Studies on plant growth‐regulating substances

Abstract

SUMMARYRoots of Pisum seedlings grown in a compact silt loam soil (bulk density 1–5 g/cm3) were shorter than those of seedlings grown in loose soil (bulk density 1 ? 1 g/cm3). Incorporating 3,5‐dibromo‐4‐hydroxybenzoic acid (DBHB)or 3,5‐dichloro‐4‐hydroxybenzoic acid (DCHB) into the compact soil enhanced root elongation and decreased root bending. DBHB was more effective than DCHB in promoting pea root growth but a much higher concentration was required for optimal activity. Shoot height was increased by DCHB treatment of the compact soil but DBHB had little effect. In loose soil, significant effects were detected only at high concentrations, when DBHB promoted and DCHB inhibited the root growth of pea seedlings.Although development of barley seedlings in compact soil was enhanced by DCHB, that of wheat seedlings was inhibited by this treatment.