An assessment of wheat yield sensitivity and breeding gains in hot environments

Abstract

Genetic improvements in heat tolerance of wheat provide a potential adaptation response to long-term warming trends, and may also boost yields in wheat-growing areas already subject to heat stress. Yet there have been few assessments of recent progress in breeding wheat for hot environments. Here, data from 25 years of wheat trials in 76 countries from the International Maize and Wheat Improvement Center (CIMMYT) are used to empirically model the response of wheat to environmental variation and assess the genetic gains over time in different environments and for different breeding strategies. Wheat yields exhibited the most sensitivity to warming during the grain-filling stage, typically the hottest part of the season. Sites with high vapour pressure deficit (VPD) exhibited a less negative response to temperatures during this period, probably associated with increased transpirational cooling. Genetic improvements were assessed by using the empirical model to correct observed yield growth for changes in environmental conditions and management over time. These 'climate-corrected' yield trends showed that most of the genetic gains in the high-yield-potential Elite Spring Wheat Yield Trial (ESWYT) were made at cooler temperatures, close to the physiological optimum, with no evidence for genetic gains at the hottest temperatures. In contrast, the Semi-Arid Wheat Yield Trial (SAWYT), a lower-yielding nursery targeted at maintaining yields under stressed conditions, showed the strongest genetic gains at the hottest temperatures. These results imply that targeted breeding efforts help us to ensure progress in building heat tolerance, and that intensified (and possibly new) approaches are needed to improve the yield potential of wheat in hot environments in order to maintain global food security in a warmer climate.

Figure 1.

Map of 349 trial locations included in analysis, colour-coded by average yields. Also shown (in grey) are the 31 877 stations used for weather interpolation.

Figure 2.

Inferred yield response to temperature from regression model for three growth stages (veg = vegetative; rep = reproductive; GF = grain filling), with the response curves fitted separately for high and low VPD trials. The curves have been normalized to equal 0 at 12°C. The line thickness corresponds to the significance of the slope (i.e. thin: NS, medium: p ≤ 0.1, thick: p ≤ 0.05, where the p-values are from a two-sided t-test.)

Figure 3.

Map of trial locations since 1990 with estimated loss/gain from +2°C warming; multiple years and sites clustered within a 100 km distance are averaged for illustration purposes.

Figure 4.

(a,b) Observed and climate-corrected yield trends from earliest start year of nursery, binned by average temperatures in the grain-filling period for (a) ESWYT and (b) SAWYT. The error bars are at a p = 0.05 significance level from a one-sided t-test. (c,d) Trends in environmental and country effects, and observed and ‘climate-corrected’ yields plotted as a function of the start year of the trend for (c) ESWYT and (d) SAWYT nurseries.