Estimating the Genetic Effects Modifying Endosperm Composition in Sugary1 Maize

Pseudostarchy (su1-ref/su1-ref) maize (Zea mays L.) inbreds contain wild-type levels of starch and water-soluble polysaccharides (WSP), even though the su1-ref allele is present. The su1-ref allele of maize contains a single nucleotide polymorphism alteration in the Sugary1 gene that results in near-equal concentrations of WSP and starch in the mature kernel. Seven maize inbreds, fixed for the sugary1-reference (su1-ref) allele, were developed out of two divergently-selected maize populations and have starch and WSP concentrations ranging from 223-570 mg g(-1) and 26-294 mg g(-1), respectively. Determining the type and magnitude of the genetic effects controlling the pseudostarchy phenotype is important for understanding the inheritance of the trait. The seven inbreds were crossed in a complex mating design that included inbred, F-1, F-2, and BC1 generations and evaluated using a genetic model for triploid endosperm traits. This analysis allowed additive and dominance genetic effects of the endosperm to be separated from cytoplasmic effects and additive and dominance genetic effects of the diploid maternal plant. WSP and wrinkling rating and starch and WSP concentration had greater than 60% of the phenotypic variation as additive endosperm effects. Cytoplasmic inheritance was not significant for any of the traits measured. Additive diploid maternal plant effects were significant for all traits measured and contributed 36% of the phenotypic variance for kernel weight. The presence of additive and dominance diploid maternal plant effects indicates that selection among kernels on an ear can be complicated due to the genetic effect of the mother plant. Overall, the traits measured, which reflect the visual difference between the pseudostarchy and extreme sugary inbreds, were controlled primarily by additive endosperm genetic effects indicating that allele or chromosome dosage is the primary genetic effect controlling how the pseudostarchy phenotype is inherited in this population.