Field screening of Paraguayan soybean germplasm for resistance to charcoal rot

The aim of this work was to identify genetic resistance to charcoal rot (Macrophomina phaseolina) in soybean germplasm from the National Breeding Program of the Instituto Paraguayo de Tecnología Agraria (Paraguayan Institute of Agricultural Technology). During two seasons, 51 commercial and experimental lines from the local breeding program were field evaluated in Itapúa-Paraguay. The lines were planted in single rows previously infested, using a completely randomized block design with four repetitions. The charcoal rot severity was evaluated in the stems and roots at the physiological maturity stage. On a Root and Stem Severity index scale of 1-5, the median severity for the 34 early maturity genotypes was 1.5 and 1 in 2017/2018 and 2018/2019, respectively. Nine genotypes (AG-6525 xi, SP14041, SP14222, SP14583, SP15013, SP15133, SP15218, SP16020, and SPB-14146) were rated as resistant (1) in both evaluations. The median severity for the 15 semi-early genotypes was 2 and 1 in 2017/2018 and 2018/2019, respectively. This study allowed us to identify previously unreported sources of resistance to charcoal rot in maturity group IV, V and VI. We believe that germplasm screening under field conditions is a viable alternative to identify breeding lines which are less sensitive to charcoal rot.