Comparison of Diurnal Drought Response of Selected Wheat Cultivars1

Abstract

AbstractIn a 2‐year field study in Sonora, Mexico, irrigated and water‐stressed wheat (Triticum aestivum and T. durum) was grown to test the hypothesis of the existence of a substantial physiological response plateau at midday, and to assess several water‐stress characterizing techniques for field comparison of cultivars. Cultivars used were: ‘Yecora 70’, ‘Gabo’, ‘Sonora 64’, ‘Cajeme 71’ (bread wheats), and ‘Cocorit 71’ (a spring durum). Parameters examined included xylem pressure potential (ψχ), diffusive resistance (Rs), leaf osmotic potential (ψπ), and relative turgidity (RT).Diurnal studies indicate ψχ of midday (maximum stress) observations do not change statistically from 1100 to 1600 hours under the conditions studied. Thus with sufficient replication and random sequence of sampling, large numbers of cultivars can be compared daily and seasonally for their response to water stress at midday.Studies of technique indicated that pressure chamber temperature rose only 5 C when pressurizing to 20.7 bar in 10 sec and only 3 C when pressurizing in 105 sec. ψχ of plant samples tended to drop when stored in moist plastic bags after as little as 5 min. Rapid pressure increase rates resulted in statistically lower observed ψχ in one comparison (−23.5 bars in 1 min vs. − 23.2 bars in 4 min). Diffusive resistances (Rs) of abaxial leaf surfaces were larger and more variable than those observed on adaxial surfaces.Diurnal observations of ψχ, ψπ and RT showed a high degree of correlation between ψπ, RT, and ψχ, pointing to ψχ as a good overall indicator of plant water status. Data indicate there may be a significant potential gradient between the terminal stem node and the flag leaf and/head.