Pre-harvest sprouting, the germination of seeds within heads before harvest, is a major problem in global wheat production, manifested by losses of quality in affected grain. Uncertainties in weather patterns, due to ongoing climate change, are exacerbating this problem and therefore reducing farmers revenue and food availability as well as increasing price volatility. Pre-harvest sprouting is closely linked with seed dormancy and reduced dormancy is a major domestication trait in crop plants. Therefore, a balance between the opposing forces of reduced dormancy and pre-harvest sprouting needs to be established. Dormancy and germination are controlled by numerous physiological processes within a plant. While some major genes have been identified that alter the resistance or tolerance towards pre-harvest sprouting, successful breeding of sprouting-tolerant varieties is still a challenge, since it is laborious to test for pre-harvest sprouting, especially in years lacking rain around harvest season.

There is a need for the establishment of optimized methods, to differentiate susceptible breeding lines from sprouting-tolerant lines without compromising yield and other important quality or disease resistance related traits. The standard measure of sprouting damage is counting the number of sprouted grains after harvest, which is time-consuming and uninformative in years without preharvest rain. Although sprouting on grains might not be visible, it might be detectable by the Hagberg falling number test, which measures the pasting quality of starch. This test needs a substantial amount of grain and is time-consuming, so it is impractical for screening breeding lines in early generations. Moreover, measuring Hagberg falling numbers in years without pre-harvest sprouting pressure does also not provide useful data for selection. 

The aims of this study are therefore: Use historic data and conduct field trials with a diverse set of modern wheat genotypes (cultivars, breeding and pre-breeding lines) to establish methods that can successfully differentiate breeding lines and varieties by their susceptibility or tolerance towards preharvest sprouting. Evaluate a laboratory test that triggers sprouting in grain and compare the results to previously used, field sprouting tests. Comparison of the established methods for measuring sprouting damage, namely the Hagberg falling number test and counting sprouted kernels, to simpler methods, like enzymatic assays, infrared spectroscopy and image analysis. Describe the genetic architecture of dormancy and pre-harvest sprouting in a breeding population and compare it to previously published resistance loci or genes. Investigate the efficacy of recently popularized genomic tools, particularly single-trait and multi-trait genomic prediction, to enable the prediction of complex traits in wheat, especially resistance to pre-harvest sprouting in years when pre-harvest rain is absent. Develop new statistical and bioinformatic tools, that combine multiple genomic and phenomic data, to improve genomic selection strategies for pre-harvest sprouting resistance in wheat. 

Figure 1: varying degrees of spout damage on wheat kernels (image source: Saatzucht Donau)

Figure 2: head sprouting assessment scale (image source: Saatzucht Donau)