Inheritance of Stem Length and its Components in Safflower1

Mode of inheritance of two length zones of the stem and their components (internode length and node number) were studied in three crosses of safflower, Carthamus tinctorius L. The purpose was to analyze stem lengths and their components for genetic effects and for their relation to yield. The dwarf strains were used as females in separate crosses with the tall ones. Two of the tall parents did not differ in internode length or node number. The three dwarfs were similar in number of nodes for the two zones of the plant axis. One of the three dwarfs had slightly longer internodes. Except for lower stem node number, upper stem internode length, and total upper stem length, a simple additive‐dominance model could not explain the observed results. In those cases where an additive‐dominance model did not fit, the F1 and F2 means were outside the range of the parental means or large differences were observed between the F1 and F2 means. Possible explanations include heterotic effects that involve interactions between loci or variation in estimation of F1 means caused by small sample sizes in this generation. Heterosis, when it was present, tended to increase internode length, decrease node number, and increase stem length in both stem zones Correlations for yield with lower stem internode length and with upper stem node number were frequently significant; those for yield with upper stem internode length and lower stem node number were generally small and nonsignificant. The correlations indicated that selection for plant height could be conducted without altering yield.