Anther Retention Research Articles

Assessing the impact of plant growth regulators on anther retention and Fusarium head blight in spring wheat (Triticum aestivum L.) infected by Fusarium graminearum in field conditions

Fusarium head blight (FHB) resistance in wheat is often associated with undesirable agronomic traits such as tall plant height and a propensity for lodging. Plant height in wheat is genetically controlled by some semi-dwarfing alleles that alter the plant's sensitivity to gibberellins (GAs). The presence of semi-dwarfing alleles increases the frequency of anther retention, which may contribute to FHB susceptibility by providing an initiation site for infection. The application of plant growth regulators (PGRs) may enable farmers to grow the most resistant cultivars while controlling plant height to minimize lodging risk. In this study, five spring wheat cultivars that differed in level of FHB resistance, height, and semi-dwarfing alleles were tested to determine the effect of PGRs, specifically Manipulator™ and Ethrel™, on plant height, anther retention, and FHB resistance level and the interactions between them in Winnipeg and Carman, Manitoba in 2019 and 2020. Combined field results showed that Ethrel™ significantly reduced plant height. Both PGRs did not affect the anther retention or FHB resistance levels of the tested cultivars under dry conditions. There were significant interactions between variables, but they were relatively small compared to the main treatment and cultivars. Based on the results of this study, producers could benefit from the higher levels of FHB resistance often associated with tall cultivars and use PGRs to manage plant height and lodging without increased risk of FHB.

Efficiency of indirect selection for fusarium head blight resistance and mycotoxin accumulation in winter wheat (Triticum aestivum L.)

AbstractFusarium head blight (FHB) is one of the most devastating diseases of wheat and can lead to significant yield losses as well as a contamination of the crop with mycotoxins that are a major concern in cereal‐based food and feed products. The aims of this study were thus to investigate the relationship between resistance against multiple Fusarium species and to assess the potential of an indirect phenotypic and genomic selection for the resistance against the accumulation of several mycotoxins in wheat. Strong phenotypic and genetic correlations between the mycotoxin contents, FHB severity and FHB‐associated traits were observed, irrespective of if traits were assessed in trials inoculated with a DON or HT‐2/T‐2 producing Fusarium species. A multi‐stage phenotypic or genomic selection with low anther retention being used for an indirect selection among early generation selection candidates, followed by an evaluation of the pre‐selected set in disease nurseries, and lastly by assessing the mycotoxin content of the most promising genotypes is suggested as a suitable strategy to breed for wheat cultivars with reduced risk of mycotoxin accumulation.

Separation of the effects of two reduced height (Rht) genes and genomic background to select for less Fusarium head blight of short-strawed winter wheat (Triticum aestivum L.) varieties.

FHB resistance shared pleiotropic loci with plant height and anther retention. Genomic prediction allows to select for genomic background reducing FHB susceptibility in the presence of the dwarfing allele Rht-D1b. With the high interest for semi-dwarf cultivars in wheat, finding locally adapted resistance sources against Fusarium head blight (FHB) and FHB-neutral reduced height (Rht) genes is of utmost relevance. In this study, 401 genotypes of European origin without/with dwarfing alleles of Rht-D1 and/or Rht24 were analysed across five environments on FHB severity and the morphological traits such as plant height(PH), anther retention(AR), number of spikelets per ear, ear length and ear density. Data were analysed by combined correlation and path analyses, association mapping and coupling single- and multi-trait genome-wide association studies (ST-GWAS and MT-GWAS, respectively) and genomic prediction (GP). All FHB data were corrected for flowering date or heading stage. High genotypic correlation (rg = 0.74) and direct path effect (0.57) were detected between FHB severity and anther retention (AR). Moderate correlation (rg = -0.55) was found between FHB severity and plant height (PH) with a high indirect path via AR (-0.31). Indirect selection for FHB resistance should concentrate on AR and PH. ST-GWAS identified 25 quantitative trait loci (QTL) for FHB severity, PH and AR, while MT-GWAS detected six QTL across chromosomes 2A, 4D, 5A, 6B and 7B conveying pleiotropic effects on the traits. Rht-D1b was associated with high AR and FHB susceptibility. Our study identified a promising positively acting pleiotropic QTL on chromosome 7B which can be utilized to improve FHB resistance while reducing PH and AR. Rht-D1b genotypes having a high resistance genomic background exhibited lower FHB severity and AR. The use of GP for estimating the genomic background was more effective than selection of GWAS-detected markers. We demonstrated that GP has a great potential and should be exploited by selecting for semi-dwarf winter wheat genotypes with higher FHB resistance due to their genomic background.

The effect of the Rht1 haplotype on Fusarium head blight resistance in relation to type and level of background resistance and in combination with Fhb1 and Qfhs.ifa-5A

Key messageThe effect of the Rht1-genes on FHB resistance depends on anther extrusion and level of background resistance. Qfhs.ifa-5A increases resistance and anther extrusion as efficiently as semi-dwarfing alleles decrease it.The semi-dwarfing reduced height alleles Rht-D1b and Rht-B1b have been deployed in modern wheat cultivars throughout the world, but they increase susceptibility to Fusarium head blight (FHB). Here, we investigated the impact of the Rht1 genes on anther retention (AR) in relation to FHB resistance using four different sets of near-isogenic lines (NILs) with contrasting levels and types of background FHB resistance. NILs were evaluated for FHB severity, plant height and AR in three greenhouse and three field trials using artificial spray inoculation. Rht-B1b and Rht-D1b alleles increased AR and FHB susceptibility in all genetic backgrounds. The magnitude of the effects differed between NIL groups. Increased FHB susceptibility largely followed increased AR. Differences in FHB susceptibility between tall and dwarf haplotypes were largest in the NIL group with the highest changes in AR. In the most resistant NIL group, dwarfed lines had only slightly higher AR than tall lines and maintained good resistance, while both tall and dwarf lines had high levels of retained anthers in the most susceptible NIL group. We further investigated the effect of the major Fusarium resistance QTL Fhb1 and Qfhs.ifa-5A in combination with the Rht1 genes. Qfhs.ifa-5A enhanced anther extrusion in tall as well as semi-dwarf haplotypes, whereas Fhb1 did not affect AR. Qfhs.ifa-5A supported FHB resistance more efficiently than Fhb1 in lines that were more responsive to AR, while both Fhb1 and Qfhs.ifa-5A were equally efficient in NILs that had high background resistance and low response to AR.

Dissecting the Contribution of Environmental Influences, Plant Phenology, and Disease Resistance to Improving Genomic Predictions for Fusarium Head Blight Resistance in Wheat

Environmental factors like temperature and humidity are presumed to greatly influence Fusarium head blight FHB infections in wheat. Anther retention AR, on the other hand, is a morphologically neutral trait that shares a common genetic basis with FHB resistance. In this study, our aims were to: (i) Evaluate two types of corrections of FHB severity scores, namely method-1 via linear regression on flowering time (FT), and method-2 via a best-subset multiple linear regression analysis comprising FT plus accumulated thermal time variables; and (ii) assess the performance of multi-trait genomic selection (MT.GS) models for FHB severity assisted by AR. The forward prediction scenarios where GS models were trained with data from the previous years revealed average prediction accuracies (PA) of 0.28, 0.33, and 0.36 for FHB severity scores that were uncorrected or corrected by method-1 and method-2, respectively. FHB severity scores free from the influences of both environment and phenology seemed to be the most efficient trait to be predicted across different seasons. Average PA increments up to 1.9-fold were furthermore obtained for the MT.GS models, evidencing the feasibility of using AR as an assisting trait to improve the genomic selection of FHB resistance breeding lines.

Relationship between genetic variability of flowering traits andFusariummycotoxin contamination in oats

AbstractOver the last three decades,Fusariuminfections and related mycotoxin contamination have caused significant economic losses in oats (Avena sativaL.). Breeding for resistance is highly prioritized in oats, but infection processes and resistance components againstFusariumspecies are not fully identified. In this study, the genetic variation for flowering traits and its impact on mycotoxin accumulation in oats is described. The first experiment of this paper was focused on flowering traits in 50 oat genotypes (Panel 1) to identify cleistogamic oats. Then, two separateFusarium‐inoculated experiments in three (Panel 2 with 25 genotypes) and two environments (Panel 3 with 16 genotypes) were conducted to assess the relationship between the degree of anther retention (AR) and resistance toFusariuminfestation and mycotoxin accumulation in oats. Panel 2 was inoculated withFusarium culmorum,F. langsethiae, andF. sporotrichioides, and Panel 3 was inoculated with eitherF.graminearumorF. culmorum. The assessment of open flowering score and AR displayed a continuous variation from dominating chasmogamy to complete cleistogamy. Significant differences for deoxynivalenol and T‐2 were found, with a modest correlation between both mycotoxins. The lowest mycotoxin levels were found in two old and one modern cultivar, and the highest levels were found in a dwarf oat cultivar. Compared with plant height, AR was a rather ambiguous factor for the mycotoxin content, and it interfered with effects of other traits displaying high ranges such as earliness, lodging, or hull content. To unravel components of resistance toFusariumin oats more precisely, specific populations with lower ranges in plant height and heading date should be studied.

Fine-mapping of the Fusarium head blight resistance QTL Qfhs.ifa-5A identifies two resistance QTL associated with anther extrusion

Key messageFine-mapping separated Qfhs.ifa-5A into a major QTL mapping across the centromere and a minor effect QTL positioned at the distal half of 5AS. Both increase Fusarium resistance and anther extrusion.The Fusarium head blight (FHB) resistance QTL Qfhs.ifa-5A resides in the low-recombinogenic pericentromeric region of chromosome 5A making fine-mapping particularly arduous. Qfhs.ifa-5A primarily contributes resistance to fungal entry with the favorable allele descending from the highly Fusarium resistant cultivar Sumai-3. Fine-mapping a near-isogenic recombinant inbred line population partitioned the Qfhs.ifa-5A interval into 12 bins. Near-isogenic lines recombining at the interval were phenotyped for FHB severity, anther retention and plant height. Composite interval mapping separated the initially single QTL into two QTL. The major effect QTL Qfhs.ifa-5Ac mapped across the centromere and the smaller effect QTL Qfhs.ifa-5AS mapped to the distal half of 5AS. Although Qfhs.ifa-5Ac and Qfhs.ifa-5AS intervals were as small as 0.1 and 0.2 cM, their corresponding physical distances were large, comprising 44.1 Mbp and 49.2 Mbp, respectively. Sumai-3 alleles at either QTL improved FHB resistance and increased anther extrusion suggesting a pleiotropic effect of anthers on resistance. This hypothesis was supported by greenhouse experiments using the susceptible cultivar Remus and its resistant near-isogenic line NIL3 carrying the entire Qfhs.ifa-5A segment. By manually removing anthers prior to spray inoculation both, Remus and NIL3 became almost equally resistant in the early phase of the disease development and were significantly less diseased than variants without anther manipulation. At late time points the positive effect of the anther removal became smaller for Remus and disappeared completely for NIL3. Results affirm that absence of anthers enhanced resistance to initial infection but did not protect plants from fungal spreading within spikes.

Breeding strategies and advances in line selection for Fusarium head blight resistance in wheat

Fusarium head blight (FHB) is a fungal disease of worldwide importance to small grain cereals that may lead to severe losses in both yield and quality. The development of resistant varieties is the most effective approach for managing the disease. Genetic variation for FHB resistance is large, including ‘exotic’ and ‘native’ wheat germplasm. Methods for selecting improved lines include: 1) phenotypic selection with direct symptom evaluation; 2) marker-assisted selection for well-characterized QTL and 3) genomic selection employing genome-wide prediction models. Breeding programs need to find the optimal deployment of the complementary approaches according to their available facilities, resources and requirements. This review aims to summarize recent advances in FHB resistance breeding, thereby discussing the importance of morphological traits like the extent of retained anthers after flowering, its suitability for indirect selection and the pronounced association of the semi-dwarfing allele Rht-D1b with increased anther retention and FHB severity. Marker-assisted selection is successfully applied to select for large-effect QTL, especially for the most prominent resistance QTL Fhb1 in bread wheat, as well as in durum wheat as recently demonstrated. The resistance locus Fhb1 has been partly elucidated, a pore-forming toxin-like gene confers resistance against fungal spread. Genomic selection for FHB resistance appears promising especially for breeding programs deploying ‘native’ resistance sources with many small-effect QTL.

The Semidwarfing Alleles Rht-D1b and Rht-B1b Show Marked Differences in Their Associations with Anther-Retention in Wheat Heads and with Fusarium Head Blight Susceptibility.

The semidwarfing alleles reduced height (Rht)-D1b and Rht-B1b are widely deployed in wheat breeding. Both alleles have similar effects on plant height but differ in their effect on Fusarium head blight (FHB) severity. A double-haploid population and a backcross population, segregating for Rht-B1a/Rht-B1b and Rht-D1a/Rht-D1b, were evaluated for FHB severity, plant height, and anther retention in field trials in three consecutive years. The semidwarfing alleles reduced plant height and increased the proportion of retained anthers. Reduced plant height and a high proportion of retained anthers were associated with increased FHB severity. The Rht-D1b allele had a significantly greater impact on anther retention and FHB severity than the Rht-B1b allele. Fusarium graminearum establishes infection sites predominantly inside the floral cavity and retained anthers potentially support colonization and initial hyphal growth, leading to a higher disease level in genotypes with a higher proportion of retained anthers. This is the first report demonstrating that differences in disease severity associated with Rht-D1b and Rht-B1b can be partly explained by their different effect on the extent of anther retention.

Comparative mapping of quantitative trait loci for Fusarium head blight resistance and anther retention in the winter wheat population Capo× Arina.

Key messageFusarium resistance in Arina is highly quantitative and governed by multiple small effect QTL. Anther retention has a high correlation with FHB susceptibility and appears a practicable indirect selection target for enhancing FHB resistance.The Swiss winter wheat cultivar Arina possesses a high resistance level constituted by a number of small to medium effect QTL reported from three independent mapping populations. Yet these overlap only for one resistance QTL on the long arm of chromosome 1B. The present study characterized Fusarium head blight (FHB) resistance in a population of 171 recombinant inbred lines from a cross between Arina (resistant) and Capo (moderately resistant). The population was evaluated for FHB resistance under field conditions for 3 years. Additionally, we phenotyped anther retention, plant height and flowering date to analyze their association with resistance. Lines with a low proportion of retained anthers after flowering and tall plants were significantly less diseased, while flowering date had no association with FHB severity. QTL analysis identified eight small to medium effect QTL for FHB severity, of which QTL on 1BS, 3B, 4AL and 6BL likely correspond to resistance alleles already detected in previously studied Arina populations. QTL for anther retention mapped to 4AL, 6BL and 5AS. Notably, QTL on 4AL and 6BL overlapped with QTL for FHB severity. A single small effect QTL for plant height was detected on 5AS and no QTL was identified for flowering date. Genotypes having three or four resistance alleles in combination showed a good resistance level, indicating pyramiding resistance QTL as a powerful approach for breeding resistant cultivars. Selection for rapid and complete anther extrusion appears promising as an indirect selection criterion for enhancing FHB resistance.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-015-2527-8) contains supplementary material, which is available to authorized users.

Pollination biology of Luisia curtisii (Orchidaceae): indications of a deceptive system operated by beetles

A population of Luisia curtisii (Orchidaceae: Aeridinae) in northern Thailand was studied with regard to pollination biology. Although a high level of self-compatibility was demonstrated experimentally, the very low natural fruit set (1.4–1.9 %) clearly indicated that the species depends on external agents for pollination. Our observations suggest that L. curtisii is pollinated by beetles, as Lema unicolor (Chrysomelidae) and Clinteria ducalis (Scarabaeidae) were the only flower visitors observed to carry pollinaria of this species. The hypothesis of specialised cantharophily is further supported by 2-methylbutyric acid and caproic acid being striking components of the floral scent. Judging from the lack of nectar and the behaviour of visiting beetles, the pollination system seems to rely on food or brood site deception. Retention of the anther on the pollinarium for some time after pollinarium removal probably reduces the frequency of insect-mediated autogamy and geitonogamy in Luisia curtisii—a possibility that was supported by comparative data on (1) the anther retention time and inflorescence visitation time of Lema unicolor and (2) stigma and anther length in the orchid. Existing reports of specialised beetle pollination in orchids are reviewed, and we conclude that there is accumulating evidence that specialised cantharophily is more common in the Orchidaceae than previously assumed.

Anther Extrusion and Fusarium Head Blight Resistance in European Wheat

AbstractAnther extrusion has been widely discussed as a factor influencing fusarium head blight (FHB) resistance in wheat. This is despite a paucity of quantitative information on its importance, between cultivars, in contrast to that for heading date and plant height. We describe a method applicable to a plant breeding situation at 10 days postanthesis, for assessing the distinct characteristics of anther retention (anthers held within the spikelet) and trapped anthers (partially extruded and trapped between the lemma and palea of the wheat spikelet). FHB resistance was tested in field experiments in 2004 and 2005. In these experiments designed to resemble applications to a plant breeding selection scheme anther retention was significantly correlated with FHB in 2004 (r = 0.26; P < 0.05) and 2005 (r = 0.26; P < 0.05). A higher proportion of anthers retained relating, albeit weakly, with increased FHB susceptibility in European wheat.