Paulo de Souza Gonçalves

Genotype-environment interaction and phenotypic stability for girth growth and rubber yield of Hevea clones in São Paulo State, Brazil

The best-yielding, best vigour and most stable Hevea clones are identified by growing clones in different environments. However, research on the stability in Hevea brasiliensis (Willd. Adr. ex Juss.) Muell.-Arg. is scarce. The objectives of this work were to assess genotype-environment interaction and determine stable genotypes. Stability analysis were performed on results for girth growth and rubber yield of seven clones from five comparative trials conducted over 10 years (girth growth) and four years (rubber yield) in Sao Paulo State, Brazil. Stability was estimated using the Eberhart and Russell (1966) method. Year by location and location variability were the dominant sources of interactions. The stability analysis identified GT 1 and IAN 873 as the most stable clones for girth growth and rubber yield respectively since their regression coefficients were almost the unity (b = 1) and they had one of the lowest deviations from regressions (S2di). Their coefficient of determination (R2) was as high as 89.5% and 89.8% confirming their stability. In contrast, clones such as PB 235, PR 261, and RRIM 701 for girth growth and clones such as GT 1 for rubber yield with regression coefficients greater than one were regarded as sensitive to environment changes.

Genetic variability for girth growth and rubber yield in Hevea brasiliensis

Basic knowledge of genetic characteristics of populations is necessary to conduct effective breeding and selection. The objective of this paper is describing the genetic variation of rubber yield and the correlation with other traits, and estimating the genetic parameters for girth growth and total number of latex vessels. Sixty seven clones of Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg. were tested at five sites during 10 years. Characters girth growth at panel opening and rubber yield, showed broad sense heritability on plot mean level, from 0.32 to 0.66 and 0.59 to 0.92, respectively. Predicted genetic gains equal to 0.73 cm and 0.79 g increase respectively on girth and yield in the opening panel and mature phases seems realistic, even with moderate selection intensities. Genetic correlations with rubber yield, bark thickness and total number of latex vessels were very large, and almost no genotype-environment interaction was present for girth growth. High genotype-environment interaction was present for rubber yield with genetic and phenotypic correlations across the sites, ranging from 0.64 to 0.92 (genetic) and 0.63 to 0.89 (phenotypic). Total number of latex vessels rings had a high heritability, ranging from 20.0% to 64.0% in the sites E and B, respectively.

Genetic variation and realized genetic gain from rubber tree improvement

Breeding cycle in rubber extends to 20-30 years between pollination and yield assessment, distributed over three selection stages. Five hectares of small scale trial of rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.], was established in the Northwestern region of Sao Paulo State, Brazil. The population comprises 98 clones mostly derived from intensively selected plus tree in the natural forest of rubber tree in the Amazon. Three open pollinated progeny tests were established in three experimental stations. Seedlings from 98 progenies including a commercial check (CC) were planted in each one of the three locations. Assessments were made when the plants were one, two and three years old. The variation among progenies for girth was highly significant in all locations examined. In the combined analysis of variance over three locations, differences among progenies were also detected, while progeny × location interaction effect was not significant. Narrow sense heritability estimates on individual tree basis (hi2) were variable depending on the characteristic, age of assessment and experimental location. Realized genetic gains were calculated for the plant characteristics at the age of three years, by comparing the performance of improved (selected) materials to unimproved materials (CC). The total genetic gain from the genetically tested first generation clone population at Votuporanga is estimated as 25% for girth, 14% for rubber yield and 25% for bark thickness. Improvement of rubber tree by selection, establishment of clonal population (isolated garden) and progeny testing is a very promising and profitable operation.

Stock-scion interactions on growth and rubber yield of Hevea brasiliensis

Rubber tree cultivation [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.] uses mostly the budding propagation method, however the expected stand uniformity due to the use of vegetative propagation is theoretical, since high variation for yield and vigor is caused by rootstock influence. The objective of this study was to assess several combinations between clonal rootstocks and clone scions through diallel analysis, aiming at high productivity and vigor. Data consisted of five years of dry rubber yield and girth at panel opening from an experiment using a split-plot design with four replications, conducted at Pindorama, SP, Brazil, considering six rootstocks (GT 1, IAN 873, PB 235, RRIM 600, RRIM 701 and unselected seedlings) and six scions (GT 1, IAN 873, PB 235, PR 107, RRIM 600 and RRIM 701). A 6 ´ 6 partial diallel analysis summing up 36 combinations was undertaken, and general compatibility for each group of materials (rootstocks and scions) and specific compatibility among all combinations were estimated. The results have shown that PB 235 and IAN 873 rootstocks provided high yields and general compatibility values (7.9348 and 2.7647, respectively). The use of unselected seedlings as rootstocks is not recommended because they presented very low compatibility values for dry rubber yield. Towards growth vigor, the tested rootstocks have shown similar performance.

Selection and genetic gains for juvenile traits in progenies of Hevea in São Paulo State, Brazil

Five yield traits were investigated in three-year-old progenies from open-pollinated rubber trees [Hevea brasiliensis (Willd. ex Adr. de Juss) Muell.-Arg.]. Twenty progenies were evaluated in a randomized, complete block design replicated three times using 10 plants per linear plot at the North Central Experimental Station in Pindorama, Sao Paulo State, Brazil. The characters evaluated included the average yield of rubber, growth vigor, bark thickness, total number of latex vessel rings and latex vessel size. Highly significant (p < 0.01) genetic differences were observed among progenies for most traits. The genotypic variance components accounted for 13.2%, 12.3%, 9.4%, 3.4% and 0.23% of the phenotypic variance for yield, growth vigor, bark thickness, total number of latex vessel rings and latex vessel size, respectively. Heritabilities, as well as genotypic and phenotypic correlations among traits, were estimated. Heritabilities for the above traits at the individual plant level () were 37%, 35%, 69%, 10% and 16%, respectively. Significant positive genotypic and phenotypic correlations were found between the yield of rubber and growth vigor (rg = 0.73, rp = 0.70), bark thickness (rg = 0.70**, rp = 0.75**) and the total number of latex vessel rings (rg = 0.64, rp = 0.80). There was no relationship between yield and latex vessel size, growth vigor or total number of latex vessel rings. Based on these data, selecting the best two out of 20 progenies would result in a genetic gain of 12.3% and 6.8% for yield of rubber and growth vigor, respectively. The two best individual ortets within each progeny would result in a genetic gain of 27.7% and 9.1%, with a total gain of 40% and 16% for these two traits, respectively.

Performance of new Hevea clones from IAC 400 series

O programa de melhoramento de Hevea do Instituto Agronomico de Campinas (IAC) completou a avaliacao dos clones da serie IAC 100, IAC 200 e IAC 300. O desempenho medio em torno de 22 clones de [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.], desenvolvidos pelo IAC, por um periodo de 11 anos foi avaliado na regiao Centro Oeste do estado de Sao Paulo. Dentre os 22 novos clones, seis sao resultantes de hibridacao intraespecifica (IAC 400, IAC 404, IAC 405, IAC 406, IAC 410, IAC 412) e o restante, clones primarios resultantes de ortetes selecionados dentro de progenies de meios irmaos. O clone RRIM 600, de origem Malaia, foi usado como testemunha. O experimento foi conduzido sob delineamento de blocos ao acaso com tres repeticoes. Desempenho da producao sob o periodo de quatro anos, media do perimetro do caule no decimo primeiro ano, incremento medio anual do perimetro antes e durante a sangria, espessura de casca, numero de aneis de vasos laticiferos no setimo ano de casca virgem, analise por termogravimetria da borracha produzida, percentagem de incidencia de seca do painel de sangria, danos causados pelo vento e doencas como antracnose do painel e das folhas foram observados. A maioria dos clones foi superior em producao em relacao ao clone RRIM 600. O clone IAC 400 registrou a mais alta producao (97,40 g arvore-1 sangria-1) em quatro anos de sangria o qual foi seguido pelo IAC 411 (78,87 g arvore-1 sangria-1) visto que o clone testemunha registrou 50,36 g arvore-1 sangria-1. Todos os clones selecionados tiveram crescimento vigoroso. Incrementos do perimetro do caule estiveram acima da media. Exceto o IAC 423, outros clones apresentaram espessura de casca virgem na abertura do painel (mm) variando de 4.84mm (IAC 401) a 6.38 mm (IAC 416). As borrachas estudadas apresentaram boa estabilidade termica ate cerca de 300oC e nao foram observadas diferencas no comportamento termico entre as amostras dos clones da serie IAC e as do clone RRIM 600.

Temporal stability for unpredictable annual climatic variability for Hevea genotype selection

The objective of this study was to assess genotype-year interaction and determine temporal stable genotypes across six years of rubber yield evaluation. Stability analyses were performed by Eberhart and Russell method for rubber yield. Twenty-five genotypes were analyzed in a randomized complete block design with three replications. The best genotype in one year was not same always in the other year. The genotype components were partitioned into linear (genotypes within year) and nonlinear (pooled deviations) components. Significant mean square for linear components was predictable. This indicated that the performance of genotypes across the years for rubber yield could be predicted. Among the analyzed genotypes the IAC 40 also was considered highly productive and vigorous, with suitable adaptation.

Caracterização mecânica e térmica da borracha natural formulada e vulcanizada dos clones: GT 1, IAN 873, PB 235 e RRIM 600

The objective of this work was to study the mechanical and thermal performance of natural rubber (Hevea brasiliensis) compounds of different types of clones (GT 1, IAN 873, PB 235 and RRIM 600), as well as a mixture made from these clones and a commercial rubber GEB-1. These rubbers were formulated and prepared in a two-roll mill and vulcanized at different times (5, 7 and 9 minutes). The evaluation of the mechanical and thermal performance of different natural rubber compounds was carried out by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), mechanical properties (tensile and hardness tests), dynamic mechanic thermal analysis (DMTA), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR). The values obtained for glass transition temperature (Tg) for vulcanized rubbers were found to be around -62 °C, while in the hardness test the values obtained were close to 60, with no great variations when the vulcanization time and type of clone were varied. The tensile tests showed that the best performance was obtained for the clone RRIM 600. All the samples studied were in agreement with standard specifications required for application in the rubber industry, indicating that all clones can be used, in principle, in the rubber industry in blended or unblended forms.The objective of this work was to study the mechanical and thermal performance of natural rubber (Hevea brasiliensis) compounds of different types of clones (GT 1, IAN 873, PB 235 and RRIM 600), as well as a mixture made from these clones and a commercial rubber GEB-1. These rubbers were formulated and prepared in a two-roll mill and vulcanized at different times (5, 7 and 9 minutes). The evaluation of the mechanical and thermal performance of different natural rubber compounds was carried out by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), mechanical properties (tensile and hardness tests), dynamic mechanic thermal analysis (DMTA), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR). The values obtained for glass transition temperature (Tg) for vulcanized rubbers were found to be around -62 °C, while in the hardness test the values obtained were close to 60, with no great variations when the vulcanization time and type of clone were varied. The tensile tests showed that the best performance was obtained for the clone RRIM 600. All the samples studied were in agreement with standard specifications required for application in the rubber industry, indicating that all clones can be used, in principle, in the rubber industry in blended or unblended forms.