QTL controlling grain filling under terminal drought stress in a set of wild barley introgression lines

Abstract

Drought is a major abiotic stress impeding the yield of cereal crops globally. Particularly in Mediterranean environments, water becomes a limiting factor during the reproductive developmental stage, causing yield losses. The wild progenitor of cultivated barley Hordeum vulgare ssp spontaneum (Hsp) is a potentially useful source of drought tolerance alleles. Wild barley introgression lines like the S42IL library may facilitate the introduction of favorable exotic alleles into breeding material. The complete set of 83 S42ILs was genotyped with the barley 9k iSelect platform in order to complete genetic information obtained in previous studies. The new map comprises 2,487 SNPs, spanning 989.8 cM and covering 94.5% of the Hsp genome. Extent and positions of introgressions were confirmed and new information for ten additional S42ILs was collected. A subset of 49 S42ILs was evaluated for drought response in four greenhouse experiments. Plants were grown under well-watered conditions until ten days post anthesis. Subsequently drought treatment was applied by reducing the available water. Several morphological and harvest parameters were evaluated. Under drought treatment, trait performance was reduced. However, there was no interaction effect between genotype and treatment, indicating that genotypes, which performed best under control treatment, also performed best under drought treatment. In total, 40 QTL for seven traits were detected in this study. For instance, favorable Hsp effects were found for thousand grain weight (TGW) and number of grains per ear under drought stress. In particular, line S42IL-121 is a promising candidate for breeding improved malting cultivars, displaying a TGW, which was increased by 17% under terminal drought stress due to the presence of an unknown wild barley QTL allele on chromosome 4H. The introgression line showed a similar advantage in previous field experiments and in greenhouse experiments under early drought stress. We, thus, recommend using S42IL-121 in barley breeding programs to enhance terminal drought tolerance.

Evaluation of wild barley introgression lines for agronomic traits related to nitrogen fertilization

“…Each S42IL carries a specific exotic chromosome segment bearing the potential for several trait improvements important for further barley breeding. Thus far, a number of studies on S42IL performance under greenhouse and field conditions have been carried out (Schmalenbach et al 2008Wang et al 2010;Saal et al 2011;Schmalenbach et al 2011;Hoffmann et al 2012;Schnaithmann and Pillen 2013;Honsdorf et al 2014a, b;Naz et al 2014;Reuscher et al 2016;Honsdorf et al 2017;Soleimani et al 2017). However, only two of these focused on nitrogen stress, conducted in a hydroponic system (Hoffmann et al 2012) and in greenhouse.…”

“…For the present study the S42IL library was used, established by introgressive hybridization of wild type alleles from ISR42-8 into the gene pool of spring barley cultivar 'Scarlett' (Von Korff et al 2004). Pre-ILs (BC2) were backcrossed again (BC3) with the recurrent parent 'Scarlett' followed by repeated rounds of two to four selfings, as described in Schmalenbach et al (2011), resulting in a population of 83 S42ILs (Honsdorf et al 2017). Each S42IL carries one (occasionally multiple) small wild barley genetic introgression, which usually overlaps with the neighboring S42IL.…”

“…Each S42IL carries one (occasionally multiple) small wild barley genetic introgression, which usually overlaps with the neighboring S42IL. In total, the 83 S42IL library covers 94.5% of the 'ISR42-8' genome (Honsdorf et al 2017). Thereof, a set of 41 S42ILs, covering 75.3% of the exotic genome, was selected for field experiments.…”

“…The presence of a QTL was accepted, if a S42IL revealed a significant LSMeans difference from 'Scarlett' with p \ 0.05 within a single treatment or across both treatments. If significant lines were carrying overlapping or flanking introgressions showing similar effects in the same direction (based on the genetic map of Honsdorf et al 2017), a single QTL was assumed. The relative performance (RP) of a S42IL, describing the deviation from 'Scarlett' in %, was calculated by the following equation:…”

“…This way, the genetic basis of trait variation can be revealed. Until now, exotic introgressions in S42IL and its precursor population S42 could be associated with a broad spectrum of traits like threshability (Schmalenbach et al 2011), root and shoot related parameters (Hoffmann et al 2012;Naz et al 2012), grain parameters and yield related traits (Schnaithmann and Pillen 2013;Honsdorf et al 2017;Arifuzzaman et al 2014), nutrient accumulation (Reuscher et al 2016;Soleimani et al 2017) as well as drought stress tolerance traits (Honsdorf et al 2014a, b) in greenhouse trials. Furthermore, field trials showed associations of exotic introgressions with yield and yield-related parameters (Von Korff et al 2006;Saal et al 2011), powdery mildew and leaf rust resistance (Schmalenbach et al 2008), malting quality ) and growth phenology (Wang et al 2010).…”