Estratégias de melhoramento em Eucalyptus pellita F. Muell a partir da distância genética
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Data
2020-03-03
Autores
Andrade, Mateus Chagas
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Universidade Estadual Paulista (Unesp)
Resumo
Eucalyptus pellita F. Muell é uma das espécies de importante interesse nos programas de melhoramento visando agregar alelos complementares, por meio da hibridação com espécies amplamente cultivadas, como o E. grandis e E. urophylla. Para isto, torna-se necessário o conhecimento da variabilidade genética e identificar possíveis grupos heteróticos de modo a orientar os programas de hibridação com o E. pellita. Neste sentido, a presente pesquisa objetivou estimar a variabilidade e a distância genética existente em procedências e progênies de E. pellita, por meio de caracteres quantitativos, a fim de subsidiar possíveis estratégias a serem executadas em um programa de melhoramento da espécie. Foi avaliado um teste de procedências e progênies, com 118 progênies pertencentes a sete procedências, além de um clone comercial como controle. O experimento foi delineado em blocos casualizados com cinco repetições, em parcelas lineares com nove plantas. Foram mensurados os caracteres quantitativos diâmetro a altura do peito (DAP), altura, volume individual e sobrevivência (%) aos sete anos de idade. Os dados foram submetidos a análise REML/BLUP, obtendo-se estimativas das componentes de variância, parâmetros genéticos e valores genéticos preditos (BLUP). Foi estimada a distância genética das procedências e progênies a partir da distância generalizada de Mahalanobis (D²), e posterior formação de grupos heteróticos pelo método de agrupamento de Tocher e método da ligação média (UPGMA). Além disso, foi realizada a análise de componentes principais, para identificar o comportamento das procedências e progênies quanto aos caracteres de crescimento. Pelo teste LRT (p<0,01) houve efeito significativo de procedências e progênies para os caracteres avaliados, exceto para procedências quando considerado o volume individual. De modo geral a variabilidade encontrada entre procedências e progênies foi de baixa magnitude. As herdabilidades individuais no sentido restrito para os caracteres avaliados, variaram de 0,03 a 0,06, sendo a altura com a maior herdabilidade encontrada (0,06). Considerando o caráter volume, a maior divergência genética está dentro das progênies e a menor entre as procedências. Portanto, ganhos de seleção tendem a ser maiores se a seleção for feita dentro de populações e progênies. As distâncias genéticas mínima e máxima entre pares de progênies foram, D²= 0,101 e D²=5,702, respectivamente. O método de agrupamento de Tocher resultou na formação de 29 grupos divergentes entre as progênies. O método UPGMA resultou na formação dos mesmos 29 grupos, porém estes não foram totalmente correspondentes aos grupos formados pelo método de Tocher. Comparando os coeficientes de correlação cofenéticos, o agrupamento das progênies obtido pelo método de Tocher apresentou maior confiabilidade (0,89) em relação a UPGMA (0,63). O agrupamento das procedências pelo método de Tocher resultou em três grupos divergentes com CCC de 0,69, ao passo que o método UPGMA resultou em quatro grupos divergentes com CCC de 0,86, demonstrando maior confiabilidade do agrupamento. As procedências Connl. A e “Orchard” foram as mais divergentes em relação às demais avaliadas, enquanto as procedências M. Ray e Tully apresentaram a maior similaridade. A altura foi o caráter de maior importância relativa para a estimativa da distância genética, tanto para progênies (73,9%) quanto para as procedências (81,6%). A análise de componentes principais (PCA) indicou maior divergência entre as procedências Connl. A e Orchard, corroborando com o que foi encontrado pelos métodos de agrupamento. Ainda pela análise de PCA, algumas progênies (67, 15, 120) tiveram bom desempenho para BLUP de volume. Os resultados obtidos geram informações importantes para que cruzamentos entre indivíduos contrastantes entre e dentro das procedências sejam realizados, a fim de obter híbridos de E. pellita, de modo a validar os possíveis grupos heteróticos obtidos a partir da distância genética e pelos métodos de agrupamento.
Eucalyptus pellita F. Muell is an important species used in breeding programs to add complementary alleles through hybridization with widely cultivated species, such as Eucalyptus grandis and Eucalyptus urophylla. To guide hybridization programs with E. pellita, information about the genetic variability and the identification of possible heterotic groups of the species is necessary. As such, the present study aimed to estimate the variability and genetic distance among E. pellita provenances and progenies using quantitative traits. The goal was to inform possible strategies to be implemented in a species improvement program. A provenance and progeny test with 118 progenies belonging to seven E. pellita provenances was analyzed, with a commercial clone used as the control. The experiment was designed in randomized blocks with five replications in linear plots, and nine plants per plot. The following quantitative traits were measured at seven years of age: diameter at breast height (DBH), height, individual volume, and survival (%). The data were submitted to REML/BLUP analysis to obtain estimates of the variance components, genetic parameters, and predicted genetic values (BLUP). The genetic distance of the provenances and progenies was estimated from the generalized Mahalanobis distance (D²). The formation of heterotic groups was subsequently identified using Tocher’s clustering method and the unweighted pair group method with arithmetic mean (UPGMA). In addition, principal component analysis (PCA) was carried out to identify the behavior of the provenances and progenies in terms of growth traits. Based on the Likelihood-ratio Test (LRT; p <0.01) there was a significant effect of provenances and progenies for the evaluated traits, except for provenances when considering individual volume. In general, the variability found between provenances and progenies was of low magnitude. Strict-sense individual heritabilities ( 2 i h ) for the evaluated traits ranged from 0.03 to 0.06, with height showing the highest 2 i h (0.06). Considering volume, the greatest genetic divergence occurred within progenies ( Qd ˆ = 0.96) and the smallest among provenances ( QST ˆ = 0.01). Therefore, the gains tend to be greater if selection is made within populations and progenies. The minimum and maximum genetic distances between pairs of progenies were D² = 0.101 and D² = 5.702, respectively. Tocher's clustering method resulted in the formation of 29 divergent groups among the progenies. The results of UPGMA also showed the formation of 29 groups, but they did not fully correspond to the groups identified by Tocher. Comparing the cophenetic correlation coefficients, the grouping of progenies obtained by Tocher showed greater reliability (0.89) compared to UPGMA (0.63). Grouping of the provenances based on Tocher clustering resulted in three divergent groups with a CCC of 0.69, whereas the UPGMA resulted in four divergent groups with a CCC of 0.86, demonstrating greater reliability of the later method. The provenances Connl. A and Orchard were the most divergent in relation to the others, while the provenances M. Ray and Tully showed the greatest similarity. Height was the most important trait for estimating genetic distance, both for progenies (73.9%) and provenances (81.6%). PCA indicated greater divergence between provenances Connl.A and Orchard, corroborating what was found by the grouping methods. PCA also showed that some progenies (67, 15, 120) performed well for volume based on the BLUP. The results generate important information that crosses between contrasting individuals among and within the provenances are carried out, in order to obtain E. pellita hybrids to validate the possible heterotic groups obtained from the genetic distance and by the grouping methods.
Eucalyptus pellita F. Muell is an important species used in breeding programs to add complementary alleles through hybridization with widely cultivated species, such as Eucalyptus grandis and Eucalyptus urophylla. To guide hybridization programs with E. pellita, information about the genetic variability and the identification of possible heterotic groups of the species is necessary. As such, the present study aimed to estimate the variability and genetic distance among E. pellita provenances and progenies using quantitative traits. The goal was to inform possible strategies to be implemented in a species improvement program. A provenance and progeny test with 118 progenies belonging to seven E. pellita provenances was analyzed, with a commercial clone used as the control. The experiment was designed in randomized blocks with five replications in linear plots, and nine plants per plot. The following quantitative traits were measured at seven years of age: diameter at breast height (DBH), height, individual volume, and survival (%). The data were submitted to REML/BLUP analysis to obtain estimates of the variance components, genetic parameters, and predicted genetic values (BLUP). The genetic distance of the provenances and progenies was estimated from the generalized Mahalanobis distance (D²). The formation of heterotic groups was subsequently identified using Tocher’s clustering method and the unweighted pair group method with arithmetic mean (UPGMA). In addition, principal component analysis (PCA) was carried out to identify the behavior of the provenances and progenies in terms of growth traits. Based on the Likelihood-ratio Test (LRT; p <0.01) there was a significant effect of provenances and progenies for the evaluated traits, except for provenances when considering individual volume. In general, the variability found between provenances and progenies was of low magnitude. Strict-sense individual heritabilities ( 2 i h ) for the evaluated traits ranged from 0.03 to 0.06, with height showing the highest 2 i h (0.06). Considering volume, the greatest genetic divergence occurred within progenies ( Qd ˆ = 0.96) and the smallest among provenances ( QST ˆ = 0.01). Therefore, the gains tend to be greater if selection is made within populations and progenies. The minimum and maximum genetic distances between pairs of progenies were D² = 0.101 and D² = 5.702, respectively. Tocher's clustering method resulted in the formation of 29 divergent groups among the progenies. The results of UPGMA also showed the formation of 29 groups, but they did not fully correspond to the groups identified by Tocher. Comparing the cophenetic correlation coefficients, the grouping of progenies obtained by Tocher showed greater reliability (0.89) compared to UPGMA (0.63). Grouping of the provenances based on Tocher clustering resulted in three divergent groups with a CCC of 0.69, whereas the UPGMA resulted in four divergent groups with a CCC of 0.86, demonstrating greater reliability of the later method. The provenances Connl. A and Orchard were the most divergent in relation to the others, while the provenances M. Ray and Tully showed the greatest similarity. Height was the most important trait for estimating genetic distance, both for progenies (73.9%) and provenances (81.6%). PCA indicated greater divergence between provenances Connl.A and Orchard, corroborating what was found by the grouping methods. PCA also showed that some progenies (67, 15, 120) performed well for volume based on the BLUP. The results generate important information that crosses between contrasting individuals among and within the provenances are carried out, in order to obtain E. pellita hybrids to validate the possible heterotic groups obtained from the genetic distance and by the grouping methods.
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Palavras-chave
Análise multivariada, Melhoramento florestal, Grupos heteróticos, Híbridos, Multivariate analysis, Forest improvement, Heterotic groups, Hybrids