The Pima Enhancer Factor is a modifying gene(s) known to amend pollen fertility levels in F₁ hybrids when incorporated into Gossypium harknessii derived restorer lines (1). In particular, Upland restorer lines carrying a 'Dixie King' or Pee Dee 4461 genetic background in addition to the Pima Enhancer Factor consistently confer good fertility in F₁ hybrids (2). Thus, the transfer of the Pima Enhancer Factor, which may express incomplete dominance in some cases (1), into cytoplasmic male sterile (CMS) lines may further augment fertility levels in F₁ hybrids (CMS Upland x Upland restorer with Pima Enhancer Factor) as well as ensuring adequate fertility levels in F₁ CMS Upland x Upland restorer without the Pima Enhancer Factor. In the latter case, CMS lines possessing the Enhancer Factor enable utilization of poor restorers (Upland restorers without the Enhancer Factor) which are of little value in the production of F₁ cotton hybrids at present, and decrease the necessity of developing good restorers (Upland restorers with the Enhancer Factor), which is an arduous task.