Summary 1We fitted species-area curves to the power function and examined changes in the parameters to quantify changes in species richness of all plants together, trees only and non-trees over five scales of magnitude (0.01 m 2 to 400 m 2 ) after a wildfire in the Linville Gorge Wilderness Area, North Carolina, USA. 2 Increases in species richness of all plants together occurred after the fire at all scales and increased in magnitude as scale increased. However, a lack of change in the slopes ( z -values) of species-area curves indicates that proportional changes were independent of scale of observation below 400 m 2 . Changes in species richness were predominantly driven by immigration, which was significantly related to fire severity. Survival of species present pre-fire was greater than local extinction, but neither was related to severity. 3 Species richness of trees increased at all scales but proportional increases were smaller at larger scales and slopes of species-area curves decreased after the fire. Local seedling recruitment increased species richness at small scales, but low rates of immigration due to dispersal limitation in most species limited increases at larger scales. 4 Directional changes in species richness of non-trees were not always consistent at fine scales but both absolute and relative changes were positive at scales ≥ 1 m 2 and increased with increasing scale. Slopes of species-area curves increased post-fire because localized patterns of immigration within plots resulted in little mixing of species at small scales but large changes in species richness at larger scales. 5 Fire in the southern Appalachians increases plant species richness within local communities, but rates of species turnover and patterns of beta diversity are maintained by local recruitment of tree seedlings at small scales and immigration of herb, shrub and vine species at larger scales. 6 Although decreased levels of competition after disturbance promote species coexistence at small scales, changes in species richness at larger scales are determined by the degree that the local community is linked to the species pool of the surrounding landscape through processes related to dispersal, particularly mass effects.

Wheat is one of the world’s most important sources of food. However, due to its evolution its genetic base has narrowed, which is severely limiting the ability of breeders to develop new higher yielding varieties that can adapt to the changing environment. In contrast to wheat, its wild relatives provide a vast reservoir of genetic variability for most, if not all, agronomically important traits. Genetic variation has previously been transferred to wheat from one of its wild relatives, Ambylopyrum muticum (previously known as Aegilops mutica). However, before the genetic variation available in this species can be assessed and exploited in breeding and for research, the transmission of the chromosome segments introgressed into wheat must first be stabilized. In this paper we describe the generation of 66 stably inherited homozygous wheat/Am. muticum introgression lines using a doubled haploid procedure. The characterisation and stability of each of these lines was determined via genomic in situ hybridization and SNP analysis. While most of the doubled haploid lines were found to carry only single introgressions, six lines carried two. Three lines carried only complete Am. muticum chromosomes, 43 carried only small or very small introgressions and the remainder carried either only large introgressions or a large plus a small introgression. The strategy that we are employing for the distribution and exploitation of the genetic variation from Am. muticum and a range of other species is discussed.

Stripe rust resistance in the German winter wheat cv. Alcedo has been described as durable, the resistance having remained effective when grown extensively in Germany and Eastern Europe between 1975 and 1989. Genetic characterisation of field resistance in a cross between Alcedo and the stripe rust susceptible UK winter wheat cv. Brigadier identified two major QTL in Alcedo located on the long arms of chromosomes 2D (QPst.jic-2D) and 4B (QPst.jic-4B). Stripe rust resistance was evaluated by measuring the extent of fungal growth, percentage infection (Pi) and the necrotic/chlorotic response of the plant to infection, infection type (IT). Both QPst.jic-2D and QPst.jic-4B contributed significantly to the reduction in stripe rust infection (Pi), with QPst.jic-2D explaining up to 36.20% and QPst.jic-4B 28.90% of the phenotypic variation measured for Pi. Both QTL were identified by the IT phenotypic scores, with QPst.jic-2D in particular being associated with a strong necrotic phenotype (low IT), QPst.jic-2D explaining up to 53.10% of IT phenotypic variation and QPst.jic-4B 22.30%. In addition, two small effect QTL for field stripe rust resistance were identified in Brigadier, QPst.jic-1B on the long arm of chromosome 1B and QPst.jic-5A on the short arm of chromosome 5A. The influence of QPst.jic-1B was primarily seen with the Pi phenotype, contributing up to 13.10% of the explained phenotypic variation. QPst.jic-5A was only detected using an approximate multiple-QTL model and selecting markers linked to the major effect QTL, QPst.jic-2D and QPst.jic-4B as co-factors. Seedling stripe rust resistance was also mapped in the cross, which confirmed the location of Yr17 from Brigadier to the short arm of chromosome 2A. A seedling expressed QTL was also located in Alcedo that mapped to the same location as the field stripe rust resistance QPst.jic-2D.

Yellow rust (causal agent: Puccinia striiformis f.sp. tritici) resistance in the UK wheat cultivar Guardian is developmentally regulated, resistance increasing as the plant matures. Yellow rust resistance was assessed under field conditions on plants after ear emergence to ensure maximum expression of resistance. Three quantitative trait loci (QTL) for yellow rust resistance were identified, being located on chromosomes 1B (QPst.jic-1B), 2D (QPst.jic-2D) and 4B (QPst.jic-4B). The largest resistance effect, QPst.jic-1B located to the same position on the long arm of chromosome 1B as the known durable source of yellow rust resistance, Yr29. Microscopic studies were carried out to determine what effect the resistance in Guardian had on the development of P. striiformis f.sp. tritici. While the adult plant resistance in Guardian did not prevent germinated urediniospores from establishing an effective infection site, the growth of hyphae within flag leaf tissue was significantly inhibited, slowing the development of microcolonies. 3,3-diaminabenzadine (DAB) and trypan blue staining indicated that this inhibition of hyphal growth was not associated with hydrogen peroxide accumulation or extensive plant cell death.

Wheat is one of the most important food and protein sources in the world and although, in recent years wheat breeders have achieved yield gains, they are not sufficient to meet the demands of an ever-growing population. Development of high yielding wheat varieties, resilient to abiotic and biotic stress resulting from climate change, has been limited by wheat’s narrow genetic base. In contrast to wheat, the wild relatives of wheat provide a vast reservoir of genetic variation for most, if not all, agronomic traits. Previous studies by the authors have shown the transfer of genetic variation from T. urartu into bread wheat. However, before the introgression lines can be exploited for trait analysis, they are required to have stable transmission of the introgressions to the next generation. In this work, we describe the generation of 86 doubled haploid (DH) wheat-T. urartu introgression lines that carry homozygous introgressions which are stably inherited. The DH lines were characterised using the Axiom® Wheat Relative Genotyping Array and 151 KASP markers to identify 65 unique T. urartu introgressions in a bread wheat background. DH production has helped accelerate the breeding process and facilitated the early release of homozygous wheat-T. urartu introgression lines. Together with the KASP markers, this valuable resource could greatly advance identification of beneficial alleles that can be used in wheat improvement.

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The expression of the resistance phenotypes of QPst.jic-2D and QPst.jic-4B, two quantitative trait loci (QTL) for stripe rust resistance in wheat cv. Alcedo, were assessed relative to plant growth stage, while a histopathology analysis was undertaken to characterize the cellular interaction between Puccinia striiformis f. sp. tritici (the causal agent of stripe rust) and each QTL. QPst.jic-2D expressed a partial resistant phenotype at seedling growth stages, with the level of resistance increasing as the wheat plant matured, conferring a disease-free phenotype at heading. QPst.jic-4B, however, did not express a resistant phenotype until booting (growth stage 41 on the Zadoks scale), displaying its full resistant phenotype at heading. Microscopic examination in flag leaves showed that infection sites formed in all genotypes tested, with full infection-site establishment being observed by 36 h post-inoculation (hpi). In lines carrying both QPst.jic-2D and QPst.jic-4B, as well as the parental cv. Alcedo, no microcolony formation, defined by the appearance of runner hyphae, was observed. Microcolony formation was observed in lines carrying only one, or neither QTL. Cell death associated with infection sites was observed for all genotypes, although the timing of first appearance and the extent of the cell death response varied considerably. In lines carrying both QPst.jic-2D and QPst.jic-4B cell death did not extend beyond one to three cells. In lines carrying only one QTL more extensive cell death was observed and cell death appeared later in lines with QPst.jic-4B than QPst.jic-2D. Cell death was also occasionally observed in lines without either QTL, although only at 264 hpi.

Hybridization is common in many ferns and has been a significant factor in fern evolution and speciation. However, hybrids are rare between the approximately 30 species of Dicksonia tree ferns world-wide, and none are well documented. In this study we examine the relationship of a newly-discovered Dicksonia tree fern from Whirinaki, New Zealand, which does not fit the current taxonomy of the three species currently recognized in New Zealand. Our microsatellite genotyping and ddRAD-seq data indicate these plants are F1 hybrids that have formed multiple times between D . fibrosa and D . lanata subsp. lanata . The Whirinaki plants have intermediate morphology between D . fibrosa and D . lanata subsp. lanata and their malformed spores are consistent with a hybrid origin. The Whirinaki plants– Dicksonia fibrosa × D . lanata subsp. lanata –are an example of hybridization between distantly related fern lineages, with the two parent species estimated to have diverged 55–25 mya. Our chloroplast sequencing indicates asymmetric chloroplast inheritance in the Whirinaki morphology with D . lanata subsp. lanata always contributing the chloroplast genome.