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Inheritance Studies of Bract Size in Cotton¹

Bracts in Upland cotton, Gossypium hirsutum L., have been implicated in byssinosis, a lung disorder associated with textile mill workers. Before initiating a breeding program with the objective of reducing bract trash in machine-harvested seedcotton, inheritance studies were performed on the trait bract size or bract surface area.

In the first study, heritability was calculated from regression of 83 F₃ plot means on F₂ plant values from a cross involving a small bract parent and a nectariless normal bract breeding llne. Correlation coefficients were calculated to determine herltability in standard units. Highly significant regression and correlation coefficients of 0.69 and 0.75, respectively, were computed for heritability estimates.

In the second study a seven parent diallel was used and analyzed by the procedures outlined by Jinks and Hayman. The experiment included the seven parents, their 21 F₁'s, and their 21 F₂'s and was performed at two locations for 2 years.

Partial failure of the assumptions of no epistatis, no multiple allelism, and independent gene distribution was observed in the three general tests. Epistasis and multiple allelism were tested and considered negligible. Discrepancies were noted between populations for estimates of frequency of alleles and dominance gene effects. Partial dominance was expressed at most loci where dominant alleles governed bract surface area. Narrow-sense heritability estimates indicated that bract size heritability was primarily additive although dominance gene effects contributed significantly. Parents were identified with bract size and levels of dominance suitable for cultivar breeding programs.

Key Words: Byssinosis • Cultivar • Diallel analysis • Gossypium hirsutum L. • Heritability

² Former research associate (presently assistant professor, Crop Science Dep., North Carolina State Univ., Raleigh, NC 27650), and professor Dep. of Agronomy, Louisiana Agric. Exp. Stn., Baton Rouge, LA 70803.

Received for publication December 21, 1981.