Dynamics of expression between onion line traits on the basis of phenotypic and genotypic correlations
The cultivation of onion in Brazil has a relevant socioeconomic contribution. Despite the potential, there are few onion breeding programs for tropical conditions. One of the major obstacles is related to the complexity during the selection steps, since in onion, quantitative characters and low heritability predominate. For this reason, the purpose of this study was to assess the dynamics of expression between onion line traits based on phenotypic and genotypic correlations. Four sets of onion genotypes were assessed, comprising both advanced and segregating lines. The traits assessed were plant vigor, diameter of pseudostem, plant architecture, plant cycle, average bulb mass, bulb firmness and bulb postharvest. Phenotypic and genotypic correlations were calculated. Path analysis provided the estimate of the direct and indirect effects based on average bulb mass as the main variable. There was dynamics in trait expression. Coherence was reported for the correlation values of the different traits among the different germplasms (experiment 1 with 109 advanced lines; experiment 2 with 227 segregating lines; experiment 3 with 53 advanced lines; and experiment 4 with110 segregating lines). Correlations were positive for all average bulb mass x plant vigor experiments; plant architecture x plant vigor was also positive in all experiments, except for experiment 1 (109 advanced lines). The correlations which were larger in magnitude were those between bulb postharvest and plant cycle, and between bulb postharvest and average bulb mass. The phenotypic and genotypic correlations showed low association between traits in all experiments, except for experiment 3 (53 advanced lines), in which some pairs of correlations were moderate to high; however, the path analysis confirmed that the cycle (in days) and bulb postharvest showed weak cause-and-effect relationship with the main variable, rendering indirect selection impracticable for onion average bulb mass.