Genetic control of number of flowers and pod set in common bean.

This article aimed to study the genetic control of some flowers and pod set of common bean and to verify if its estimate varies with environmental conditions and gene pool. A complete diallel was used among six lines, but no reciprocal ones. The treatments were evaluated in three harvests/generations - F2, F3, and F4 - in 2015/2016, in a randomized complete block design with four replications. The plot consisted of 3 lines with 4 m. In the center line, a receptacle to collect the aborted flowers/pods was placed. The traits considered were the number of flowers/plant (N), the percentage of pod set (V), and the production of grain/plant (W). A joint diallel analysis was performed, and the correlations between N, V, ​​and W were estimated. N was 31.9 on average, and V was 40.4%. The average of Mesoamerican parents, for N and V, was higher than for Andean. Specific combining ability explained most of the variation for N, evidencing predominance of dominance effect. For V, specific combining ability was slightly lower than general combining ability, indicating additive loci and also dominance effects. These two traits were very influenced by environment and should be considered a strategy for greater grain yield stability of common bean.

Genetic progress estimation strategy for upright common bean plants using recurrent selection.

Common bean producers in Brazil tend to grow plants as upright as possible. Because the control of this trait involves a large number of genes, recurrent selection (RS) is the best approach for successful plant improvement. Because plant architecture (PA) is evaluated using scores and usually has high heritability, RS for PA is performed through visual selection in generation S0. The aim of the present study was to evaluate selection progress and investigate whether this progress varies with the number of selected progenies or the generation evaluated. In addition, the effect of RS for the upright (PA) trait on progeny grain yield (GY) was investigated. Data of progenies S0:3 and S0:4 of the fifth, eighth, and twelfth cycles were used. A combined analysis of variance was performed using the adjusted means of the 47 best progenies from each generation and cycle, using two control cultivars as reference. A joint analysis of the two generations used during the evaluation of progenies for the different cycles was also performed. The genetic progress (GP) was estimated by fitting a linear regression equation to the relationship between the adjusted mean of each cycle and the number of cycles. We found that RS was efficient and the estimated GP of the evaluated progenies was 4.5%. Based on the GY heritability estimates, in more advanced generation selection for GY can be successfully performed on progenies. Thus, the selection already done for PA in F2 could be associated to the most productive progenies.

Genotype x environment interaction and its implication in identification of common bean populations with high calcium content.

The common bean is a food with high mineral content. Of the various types of beans cultivated in Brazil, carioca type beans are the most consumed. The aim of this study was to identify promising common bean populations with an emphasis toward the selection of carioca type bean lines with high calcium content. We also aimed to verify whether and how the crop season and the genotype (parental line and hybrid populations) x crop season interaction affect calcium content. A group of 3 lines of good agronomic characteristics were crossed with a group of 4 lines with high calcium content in a 3 x 4 partial diallel design. Great variability was identified among both the parental lines and the hybrid populations derived from the diallel crosses among the parental lines. We found significant interactions between crop season and both parental line and hybrid population. In the diallel analysis, only the general combining ability was significant, explaining 89.4% of the sum of squares. The RP-1, CNF05, and Safira lines exhibited the greatest calcium contents and a positive GCA. RP-1 is a line that presents high calcium content, in addition to having carioca type beans and an upright plant with high yield. To further increase the calcium content of the RP-1 line, we suggest crossing it with the CNF05 and Safira lines. Although there was a hybrid population x crop season interaction, it was possible to identify populations that performed best in terms of calcium content in both crop seasons.

Epistasis in intra- and inter-gene pool crosses of the common bean.

Epistasis has been shown to have an important role in the genetic control of several quantitative traits in the common bean. This study aimed to investigate the occurrence of epistasis in intra- and inter-pool gene crosses of the common bean. Four elite lines adapted to Brazilian conditions were used as parents, two from the Andean gene pool (ESAL 686; BRS Radiante) and two from the Mesoamerican gene pool (BRSMG Majestoso; BRS Valente). Four F2 populations were obtained: "A" (ESAL 686 x BRS Radiante), "B" (BRSMG Majestoso x BRS Valente), "C" (BRS Radiante x BRSMG Majestoso), and "D" (BRS Valente x ESAL 686). A random sample of F2 plants from each population was backcrossed to parents and F1 individuals, according to the triple test cross. Three types of progenies from each population were evaluated in contiguous trials. Seed yield and 100-seed weight were evaluated. Dominance genetic variance was predominant in most cases. However, the estimates of genetic variance may be biased by the occurrence of linkage disequilibrium and epistasis. Epistasis was detected for both traits; however, the occurrence differed among the populations and between the two traits. The results of this study reinforce the hypothesis that epistasis is present in the genetic control of traits in the common bean and suggest that the phenomenon is more frequent in inter-gene pool crosses than in intra-gene pool crosses.

Aggressiveness of Pseudocercospora griseola strains in common bean genotypes and implications for genetic improvement.

The fungus Pseudocercospora griseola, the causal agent of angular leaf spot in the common bean (Phaseolus vulgaris L.), exhibits a broad pathogenic variability that complicates the development of resistant cultivars. For breeding programs to successfully obtain common bean cultivars with durable resistance, knowing the aggressiveness of different strains, as well as the mechanisms of genetic resistance, is important. The aims of this study were to study the variation within race 63.63 by evaluating the aggressiveness of different strains, to analyze the genetic resistance of common bean lines to P. griseola, and to ascertain the implications for genetic improvement in obtaining resistance in this pathosystem. Four strains, collected from different locations, were inoculated in three groups of common bean lines in a greenhouse, and the severity of the disease was subsequently evaluated. Statistical analyses were carried out using the diallel method, which provided information on the vertical and horizontal resistance of host plants, in addition to information regarding the aggressiveness of the strains. The aggressiveness of P. griseola differed between the strains of race 63.63. The diallel method proved to be promising for the identification of horizontal and vertical resistance in the common bean-P. griseola pathosystem, with a predominance of horizontal resistance. Gene pyramiding, using marker-assisted selection, may not be the most effective strategy for obtaining durable resistance.

Implications of the progeny x environment interaction in selection index involving characteristics of the common bean.

Breeders normally select simultaneously for several traits in various environments. We investigated the effects of the progeny x environment interaction on success in selection for several traits. The population used was obtained from a cross between the CVIII-85-11 line, which has a semi-erect to prostrate plant architecture and a cream with brown streaks bean type, and the BRS-Supremo cultivar, which has an erect plant architecture and black grains. In experiments conducted in the field, 47 progenies F(4:6) and F(4:7) were evaluated for two seasons for grain yield, plant architecture and grain type score. The variables were standardized and we obtained the sum of Z. The components of genetic variance in the average of the two environments were nil due to the progeny x environment interaction, which would hinder successful simultaneous selection of characters.

Strategies in identifying individuals in a segregant population of common bean and implications of genotype x environment interaction in the success of selection.

The objective of this study was to compare the BLUP selection method with different selection strategies in F(2:4) and assess the efficiency of this method on the early choice of the best common bean (Phaseolus vulgaris) lines. Fifty-one F(2:4) progenies were produced from a cross between the CVIII8511 x RP-26 lines. A randomized block design was used with 20 replications and one-plant field plots. Character data on plant architecture and grain yield were obtained and then the sum of the standardized variables was estimated for simultaneous selection of both traits. Analysis was carried out by mixed models (BLUP) and the least squares method to compare different selection strategies, like mass selection, stratified mass selection and between and within progeny selection. The progenies selected by BLUP were assessed in advanced generations, always selecting the greatest and smallest sum of the standardized variables. Analyses by the least squares method and BLUP procedure ranked the progenies in the same way. The coincidence of the individuals identified by BLUP and between and within progeny selection was high and of the greatest magnitude when BLUP was compared with mass selection. Although BLUP is the best estimator of genotypic value, its efficiency in the response to long term selection is not different from any of the other methods, because it is also unable to predict the future effect of the progenies x environments interaction. It was inferred that selection success will always depend on the most accurate possible progeny assessment and using alternatives to reduce the progenies x environments interaction effect.