Estimates of genetic parameters of late seed-coat darkening of carioca type dry beans

Abstract

In order to facilitate commercialization of cultivars of carioca type dry beans, the grains must have the lightest possible cream color and this phenotype must be persistent (late seed-coat darkening). There are reports of genetic variability for this trait. The objectives of this study were to obtain information regarding genetic control of the trait, with emphasis on the estimate of heritability and if it varies according to days after harvest, to verify the effect of locations and/or crop season on seed-coat darkening of the grains and to estimate the genetic and phenotypic correlations of the trait with cooking time, tannin content and grain yield. F 2:3 and F 2:4 progenies derived from crossing of the cultivar BRSMG Madrepérola (late seed-coat darkening) and the line RP-2 (early seed-coat darkening) were used. It is concluded that seed-coat darkening is influenced by the environment, crop season or locations; nevertheless, the interaction progenies x environments and progenies x locations is predominantly simple, not expressively changing classification of the progenies. Although the heritability of the darkening scores tends to increase with the storage time of the grain, the interaction progenies x time periods of assessment was not observed. Grains with late seed-coat darkening present a lower tannin content and require less cooking time. The genetic correlation between a dark seed-coat and grain yield was practically null.Index terms: Phaseolus vulgaris L., genetic plant breeding, quantitative genetics, grain quality. RESUMOPara facilitar a comercialização das cultivares de feijão carioca, estas devem possuir cor creme dos grãos o mais claro possível e esse fenótipo deve ser persistente (escurecimento tardio). Há relatos de variabilidade genética para esse caráter. Os objetivos deste trabalho foram obter informações sobre o controle genético do caráter, com ênfase na estimativa da herdabilidade e se ela varia com os dias após a colheita, verificar o efeito de locais e/ou safras sobre o escurecimento dos grãos e estimar as correlações genéticas e fenotípicas do caráter com o tempo de cozimento, teor de tanino e produtividade de grãos. Para isso foram utilizadas progênies F 2:3 e F 2:4 derivadas do cruzamento entre a cultivar BRSMG Madrepérola (escurecimento tardio) e a linhagem RP-2 (escurecimento precoce). Concluiu-se que o escurecimento é influenciado pelo ambiente, safras ou locais; contudo a interação progênies x ambientes e progênies x gerações é predominantemente simples, não alterando expressivamente a classificação das progênies. Embora a herdabilidade das notas de escurecimento tenha tendência de aumentar com o tempo de armazenagem dos grãos, não foi constatada interação progênies x épocas de avaliação. Grãos com escurecimento tardio possuem menor teor de tanino e exigem menor tempo de cocção. A correlação genética entre escurecimento e produtividade de grãos foi praticamente nula. Termos para indexação:Phaseolus vulgaris L., melhoramento genético de plantas, genética quantitativa, quali...

Genetic control and estimation of genetic parameters for seed-coat darkening of carioca beans

“…Junk-Knievel et al (2008), upon evaluating pinto beans, verified that grain darkening was controlled by a single gene with dominance being conferred by the allele expressing normal darkening. Similar results were obtained by Silva et al (2008) and Araújo et al (2012), who described an analogous genetic control upon evaluation of progenies from a single carioca bean population. On the other hand, Elsadr et al (2011) determined that two genes in recessive epistasis, expressing three phenotypic classes, controlled grain darkening in bean populations that originated from pinto beans, cranberry-like beans, and two genetic testers for the j allele.…”

“…According to Basset (1996), seed-coat darkening is controlled by a single gene with alleles J and j, and the expression of the recessive allele j results in genotypes that are less susceptible to tegument darkening when compared with seeds of plants carrying the dominant allele. Results confirming that the trait is controlled by one gene with the dominance of the allele being responsible for seed-coat darkening were reported by Junk-Knievel et al (2008), Silva et al (2008), and Araújo et al (2012) using different lines. On the other hand, Elsadr et al (2011) described a model with two genes interacting under epistasis, leading to three phenotypic classes for seed-coat darkening.…”

“…Junk-Knievel et al (2007) observed that beans that were produced under irrigation presented lighter seed coats than those grown under dry land conditions. Araújo et al (2012) indicated that grain darkening is greatly influenced by the environment, growing season, and location. Other results demonstrated that the variability in rate of darkening was due to the sensibility of the genotypes to environmental variations and to the effects of GxE interactions upon the trait (Ribeiro et al, 2004;Filho et al, 2006;Junk-Knievel et al, 2007).…”

“…At first, monogenic segregation based on dominance of the allele conferring normal darkening was tested, because this was the genetic model identified by Silva et al (2008) and Araújo et al (2012). Thus, the expected segregation in the F 2 generation would be three progenies with normal darkening (ND) to one progeny with slow darkening (SD).…”

“…Under this model, the J gene, responsible for darkening (yes or no), interacts epistatically with a second gene Sd, that is responsible for the rate of darkening (slow or normal), where the latter recessive allele is responsible for the slow rate. Despite such discordant results and the paucity of information for such a characteristic, it is common knowledge that it is possible to select lines with slow seed-coat darkening (Faria et al, 2004;Junk-Knievel et al, 2008;Silva et al, 2008;Araújo et al, 2012;Carneiro et al, 2012).…”