Pollen-parent effects on protein quality and endosperm modification of quality protein maize
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Quality protein maize (Zea mays L.) (QPM) has protein of high nutritional value conferred by the opaque-2 (o2) gene and vitreous endosperm because of numerous modifier genes. Superior protein quality is only expressed when endosperm tissue is homozygous recessive (o2o2). During QPM research and development, it is common to evaluate trials in which QPM genotypes randomly interpollinate. We do not know if protein quality determinations for entries in such trials are valid measures of what would be expressed in a pure stand. In this study, we used nine QPM and three o2 (unmodified, soft endosperm) cultivars as females for six pollen treatments to measure the effect of pollen source on protein concentration of grain, tryptophan concentration in grain, tryptophan concentration in protein, and endosperm modification (translucency) in three environments. The pollen treatments were four QPM hybrids, one normal-endosperm maize cultivar, and self-pollination. Pollen of normal-endosperm maize reduced tryptophan in grain by 37% and tryptophan in protein by 38% but improved endosperm modification of QPM females by 36% relative to pollen of QPM males. Pollen of normal-endosperm maize and QPM did not differ in effect on protein concentration of grain. Protein quality traits did not differ for QPM cultivars pollinated by self or by other QPM males. Kernels were slightly more vitreous, however, for females pollinated by other QPM males than for those that were self-pollinated. Effects of females were significant (P < 0.01) and the interaction of males x females not significant for QPM entries for all traits. We conclude that it is valid to evaluate QPM germplasm in trials where entries randomly interpollinate, provided that pollen of normal-endosperm maize is excluded.
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