The Influence of Environment on the Sex Ratio and Fitness of Spinach

Spinach, Spinacia oleracea var. americana, was grown under water-limited (DRY) and -abundant (WET) conditions in a number of controlled experiments. Four factors influenced the observed sex ratios of spinach: (1) precocious flowering of males, (2) WET and DRY conditions, (3) photoperiod, and (4) seed source. The reproductive potentials of male, female, and monoecious plants differed between WET and DRY environments, and environmental sex determination (ESD) operated as an adaptive response to a differential in fitness between the sexes. The data also indicated that compensation, differential movement of gametes between the sexes, partial niche separation, and ESD may have played a role favoring the dioecious state in spinach.