Molecular mapping of QTLs for Fusarium head blight resistance in spring wheat. II. Resistance to fungal penetration and spread

Fusarium head blight (FHB, scab) causes severe yield and quality losses, but the most serious concern is the mycotoxin contamination of cereal food and feed. The cultivation of resistant varieties may contribute to integrated control of this fungal disease. Breeding for FHB resistance by conventional selection is feasible, but tedious and expensive. The aim of this work was to detect QTLs for combined type I and type II resistance against FHB and estimate their effects in comparison to the QTLs identified previously for type II resistance. A population of 364, F1 derived doubled-haploid (DH) lines from the cross 'CM-82036' (resistant)/'Remus' (susceptible) was evaluated for components of FHB resistance during 2 years under field conditions. Plants were inoculated at anthesis with a conidial suspension of Fusarium graminearum or Fusarium culmorum. The crop was kept wet for 20 h after inoculation by mist-irrigation. Disease severity was assessed by visual scoring. Initial QTL analysis was performed on 239 randomly chosen DH lines and extended to 361 lines for putative QTL regions. Different marker types were applied, with an emphasis on PCR markers. Analysis of variance, as well as simple and composite interval mapping, revealed that two genomic regions were significantly associated with FHB resistance. The two QTLs on chromosomes 3B (Qfhs.ndsu-3BS) and 5A (Qfhs.ifa-5A) explained 29 and 20% of the phenotypic variance, respectively, for visual FHB severity. Qfhs.ndsu-3BS appeared to be associated mainly with resistance to fungal spread, and Qfhs.ifa-5A primarily with resistance to fungal penetration. Both QTL regions were tagged with flanking SSR markers. These results indicate that FHB resistance was under the control of two major QTLs operating together with unknown numbers of minor genes. Marker-assisted selection for these two major QTLs appears feasible and should accelerate the development of resistant and locally adapted wheat cultivars.     

Genetic variation for foot-rot and Fusarium head-blight resistances among full-sib families of a self-incompatible winter rye (Secale cereale L.) population

The amount of genetic variation for resistance to foot rot caused by Pseudocercosporella herpotrichoides, Fusarium spp., and Microdochium nivale and for resistance to head blight caused by Fusarium culmorum are important parameters when estimating selection gain from recurrent selection in winter rye. One-hundred and eighty-six full-sib families of the selfincompatible population variety Halo, representing the Petkus gene pool, were tested for foot-rot resistance at five German location-year combinations (environments) and for head-blight resistance in three environments with artificial inoculation in all but one environment. Foot-rot rating was based on 25 stems per plot scored individually on a 1–9 scale. Head-blight resistance was plotwise scored on a 1–9 scale and, additionally, grain-weight per spike was measured relative to the non-inoculated control plots. Significant estimates of genotypic variance and medium-sized heritabilities (h ²=0.51–0.69) were observed in the combined analyses for all resistance traits. In four out of five environments, the amount of genetic variance was substantially smaller for foot-rot than for head-blight rating. Considerable environmental effects and significant genotype-environment interactions were found for both foot-rot and head-blight resistance. Coefficients of error-corrected correlation among environments were considerably closer than phenotypic correlations. No significant association was found between the resistances to both diseases (r=-0.20 to 0.17). In conclusion, intra-population improvement by recurrent selection should lead to substantial higher foot-rot and head-blight resistances due to significant quantitative genetic variation within Halo. Selection should be carried out in several environments. Lack of correlation between foot-rot and head-blight resistance requires separate infection tests for improving both resistances.     

High accuracy of predicting hybrid performance of Fusarium head blight resistance by mid-parent values in wheat

Key message

Mid-parent values of Fusarium head blight (FHB) resistance tested across several locations are a good predictor of hybrid performance caused by a preponderance of additive gene action in wheat.

Abstract

Hybrid breeding is intensively discussed as one solution to boost yield and yield stability including an enhanced biotic stress resistance. Our objectives were to investigate (1) the heterosis for Fusarium head blight (FHB) resistance, (2) the importance of general (GCA) vs. specific combining ability (SCA) for FHB resistance, and (3) the possibility to predict the FHB resistance of the hybrids by the parental means. We re-analyzed phenotypic data of a large population comprising 1604 hybrids and their 120 female and 15 male parental lines evaluated in inoculation trials across seven environments. Mid-parent heterosis of FHB severity averaged ?9%, with a range from ?36 to +35%. Mean better parent heterosis was 2% and 78 of the hybrids significantly (P < 0.05) outperformed the best commercial check variety included in our study. FHB resistance was not correlated with grain yield in healthy status for lines (r = 0.01) and hybrids (r = 0.09, P < 0.01). While a preponderance of GCA variance (P < 0.01) was found, SCA variance was not significantly different from zero. Accuracy to predict hybrid performance of FHB severity based on mid-parent values and on GCA effects was high (r = 0.70 and 0.86, respectively; P < 0.01). Similarly, line per se performance and GCA effects were significantly correlated (r = 0.77; P < 0.01). The substantial level of mid-parent heterosis in the desired direction of decreased susceptibility and the negligible better parent heterosis suggest that hybrids are an attractive alternative variety type to improve FHB resistance.

     

QTL mapping and comparative genome analysis of agronomic traits including grain yield in winter rye

Key message

Genetic diversity in elite rye germplasm as well as F _2:3 testcross design enables fast QTL mapping to approach genes controlling grain yield, grain weight, tiller number and heading date in rye hybrids.

Abstract

Winter rye (Secale cereale L.) is a multipurpose cereal crop closely related to wheat, which offers the opportunity for a sustainable production of food and feed and which continues to emerge as a renewable energy source for the production of bioethanol and biomethane. Rye contributes to increase agricultural crop species diversity particularly in Central and Eastern Europe. In contrast to other small grain cereals, knowledge on the genetic architecture of complex inherited, agronomic important traits is yet limited for the outbreeding rye. We have performed a QTL analysis based on a F_2:3 design and testcross performance of 258 experimental hybrids in multi-environmental field trials. A genetic linkage map covering 964.9 cM based on SSR, conserved-orthologous set (COS), and mixed-phase dominant DArT markers allowed to describe 22 QTL with significant effects for grain yield, heading date, tiller number, and thousand grain weight across seven environments. Using rye COS markers, orthologous segments for these traits have been identified in the rice genome, which carry cloned and functionally characterized rice genes. The initial genome scan described here together with the existing knowledge on candidate genes provides the basis for subsequent analyses of the genetic and molecular mechanisms underlying agronomic important traits in rye.

     

Fine mapping of the restorer gene <Emphasis Type="Italic">Rfp3</Emphasis> from an Iranian primitive rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.)

Key message

A comparative genetics approach allowed to precisely determine the map position of the restorer gene Rfp3 in rye and revealed that Rfp3 and the restorer gene Rfm1 in barley reside at different positions in a syntenic 4RL/6HS segment.

Abstract

Cytoplasmic male sterility (CMS) is a reliable and striking genetic mechanism for hybrid seed production. Breeding of CMS-based hybrids in cereals requires the use of effective restorer genes as an indispensable pre-requisite. We report on the fine mapping of a restorer gene for the Pampa cytoplasm in winter rye that has been tapped from the Iranian primitive rye population Altevogt 14160. For this purpose, we have mapped 41 gene-derived markers to a 38.8 cM segment in the distal part of the long arm of chromosome 4R, which carries the restorer gene. Male fertility restoration was comprehensively analyzed in progenies of crosses between a male-sterile tester genotype and 21 recombinant as well as six non-recombinant BC₄S₂ lines. This approach allowed us to validate the position of this restorer gene, which we have designated Rfp3, on chromosome 4RL. Rfp3 was mapped within a 2.5 cM interval and cosegregated with the EST-derived marker c28385. The gene-derived conserved ortholog set (COS) markers enabled us to investigate the orthology of restorer genes originating from different genetic resources of rye as well as barley. The observed localization of Rfp3 and Rfm1 in a syntenic 4RL/6HS segment asks for further efforts towards cloning of both restorer genes as an option to study the mechanisms of male sterility and fertility restoration in cereals.

     

Association between line per se and testcross performance for eight agronomic and quality traits in winter rye

Key message

We investigated associations between line per se and testcross performance in rye and suggested that selection for per se performance is valuable for several traits in multi-stage selection programs.

Abstract

Genotypic correlation between line per se and testcross performance is an important quantitative-genetic parameter for optimizing hybrid breeding programs. The main goal of this survey was to study the association of line per se and testcross performance at the phenotypic level. We used experimental data from the line per se and testcross performance of two segregating winter rye populations (A, B) with each of 220 progenies tested in six environments for eight agronomic and quality traits. Genotypic variances were considerably larger for per se than for testcross performance of all investigated traits resulting in higher heritabilities of the former in most instances. Genotypic correlations (r _g) between testcross and line per se performance decreased with increasing complexity of the trait as shown by the respective heritabilities. They were highest (r _g ≥ 0.7) for plant height and test weight in population B, and thousand-kernel weight, falling number and starch content in both populations. A selection of these traits for line per se performance in early generations will save field plots in further testing testcross performance and increase efficiency of hybrid breeding.     

Mapping QTLs with main and epistatic effects underlying grain yield and heading time in soft winter wheat

There is increasing awareness that epistasis plays a role for the determination of complex traits. This study employed an association mapping approach in a large panel of 455 diverse European elite soft winter wheat lines. The genotypes were evaluated in multi-environment trials and fingerprinted with SSR markers to dissect the underlying genetic architecture of grain yield and heading time. A linear mixed model was applied to assess marker-trait associations incorporating information of covariance among relatives. Our findings indicate that main effects dominate the control of grain yield in wheat. In contrast, the genetic architecture underlying heading time is controlled by main and epistatic effects. Consequently, for heading time it is important to consider epistatic effects towards an increased selection gain in marker-assisted breeding.     

Analysis of Covariation of Grain Yield and Dry Matter Yield for Breeding Dual Use Hybrid Rye

Winter rye (Secale cereale L.) is becoming increasingly important as substrate for biogas production in Central Europe. Dry matter yield has evolved as a breeding goal comparably important to the traditional grain yield. We analyzed the covariation between both traits and tested other agronomic traits for their correlation to dry matter yield that could be used for prediction of biomass yield. A set of 258 experimental hybrids were tested for dry matter yield harvested at late milk stage and grain yield harvested at full ripening at three to four locations in Germany in 2011 and 2012. We observed a wide range of dry matter yield (10–24 Mg ha^?1) and grain yield (6–15 Mg ha^?1) among testcross progenies. Genetic variances were significantly (P?<?0.01) different from zero for all traits. High entry-mean heritabilities (0.92–0.94) were found for plant height measurements and moderate heritabilities for grain and dry matter yield (0.52 and 0.49, respectively). Relative efficiencies for selection of dry matter yield estimated by second (EC 51–55) and third (EC 73) measurements of plant height were 1.24 and 0.98 respectively, compared to 0.52 for grain yield. Indirect selection for high dry matter yield using late plant height measurements should be successful. Using grain yield for indirect selection was less effective. The observed broad genetic variation for biomass yield in elite hybrid rye gives good prospects for the use as a resource of renewable energy. Plant height is a good predictor of dry matter yield but should be selected together with improved lodging resistance.     

<Emphasis Type="Italic">Rht24</Emphasis> reduces height in the winter wheat population ‘Solitär × Bussard’ without adverse effects on Fusarium head blight infection

Key message

The dwarfing gene Rht24 on chromosome 6A acts in the wheat population ‘Solitär × Bussard’, considerably reducing plant height without increasing Fusarium head blight severity and delaying heading stage.

Abstract

The introduction of the Reduced height (Rht)-B1 and Rht-D1 semi-dwarfing genes led to remarkable increases in wheat yields during the Green Revolution. However, their utilization also brings about some unwanted characteristics, including the increased susceptibility to Fusarium head blight. Thus, Rht loci that hold the potential to reduce plant height in wheat without concomitantly increasing Fusarium head blight (FHB) susceptibility are urgently required. The biparental population ‘Solitär × Bussard’ fixed for the Rht-1 wild-type alleles, but segregating for the recently described gibberellic acid (GA)-sensitive Rht24 gene, was analyzed to identify quantitative trait loci (QTL) for FHB severity, plant height, and heading date and to evaluate the effect of the Rht24 locus on these traits. The most prominent QTL was Rht24 on chromosome 6A explaining 51% of genotypic variation for plant height and exerting an additive effect of ? 4.80 cm. For FHB severity three QTL were detected, whereas five and six QTL were found for plant height and heading date, respectively. No FHB resistance QTL was co-localized with QTL for plant height. Unlike the Rht-1 semi-dwarfing alleles, Rht24b did not significantly affect FHB severity. This demonstrates that the choice of semi-dwarfing genes used in plant breeding programs is of utmost consideration where resistance to FHB is an important breeding target.