Abstract
Drought after the jointing stage restricted the growth and yield formation in wheat. Supplemental irrigation (SI) at Z31 (Zadoks Stage 31) reduced the ABA concentrations in the leaves of the inferior tillers (T3 and T10) and improved the survival rate of the tillers. Additional SI at Z60 reduced the ABA concentrations in the flag leaves of ear-bearing stems after anthesis and increased the assimilate accumulation and the 1000-grain weight. These two SIs increased the yield by 16.7-32.2 % compared with a rainfed control (W0). Delaying the first SI from Z31 to Z34 or Z39 reduced the ABA concentrations in the leaves of the main stem and superior tillers (T1 and T2) but increased the ABA concentrations in the leaves of the inferior tillers at Z45 and reduced the survival rate of the tillers. Delaying SI from Z31 and Z60 (W1) to Z34 and Z69 (W2) increased the partitioning of the recent (C-14-labelled) assimilate to the stems plus sheaths and stalk plus glume at anthesis and the grains at maturity and increased the 1000-grain weight and the grain yield significantly. However, if SI was applied too late, i.e., at Z39 and Z77 (W3), the redistribution of the recent assimilate from the vegetative organs to the grain after anthesis and the grain yield at maturity were reduced. These data suggested that: (1) a lower soil moisture at the early jointing stage elevated the ABA concentrations in the inferior tillers and inhibited their growth; (2) if SI was applied too late (W3) senescence of the inferior tillers could not be halted; and (3) low ABA concentrations in the leaves during the later grain filling following the late SI (W3) were correlated with a reduced transfer of assimilates from the vegetative organs to the grain, leading to a significant reduction in the grain weight at maturity.