INFLUENCE OF PHOTOPERIOD AND WATER STRESS ON GROWTH, YIELD AND DEVELOPMENT RATE OF BARLEY MEASURED IN HEAT UNITS

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Abstract
Barley (Hordeum vulgare ’Bruce’) was grown in a greenhouse under three photoperiods (8, 12 and 16 h) and nine watering treatments, resulting in different timing, duration and intensity of water stress. Phenological development, according to the Feekes scale, was monitored three times a week and leaf area was measured weekly from tillering to ripening. Final aboveground and root dry matter production and grain yield were obtained at harvest. Phenological observations were fit to a nonlinear photothermal model that expressed phenological development as a function of heat units modified by photoperiod. In the absence of water stress, maximum leaf area was directly proportional to photoperiod and the time of maximum leaf area was delayed at longer photoperiods. Water stress hastened leaf area senescence and, in general, the more severe the stress, the greater the reduction in leaf area. Most stress treatments also resulted in lower shoot/root ratios than found in well-watered controls, as well as significant yield reductions. Reduction in biomass and yield components appeared independent of photoperiod. In contrast, not only was phenological development rate proportional to photoperiod, but the effect of water stress on development rate was modified by photoperiod. Development was significantly delayed by several water stress treatments; no treatment significantly hastened development. A stress period from tillering to the beginning of stem extension caused the largest, and most consistent, delay and the duration of the delay was inversely proportional to the photoperiod.Key words: Barley, degree days, phenology, leaf area, biomass
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