Virgin Bark Research Articles

Long Term Effect of Low Frequency Tapping Systems Applied to Rubber Tree (Hevea brasiliensis), Clone RRIT 251, on Agronomic Performance in Upper Southern Thailand

Clone RRIT 251, a primary clone, was developed by RAOT (Thailand) with promising high yield potential. Low frequencies of tapping (LFT) was tested using 8-year-old trees to characterize the performance of the clone RRIT 251 under such latex harvesting systems. The aim of the study was to assess the response of the yield to LFT related to some biochemical indicators of the latex cells’ metabolism. The experiment was established at the Sithiporn Kridakorn Research Station of Kasetsart University, Prachuap Khirikhan Province, Thailand. The experimental randomized Fisher block design consisted of the 3 treatments. These were abbreviated to T1: S/2 d2 opening BO-1 at 1.5 m, T2: S/2 d3 ET 2.5 % Pa1 (1) 6/y opening BO-1 at 1.3 m and T3: S/2 d4 ET 2.5 % Pa1 (1) 8/y opening BO-1 at 1.2 m. Three replications were conducted with 55 trees per treatment in each experimental plot. Analysis of variance (ANOVA; F test) has been used to compare treatments using Duncan’s multiple range test (DMRT) at a significant level of p < 0.05. Results showed that daily yield greatly increased when using lower tapping frequencies. More than 10 years of tapping, panel management and location of the tapping cut on the panel in downward tapping have significantly impacted yield. Tapping on virgin bark at d3 and d4 frequencies gave higher yield than d2 frequency on renewed bark. Good panel management, combined with tailored stimulation and reduced tapping frequency showed greater efficiency. Results were encouraging. It might be considered that these low tapping frequencies systems can be tested by smallholders and then transferred at the farm gate in Thailand. GRAPHICAL ABSTRACT

A review of low-frequency latex harvesting systems that lessen the tapper shortage problem of the smallholders' natural rubber production

Smallholders' rubber production is encountering problems of skilled tapper shortage and high production costs resulting from increased worker wages and the substantial growth of new mature areas. Low-frequency latex harvesting system (LFLHS) effectively improves tapper productivity with long-term optimum yield by reducing the tapper requirement. LFLHS reduces tapper requirement by 33% to 67% of the conventional harvesting systems. Under the d3 (tapping every three days) frequency harvesting system, a tapper is assigned to cover three tasks, and his productivity is at least 30% higher than that of the d2 (alternative daily) frequency harvesting system. The cumulative yield of LFLHS is comparable to that of d2 frequency. It is economically profitable when the cumulative yield of LFLHS reaches 90% of the d2 frequency tapping as a break-even yield. Its low number of tapper requirement and high productivity saves tapping cost. 20% to 55% of tapping cost can be reduced by shifting the harvesting frequency from d2 to d3. The virgin bark of basal panels could be tapped at least four to ten years more than conventional tapping systems. The low bark consumption allows sufficient time for the regeneration of bark tissues resulting in a potentially higher yield from the renewed bark. Thus, sustainable economic yield is achievable for a productive lifespan of 30 to 35 years from the LFLHS. These advantages of LFLHS contribute to reducing the tapper requirement and cost of production, ensuring increased profits and a longer economic lifespan of rubber production.Keywords: Latex harvesting system, Tapper requirement, Tapper productivity, Tapping cost

Genetic variability of traits of the laticiferous system and association with rubber yield in juvenile and adult rubber tree progenies

The objectives of this study were to investigate genetic variation and association of the traits of the laticiferous system with rubber yield in young and adult rubber tree progenies Hevea brasiliensis, and compare the traits of the laticiferous system at different heights of the adult trees. The genetic material is composed of progenies from open pollination from the rubber tree breeding program of IAC, evaluated in the experimental field of UNESP in Ilha Solteira, SP, Brazil, in the young and adult phases, and in the Polo Regional Alta Mogiana of the Agência Paulista de Tecnologia do Agronegócio in Colina, SP, Brazil in the young phase. A randomized block experimental design was used with 30 treatments (progenies), three replications, and 10 plants per plot. The following traits were evaluated: rubber yield (RY), virgin bark thickness (BT), number of rings of laticiferous vessels (NR), and mean distance between consecutive rings of the laticiferous vessels (MD). The individual statistical analyses and repeated measurements were performed through mixed linear models using the REML/BLUP (Restricted Maximum Likelihood/Best Linear Unbiased Prediction) procedure. Genetic and phenotypic correlations were also estimated. The accuracy estimates (Aˆc) for the traits in the two locations were higher (> 0.7), indicating good perspectives in a breeding program. The coefficient of genetic variation (CVg %) showed low variation between the sites: BT (4.5–7 %), NR (14.1–18.3 %), and MD (15–18.2 %). The NR expressed higher heritabilities and was therefore the best trait of the laticiferous system for predicting genetic values; it showed expressive genetic correlations with RY, and may be used in indirect selection. BT did not show progeny × height interaction, indicating that the classification of the progenies was the same, regardless of the tree height at collection. To select progenies in common in the young and adult ages, using analysis of measurements repeated in time, the most suitable height for collection of samples in the adult progenies for the traits of the laticiferous system was up to 80 cm. The traits of the laticiferous system collected at 30 cm in young progenies are associated with RY, both in the youth phase and in the adult phase. They can be used to assist in early or indirect selection of rubber tree progenies.

Quantitative Assessment of the Agro-physiological Advantages of Upward Tapping in Relation to the Downward Tapping of the GT 1 and PB 260 Rubber Clones [Hevea brasiliensis, Muell. arg. (Euphorbiaceae)] in Southwest Côte d'Ivoire

The downward tapping on virgin bark of the lower panel (BO) is immediately followed by the upward tapping on virgin bark of the upper panel (HO), consecutively. To determine the agro-physiological advantages of one tapping over another, a study of the downward and upward tapping of the GT 1 and PB 260 clones of Hevea brasiliensis was carried out in southwestern Côte d'Ivoire. For this purpose, the rubber trees were tapped in a downward half-spiral (S/2) at the opening for nine consecutive years, followed by upward quarter-spiral tapping (S/4U) for four consecutive years. The agronomic parameters (rubber production and vegetative growth), tapping panel dryness and the latex micro-diagnosis, were evaluated. For GT 1 clone, the transition from the downward tapping panels to the upward tapping panels resulted rubber productivity gain of 35%. Meanwhile for PB 260, rubber productivity gain was 37%. Regardless of the clone and tapping direction, the higher the rubber productivity of a respective tapping panel, the lower the isodiametric growth of the tree trunk was recorded. Latex harvesting systems, and clone’s combination, did not influence the tapping panel dryness or the physiological profile of the trees. Finally, it should be concluded that upward tapping is more productive than downward tapping, but the quantification of the gains in this rubber production depends on the clone.

Incidence Des Fortes Fréquences De Stimulation Hormonale Sur Deux Régimes de Saignée Descendante Du Clone PB 215 : Faible (d6) et Modéré (d4), Au Sud-Est De La Côte D’Ivoire

The clone PB 235 of Hevea brasiliensis is characterized by a rapid growth, homogeneity, and a virgin bark which is suitable for tapping. However, it is sensitive to the very intense latex systems harvesting technologies. This paper focuses on determining the incidence of strong frequencies of stimulation on two downward tapping systems of clone PB 215: low (d6) or moderate (d4). Rubber trees were planted with the density of 510 trees/ha (7 m x 2.8 m) in accordance with a randomized complete block design. Tapping at d6 frequency with 8 and 12 hormonal stimulations and the d4 stimulated 0 and 8 times per year were evaluated. The intensification of hormonal stimulation with the d6 did not have any worthy beneficial effect on the dry rubber yield of the rubber trees. In d4, the stimulation involved a reduction in the sucrose content which led to a significant increase of the dry rubber yield. However, it contributed to an increase in the tapping panel dryness. At moderate tapping, the application of hormonalstimulation allowed us to distinguish between the two latex harvesting technologies. At d6, the two treatments were similar regardless of the stimulation level. Tapping at d6 supports a reduction of tapping workforce and a longer economical durability of the trees, compared to tapping at d4. The intensification of hormonal stimulation applied to lower tapping frequencies (d6) did not have any negative incidence on the clone PB 235. However, it has promoted tapping panel dryness in tapping at d4 frequency.

Potential Genotypes of the 1995 RRIM Hevea Germplasm Collection for Future Rubber Breeding and Selection Programme

Malaysia received a large share of the Hevea germplasm collection from the 1995 Rubber Research Institute of Malaysia (RRIM) expedition. About 50,000 wild genotypes of eight Hevea species originating from the state of Amazonas of Brazil are conserved ex-situ in Rantau Panjang Reserve Forest, Batu Arang, Selangor. As management of such massive numbers of individuals covering extensive areas is demanding, the wild genotypes planted in this germplasm are evaluated in a phased manner. A total of 5,789 wild genotypes of six Hevea species (Hevea brasiliensis, Hevea spruceana, Hevea guainensis, Hevea nitida, Hevea benthamiana and Hevea pauciflora) originating from different locations in the Amazonas, planted in Phase 1 area (58.88 ha) of this germplasm were assessed for their main characteristics specifically latex yield, clear bole volume, girth at opening, annual girth increment and virgin bark thickness. In general, the wild genotypes of the 1995 RRIM Hevea germplasm produced a considerably low amount of latex yield. Up to 80.84% of these materials were found to produce latex yield of less than 25.00 g/t/t. Nevertheless, Hevea brasiliensis demonstrated superiority compared with the other five Hevea species in this germplasm. Selection of potential genotypes in this germplasm was to gather good performance genotypes as well as to retain as much genetic variability possible. This process was performed using multiple characteristics selection index on latex yield, clear bole volume and girth at opening. The selection process resulted in a working collection consisting 616 potential genotypes of mainly Hevea brasiliensis. Assessment of major leaf diseases revealed that most of the selected genotypes were free from or only lightly affected by Oidium and Colletotrichum secondary leaf fall while all of them were completely free from Corynespora leaf disease and Fusicoccum leaf blight. These selected materials will be used for further evaluation, genetic improvement and incorporation in the Malaysian Rubber Board’s rubber breeding programme for the development of superior latex timber clones.

Replacing traditional half spiral cut by a quarter cut with Ethephon; a simple approach to solve current issues related to latex harvesting in rubber industry

Harvesting rubber latex is rather labour intensive since trees are traditionally tapped half spiral, once in two days (S/2 d2) resulting in unnecessary waste of tree bark. High cost of production, shortage of harvesters and reduced economic lifespan are the key issues in rubber plantations related to harvesting. Low intensity harvesting (LIH) systems (i.e. either reduction in harvesting frequency and/or tapping cut length) of rubber appear to be a practical solution to these issues by bringing down the labour requirement and the cost of production. Of these, only the reduction in harvesting frequency has been tried in Sri Lanka. Hence, the present study was aimed to develop new LIH systems with shorter tapping cuts. This study comprised two stage stimulant (Ethephon) based field trials to evaluate a wide range of LIH systems. The overall yield given by traditional S/2 d2 was used as the standard in evaluation. Stimulation protocols of different harvesting systems were adjusted from time to time to achieve this standard. In addition, growth and physiological parameters of latex and the financial viability of the principal system were also assessed. Among the LIH systems tested, S/4 d3 (tapping quarter spiral once in three days) was successful in providing benefits, such as increase in both overall profits and harvesters' income and reduction in harvesting cost and overall cost of production. The overall bark consumption was also greatly reduced. Above all, it allows tapping the virgin bark of base panels for over 24 years. Popularization of this approach is proposed after large scale commercial testing. Doi: http://dx.doi.org/10.4038/jnsfsr.v40i4.5042 J.Natn.Sci.Foundation Sri Lanka 2012 40 (4):283-291

Tapping panel diagnosis, an innovative on-farm decision support system for rubber tree tapping

Latex is a key product for many tropical countries, of which 80% is produced by smallholders. Latex is produced by the rubber tree (Hevea brasiliensis). Given the 7-year immature unproductive period, establishing a rubber plantation requires considerable investment by smallholders, emphasizing the need for sustainable management. The difficulty of performing an agronomic diagnosis of a tree crop is to obtain an accurate picture of current and past cultivation practices, to be able to assess their impacts on the agro-ecosystem as well as on sustainability. Smallholders do not usually keep records of latex yield or of their technical practices, making it impossible to perform a diagnosis based on productivity. As latex harvesting involves tapping the bark, which leaves scars on the trunk, we hypothesised that these morphological traces would be good indicators of current and past practices and would thus enable a diagnosis based on the economic lifespan of plantation. To this end, we formalised a tapping panel diagnosis that involved reproducing the scars on tapping panel diagrams, and analysing them using two indicators: the amount of virgin bark consumed and the number of tapping years that remained. We validated this tapping panel diagnosis in a sample of 25 smallholder plantations in Cameroon, where we characterised eight tapping management systems reflecting different levels of tapping intensity. The assessment of the respective share of each tapping practice on virgin bark consumption revealed major effects of tapping frequency and of shaving thickness. We showed that the tapping panel diagnosis used as a decision support tool can increase remaining tapping years by 33% to 355%. To conclude, the tapping panel diagnosis formalised here for the first time will be a useful support for the participatory development of innovating tapping management schemes involving both technicians and smallholders.

Correlações e análise de trilha em clones de seringueira

O conhecimento das características presentes nos genótipos é de extrema importância na condução de trabalhos de seleção e melhoramento. O objetivo foi avaliar as relações entre os caracteres agronômicos e anatômicos da casca, bem como seus efeitos diretos e indiretos sobre a produção de borracha seca da seringueira, mediante análise de trilha. Avaliaram-se seis clones de seringueira no delineamento experimental em blocos casualizados com quatro repetições, no Pólo Regional de Desenvolvimento Tecnológico dos Agronegócios do Centro Norte da Agência Paulista de Tecnologia dos Agronegócios, município de Pindorama, São Paulo, Brasil, no ano de 2005. Valor de correlação positivo e significativo foi observado apenas entre a produção de borracha seca e o número de anéis de vasos laticíferos (r = 0,88). Os caracteres perímetro do caule e número de anéis de vasos laticíferos apresentaram os maiores efeitos diretos sobre a produção de borracha seca. Por outro lado, a espessura da casca e o diâmetro dos anéis de vasos laticíferos mostraram efeitos diretos negativos e com altas magnitudes. A seleção indireta via número de anéis de vasos laticíferos proporcionará ganhos durante o processo de seleção em programas de melhoramento da seringueira.

Performance of new Hevea clones from IAC 400 series

The Hevea breeding program of Instituto Agronômico de Campinas (IAC) has completed clonal evaluation on the following series: IAC 100, IAC 200 and IAC 300. The performance of 22 clones of Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg., evolved at IAC, over a period of eleven years was evaluated in the Western Central part of the São Paulo State, Brazil. Among these 22 new clones, six were intraspecific hybrid clones (IAC 400, IAC 404, IAC 405, IAC 406, IAC 410, IAC 412) and the remaining are primary those resulted from selected ortets within half-sib progenies. An old popular clone RRIM 600, of Malaysian origin, was used as the control. The trial was laid out in a randomized block design with three replications. Yield performance over a period of four years, mean girth at the 11th year, girth increment before tapping and on tapping, thermal property of natural rubber produced, bark thickness, number of latex vessel rows in seven year virgin bark, percentage incidence of tapping panel dryness, wind damage and diseases like leaf and panel anthracnose have been observed. Sixty one percent of the clones were superior in relation to the control for yield. The clone IAC 400 recorded the highest yield (97.40 g tree-1 tap-1) over four years of tapping, followed by IAC 411 (78.87 tree-1 tap-1), whereas the control clone RRIM 600 recorded 50.86 g tree-1 tap-1. All selected clones were vigorous in growth. Girth increment of these clones was average to above average. Except for IAC 423, other clones had thick virgin bark at opening ranging from 4.84 mm for IAC 401 to 6.38 mm for IAC 416. The natural rubbers from IAC clones have shown good thermal stability up to 300ºC and no differences in the thermal behavior among rubber from clones of the IAC series and the clone RRIM 600 were found in inert atmosphere.

Expressão fenotípica de clones de seringueira na região noroeste do estado de São Paulo

O desenvolvimento de novos clones de seringueira [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.] com alto potencial de produção aliado a outros caracteres secundários desejáveis é de fundamental importância para uma heveicultura sustentável e competitiva. O objetivo deste trabalho foi avaliar a expressão fenotípica de caracteres superiores em 17 clones de seringueira, tendo em vista a escolha dos mais promissores. Em campo, o experimento obedeceu ao delineamento de blocos ao acaso com três repetições e parcelas lineares de seis plantas. Pelos resultados, verificou-se que o clone IAC 40 foi o mais produtivo, com média de 2.316 kg de borracha seca ha-1 ano-1 no período de seis anos, seguido pelo clone IAC 300 (1.921 kg), enquanto o clone-testemunha, RRIM 600 produziu 1.493 kg. Observou-se na maior parte dos clones, crescimento superior em relação à testemunha. A porcentagem de plantas aptas à sangria variou de 40% (IAC 329) a 100% (IAC 327). Exceto nos clones IAC 56, IAC 331 e IAN 3156 com 7,21 mm, 7,18 mm e 6,40 mm respectivamente, em todos os demais notou-se espessura de casca virgem inferior ao clone RRIM 600 (6,38 mm). Com exceção do IAN 3156, os demais clones tiveram baixa incidência de secamento de painel. O bom desempenho de todos os clones IAC e amazônicos (IAN, Fx e RO) permite que sejam recomendados para plantio em pequena escala, ao tempo em que serão avaliados para futura recomendação em grande escala envolvendo diferentes ambientes do Estado de São Paulo.

Desempenho de clones de seringueira de origem amazônica no planalto do Estado de São Paulo

O objetivo deste trabalho foi avaliar a adaptabilidade e expressão fenotípica de caracteres superiores de dez clones amazônicos de seringueira (Hevea spp.) no planalto do Estado de São Paulo em um período de 10 anos, obedecendo ao delineamento de blocos ao acaso com três repetições e parcelas lineares de seis plantas. O clone IAN 3156 foi o mais produtivo, com média de 65,57 g de borracha seca/árvore/sangria, no período de quatro anos, seguido pelo clone RO 45 com 52,29 g de borracha seca/árvore/sangria, enquanto o clone-testemunha, RRIM 600, produziu 41,04 g/árvore/sangria. Todos os clones apresentaram crescimento vigoroso. O perímetro do caule na abertura do painel variou de 37,01 cm (IAN 3193) a 49,41 cm (IAN 4493). A porcentagem de plantas aptas à sangria variou de 30,0% (IAN 3703) a 93,75% (IAN 6323). Exceto os clones IAN 3156 e IAN 4493 com 7,00 mm e 6,32 mm, respectivamente, todos os outros clones apresentaram espessura de casca virgem inferior ao clone RRIM 600, que apresentou 6,18 mm. O clone IAN 3193 apresentou maior incidência de quebra do ponteiro pelo vento. Todos os clones estudados apresentaram baixa incidência de secamento de painel. O bom desempenho dos clones IAN 3156, RO 45, Fx 3899 e IAN 4493 permite que possam ser experimentados em larga escala, envolvendo diferentes ambientes no Estado de São Paulo.

Clones promissores de seringueira para a região do Vale do Ribeira, São Paulo

Este trabalho objetivou apresentar resultados da primeira seleção de clones de seringueira (Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.Arg.) da série IAC 300, e amazônicos das séries IAN e Fx, em experimento de pequena escala, visando produção, crescimento e resistência ao mal-das-folhas. A produção e o vigor de 20 clones foram avaliados por dois e nove anos, respectivamente, em PariqüeraAçú, no Vale do Ribeira, SP. Os clones IAC 301, IAC 304, IAC 306 e IAC 319 produziram satisfatoriamente nos dois primeiros anos de sangria. Os clones amazônicos IAN 6323, Fx 3864 e IAN 2903, com produções de 1.078 kg, 945 kg e 900 kg/ha/ano, respectivamente, foram superiores à testemunha IAN 873 (878 kg/ha/ano). Os clones selecionados apresentaram crescimento vigoroso, com extremos de perímetro do caule, na abertura do painel, de 37,40 cm (IAN 4493) a 53,75 cm (IAN 6323), e percentual de plantas aptas à sangria de 7,0% (IAN 4493) a 100% (IAN 6323 e IAC 302), exceto os clones Fx 3899 e IAN 3044. O IAC 315, com 7,37 mm, mostrou maior espessura de casca virgem que o IAN 873 (6,44 mm). Os clones IAC 320, IAC 306 e IAC 315 foram os mais resistentes ao Microcyclus ulei.

Genetics of anthracnose panel canker disease resistance and its relationship with yield and growth characters in half-sib progenies of rubber tree (Hevea brasiliensis)

Rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell-Arg] anthracnose panel canker disease resistance, caused by Colletotrichum gloeosporioides (Penz.) Sacc., and growth and yield characters were assessed at three years old in the nursery, in 18 half-sib progenies. There were highly significant (P < 0.01) genetic differences among progenies for most characters. The genetic component of variance accounted for 3.37, 6.07, 12.74, 12.13, 19.82 and 3.58% of the phenotypic variance for anthracnose-infected area, anthracnose lesion stripe length, yield, girth, virgin bark thickness and total number of latex vessel rings, respectively. Narrow-sense heritability estimates for the above characters were 13.45, 24.30, 50.97, 48.52, 79.30 and 14.30%, respectively. No significant genetic correlations were found among anthracnose panel canker resistance, yield and growth characters. The frequency distribution of anthracnose-infected area and anthracnose lesion stripe length suggests polygenic control. Selecting the best three progenies out of 18 progenies would result in a genetic gain of 12.87 and 24.24% for infected area and lesion stripe length, respectively. The best five selected individuals out of 50 individuals within each progeny would result in a genetic gain of 9.47 and 24.62%, with a total gain of 22.34 and 48.87% for these two characters, respectively.

Anatomical and Histochemical Aspects of Bark Regeneration in Hevea brasiliensis

Natural rubber is obtained from the bark of Hevea brasiliensis. Both virgin and renewed bark are exploited for this purpose by a process known as tapping which involves controlled wounding and excision of bark tissues. The process of bark renewal and its nature and consequences thus assume importance. Anatomical and histochemical changes encountered with tapping were the deposition of lignin and suberin in the peripheral cells, enlargement of tray cells near the cut surface and the formation of a wound periderm. In the course of development, the wound phellogen made tangential continuity with the original phellogen in the virgin bark and functioned as a single phellogen. Vascular cambial activity was enhanced due to wound stimulus and the newly differentiated sieve tubes and ray cells were larger in size. The first periderm was functional for only a short period of time, after which a new meristematic zone developed in the inner tissues. Virgin and renewed bark differed in the proportion of soft and hard bark, amount and distribution of sclereids, tannin cells and crystals.

Ethrel (Ethylene Releaser)-Induced Increases in the Adenylate Pool and Transtonoplast ΔpH within Hevea Latex Cells

The treatment of rubber tree (Hevea brasiliensis) bark with chloro-2-ethyl phosphonic acid (ethrel), an ethylene-releasing chemical, induced, after a lag period of 13 to 21 hours, a marked increase in the total adenine nucleotides (essentially ATP and ADP) of latex cells. This rise in the latex adenylate pool was concomitant with a marked decrease in the [ATP]/[ADP] ratio without significant changes in the adenylate energy charge. The apparent equilibrium constant for the adenylate kinase, which appeared to behave as a key enzyme in maintaining the adenylate energy charge in the latex, was considerably reduced, probably as a consequence of the alkalinization of the latex cytosol induced by the treatment with ethrel. To reduce the "sink effect" and activation of the metabolism induced in Hevea bark by regular tapping, the latex was collected by micropuncture (few drops) at increasing distance (5-50 centimeters) above and below an ethrel-treated area on the virgin bark of resting trees. The effect of ethrel was shown to spread progressively along the trunk. The increase in the adenylate pool (essentially ATP) was detectable as early as 24 hours after the bark treatment and was maximum after 6 or 8 days, 5 centimeters as well as 50 centimeters above and below the stimulated bark ring. The correlative vacuolar acidification and cytosolic alkalinization, i.e. the increase in the transtonoplast DeltapH, induced in the latex cells by ethrel were shown to be concomitant with the rise in ATP content of the latex. This suggests that the tonoplast H(+)-pumping ATPase, which catalyzes vacuolar acidification in the latex, is directly and essentially under the control of the availability of its substrate (i.e. ATP) in the latex. The results are discussed in relation to energy-dependent activation of metabolism, and increased rubber production, as induced by the stimulation of rubber trees with ethrel.

Estimates of genetic parameters of certain characters in Hevea brasiliensis

Heritability estimates of five quantitative characters, namely, yield, girth, girth increment, virgin bark and renewed bark thickness, of the breeding Phase III Hevea families have been obtained by variance component analyses. In general, the combined heritability estimates for various characters were low to moderate. The heritabilities of these characters based on female variance components, however, were high, suggesting that considerable improvement of each of the characters could be achieved in properly designed experiments.Estimates of heritability for average yields (Range: 0.11-0.34) over different years showed that the first three years' yield was adequate for predicting estimates of genetic variance for the average of five years' yield.Correlation studies on yield with other characters indicated considerable influence of environment, with genetic correlations accounting for about 0.07 to 0.36 in the characters studied.Expected direct response to selection in yield and correlated response in yield to selection for girth at opening and virgin bark thickness have been calculated using three arbitrary values of selection intensity. The efficiency of the correlated response was found to be approximately half that of the direct response. However, the indirect selection for yield using virgin bark thickness appeared to be more favourable than that using the girth at opening favoured by earlier workers.