Spike and Leaf Development of Sal‐Stressed Wheat

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Abstract
Drought or salt stress while the shoot apex is in vegetative stage can markedly affect spike development and decrease yields of cereal grains. This study was conducted to determine the effects of salinity on shoot apex differentiation, particularly spike and spikelet development, and the number of tillers per plant on two wheat species (Triticum aestivum L. ‘Probred’ and T. turgidum L. ‘Aldura’). Plants were grown in greenhouse sand cultures that were irrigated four times daily with modified Hoagland's solution. Two saline treatments with osmotic potentials (Ψs) of −0.45 and −0.65 MPa were imposed beginning 4 d after planting by adding NaCI and CaCI2 (5:1 molar ratio) to the base nutrient solution and were compared to a nonsaline control treatment at −0.05 MPa. Salt stress accelerated development of the shoot apex on the mainstem and decreased the number of spikelet primordia in both species. Terminal spikelet stage occurred 12 and 18 d (≈280 and 420 thermal units) sooner Aidurand Probred plants, respectively, stressed at −0.65 than at −0.05 MPa. Anthesis also occurred earlier, but tillering was delayed 3 to 4 d. Compared with −0.05 MPa, Ψs of −0.45 and −0.65 MPa decreased seed yield 38 and 54% in Aldura and 7 and 43% in Probred, respectively. These decreases resulted from fewer spikes per plant and fewer kernels per spike. Salt stress increased the phyllochron and reduced the final number of leaves initiated on the main stem. In sam, salt stress prior to and during spikelet development significantly decreased the yield potential of individual spikes of Aldura, but not of the more tolerant Probred. Salt stress decreased the yield potential of both species most by reducing the number of tiller spikes.