Charcoal rot [Macrophomina phaseolina (Tassi) Goid] is a major yield-limiting disease throughout the soybean production regions of the USA. This disease, greatly favored by hot, dry soil conditions, is essentially impossible to manage since no resistant material has been available until the discovery of soybean [Glycine max (L.) Merr.] line DT97-4290. DT97-4290 is a late maturity group IV indeterminate soybean line exhibiting field tolerance to charcoal rot based on field evaluations from 2002 to 2004 in artificially infested sandy loam soil at Stoneville, MS. Host tissue colonization by M. phaseolina was assessed in three replications by destructively sampling ten plants at the R7 growth stage. The severity of internal discoloration for stem and root was measured on a scale of 1-5 (where 1= resistant and 5= susceptible). The disease severity ratings over the three years averaged 1.6 and 3.6 for DT97-4290 and Manokin, respectively, with 4,388 and 8,331 colony forming units for DT97-4290 and Manokin, respectively. Preliminary yield tests indicate that DT97-4290 does not exhibit significant yield differences when grown on soils infested with charcoal rot compared to those soils free of the disease. These results indicate that DT97-4290 is a valuable source of resistance to charcoal rot.
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