Preliminary Genetic Studies of the Phenotype of Betaine Deficiency in Zea mays L.

Abstract

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 betained levels. Betaine-deficient inbreds are characterized by extremely low betaine: total free amino acid ratios (< 0.0015). Highly significant correlations are demonstrate between the expected mid-parent and 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 .times. 1074 and 1146 .times. 1506, were chose for further genetic analysis. The common female parent (1146) and inbred 1074 both exhibit betamine: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 .times. 1074 exhibits almost exactly twice the betaine:amino acid ratio of hybrid 1146 .times. 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 .times. 1074 and 1146 .times. 1506. Evidence is presented from both greenhouse and field evaluations of F2 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 F2 segregants from 1146 .times. 1506 exhibited extremely low betaine:amino acid ratios (<0.0015), whereas 0% of the F2 segregants from 1146 .times. 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 .times. 1506-F1 population.