Genetic mapping of soybean resistance genes to frogeye leaf spot in five Chinese plant introductions and efficiency of early generation selection for low phytate soybean lines
Hoskins, Aaron Jacob
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Frogeye leaf spot (FLS), caused by Cercospora sojina, is a disease found on soybean (Glycine max) in many areas of the world. The Rcs3 resistance gene was previously discovered in the soybean cultivar Davis and genetically maps to chromosome 16 (Gm16;Lg-J) near Satt244. Rcs3 is currently resistant to all known isolates of C. sojina. Five plant introductions (PIs) from China (PI594619, PI594661, PI594662A, PI594774, and PI594891) were found to have broad resistance to FLS. The objective of this study was to determine if these FLS-resistant PIs contain unique genes for resistance to FLS. Results indicate resistance genes in PI594619 and PI594662A were found near Satt501 on Gm18(Lg-G) and near Satt547 and Satt244 on Gm16(Lg-J), respectively. A resistance gene in PI594661 was found near Satt244 on Gm16(Lg-J). The resistance gene in PI594774 and PI594891 mapped to Gm13(Lg-F) near Satt114. These results indicate that four of the plant introductions (PI594619, PI594662A, PI594774, and PI594891) contain unique resistance genes. Phosphorus stored in the seeds of soybean is primarily stored as phytic acid, a form unavailable to monogastric animals. The objectives of the current research were (i) to determine the effect of soybean maturity on the effectiveness of single-plant selection for inorganic phosphorus levels in soybean seeds containing alleles from CX1834-1-2, a low phytate, high inorganic P soybean line, and (ii) to determine effects of backcross generations on levels of inorganic P in soybean seeds. There were weak, but significant (P = 0.05) correlations between temperature 15, 30, and 45 d prior to maturity and Pi levels in the Boggs (r = -0.14 to 0.18) and Benning (r = -0.13 to -0.21) populations in 2008, but not 2009. In 2009 the lines in the high Pi classes of Boggs (1228 vs. 203 ng g-1 P), Benning (1445 vs, 87 ng g-1 P), and Prichard (1359 vs. 103 ng g-1 P) averaged significantly (P = 0.05) higher in Pi than the lines in the low Pi class. Using single plants in a single environment may not be the most efficient means of selection when making selections for inorganic phosphorus in a breeding program.