High yield stability and susceptibility to stripe rust associate with large yield gaps in rainfed winter wheat

Abstract

Context

Narrowing yield gaps, that is the difference between water-limited yield potential and actual yield, is critical for food security. Phenotypic plasticity of grain yield and resistance to stripe rust (Puccinia striiformis f. sp. tritici) have been analyzed independently, but their combined contribution to yield gaps in wheat (Triticum aestivum L.) is uncertain.

Hypotheses

This study tested three hypotheses. First, yield gap increases with decreasing yield plasticity, i.e. there is a tradeoff between yield stability and yield gap. Second, resistant phenotypes have smaller yield gaps under conditions favoring stripe rust development. Third, under conditions that do not favor disease development or in protected crops, yield differences between resistant and susceptible cultivars to stripe rust depend on whether resistance involves metabolic costs. By exploring these hypotheses, we aim to understand trade-offs and synergies between stripe rust resistance and yield phenotypic plasticity under varying management and environment.

Method

Data on grain yield and stripe rust ratings were obtained from a factorial experiment in 21 location-years in the southern Great Plains of the United States (US) where we compared 20–55 cultivars under two management intensities: standard grower practices where crops received enough N for a yield goal of 4 Mg ha⁻¹ and no fungicide, and higher inputs including an additional 45 kg N ha⁻¹, one fungicide application at jointing and a second at heading. We estimated cultivar-specific yield phenotypic plasticity (i.e., the inverse of yield stability) as the ratio between the yield variance of a given genotype and the total yield variance for the pooled data. Water-limited yield potential was estimated using quantile regression, and used to derive yield gaps.

Results

Cultivars with high yield phenotypic plasticity (less stable yield) had narrower yield gaps in environments with high water-limited yield potential. Combining the addition of N and fungicide with cultivars with high yield plasticity narrowed yield gaps regardless of environmental potential. Under conditions favorable for disease development, stripe rust resistance narrowed yield gaps, particularly where disease chemical control was absent or ineffective. The null yield difference between stripe rust resistant and susceptible phenotypes when protected with foliar fungicides reflects lack of significant cost of disease resistance.

Conclusion

Both yield stability and stripe rust susceptibility increased the magnitude of yield gaps in winter wheat regardless of the environment’s yield potential and conditions conducive to stripe rust development.

Implications

In the absence of disease, stripe rust resistance does not have a yield penalty, suggesting that cultivars that combine high yield plasticity and stripe rust resistance would be superior in environments where stripe rust is present but uncommon, such as the western portion of the US southern Great Plains. Developing forecasting models to quantify the economic benefits of crop protection under varying environments and disease resistance scenarios can contribute to targeting crop protection to conditions where positive economic benefits are more likely, and reducing the environmental footprint from fungicide use.