Fusarium solani f. sp. glycines (FSG; syn. F. virguliforme Akoi, O'Donnell, Homma & Lattanzi) is a soil-borne fungus that infects soybean roots and causes sudden death syndrome (SDS), a widespread and destructive soybean disease. The goal of this study was to develop and use a real-time quantitative polymerase chain reaction (QPCR) assay to compare the accumulation of genomic DNA among 30 FSG isolates in inoculated soybean roots. Isolates differed significantly (P < or = 0.05) in their DNA accumulation on a susceptible soybean cultivar when detected and quantified using a FSG-specific probe/primers set derived from the sequences of the nuclear-encoded, mitochondrial small subunit ribosomal RNA gene. QPCR results that were normalized as the fold change over the sample collection times after inoculation were significantly (P < or = 0.001) correlated with the log(10) transformed colony-forming unit (CFU) values of FSG obtained from plating of inoculated ground roots on FSG semi-selective agar medium. Several isolates were identified that accumulated more FSG DNA and had higher CFU values than the reference isolate FSG1 (Mont-1). Compared to other isolates, FSG5 was the most aggressive root colonizer based on DNA accumulation and CFU values in infested roots. The described QPCR assay should provide more specificity, greater sensitivity, and less variability than alternatives to the culturing-dependent and time-consuming plating assays. Evaluation of isolate relative DNA differences on host plants using the QPCR approach provides useful information for evaluating isolates based on the extent and/or degree of colonization on soybean roots and for selecting isolates for breeding SDS-resistant soybean lines.
Soybean rust, caused by Phakopsora pachyrhizi Syd. & P. Syd., is one of the most destructive diseases of soybean [Glycine max (L.) Merr.] worldwide. To identify sources of resistance to domestic soybean rust fungus populations for plant breeding, our strategy has been to evaluate soybean lines that were previously identified as resistant to foreign isolates. In this study, two sets of plant introductions (PI) were evaluated using P. pachyrhizi urediniospores collected in Mississippi in 2006. The first set of PIs contained 10 lines previously identified as resistant in Paraguay, four PIs with known single genes for resistance to P. pachyrhizi, and Freedom and Williams 82 as susceptible checks. The second set included 17 lines that were selected based on information from Germplasm Resources Information Network (GRIN) and susceptible Williams 82. PI567102B was one of the most resistant lines to a Mississippi bulk isolate of P. pachyrhizi with the lowest severity rating, no sporulation, and red-brown lesion type. Accepted for publication 25 April 2009. Published 15 June 2009.
High demand for early‐maturing conventional (non‐genetically modified [GMO]) high‐oil soybean [Glycine max (L.) Merr.] cultivars in the food and special niche markets led to the development and release of ‘S13‐2743C’ (Reg. no. CV‐538, PI 695097). It is a tall, early maturity group IV (relative maturity 4.1) non‐GMO soybean developed and released by the University of Missouri–Fisher Delta Research Center soybean breeding program. This early maturing, indeterminate type cultivar is desired by growers in the southern United States to plant along with later maturity groups to allow flexibility during the harvest season. S13‐2743C has high oil content (238.4 g kg−1) and a broad disease resistance package, including resistance to soybean cyst nematode race 3, phytophthora root rot, stem canker, sudden death syndrome, and frogeye leaf spot. It has white flowers, grey pubescence, and brown pod walls. Seeds have buff hila and intermediate luster. S13‐2743C was tested in 103 environments across eight states and showed high yield potential in Missouri and other southern states, including Arkansas, Kansas, Kentucky, Louisiana, Mississippi, and Tennessee.
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