Individual And Joint Analyses Of Sugarcane Experiments To Select Test Lines

In the early stages of a breeding program many field trials are conducted, considering several soil and weather conditions. In the case of sugarcane, these experiments are installed using a large number of test lines, but limitations in the field and of the amount of genetic material do not allow the replication of many. This work evaluated 21 trials from different regions, from a Brazilian sugarcane breeding program. Each of these experiments occupied a rectangular array of around 20 rows by 25 columns in most instance, the plots were 12 m longer, double-furrows with 0.9m between furrows within the plot and 1.5m spacing between different plots and 1m between columns. All the trials had at least 79% of the area planted with unreplicated test lines, the at most 21% of the plots were occupied by four commercial varieties, check. A special check, interspersed along diagonals, was planted systematically on a diagonal grid, the other three were equally replicated and each replicate was spread out in three neighbouring row plots. Seven of the 21 experiments had no significant direct genetic effects, 11 presented significant competition at the residual level and only one had significant competition at the genetic level. The correlation between the selected test lines for the different experiments in a same region was less than 0.54. However, the genetic correlation was significant in the joint analyses and stronger than that from the individual analyses. Two simulation studies were performed: the first investigated the analysis for a single experiment and the results show that it is difficult to fit a model when there is genetic competition with or without residual competition. The same difficulty was observed in the second study, which compared the results from individual and joint analyses. It showed that, even for the joint analyses, only around 45 to 55% of the true best test lines were selected.