Plant Growth Regulator and Daylength Effects on Preanthesis Main Shoot and Tiller Growth in Conventional and Dwarf Oat

Abstract

Plant growth regulators (PGRs) alter tiller growth in cereals. This response may be dependent on daylength (DL). Standard height (HE) and dwarf oat cultivars were grown at 14‐ and 18‐h DLs. Foliage was sprayed with chlormequat chloride (CCC) and ethephon at early growth stages to evaluate PGR effects on the growth of the main shoot and tillers. Two successive experiments with 10 replicates were arranged in two growth chambers (14‐h and 18‐h DL) at the University of Minnesota. Preanthesis main shoot and tiller HEs and dry weights (DWs) were measured. In Exp. 1, the numbers of leaves and green leaves were counted. Relative growth rate (RGR), relative elongation rate (RER), and shoot DW:HE ratio were measured. Plant growth regulators retarded growth of the main shoot in conventional oat cultivars without stimulating growth of T1 and T2 tillers. Response of the dwarf cultivar to PGRs was modest. Only ethephon enhanced T1 tiller growth at 18‐h DL. However, PGR‐treated plants had up to five more green leaves per plant at preanthesis due to stimulated leaf emergence on T3 and T4 tillers especially at the 18‐h DL. In Exp. 1, PGR treatments reduced the DW to HE ratio, that is, shortened rather than strengthened the stem. In Exp. 2, measurements were made more frequently and ethephon first increased this ratio followed by a decrease. Thus, even though long‐day conditions somewhat enhanced DW accumulation and stem elongation, few marked differences in oat response to PGR treatments were noted when comparing short‐ and long‐day conditions.