Uni and multivariate approaches for diallel analysis in early generation trials for soybean tolerance to rust

Due to the high impact of Asian soybean rust (SBR) in Brazilian croplands, several studies have been conducted in order to maintain or increase the grain yield gain over years in the presence of the pathogen. The aim of this study was to define a breeding strategy applying uni and multivariate approaches for diallel analyzes in early generation trials and contrasting disease conditions. Thus, assessing genetic parameters to identify traits related to greater tolerance to soybean rust. Deploying a North Carolina design II scheme (4 elite commercial cultivars x 10 rust-tolerant experimental lines), we obtained 40 F-2 crosses that were evaluated in a randomized complete block design with 4 replicates. The crosses were conducted in two environments, contrasting only for the fungicide management (with and without rust control), enabling the estimation of the rust impact on 11 traits, divided into two groups: adaptive and reproductive. A multi-environment diallel model was applied assuming all effects as fixed in order to estimate the general (GCA) and the specific (SCA) combining abilities. The multivariate diallel analysis was performed in each rust management using MANOVA to test the genetic effects. The rust conditions were the most important source of variation for almost all evaluated traits. Using the contrasting disease conditions, we were able to identify crosses with desirable SCA and parents with GCA, which implies that tolerance can be used as a strategy to deal with SBR. The implementation and the use of multivariate diallel analysis aiming to increase the efficiency of genotype selection for rust tolerance is discussed.