The nature of the inheritance of permanently induced changes in Nicotiana rustica II. F4 and F5 generations of selected crosses

Summary The F 4 and F 5 generations of the two selected crosses, nk 2 × nil 1 and p 3 × nil 3 , from a dialle of all possible crosses between the three conditioned lines p, nil and nk were grown in successive years in the summers of 1970 and 1971 respectively in order to study (1) the persistence of the segregation between F 1 individuals seen in earlier generations and (2) the conventional segregation in the later generations. In the F 4 generation V 1 segregation in the cross nk 2 × nil 1 approaches significance for the character final height. In the F 6 generation significant segregation between F 1 individuals was not found for the characters final height and flowering time for either cross. However, in the cross nk 2 × nil 1 significant F 1 segregation was found for two other characters, height at flowering time and the diameter of the eighth leaf. The presence of segregation at the F 2 , F 3 and F 4 levels was confirmed for both characters in both crosses by the fitting of a standard additive genetical and additive environmental model. From the estimates of D obtained the numbers of effective factors by which these lines differ were found to range from three to five.