Evaluation of Soybean Genotypes for Resistance to Charcoal Rot

Abstract

Charcoal rot, caused by Macrophomina phaseolina, significantly reduces yield in soybean more than most other diseases in the midsouthern United States. There are no commercial genotypes marketed as resistant to charcoal rot. Reactions of 27 maturity group (MG) III, 29 Early MG IV, 34 Late MG IV, and 59 MG V genotypes were evaluated for M. phaseolina between 2006 and 2008 in a non-irrigated, no-till field that had been artificially infested for three years. There was significant variation in root colonization among genotypes and years, indicating the value of screening genotypes over multiple years. Based on CFUI there was no genotype that was consistently immune to charcoal rot each year. However, there were a total of six genotypes (one genotype in MG III, one in Late MG IV, and four in MG V) that were identified as moderately resistant. Some of the commercial and public genotypes were resistant to M. phaseolina at levels equal to or greater than the standard DT97-4290, a moderately resistant cultivar. The genotypes identified as having moderate resistance across the three years could be useful as sources for developing resistant soybean genotypes. Accepted for publication 27 July 2011. Published 26 September 2011.

Registration of DT99‐16864 Soybean Germplasm Line with Moderate Resistance to Charcoal Rot [Macrophomina phaseolina (Tassi) Goid.]

“…The methods to evaluate CFU, CFUI, RSS, and percent height of stem internal vascular discoloration (PHSD) were more fully described in Mengistu et al (2007). Data from charcoal rot screens in Stoneville in 2002 to 2003 and Jackson, TN, in 2006 to 2008 were reported and analyzed by Mengistu et al (2007) and Mengistu et al (2011a), respectively. Briefly, to evaluate RSS, the lower stem and root are collected at R7 (Fehr et al, 1971) split lengthwise, and the internal color rated on a scale from 1 (no microsclerotia visible in tissue) to 5 (vascular tissue darkened due to high numbers of microsclerotia both inside and outside of the stem and root tissues) (Mengistu et al, 2007).…”

“…From the CFU data, the CFU Index (CFUI) is calculated for each line as the CFU of each line divided by the CFU of the susceptible check (Mengistu et al, 2007). The susceptible checks were MD98‐5579, a breeding line from the Maryland Agricultural and Experiment Station and USDA‐ARS (Paris, 2003), in the Stoneville trials (Mengistu et al, 2007), and Pharaoh (Schmidt et al, 1993) in the Jackson trials (Mengistu et al, 2011a).…”

“…Methods for statistical analysis for data from charcoal rot screens in Stoneville in 2002 to 2003 and Jackson in 2006 to 2008 are reported in Mengistu et al (2007) and Mengistu et al (2011a), respectively. Additionally, we calculated the mean CFUI across years for the maturity group V trials from Mengistu et al (2011a) using the Mixed Procedure of SAS (SAS Institute, 2010). The genotype means for each year were used for the analysis, and the model used genotype as a fixed effect and years as a random effect.…”

“…DP3478 is the only line in common between the two studies. It is reasonable to suggest that the southern lines evaluated in Mengistu et al (2011a) had overall higher levels of resistance than the lines evaluated in Smith and Carvil (1997). Therefore, DP3478 appeared susceptible relative to the lines in Mengistu et al (2011a) but moderately resistant relative to the lines in Smith and Carvil (1997).…”

“…DT99‐16864 was next determined to be moderately resistant to charcoal rot on the basis of field trials on nonirrigated, no‐till fields infested with M. phaseolina ‐infected millet seed in 2006, 2007, and 2008 at the West Tennessee Research and Education Center at the University of Tennessee in Jackson (Mengistu et al, 2011a). In these trials, the overall mean CFUI score of DT99‐16864 (13) was significantly lower than susceptible check Pharaoh (100), moderately susceptible cultivars Progeny 5250 (56) and Stoddard (51) (Shannon et al, 2007), and susceptible cultivar Stine 5142 (68).…”