
High temperature, low rainfall and strong winds are the major constraints curtailing the growth and productivity of the natural rubber crop in the Odisha state (17˚ N and 87˚ E) located in the eastern region of India. Rubber is comparatively a new crop introduced in this nontraditional dry sub humid region of Odisha state; though preliminary study reported wide variability in growth and yield among polycross population (Gupta et al., 2001). Another study reported selection of ten ortet from the polyclonal seedlings and ample scope of evolving of clone for the dry sub humid climate (Krishan, 2013). The present study reports the performance of another set of ten elite mother polyclonal seedlings identified among polycross population and attempts to compare the performance of the polycross seedling population and a multiclonal population under the sub optimal environmental conditions of Odisha.
1 Results and Discussion
The region where rubber tree plantation were studied represents dry sub humid climate with stressful climatic conditions and sub optimal rubber growing conditions. The region received an annual rainfall of 1296 mm during the study period and mainly confined to mid-June to October. The distribution of rainfall is far from satisfactory which results in long dry spells extending from November to May, during which the drought conditions become very severe. The summer months exhibited severe soil moisture stress conditions. The daily minimum temperature was low in November, December, and January and in the remaining months they were considerably higher. Daily maximum temperature exceeds 35˚C during March, April, and May. During the month of May, the mean maximum temperature nearly 40˚C was recorded. The sunshine hours during July and August were low, moderate in June and September and more than seven hours daily in the remaining months (Figure 1).

Figure 1 Weather parameters of experimental site (1991-2006)

A comparison of the polyclonal seedling trees to the multiclonal population comprising of RRII 105, RRIM 600 and GT1 revealed that seedling population was more heterogeneous with respect to yield, girth and other secondary characters. Growth in Hevea brasiliensis is considered as an important criterion for assessing the age of attaining tappability and of timber value (Hashim and Aziz, 1994). The polyclonal seedlings attained tappable girth by the eighth year, while the multiclonal plantation only by the ninth year. Girth at the opening of tapping and percent tappability was higher among polyclonal population (50.41 cm, 54.38 %, respectively) than the multiclonal population (40.50 cm, 23.30 % respectively). The annual girth increment recorded was also higher in the seedling population (Table 1).

Table 1 Comparative performance of polyclonal seedlings with multiclonal population

Mean annual rubber yield over five years in polyclonal seedlings was high as 34.02 g t̵ ˡ t̵ ˡ, than that of multiclonal population 25.10 g t̵ ˡ t̵ ˡ (Table 1). Monthly rubber yielding pattern of the seedling population was compared with multiclonal population. The performance of the polyclonal seedlings base population was comparable to multiclonal population. Interestingly, polyclonal trees maintained comparatively high yield in the summer months (Figure 2). The better yield during stressful month further supports good adaptability and higher yield attributes of polyclonal seedlings under stressed environment. The variability in yield observed in this study is comparable to the results reported for the trees raised from seeds in dry sub humid conditions (Chandrasekhar et al., 2002; Krishan, 2013).

Figure 2 Rubber yield trend of multiclonal population, polyclonal population and polyclonal elite trees over five year period

The damage due to wind was low (2.72%) in the seedling population, compared to the multiclone population (3.91%). No uprooting of seedling trees was recorded which might be due to comparatively strong deep tap root system. Polyclonal population was found least effected by tapping panel dryness as compared to multiclonal population (Table 1).
Bark thickness is an important feature as thick bark minimize wounding incidence, which is known to affect yield productivity on latter panels (Goncalves et al., 2006). Bark thickness was reported higher among polyclonal seedlings (10.16 mm) as compared to multiclonal population (9.23 mm) (Table 1).
Clear bole volume is an important indicator of the timber yield (Najib et al., 1995). Polyclonal seedling population was having significantly higher bole volume of 0.27 m³/tree in camparison to 0.08 m³/tree in multiclonal population (Table 2). The mean height at forking was also recorded higher in polyclonal population (4.5 m) against the multiclonal population (3.0 m). However, the number of primary branches was found less as compared to multiclonal population (Table 2). The primary branch contributes a significant role in the formation of canopy and plays an important role in wind resistance.

Table 2 Timber volume associated attributes of polyclonal and multiclonal Population in 20th year of growth age

Yield evaluation of the polyclonal seedling population over the years revealed that certain genotypes are exceptionally good performers. The performance of these elite seedlings was closely assessed for growth, yield and other secondary characters. The criteria for selection were consistent yield over months and years, good girth increment and other secondary characters as branching and canopy structure. Based on which ten numbers of elite mother trees (ortets) were selected for further multiplication.
The mean dry rubber yield of the ten elite mother seedling trees over the five years was comparatively high and ranged from 36.32 gt-1t-1 to 75.40 gt-1t-1. The elite seedling trees showed higher yields as against the base polyclonal seedling population as well as the multiclonal population (Table 1; Table 3). The mean annual dry rubber yield of the ten elite seedling mother trees was two to three folds higher than that of the multiclonal population. The mean annual yield was recorded highest in the elite seedling OR2 (75.40 gt-1t-1) followed by OR3 (69.04 gt-1t-1) and OR7 (64.18 gt-1t-1) (Table 3). Gupta et al., (2001) and Krishan (2013) have also reported reasonable yield of polyclonal population in the dry sub humid region. The rubber yield increased gradually with the onset of monsoon particularly in the month of August, peaked in subsequent period, sustained up in November and started slight decline thereafter. Yields were comparatively low during the period from April to July, high during October and November and moderate during the remaining months (Figure 2). The general trend observed is in agreement with the earlier reports in the dry sub humid region (Chandrasekhar et al., 1990; Birari et al., 1998) and north eastern region (Sasikumar et al., 2001; Mondal et al., 2006).

Table 3 Performance of polyclonal elite mother trees

Growth during the initial years is crucial for Hevea 
brasiliensis especially with respect to the attainment of tappable girth (Sethuraj and George, 1980). The  elite mother tree OR1 attained highest girth (84.4 cm) followed by OR2 (82.2 cm) and OR9 (81.5 cm) at the opening of tapping (Table 3). Following the trend highest annual girth increment before opening of tapping was recorded in OR1 (10.16 cm) followed by OR2 (9.91 cm) and OR9 (9.86 cm). However, after commencement of tapping annual girth increment over eight years was recorded highest in OR7 (4.68 cm) followed by OR6 (4.43 cm) and OR5 (4.13 cm) (Table 3). Similar performance of seedlings also has been reported from Konkan region of Maharastra (Birari et al., 1998; Chandrasekhar et al., 2002) and from the northeastern region (Sasi kumar et al., 2001; Mondal et al., 2006). Clear bole volume is an indicator of timber yield. Among the elite mother trees the bole volume ranged between 0.13 m³/tree (OR9) to as high as 0.50 m³/tree (OR 10) (Table 3). The high timber volume attainment of polyclonal seedlings over multiclonal population further meets the need of the preferred high yielding “latex-timber” planting material. Bark thickness was recorded highest in OR10 (13.00 mm) followed by OR3 (12.00 mm) and OR2 (11.00 mm) (Table 3).
The polyclonal seedlings exhibited early attainment of tappability, high girth, girth increment, and high timber volume and bark thickness compared to multiclonal population. Polyclonal population was found more wind resistant and with almost negligible reports of tapping panel dryness. Further most, the significant good yield and in particular two to three folds higher yield of selected elite mother seedling trees offers the possible scope of selection of promising clones/genotypes for the dry sub humid region.
Polyclonal seedlings are expected to adapt well to new areas due to their genetic heterogeneity (Simmonds, 1989). The climate change and further requirement of expansion of cultivation to less congenial marginal regions has necessitated the selection of advanced polycross progenies. The selection of poly cross progenies can be further useful to the normal hand pollination programme (Tan et al., 1996). The polyclonal seedlings exhibit excellent variability and suggest the scope of further selection of desired superior genotypes. Over the years, ten elite selections from polyclonal population yields significantly higher than the multiclonal population and clearly suggests the need to be cloned and evaluated further for ascertaining the genetic potential to evolve the most suitable planting material for the region. Accordingly, the selected ten elite mother trees were further multiplied. Bud grafted trees derived from theses mother genotypes were field planted and under further evaluation to ascertain their genetic potential to include them as clonal composites/ recommended planting material in the region.
The present study reveals the existing variability and superiority of polyclonal trees, particularly in growth, yield, timber and adaptability and selection of ten elite polyclonal trees. The present study suggests the importance of maintenance of genetic variability through planting of polyclonal seedlings and possible development of clones for stressful environment.
2 Materials and Methods
The study was conducted at the Regional Research Station of Rubber Research Institute of India at Kadalipal, Dhenkanal (20˚ 49’40’’ N, 85˚ 30’ 45” E, altitude 100 m above msl)) in Dhenkanal district of Odisha. The soil is an Alfisols order with pH 5.5 and is of lateritic in nature. The fertility status shows that the soils are low in organic carbon, available phosphorus and potassium. The available magnesium was in the high range. The region represents dry sub-humid climate with stressful conditions. In the present study compared the budded multiclonal population comprising of RRII 105, RRIM 600 and GT 1 with a nearby similar aged polyclonal seedling population and identified elite polyclonal trees. The clones under study are most popular and widely planted planting material in India. RRII 105 occupies the dominant position with 85.0 percent share in the total rubber planted area. Clones RRIM 600, GT 1 and polyclonal trees have a dominant position in the nontraditional region, besides satisfactory planted area in the traditional region of the country (Veerputharan, 1998). Generally rubber plantations are raised from clonal bud grafts; though polyclonal tree plantations have high genetic variation in growth and yield. These plantations have potential to screen and evolve higher yielder clones besides several advantages such as ease in establishment, vigorous growth and good survival in adverse conditions (Simmonds, 1989).
In polyclonal seedling experiment, stumps of 776 polyclonal seedling of Hevea brasiliensis were field planted in 1989. The experiment was laid out in completely randomized, single tree- single plot design planted at a spacing of 4.6 m×4.6 m. The seedling trees were raised from seeds procured from polyclonal seed gardens in Kanyakumari district in Tamil Nadu state in the traditional belt of India. Experiment comprising of the budded multiclonal population was planted in the nearby field. In the multiclonal experiment three clones RRII 105, RRIM 600 and GT 1 (Table 4), were laid out in randomized block design with 36 plants per plot in eight replications. Brown budded stumps were used as planting material and field planted at a spacing of 4.6 m×4.6 m. The multiclonal and polyclonal trees were raised following similar cultural practices recommended for the growing of rubber (RRII, 1990). In the first two years of field planting of polyclonal seedlings and multiclonal population, the plants were provided partial life saving irrigation of 20 L per week during summer months.

Table 4 Parentage and country of origin of multiclonal population

The growth was recorded as the girth of the trunk. The trunk girth was recorded at regular intervals as per standard practice at above ground level of 110 cm for polyclonal seedling trees and at 150 cm for the multiclonal population. The standard of recording is different for seedling and budded multiclonal owing in the difference in the anatomy of bark and shape of the trunk.
The trees were opened for tapping at the eighth year after planting under 1/2S d/2 6d/7 tapping system (Half spiral, alternate daily, six days in tapping followed by one day rest). Dry rubber yield was recorded twice a month. Yield recording is done by cup coagulation. Two coagulations representing the first half and the second half of a month are carried out. Coagulation is effected by mixing a few drops of dilute (0.5%) formic acid with the latex in the cups after the flow has ceased. The resultant cup lumps are hooked on to labeled hooks on the day after coagulation. The hooked cup lumps are dried in the smoke house for a month and weight of dried cup lumps are recorded. The yield is estimated from the weight of cup lumps thus recorded. Data on the yield over five years of tapping from the fourth year to ninth year were utilized for evaluating the performance of polyclonal and multiclonal population. Ten polyclonal elite mother trees were identified as potential ortets based on yield and secondary attributes.
Clear bole volume of polyclonal and multiclonal population was estimated using first branch height and girth in the twentieth year after planting following the quarter girth method (Chathurvedi & Khanna, 1982). The bark thickness of polyclonal and multiclonal population was measured in the twentieth year after field planting. Recording on the tapping panel dryness and wind damage was also undertaken. Plants with 80%~100% panel dryness incidence were considered as tapping panel dryness affected trees. Wind damage category included uprooted or trunk snapped trees. The data were statistically analyzed followed Sukhatme and Amble (1989).
The author is thankful to Director, Rubber Research Institute of India for his constant encouragement. The help of all associated scientists and field staff is also acknowledged.
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