The unstable tubular ray flower allele of sunflower:: inheritance of the reversion to wild-type

The tubular ray flower (turf) mutant of sunflower (Helianthus annuus L.) is characterized by a change from a zygomorphic corolla to a nearly actinomorphic tubular-like corolla of ray flowers that also achieves the ability to differentiate fertile stamens and ovules. The recessive turf mutation is found to be unstable, spontaneously reverting to a wild-type or nearly wild-type phenotype. Reversion frequencies were 1.70% in the original inbred line R1634 (where turf was first identified), 0.17% and 3.20% in two turf/turf homozygous F-3 progenies, derived from crossing a turf mutant with two different inbred lines. As no chimeric plant was found it is likely that the reversion had occurred either in the germ line or within the zygote. Self-pollinated wild-type reverted plants segregated into normal and mutant phenotypes fitting a monogenic 3 : 1 ratio, thus indicating that the reversion affected a single allele. The hypothesis of an epigenetic mechanism is discussed.