Genetic parameter estimates and efficiency of three selection procedures in carrot breeding, variety Campinas

RESUMO

The potential for genetic breeding of the carrot variety "Campinas" was assessed through estimates of the genetic-statistical parameters of 16 traits of agronomic importance. The parameters were obtained from 102 half-sib progenies, harvested in a seed production field. Two experiments were carried out in Randomized Complete Blocks in the fall-winter and spring-summer planting periods. To compare the three selection methods, usually employed in population breeding genetics the expected genetic gains were estimated considering each blockor plot as strata, and mass selection between and within the half-sib progenies. Samples of 15 marketable roots per plot were evaluated at the individual level for the characters root length (RL) and root shape index (SI). A joint analysis of variance, weighted for the differences in number of replications between the experiments was performed for the six common traits. The results of the genetic parameter estimates of the single variance analysis indicated that the variety Campinas was best adapted to the fall-winter planting period. Heritabilities greater than 60 per cent were observed for the majority of traits assessed at the plot level. The selecction against the trait premature flowering (PF) may result in satisfactory genetic gain in the two environmental conditions because of the high genetic variability coefficients obtained. The percentage of marketable cylindrical roots (MCR) demonstrated an expected genetic gain per cycle of only 4.82 per cent in the fall-winter period, probably because it had already been selected, for various cycles, under these environmental conditions. On the other hand, in the spring-suminer planting period, the genetic gain was estimated to be 14.44 per cent. Total and marketable yields were high in the fall-winter period and low in the spring-summer period. For the traits RL and SI, assessed at the individual level, the stratified mass selection, considering each plot as strata, was less efficient in relation to the other proposed selection methods. Therefore it is concluded that breeding of the variety Caampinas, based on the performance of the half-sib progenies for root quality and yield is fairly promising within each planting period, but simultaneous selection for both periods is difficult.