KEY MESSAGE: We developed 'Golden SusPtrit', i.e., a barley line combining SusPtrit's high susceptibility to non-adapted rust fungi with the high amenability of Golden Promise for transformation. Nonhost and partial resistance to Puccinia rust fungi in barley are polygenically inherited. These types of resistance are principally prehaustorial, show high diversity between accessions of the plant species and are genetically associated. To study nonhost and partial resistance, as well as their association, candidate gene(s) for resistance must be cloned and tested in susceptible material where SusPtrit would be the line of choice. Unfortunately, SusPtrit is not amenable to Agrobacterium-mediated transformation. Therefore, a doubled haploid (DH) mapping population (n = 122) was created by crossing SusPtrit with Golden Promise to develop a 'Golden SusPtrit', i.e., a barley line combining SusPtrit's high susceptibility to non-adapted rust fungi with the high amenability of Golden Promise for transformation. We identified nine genomic regions occupied by resistance quantitative trait loci (QTLs) against four non-adapted rust fungi and P. hordei isolate 1.2.1 (Ph.1.2.1). Four DHs were selected for an Agrobacterium-mediated transformation efficiency test. They were among the 12 DH lines most susceptible to the tested non-adapted rust fungi. The most efficiently transformed DH line was SG062N (11-17 transformants per 100 immature embryos). The level of non-adapted rust infection on SG062N is either similar to or higher than the level of infection on SusPtrit. Against Ph.1.2.1, the latency period conferred by SG062N is as short as that conferred by SusPtrit. SG062N, designated 'Golden SusPtrit', will be a valuable experimental line that could replace SusPtrit in nonhost and partial resistance studies, especially for stable transformation using candidate genes that may be involved in rust-resistance mechanisms.
The growing human population and a changing environment have raised significant concern for global food security, with the current improvement rate of several important crops inadequate to meet future demand 1 . This slow improvement rate is attributed partly to the long generation times of crop plants. Here, we present a method called 'speed breeding', which greatly shortens generation time and accelerates breeding and research programmes. Speed breeding can be used to achieve up to 6 generations per year for spring wheat (Triticum aestivum), durum wheat (T. durum), barley (Hordeum vulgare), chickpea (Cicer arietinum) and pea (Pisum sativum), and 4 generations for canola (Brassica napus), instead of 2-3 under normal glasshouse conditions. We demonstrate that speed breeding in fully enclosed, controlled-environment growth chambers can accelerate plant development for research purposes, including phenotyping of adult plant traits, mutant studies and transformation. The use of supplemental lighting in a glasshouse environment allows rapid generation cycling through single seed descent (SSD) and potential for adaptation to larger-scale crop improvement programs. Cost saving through light-emitting diode (LED) supplemental lighting is also outlined. We envisage great potential for integrating speed breeding with other modern crop breeding technologies, including high-throughput genotyping, genome editing and genomic selection, accelerating the rate of crop improvement.
Rphq2, a minor gene for partial resistance to Puccinia hordei , was physically mapped in a 188 kbp introgression with suppressed recombination between haplotypes of rphq2 and Rphq2 barley cultivars.
Adhesion of the barley husk to the underlying caryopsis requires the development of a cuticular cementing layer on the caryopsis surface. Differences in adhesion quality among genotypes have previously been correlated with cementing layer composition, which is thought to influence caryopsis cuticle permeability, the hypothesised mechanism of adhesion mediation. It is not yet known whether differences in adhesion quality among genotypes are determined by changes in caryopsis cuticle permeability. We examined changes in candidate cementing layer biosynthetic and regulatory genes to investigate the genetic mechanisms behind husk adhesion quality. We used both commercially relevant UK malting cultivars and older European lines to ensure phenotypic diversity in adhesion quality. An ethylene responsive transcription factor (NUD) is required for the development of the cementing layer. To examine correlations between gene expression, cementing layer permeability and husk adhesion quality we also treated cultivars with ethephon (2-chloroethylphosphonic acid) which breaks down to ethylene, and silver thiosulphate which inhibits ethylene reception, and measured caryopsis cuticle permeability. Differential adhesion qualities among genotypes are not determined by NUD expression during development of the cementing material alone, but could result from differences in biosynthetic gene expression during cementing layer development in response to longer-term NUD expression patterns. Altered caryopsis cuticle permeability does result in altered adhesion quality, but the correlation is not consistently positive or negative. Cuticle permeability is therefore not the mechanism that determines husk adhesion quality, but is likely a consequence of the required cuticular compositional changes that determine adhesion.