Preliminary Genetic Studies of the Phenotype of Betaine Deficiency in Zea mays L.
Glycinebetaine-deficient inbreds of Zea mays do not exhibit a general deficiency of nitrogenous solutes; the total free amino acid levels of betaine-deficient lines are not significantly less than those of inbreds which exhibit >100-fold higher betaine levels. Betaine-deficient inbreds are characterized by extremely low betaine: total free amino acid ratios (<0.0015). Highly significant correlations are demonstrated between the expected mid-parent and observed betaine:amino acid ratios of 30 hybrids of known pedigree. In 12 hybrids constructed from a betaine-deficient male parent (inbred 1506), the observed betaine:amino acid ratios of the hybrids are proportional to the betaine:amino acid ratios of the female parents (r = 0.83). Two hybrids, 1146 x 1074 and 1146 x 1506, were chosen for further genetic analysis. The common female parent (1146) and inbred 1074 both exhibit betaine:amino acid ratios of 0.090, a value which is approximately 90-fold greater than the betaine:amino acid ratio of inbred 1506. Hybrid 1146 x 1074 exhibits almost exactly twice the betaine:amino acid ratio of hybrid 1146 x 1506. If inbred 1506 is homozygous recessive for a single nuclear gene responsible for the phenotype of betaine deficiency, and if inbreds 1146 and 1074 are homozygous dominant for this allele, then this twofold difference in betaine:amino acid ratio must be associated with the homozygous dominant and heterozygous conditions, respectively, for 1146 x 1074 and 1146 x 1506. Evidence is presented from both greenhouse and field evaluations of F(2) populations of these hybrids that a single nuclear recessive gene is most likely responsible for the phenotype of betaine-deficiency in inbred 1506. Approximately 25% of the F(2) segregants from 1146 x 1506 exhibited extremely low betaine:amino acid ratios (<0.0015), whereas 0% of the F(2) segregants from 1146 x 1074 exhibited this phenotype. The segregation patterns with respect to betaine:amino acid ratio suggest a 1:2:1 segregation ratio for homozygous recessive:heterozygous:homozygous dominant individuals within the 1146 x 1506-F(2) population.
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Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907.
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