Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2008
Publication Date: 6/1/2008
Citation: Twizeyimana, M., Ojiambo, P.S., Ikotun, T., Ladipo, J.L., Hartman, G.L., Bandyopadhyay, R. 2008. Evaluation of Soybean Germplasm for Resistance to Soybean Rust (Phakopsora pachyrhizi) in Nigeria. Plant Disease. 92(6):947-952.
Interpretive Summary: Soybean rust is one of the most important constraints to soybean production worldwide. The absence of high levels of host resistance to the pathogen has necessitated the continued search and identification of sources of resistance. Renewed efforts to identify resistant genotypes have been initiated in the last 10 years primarily due to discovery of the pathogen in Africa, South America and the US. The objectives of this study were to evaluate IITA breeding lines for resistance to P. pachyrhizi and identify accessions from USDA-ARS that are potential sources of rust resistance in Africa. Six soybean lines had consistently the lowest level of disease severity across years and locations. These results indicate that these lines could be useful sources of soybean rust resistance that could be incorporated into high yielding and adapted soybean cultivars. This research is important to soybean researchers that are interested in developing resistance to soybean rust.
Technical Abstract: Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important constraints to soybean production worldwide. The absence of high levels of host resistance to the pathogen has necessitated the continued search and identification of sources of resistance. In one set of experiments, 178 IITA soybean breeding lines were rated for rust severity in the field in 2002 and 2003 at Ile-Ife, Yandev and Ibadan, Nigeria, Thirty six lines with disease severity '2 (based on a 0-5 scale) were selected for a second round of evaluation in 2004 at Ibadan. In the third round of evaluation under inoculated field conditions, 11 breeding lines with disease severity '2 were further evaluated for rust resistance at Ibadan in 2005 and 2006. The breeding lines TGx 1835-10E, TGx 1895-50F and TGx 1903-3F had consistently the lowest level of disease severity across years and locations. In another set of experiments, 98 accessions from USDA-ARS were evaluated in the first round in 2005 under inoculated in the greenhouse; 12 accessions with disease severity '20% leaf area infected were selected for evaluation in the second round in 2005 and 2006 under inoculated field conditions at Ibadan. Highly significant differences (P < 0.0001) in disease severity were observed among the 98 accessions during this first round of rust evaluation. Significant (P < 0.0001) differences in rust severity and sporulation were also observed among the 12 selected accessions. Accessions PI 594538A, PI 417089A and UG-5 (resistant check) had significantly (P < 0.05) lower disease severity than all other selected accessions in both years of evaluation with rust severities ranging from 0.1% to 2.4%. These results indicate that the breeding lines (TGx 1835-10E, TGx 1895-50F and TGx 1903-3F) and accessions (PI 594538A, PI 417089A and UG-5) could be useful sources soybean rust resistance genes for incorporation into high yielding and adapted varieties.