Main content area

Inheritance of lint percentage in cotton

Ware, J.O.
Agronomy journal 1929 v.21 no.9 pp. 876-894
Gossypium hirsutum, Gossypium barbadense, plant breeding, hybridization, varieties, lint cotton, traits, inheritance (genetics)
Four sets of crosses, A, B, C, and D, were made and carried through the second generation with back crossing on the two respective parental strains in each hybrid group. A condensed tabulation of the number of individuals in each population and the statistical constants for these groups are given in Table 7. The sets of curves differed in the amount of lint percentage that the parental strains were separated. The mean percentage of the parental strains stand apart in the A crosses by 0.93 +/- .24, in the B crosses by 7.38 +/- .31, in the C crosses by 9.90 +/- .25, and in the D crosses by 28.76 +/- .16. The value of the study from the standpoint of determining parental resemblance in the offspring increases as the degree of difference between the parental means widens. The data from the A, B, and C crosses show only tendencies in inheritance, except with the F1 generation. The first generation population indicates in the A crosses not only dominance of low lint percentage but intensification of this character condition, in the B crosses complete dominance of low lint percentage, and in the C crosses incomplete or intergrade dominance of high lint percentage. The data from the D crosses give much clearer cut evidence as to the actual transmission of lint percentage than the first three crosses. The lint percentage of the scant or sparse lint parents are so widely removed from the lint percentage of the normal lint parents that segregation appears in the population of the back cross on the recessive parents and the F2 generation. High or normal lint percentage is incompletely dominant as shown in the F1 generation and the population from the back cross on the normal parents. The mean of the F1 population is 22.31 +/- .16 higher than the mean of the scant lint parental strain and 6.45 +/- .16 lower than the F1 mean. The mean of the population from the back cross on the normal parents is 4.51 +/- .21 higher than the F1 mean and 1.94 +/- .18 lower than the mean of the normal lint parental strain. The means of both the F1 cross and the back cross are nearer the higher % parent than the lower % parent. The population from the back cross on the recessive or scant lint parental strain exhibits almost a perfect 1:1 ratio. This population falls into two separate distributions with 154 plants in the lower group and 151 plants in the upper group. The F2 population is bimodal with practically one-fourth of the plants in the lower modal group. The two modes are not entirely separated, but the tendency is for the lower group to fluctuate around a scant lint mean somewhat higher than that of the scant lint parental strain and for the upper group to fluctuate around a normal lint mean located between the means of the F1 and the normal lint parental strain. The upper distribution contains 532 plants and the lower distribution 174 plants. These numbers approximate a 3:1 ratio. The standard deviation of the F1 population is slightly less than the average of the respective parental standard deviation in the A, B, and C crosses and slightly larger than these parental averages in the D crosses. The back cross populations fluctuate more than the F1 generation or either parental strain. The F2 populations exhibit more variation than any back cross on one of the parental strains, but the two back crosses taken together vary over about the same range as the plants of the F2 generation. In no case does the F2 population extend beyond the limit of both parental strains. In considering the limits of variation the segregated back cross and the bimodal F2 of the D crosses were each taken as a single group. Where low lint percentage is dominant, the F2 generation mean tends to swing toward low percentage and where high lint percentage is of a dominant nature the mean of the F2 population inclines in the direction of high lint percentage. In the D crosses the 1:1 back cross ratio and the 3:1 F2 ratio are good evidences of the single factor control of lint pe