Resistance to Charcoal Rot Identified Within Soybean Cyst Nematode Resistant Accessions

Two infectious root diseases that cause significant yield losses worldwide in soybean (Glycine max [L.] Merr.) are charcoal rot caused by Macrophomina phaseolina (Tassi) Goid. and the soybean cyst nematode, caused by Heterodera glycines Ichinohe. The objective of this research was to evaluate resistance to charcoal rot in a set of 120 soybean accessions reported to have resistance to one or more races of soybean cyst nematode so that lines with combined resistance could be identified. These accessions were screened in an infested field in 2006 and 2007. Charcoal rot severity ranged from 1 to 5, where 1 is resistant and 5 susceptible. The results showed that out of the 120 soybean accessions tested for charcoal rot resistance 12 were identified to have moderate levels of resistance, 51 had moderate susceptibility, and 60 were susceptible. Furthermore, the accessions with moderate resistance to charcoal rot had resistance for one to two races of soybean cyst nematode. Within the lines identified with moderate resistance to charcoal rot, nine had a yellow seed coat, a desirable agronomic trait. These lines can be used as parents in soybean breeding programs for developing soybean cultivars with combined resistance to both charcoal rot and soybean cyst nematode.