Inheritance of low-phytate phosphorus and its influence on agronomic and seed traits of soybean

Oltmans, Sheilah
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Phosphorus (P) in conventional soybean [Glycine max (L.) Merr.] seed consists of [nearly equal to]4% inorganic P, [nearly equal to]25% other P, and [nearly equal to]71% phytate P. Nonruminant livestock lack sufficient amounts of the phytase enzyme in their digestive system and are unable to utilize phytate P. A low-phytate (LP) mutant with [nearly equal to]25% phytate P, [nearly equal to]37% other P, and [nearly equal to]38% inorganic P was developed by the USDA-ARS and Purdue University. The first objective of this study was to determine the inheritance of low phytate in progeny of a line derived from the LP mutant. Reciprocal crosses were made with a normal phytate (NP) line and all the F1 seeds had NP, indicating complete dominance for NP and no maternal effects. A phenotypic ratio of 15 NP: 1 LP satisfactorily fit the segregation of a 2-gene model, based on a sample of 210 F2 seeds. The F2-derived lines satisfactorily fit a ratio of 7 homogeneous NP: 8 segregating: 1 homogeneous LP. The segregation indicated that LP was controlled by two recessive alleles at two independent loci that exhibited duplicate dominant epistasis. The alleles were designated pha1 and pha2. The second objective of this study was to determine the influence of LP on agronomic and seed traits of three soybean populations. From each population, 10 LP and 10 NP lines were grown in replicated tests at three Iowa environments in 2003. Phytate P, inorganic P, and other P were significantly different between LP and NP lines, but mean total P was not significantly different. Emergence of LP lines averaged 45% and NP lines averaged 68%. Correlation coefficients between emergence and inorganic P, total P, and other P were negative for LP lines in all populations. These results indicated that by selecting for increased emergence among LP lines would likely lead to a decrease in inorganic P, total P, and other P. Correlation coefficients were positive between yield and emergence for LP lines. LP lines were comparable to the NP lines for other agronomic and seed traits. Reduced emergence in LP lines with the genotype pha1pha1pha2pha2 will be a major consideration in the development of LP cultivars.