Wheat recovery from drought stress at the tillering stage of development

Abstract

A greenhouse experiment was performed to study how three spring-wheat (Triticum sp.) cultivars recovered from drought stress at tillering. Plants were grown in soil in large pots and drought was imposed at the onset of tillering (about Feekes stage 2) and at late tillering (about Feekes stage 3). At each stage, plants underwent stress to a mean midday Ψ1 of about −2.6 MPa (low stress) or about −3.3 MPa (high stress), before irrigation was applied and maintained to maturity. Wheat yield recovery after drought stress at tillering depended on the maintenance of kernel number in ears developed under stress and the production of many ears upon recovery. As drought stress developed into the later tillering stage, yield recovery became poorer because kernels per ear and tillering upon recovery were reduced. Under non-stress conditions, tillers accumulated linearly at a mean rate of 26 degree-days per tiller, until about 300 degree-days before heading. Stressed plants tillered at about the same rate until tillering stopped under the effects of stress. Upon recovery, the rate increased immensely with respect to thermal time. Variation in tillering among cultivars was dependent on either the rate or the duration of tillering. Duration was independent of the cultivar heading date. Weight of tillers at maturity declined with time to their appearance. Kernel number per ear was positively correlated with tiller weight at maturity across all treatments (R = 0.99), depending on cultivar. Late tillers were lighter, headed earlier, bore less grain, and had smaller kernel weight than early tillers, irrespective of temperature and photoperiod. Thus, the yield contribution of tillers that developed after stress was mainly in their numbers but not in their size or fertility. The highest grain-yield per plant was usually from the cultivar that excelled in kernels per ear, even though it was lowest in potential tillering.