Identification of Soybean Genotypes Resistant to Charcoal Rot by Seed Inoculation With Macrophomina phaseolina

Soybean charcoal rot is a widespread root disease caused by the fungus Macrophomina phaseolina, a natural soil inhabitant that has great pathogenic variability and high survival capacity under adverse conditions. There are no registered fungicides or genotypes genetically resistant to this disease, although differences in susceptibility have been observed. As the fungus is a seed-borne pathogen, screening methods based on seed inoculation are quick and efficient. The objective of this work was to assess the efficiency of soybean seed infestation by incubation for 48 h with colonies of M. phaseolina, comparing two germination environment methods (germination paper or in pots with substrate), and to correlate the relative germination of genotypes of both methods with the severity of charcoal rot observed in a field test. The results showed that 48 h were sufficient to infest seeds and reduce the germination. The germination in paper was higher at 5 days after sowing (DAS) than that in pots at 8 DAS in a greenhouse. Both environments exhibited a highly negative correlation between seed germination and field disease severity (r = -0.775 in germination paper and r = -0.779 in pots with substrate). It is recommended that the germination test be performed in germination paper due to practicality and economy of space, material, and labor besides the better control of the environment.