Fig 1.
The experimental design of the two heat stress experiments.
C refers to no heat stress treatment-control; SE refers to 10 days of heat stress treatment at the stem elongation stage; B refers to 10 days of heat stress treatment at the booting stage; CH refers to 10 days of heat stress treatment at full heading; SE+B refers to 5 days of heat priming at the stem elongation stage + 5 days of heat stress at the booting stage; and SE+CH refers to 5 days of heat priming at the stem elongation stage + 5 days of heat stress at full heading.
Table 1.
Temperature values for the photosynthetic measurements in LI-6400 and temperature values of the stress chambers.
Fig 2.
Comparison of various examined properties in the control treatments of the two heat stress experiments.
PH—Plant height, LIN—Last internode length, FBIOM—Total aboveground biomass (straw + all ears), GY—Grain yield, HI—Harvest index, TKW—Thousand kernel weight, SPS—Grain number per spikelet, and AS—Average seed number; ns—not significant and *—significant at the P≤ 0.05 level.
Fig 3.
Effects of single and repeated heat stress treatments on various yield-related traits in two experiments.
The results are averaged over 51 wheat cultivars at different developmental stages. I.: Experiment I., II.: Experiment II.; C: Control, SE: Stem elongation, B: Booting, CH: Full heading, SE+B: Stem elongation + booting; SE+CH: Stem elongation + full heading, GY: Grain yield per plant, AS: Average seed number, HI: Harvest index, TKW: Thousand kernel weight, FBIOM: Total aboveground biomass (straw + all ears), PH: Plant height, LIN: Last internode length, and SPS: Grain number per spikelet. The data are means ± LSD (n = 51). Least significant differences (LSD5%) denoted by bars on the columns represent significance at the P≤ 0.05 level.
Fig 4.
Effects of single and repeated heat stress treatments on photosynthetic parameters in two independent experiments.
The results are averaged over 51 wheat cultivars at different developmental stages. I.: Experiment I., II.: Experiment II.; C: Control, B: Booting, SE+B: Stem elongation and booting, CH: Full heading, SE+CH: Stem elongation and full heading, PN: Net assimilation, GS: Stomatal conductance, E: Transpiration, CI: Intercellular CO2 concentration, and CLR: Chlorophyll content.
Fig 5.
Discriminant analysis of the 7 phenotypic clusters of 51 wheat genotypes.
The seven phenotypic clusters were established by K-means clustering of the grain yield data matrix, which was derived from the various heat stress treatment of Experiments I. and II.
Fig 6.
Grain yield profiles of the 7 phenotypic clusters of 51 wheat genotypes.
(A) across the various heat stress treatments of Experiments I. and II. and (B) measured by the effect of repeated heat stress to the single heat stress treatment in two developmental phases expressed as % of change. C (averages of the grain yield of the two controls in Exp. I. and II.); SE (averages of the grain yield of the two SE treatments in Exp. I. and II.); B (grain yield of the single heat stress at the booting stage) and SE+B (grain yield of the repeated heat stress at the stem elongation and booting stages) from Exp. I.; and CH (grain yield of the single heat stress at full heading) and SE+CH (grain yield of the repeated heat stress at stem elongation and full heading) from Exp. II.
Table 2.
The most characteristic members of the 7 phenotypic wheat groups identified via K-means clustering and discriminant analyses based on their grain yield profiles.