Abstract/Summary

Maintaining wheat grain yield under expected more frequent and maybe severe drought episodes requires identifying the drought tolerance traits as well as deciphering the genetic basis of these traits responses to drought, and utilising potential symbiotic endophytes to alleviate drought effects. The aim of this project was to conduct an in-depth study of the genetic architecture of wheat responses to drought, deciphering the genetic basis of both source and sink traits under field conditions, as well as, investigating the ability of the endophyte fungus Piriformospora indica to increase yield in both well-watered and drought conditions and identify QTL underpinning drought-resistance traits influenced by endophytic growth. In the field trial, a representative subset of the elite eight-founder population, comprising 384 RILs, the founders and a check variety 'Kielder' were tested in rainfed vs irrigated field blocks, monitoring soil moisture content at different depth intervals. Field plots were phenotyped throughout the growing season using integrative drone-based and proximal sensing approaches. The results showed maximum soil moisture deficit (SMD) peaking over 120 mm in the rain fed plots, with large deficits (>75 mm) from late April that coincided with tillering and more prolonged large deficits from mid-June to mid-July(> I 00 mm), significantly decreasing crop canopy indices at all measured dates post-irrigation and causing significant increase in canopy temperature of rainfed plots, all driving an average yield reduction of 32.8% which was significantly genotype dependent. Also identifying traits most significantly (p:S0.00 I ) correlated with yield revealed grains.m-2 (r=0.68) and (r=0.72) and canopy temperature depression (CTD) (r=0.52) and (r=0.61) in rainfed and irrigated condition, respectively. QTL analysis for yield revealed a total of 16 novel QTL expressed commonly across both treatments explaining individually I to 4.5% as well as treatment dependent QTL. With remarkable examples of grain yield QTL collocating with major QTL such as grains.m-2 QTL on chromosome 3A and Rht-Dl pleiotropic region on chromosome 40 and highlighting significant SNP-SNP epistatic interactions for yield occasionally coinciding with QTL for crop canopy indices. Investigating the response of 200 MAGIC lines to P. indica inoculation showed the potential of the endophyte to significantly increase yield in well-watered and drought conditions, however, for most traits, there was significant difference in genotypes responses to colonization. Several QTL unique to colonized plants were detected on most chromosomes and linked to measured traits under drought, Those QTL can be investigated as candidate genes governing the symbiosis between wheat and P. indica.