Resistance to charcoal rot identified in ancestral soybean germplasm

Charcoal rot, caused by the fungal pathogen Macrophomina phaseolina, is an economically important disease on soybean and other crops including maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and sunflower (Helianthus annuus L.). Without effective cultural or chemical options to control charcoal rot in soybean [Glycine max (L.) Merr.], finding sources of genetic resistance is of high interest. In this study, 70 ancestral soybean genotypes were screened for resistance to M. phaseolina using a cut-stem inoculation technique under semi-controlled greenhouse conditions. Lesion progression on the stems in the first experiment was measured 7 to 15 d after inoculation. Three follow-up experiments were conducted to select and confirm the genotypes with the strongest partial resistance. Two experiments evaluated lesion lengths and the third experiment evaluated seedling survival. In the two experiments measuring lesion lengths, PI 548302 (42 and 38 mm) and PI 548414 (36 and 52 mm) had significantly shorter lesion lengths than the moderately resistant genotype, DT97-4290 (58 and 87 mm). In the fourth experiment, percentage survival of PI 548414 (88%), PI 548302 (81%), and PI 548178 (66%) were significantly higher than survival of DT97-4290 (32%). These three genotypes may be useful as parents for developing soybean cultivars with charcoal rot resistance.