Genetic divergence of rubber tree estimated by multivariate techniques and microsatellite markers

Genetic diversity of 60 Hevea genotypes, consisting of Asiatic, Amazonian, African and IAC clones, and pertaining to the genetic breeding program of the Agronomic Institute (IAC), Brazil, was estimated. Analyses were based on phenotypic multivariate parameters and microsatellites. Five agronomic descriptors were employed in multivariate procedures, such as Standard Euclidian Distance, Tocher clustering and principal component analysis. Genetic variability among the genotypes was estimated with 68 selected polymorphic SSRs, by way of Modified Rogers Genetic Distance and UPGMA clustering. Structure software in a Bayesian approach was used in discriminating among groups. Genetic diversity was estimated through Nei's statistics. The genotypes were clustered into 12 groups according to the Tocher method, while the molecular analysis identified six groups. In the phenotypic and microsatellite analyses, the Amazonian and IAC genotypes were distributed in several groups, whereas the Asiatic were in only a few. Observed heterozygosity ranged from 0.05 to 0.96. Both high total diversity (H T' = 0.58) and high gene differentiation (Gst' = 0.61) were observed, and indicated high genetic variation among the 60 genotypes, which may be useful for breeding programs. The analyzed agronomic parameters and SSRs markers were effective in assessing genetic diversity among Hevea genotypes, besides proving to be useful for characterizing genetic variability.

Prediction of Hevea progeny performance in the presence of genotype-environment interaction

Twenty two open-pollinated Hevea progenies from different parental clones of the Asian origin were tested at five sites in the Northwestern São Paulo State Brazil to investigate the progeny girth growth, rubber yield, bark thickness and plant height. Except for the rubber yield, the analysis of variance indicated highly significant (p<0.01) genotype x environment interaction and heterogeneity of regressions among the progenies. However, the regression stability analysis identified only a few interacting progenies which had regression coefficients significantly different from the expected value of one. The linear regressions of the progeny mean performance at each test on an environmental index (mean of all the progenies in each test) showed the general stability and adaptability of most selected Hevea progenies over the test environments. The few progenies which were responsive and high yielding on different test sites could be used to maximize the rubber cultivars productivity and to obtain the best use of the genetically improved stock under different environmental conditions.

Vinte e duas progênies de Hevea de polinização aberta obtidas de diferentes clones fenotipicamente selecionados de uma população de origem asiática Hevea brasiliensis (Willd. Adr. ex Juss.) Muell-Arg. durante três anos foram testadas em cinco locais. As variáveis perímetro do caule, produção de borracha, espessura da casca e a altura de planta foram determinadas em todos locais no Estado de São Paulo, Brasil. De acordo com as análises de variância, com exceção a produção de borracha, observou-se a existência de interações significativas entre genótipo x ambiente (p<0.01) e heterogeneidade de regressões entre as progênies. Porém, a análise de estabilidade de regressão identificou a interação de poucas progênies cujos coeficientes de regressão foram significativamente diferentes do valor esperado de um. Regressões lineares do desempenho médio das progênies para cada teste em um índice ambiental (média de todas as progênies em cada local) mostrou a estabilidade e adaptabilidade da grande maioria das progênies de Hevea nos diferentes locais. As poucas progênies que foram superiores e altamente produtivas nos diferentes testes de progênies podem ser utilizadas para maximizar a produtividade de cultivares de seringueira e determinar a melhor utilização do ganho genético dos grupos sob as diferentes condições ambientais de cultivo.

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.

A interação genótipo x ano em culturas perenes como a seringueira Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg. representa o diferencial de resposta dos genótipos às mudanças climáticas anuais. O objetivo deste trabalho foi estudar a interação genótipo-ano e determinar genótipos temporalmente estáveis por meio da avaliação de seis anos de produção de borracha. Análises de estabilidade foram realizadas pelo método de Eberhart and Russell para produção de borracha na Estação Experimental de Votuporanga, região Noroeste do Estado de São Paulo, Brasil. Vinte e cinco genótipos foram analisados num delineamento de blocos ao acaso com três repetições. Os resultados mostraram que o melhor genótipo em um ano nem sempre foi o melhor em outro. Os componentes genéticos foram repartidos em lineares (genótipos dentro do ano) e não lineares (desvios agrupados). Quadrados médios significativos para os componentes lineares foram previsíveis indicando que o desempenho dos genótipos através dos anos em relação ao rendimento de borracha é passível de previsão. Entre os clones estudados o IAC 40 também foi considerado altamente produtivo e vigoroso, com adaptabilidade adequada.

Age-age correlation for early selection of rubber tree genotypes in São Paulo State, Brazil

In a field trial involving 68 rubber tree (Hevea spp.) clones calculation of genotypic correlation coefficients revealed significant age-age correlation from age 1 to 6 (immature period) for girth A and for age 7 to 12 (mature period) for girth B and for age 7 to 12 (production of latex) for yield. Rank correlation coefficients between all immature ages of girth (girth A), all ages of mature girth (girth B) and all annual rubber production (yield) were significant for the three traits, with the coefficients decreasing with increasing age. Selection of the sets of best 30, 15, 10 and 5 clones from the available 68 clones at a given age was generally accompanied by a descending order of percentage success. It was suggested: (a) to have the best 30 clones of age 6, select the set of best 36 clones at age 2, (b) to have the best 15 clones of age 6, select the set of best 20 clones at age 3, (c) to have the best 5 clones of age 6, select the set of best 8 clones at age 4, and (d) to have the best 3 clones of age 6, select the set of best 3 clones at age 5. More than 80% of the targeted clones on girth A or girth B basis and more than 76.7% clones on yield basis were found to get selected at steps (a) through (d). For achieving early multiplication of the most productive clone for deployment, multiplication should be started with the best 36 (i.e. 60%) clones selected at age 2.

Genetic variability and selection for laticiferous system characters in Hevea brasiliensis

Six laticiferous system characters were investigated in 22 three-year-old, half-sib rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.] progenies, evaluated at three sites (Votuporanga, Pindorama and Jaú, all in the São Paulo State, Brazil). The traits examined were: average rubber yield (Pp), average bark thickness (Bt), number of latex vessel rings (Lv), average distance between consecutive latex vessel rings (Dc), density of latex vessels per 5 mm per ring averaged over all rings (Dd) and the diameter of the latex vessels (Di). The joint analysis showed that site effect and progeny x sites interaction were significant for all traits, except Lv. Estimates of individual heritabilities across the three sites were high for Bt; moderate for Lv, Pp and Dc; low for Dd and very low for Di. Genetic correlations in the joint analysis showed high positive correlations between Pp and the other traits. Selecting the best five progenies would result in genetic gains of 24.91 percent for Pp while selecting best two plants within a progeny would result in a Pp genetic gain of 30.98 percent.