Drought resistance in spring wheat cultivars. II.* Effects on plant water relations

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Abstract
We studied cultivar and drought effects on the water relations of a large set of cultivars of bread wheat (Triticum aestivum L.), durum wheat (T. turgidum), triticale (X Tritosecale Wittmack) and barley (Hordeum vulgare L.), grown in field plots in north-western Mexico in the presence and absence of simulated late drought. Leaf water potential (Ψ) and osmotic potential (π), and leaf permeability (LP) to viscous air flow were measured between 1000 and 1600 hours on many dates; leaf turgor potential (p) was calculated. Drought caused associated reductions in Ψ, π and LP. Cultivar effects on these variables were usually significant on given dates, and reasonably consistent between dates and drought intensities in the case of Ψ, but less so for π and LP. There were consistent positive phenotypic correlations between Ψ and LP, and Ψ and anthesis date, and a negative correlation between Ψ and stature in the absence of drought. The relationship of LP to Ψ for different cultivars differed significantly: in particular, tall bread wheats had lower LP than dwarf cultivars at high values of Ψ, whereas at low Ψ they had higher LP than the dwarf cultivars. There was general osmotic adjustment, and a tendency for the relationship of p to Ψ to vary between cultivars. Irrespective of statistical significance, the effects of cultivar were generally small relative to those of drought intensity.