Clonal stability of latex yield in eleven clones of Hevea brasiliensis Muell. Arg.

Eleven Hevea brasiliensis clones were evaluated for clonal stability of latex yield. A randomized complete block design was used with four replicates, two locations, seven years and three periods per year. Stability analysis was based on clone x year and clone x year x location interactions. Five stability parameters viz environmental variance, shukla's stability variance, regression of clonal latex yield on environmental index, variance due to regression and variance due to deviation from regression were applied. There was significant clone x environment effect at the two levels of interaction. Among the eleven clones, C 162 was outstanding for clonal stability and it can serve as donor parent for stability alleles. Three clones (C 76, C 150 and C 154) were also stable. The four stable clones (C 76, C 150, C 154 and C 162) are suitable for broad-spectrum recommendation for latex yield. Five clones (C 83, C 143, C 163, C 202 and RRIM 600) will require environment-specific recommendation because of their unstable phenotype. The stability feature of two clones (C 145 and C 159) was not clear and this will be investigated in subsequent studies

Natural rubber contributions to adaptation to climate change

The purpose of this paper is to present research results relative to impacts of Climate Change on natural rubber production, potential means of adaptation and contribution of rubber to livelihoods resilience to climate change following a recent workshop organized by IRSG in collaboration with CIFOR/FTA, IRRDB and CIRAD. Climate change already impacts rubber production. In some regions longer dry seasons and more variable precipitations threaten the survival of young plants. Rubber has never been planted in areas with an average temperature higher than 28°C; as latex flow after tapping depends on temperature, higher temperatures may have a severe impact on production. Abnormal rains can also disrupt tapping. These modifications will drive a shift of climatically favourable areas. Most pests and diseases affecting rubber are strongly influenced by climate conditions

Divergence and genetic variability among superior rubber tree genotypes Divergência e variabilidade genética de genótipos superiores de seringueira

The objective of this work was to estimate the genetic variability and divergence among 22 superior rubber tree (Hevea sp.) genotypes of the IAC 400 series. Univariate and multivariate analyses were performed using eight quantitative traits (descriptors), including yield. In the univariate analyses, the estimated parameters were: genetic and environmental variances; genetic and environmental coefficients of variation; and the variation index. The Mahalanobis generalized distance, the Tocher agglomerative method and canonical variables were used for the multivariate analyses. In the univariate analyses, variability was verified among the genotypes for all the variables evaluated. The Tocher method grouped the genotypes into 11 clusters of dissimilarity. The first four canonical variables explained 87.93% of the cumulative variation. The highest genetic variability was found in rubber yield-related traits, which contributed the most to the genetic divergence. The most divergent pairs of genotypes are suggested for crossbreeding. The genotypes evaluated are suitable for breeding and may be used to continue the IAC rubber tree breeding program.<br>O objetivo deste trabalho foi estimar a divergência e a variabilidade genética entre 22 genótipos superiores de seringueira (Hevea sp.) da série IAC 400. Análises univariadas e multivariadas foram realizadas com oito caracteres quantitativos (descritores), incluindo produtividade. Na análise univariada, os parâmetros estimados foram: variâncias genética e ambiental, coeficientes de variação genética e ambiental, e índice de variação. A distância generalizada de Mahalanobis, o método aglomerativo de Tocher e variáveis canônicas foram utilizados nas análises multivariadas. Nas análises univariadas, verificou-se variabilidade entre os genótipos para todas as variáveis avaliadas. O método de Tocher agrupou os genótipos em 11 grupos de dissimilaridade. As quatro primeiras variáveis canônicas explicaram 87,93% da variação acumulada. A maior variabilidade genética foi encontrada em variáveis relacionadas à produtividade de borracha, que foram as que mais contribuíram para a divergência genética. Os pares de genótipos identificados como mais divergentes são indicados para cruzamentos. Os genótipos avaliados são adequados para o melhoramento genético e podem ser utilizados para continuar o programa de melhoramento da seringueira do IAC