Temporally and Genetically Discrete Periods of Wheat Sensitivity to High Temperature

Abstract

Successive single day transfers of pot-grown wheat to high temperature (35/30°C day/night) replicated controlled environments, from the second node detectable to the milky-ripe growth stages, provides the strongest available evidence that the fertility of wheat can be highly vulnerable to heat stress during two discrete peak periods of susceptibility: early booting [decimal growth stage (GS) 41-45] and early anthesis (GS 61-65). A double Gaussian fitted simultaneously to grain number and weight data from two contrasting elite lines (Renesansa, listed in Serbia, Ppd-D1a, Rht8; Savannah, listed in UK, Ppd-D1b, Rht-D1b) identified peak periods of main stem susceptibility centered on 3 (s.e. = 0.82) and 18 (s.e. = 0.55) days (mean daily temperature = 14.3°C) pre-GS 65 for both cultivars. Severity of effect depended on genotype, growth stage and their interaction: grain set relative to that achieved at 20/15°C dropped below 80% for Savannah at booting and Renesansa at anthesis. Savannah was relatively tolerant to heat stress at anthesis. A further experiment including 62 lines of the mapping, doubled-haploid progeny of Renesansa × Savannah found tolerance at anthesis to be associated with Ppd-D1b, Rht-D1b, and a QTL from Renesansa on chromosome 2A. None of the relevant markers were associated with tolerance during booting. Rht8 was never associated with heat stress tolerance, a lack of effect confirmed in a further experiment where Rht8 was included in a comparison of near isogenic lines in a cv. Paragon background. Some compensatory increases in mean grain weight were observed, but only when stress was applied during booting and only where Ppd-D1a was absent.

Keywords: Ppd-D1; Rht; anthesis; heat stress; meiosis; wheat.

Figure 1

Effects of wheat cultivar and successive 1-day transfers to controlled environment cabinets at 20/15 (◦) and 35/30°C (•) day/night temperature (16 h day) on grain yield per pot from all stems (A,B) or only mainstems (C,D). Panels (E,F) give the growth stage distributions of the mainstems at the time of transfer in to the cabinets (boxes are limited by 25 and 75%, whiskers by 10 and 90%; points are outliers beyond 10 and 90%, and the line within the box is the median where appropriate). S.E.D. (358 d.f.) in (A,C) is for comparing temperatures within day and cultivar for both cultivars. Arrows in (E,F) denote the assumed timing of growth stage (GS) 65 (Zadoks et al., 1974). Dashed lines in (A,B) are the mean yields from eight pots per cultivar left outside.

Figure 2

Effects of increasing day temperature from 20 to 35°C in successive 1-day transfers to controlled environment cabinets on mean grain weight (A,C) and grain numbers (B,D) from main stems of winter wheat, cvs Renesansa (triangles) and Savannah (squares). Fits are double Gaussian (Table 1) constrained for peaks to have the same shape (Gaussian S, Equation 1) and timings for the different components and varieties. Error bars are 1 S.E.D. (358 d.f.) for comparison of individual points with the y = 100 line.

Figure 3

Effects of increasing day temperature from 20 to 35°C in 1-day transfers to controlled environment cabinets on yield components per pot from main stems of near isogenic lines with (•) and without (◦) Rht8 in a Paragon wheat background. Error bars in (A,B) are S.E.D.s for comparing points without (left) and with (right) Rht8 with the 100% line. Box-whisker plots (Figure 1 for description) in (C) show growth stage distributions of mainstems on day of transfer.

Figure 4

Effects of increasing day temperature from 20 to 35°C in 1-day transfers to controlled environment cabinets and growth stage (A,D = early booting; B,E = mid booting; C,F = Anthesis) on mean grain weight A–C and grain numbers (D–F) from main stems of the doubled haploid progeny of Savannah × Renesansa marked for with (solid symbols) and without (open) Rht-D1b and with (triangles) and without (squares) Ppd-D1a. Error bars are S.E.D.s for comparing any point with the 100% line. In A,C,F lines are fits corresponding to markers as described in (F): with (solid) and without (dashed) Rht-D1b; and with (light line) and without (heavy line) Ppd-D1a.