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Spike Differentiation and Floret Survival in Semidwarf Spring Wheat as Affected by Water Stress and Photoperiod¹

Previous work on the effects of water stress on wheat spike morphogenesis and floret survival has been conducted mainly on standard height (nondwarf) cultivars. Effects of water stress on the spike were therefore studied using a semidwarf spring wheat (Triticum aestivum L.). Plants were raised in the glasshouse under 8 h and 16 h photoperiods, and 7-day periods of water stress were imposed during different development phases up to spike-emergence. Water stress at critical times generally caused floret and sometimes whole spikelet death at the terminal ends of the spike. Water stress during the late vegetative phase just before spike initiation adversely affected the final number of fertile florets per spike, the reduction in fertile florets being accounted for by fewer spikelet primordia being formed. Water stress during late internode elongation prior to spike emergence resulted in death of florets and whole spikelets at the terminal and basal ends of the spike. The spike initial had minimum sensitivity to water stress during the period immediately following the initiation of the terminal spikelet. Stress effects in semidwarf wheat particularly during internode elongation, appeared to be similar to those reported for conventional standard height spring wheats. Greater spikelet number per spike was obtained in the short days (8 h) than in the long days (16 h). This was mainly due to photoperiod and possibly also because water stress of the same duration and similar intensity may have been relatively less severe in the prolonged development phases in the short days.

Key Words: Spikelet • Spikelet initiation • Internode elongation • Leaf primordia • Triticum aestivum L.

² Senior plant physiologist, Water Research Commission, present address: Soil and Irrigation Res. Inst., Private Bag X79, Pretoria 0001, Republic of South Africa; and senior lecturer, Dep. Agric. Botany, Univ. of Reading.

Received for publication November 30, 1981.