UQ eSpace

Abstract

A series of solution culture experiments was conducted from 1986 to 1989 to study the effects of nitrogen stress and water stress, imposed individually or combined, during various growth stages, on growth and panicle development of grain sorghum cv. Texas 610 SR. The first three experiments were designed to study the effects of nitrogen stress on growth and panicle development. The first experiment was conducted from day 15 to day 42 to study the effects of nitrogen stress during GS I and the second experiment from day 42 today 74 to study the effects of nitrogen stress during GS II. The third experiment was designed to cover both growth stages (GS I and GS II). The next two experiments were conducted to study the effects of water stress and the final experiment was conducted to study the effects of nitrogen and water stress on growth and panicle development of grain sorghum cv. Texas 610 SR. Polyethylene glycol (PEG) 6000 was used to decrease the osmotic potential of the solution. Both nitrogen stress and water stress caused substantial reductions in growth, and in panicle development, while the combined nitrogen stress and water stress treatments had effects that were additive. In general, the imposed nitrogen stress (complete withdrawal of nitrogen supply) had a greater effect in reducing growth and panicle development of grain sorghum than the imposed water stress (-0.4 MPa of solution osmotic potential). During both stress treatments, the developing inflorescence showed an increasing demand for nitrogen. The nitrogen demand of the developing panicle after the nitrogen supply was withdrawn was met by retranslocation of nitrogen from the other tissues. Both nitrogen and water stress imposed during early stages of plant growth reduced the dimensions of the shoot apices. Combined stress treatments had a greater effect than the individual stresses. However, the number of primary branches initiated from the surface of the shoot apices was not changed by the imposed stresses. The fertility of the primary branches was reduced when either stress was imposed at or before panicle initiation. Combined stress treatments imposed after panicle initiation reduced the fertility of the primary branches only when nitrogen stress was followed by water stress.