Genetic gain and correlations among traits for stink bug resistance in soybeans

An experiment was carried out at the State University of Londrina School Farm in a randomized complete blocks design with three replications; the plots underwent natural stink bug attacks to check correlations existing among agronomic traits and stink bug damage in 33 F₈ pure lines soybean. The seed size trait was measured by the weight of a hundred seeds (WHS) and the percentage of stink bug damage seeds (PDS) was measured by staining the seeds with tetrazolium at 0.01%. Seeds were considered damaged with at least one puncture and or with marks characteristic of stink bug. The phenotypic and genotypic correlations between the WHS and the PDS seeds were positive, being 0.51 and 0.67 ± 0.19, respectively. The relationship between the visual pod width (VPW) and PDS was also significant, being 0.41 and 0.54 ± 0.19 for phenotypic and genotypic correlations, respectively. Thus the breeder can select lines for stink bug resistance indirectly either by WHS or VPW. These two traits are very easy to assess when compared with the assessment of PDS damage, allowing the use of larger populations. However, in this case, the genetic gains by selection were smaller than those obtained by direct selection, but even so they were considered noteworthy. The VPW may be an efficient way of selection in large populations for stink bug resistance. This revised version was published online in July 2006 with corrections to the Cover Date.