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Product-Quantity Measures of Earliness of Crop Maturity in Cotton¹

We used 3 stocks of American Upland cotton, Gossypium hirsutum L., and the 3 possible crosses among them, as experimental materials for a study of productquantity estimates of earliness of crop maturity. The investigation involved 3 measures of earliness: (1) amount of crop harvested (ACH); (2) percentage of crop harvested (PCH); and (3) mean maturity date (MMD). We took data and calculated genetic and statistical parameters on the parental lines and the F₂ populations of the 3 crosses. MMD, which gave the highest heritability values, was considered to be the most discriminating and the most reliable of the 3, both for studies of the genetics of earliness and for use in breeding programs in which earliness, without regard to total or potential yield, is the prime objective. The reliability of ACH and PCH measures in genetic analyses of earliness is subject to further question because of the correlation between their variabilities and the percentage of bolls open at the time of measurements. Since the method of calculating MMD does not take yield into account directly, ACH or PCH measures will be more effective in those phases of the breeding program in which maximum-yield-in-minimumtime is a major consideration. Of the two, ACH appears to be the more desirable. The importance of the proper date or period on which to base the calculations is emphasized. while no single measure stood out as being completely acceptable in all breeding situations or under all conditions, the experiments show that reasonably reliable measures or estimates of earliness of crop maturity in cotton are available for application to specific, welldefined plant breeding problems or crop improvement objectives.

² Research Agronomist, Crops Research Division, ARS, USDA (Professor of Agronomy, Texas Agricultural Experiment Station) and Associate Agronomist, South Plains Research and Extension Center.