WINTER RYE LEAF EMERGENCE AND ITS RELATIONSHIP TO THE PHYLLOCHRON

Winter rye (Secale cereale L.) is a high-tillering cereal crop. Unders tanding the relationship between the phyllochron for mainstem leaves a nd that of tillers is useful in adequately describing plant developmen t and selecting crop management strategies. This study was conducted t o determine the phyllochrons of conventional height (CH) and semidwarf (SD) genotypes of winter rye and the relationship of the phyllochron of mainstem leaves to that of primary tillers. Three CH and two SD gen otypes were planted in a controlled-environment growth room. Leaf stag es were determined with the Haun scale and the phyllochron calculated as the inverse of the slopes of linear regressions of Haun stage to gr owing degree-days (GDD). For both CH and SD genotypes, the Haun stage increased linearly with GDD, and the phyllochron was constant in the p re-vernalization (0 < GDD less than or equal to 266) and vernalization (266 < GDD less than or equal to 566) periods. During post- vernaliza tion (566 < GDD less than or equal to 914), the phyllochron for the ma instem increased with GDD. Leaves on the coleoptile tiller (T0), T1 (t he tiller from leaf no. 1 of the mainstem), and T2 had mean phyllochro ns similar to that for the mainstem. Leaves on higher positioned tille rs (T4, T5) had a greater phyllochron than the earlier tillers. The hi gher positioned tillers also required more thermal time units to emerg e than the earlier tillers. To precisely describe winter rye developme nt using the phyllochron, one should consider that the phyllochron cha nges with leaf and tiller position on the culm.