Quantitative trait loci for resistance to fusarium head blight and deoxynivalenol accumulation in Wangshuibai wheat under field conditions

Wangshuibai is a Chinese landrace wheat with a high level of resistance to fusarium head blight (FHB) and deoxynivalenol (DON) accumulation. Using an F7 population of recombinant inbred lines (RILs) derived from the cross between Wangshuibai and Annong 8455 for molecular mapping of quantitative trait loci (QTL) for FHB resistance, the proportion of scabbed spikelets (PSS) and DON content were assessed under field conditions. Composite interval mapping revealed that two and three QTL were significantly associated with low PSS and low DON content, respectively, over 2 years. QTL on chromosomes 3B and 2A explained 17 and 11·5%, respectively, of the phenotypic variance for low PSS, whereas QTL on chromosomes 5A, 2A and 3B explained 12·4, 8·5 and 6·2%, respectively, of the phenotypic variance for low DON content. The 3B QTL appeared to be associated mainly with low PSS, and the 5A QTL primarily with low DON content in Wangshuibai. The 2A QTL had minor effects on both low PSS and DON content. Microsatellite and AFLP markers linked to these QTL should be useful for marker-assisted selection of QTL for low PSS and low DNA content from Wangshuibai.     

Identification of a Novel Fusarium Head Blight Resistance Quantitative Trait Locus on Chromosome 7A in Tetraploid Wheat

ABSTRACT Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most destructive diseases of durum (Triticum turgidum sp. durum) and common wheat (T. aestivum). Promising sources of FHB resistance have been identified among common (hexaploid) wheats, but the same is not true for durum (tetraploid) wheats. A previous study indicated that chromosome 7A from T. turgidum sp. dicoccoides accession PI478742 contributed significant levels of resistance to FHB. The objectives of this research were to develop a genetic linkage map of chromosome 7A in a population of 118 recombinant inbred lines derived from a cross between the durum cv. Langdon (LDN) and a disomic LDN-T. turgidum sp. dicoccoides PI478742 chromosome 7A substitution line [LDN-DIC 7A(742)], and identify a putative FHB resistance quantitative trait locus (QTL) on chromosome 7A derived from LDN-DIC 7A(742). The population was evaluated for type II FHB resistance in three greenhouse environments. Interval regression analysis indicated that a single QTL designated Qfhs.fcu-7AL explained 19% of the phenotypic variation and spanned an interval of 39.6 cM. Comparisons between the genetic map and a previously constructed physical map of chromosome 7A indicated that Qfhs.fcu-7AL is located in the proximal region of the long arm. This is only the second FHB QTL to be identified in a tetraploid source, and it may be useful to combine it with the QTL Qfhs.ndsu-3AS in order to develop durum wheat germ plasm and cultivars with higher levels of FHB resistance.     

Evaluation and characterization of resistance to fusarium head blight caused by Fusarium culmorum in UK winter wheat cultivars

Fusarium head blight (FHB) resistance of 50 cultivars from the National List of winter wheat cultivars approved for sale (or were undergoing trails for approval in 2003) in the UK was compared with 21 reference cultivars from continental Europe which had previously been characterized for resistance. Only three UK National List cultivars (Soissons, Spark and Vector) had stable resistance over trial sites that was significantly greater than that of the FHB susceptible cultivar Wizard. In addition, under moderate disease pressure, 21 of the National List cultivars had levels of the trichothecene mycotoxin deoxynivalenol (DON) above the proposed European Union limit of 1·25 ppm in grain. Surveys show that levels of FHB and DON in the UK crop are currently very low, however, should disease pressure increase for any reason, then an improvement in the overall levels of FHB resistance of UK winter wheat germplasm will be required. In order to infer the origin of resistance and to identify potentially novel resistance, allele sizes of microsatellite (simple sequence repeat, SSR) markers linked to quantitative trait loci (QTL) for FHB resistance were compared between the test cultivars and known, characterized resistance sources. The major FHB resistance QTL from the Chinese cv. Sumai-3 (3BS, 5A and 6B), the Romanian cv. Fundulea F201R (1B and 5A) and the French cv. Renan (5AL) were screened with 17 SSRs. No National List cultivar had haplotypes similar to any of these QTL. However, the highly resistant German reference cultivar Petrus had an identical haplotype to cv. Fundulea F201R on 1B indicating that this cultivar has an allelic FHB resistance QTL at that location.     

Main effects, epistasis, and environmental interactions of quantitative trait Loci for fusarium head blight resistance in a recombinant inbred population

ABSTRACT Chinese Spring Sumai 3 chromosome 7A disomic substitution line (CS-SM3-7ADS) is highly resistant to Fusarium head blight (FHB), and an F(7) population of recombinant inbred lines derived from the cross CS-SM3-7ADS x Annong 8455 was evaluated for resistance to FHB to investigate main effects, epistasis, and environmental interactions of quantitative trait loci (QTLs) for FHB resistance. A molecular linkage map consists of 501 simple sequence repeat and amplified fragment length polymorphism markers. A total of 10 QTLs were identified with significant main effects on the FHB resistance using MapQTL and QTLMapper software. Among them, CS-SM3-7ADS carries FHB-resistance alleles at five QTLs on chromosomes 2D, 3B, 4D, and 6A. One QTL on 3BS had the largest effect and explained 30.2% of the phenotypic variance. Susceptible QTLs were detected on chromosomes 1A, 1D, 4A, and 4B. A QTL for enhanced FHB resistance was not detected on chromosome 7A of CS-SM3-7ADS; therefore, the increased FHB resistance in CS-SM3-7ADS was not due to any major FHB-resistance QTL on 7A of Sumai 3, but more likely was due to removal of susceptible alleles of QTLs on 7A of Chinese Spring. QTLMapper detected nine pairs of additive-additive interactions at 17 loci that explained 26% phenotypic variance. QTL-environment interactions explained 49% of phenotypic variation, indicating that the environments significantly affected the expression of the QTLs, especially these epistasis QTLs. Adding FHB-enhancing QTLs or removal of susceptible QTLs both may significantly enhance the degree of wheat resistance to FHB in a wheat cultivar.     

不同小麦品种抗赤霉病性类型和抗毒素积累能力分析

赤霉病是我国小麦上的重要病害,品种抗病性利用是控制病害发生的重要措施,明确小麦抗赤霉病资源的抗性类型,有利于小麦抗赤霉病育种。2003年和2004年对9个常用抗源在穗期进行单花滴注和喷雾接种,研究其抗侵染和抗扩展性,并对病穗中的脱氧雪腐镰刀菌烯醇(DON)的含量进行分析。结果表明,望水白和苏麦3号具较好的抗侵染和抗扩展能力,其中望水白的抗扩展性最好;感染赤霉病后,DON在5个抗源穗组织中的含量差异显著,DON在望水白和繁60096穗组织中积累量明显比在苏麦3号、延岗坊主和翻山小麦低。通过对望水白/安农8455遗传群体两年的病小穗率和病穗中DON毒素含量的比较,发现二者具有一定的相关性,且受环境影响比较大。     

Quantitative Trait Loci Analysis and Mapping of Seedling Resistance to Stagonospora nodorum Leaf Blotch in Wheat

ABSTRACT Stagonospora nodorum leaf blotch is an economically important foliar disease in the major wheat-growing areas of the world. In related work, we identified a host-selective toxin (HST) produced by the S. nodorum isolate Sn2000 and determined the chromosomal location of the host gene (Snn1) conditioning sensitivity to the toxin using the International Triticeae Mapping Initiative mapping population and cytogenetic stocks. In this study, we used the same plant materials to identify quantitative trait loci (QTL) associated with resistance to fungal inoculations of Sn2000 and investigate the role of the toxin in causing disease. Disease reactions were scored at 5, 7, and 10 days postinoculation to evaluate changes in the degree of effectiveness of individual QTL. A major QTL was identified on the short arm of chromosome 1B, which coincided with the snn1 toxin-insensitivity gene. This locus explained 58% of the phenotypic variation for the 5-day reading but decreased to 27% for the 10-day reading, indicating that the toxin is most effective in the early stages of the interaction. In addition, relatively minor QTL were identified on chromosomes 3AS, 3DL, 4AL, 4BL, 5DL, 6AL, and 7BL, but not all minor QTL were significant for all readings and their effects varied. Multiple regression models explained from 68% of the phenotypic variation for the 5-day reading to 36% for the 10-day reading. The Chinese Spring nullisomic 1B tetrasomic 1D line and the Chinese Spring-Triticum dicoccoides disomic 1B chromosome substitution line, which were insensitive to SnTox1, were more resistant to the fungus than the rest of the nullisomictetrasomic and disomic chromosome substitution lines. Our results indicate that the toxin produced by isolate Sn2000 is a major virulence factor.     

Barley traits associated with resistance to fusarium head blight and deoxynivalenol accumulation

ABSTRACT Fusarium head blight (FHB) or scab is a destructive disease of barley in many countries. A better understanding of the interrelationships between plant traits and FHB resistance should help in the development of effective and efficient breeding strategies for FHB-resistant cultivars. Recent mapping studies indicate that many of the quantitative trait loci (QTL) for FHB resistance coincide with the QTL for plant height, heading date, and spike characteristics. Therefore, a study was conducted to investigate the relationship of morphological and physiological traits to FHB infection and deoxynivalenol (DON) accumulation in a barley doubled-haploid (DH) population derived from a Léger x CI9831 cross. Approximately 190 DH lines were grown at Ottawa (Ontario) for 2 years, Charlottetown (Prince Edward Island) for 1 year, and Hangzhou (Zhejiang) for 2 years. The field plots were inoculated with Fusarium graminearum at each location. FHB incidence was positively correlated with DON content. Resistance to FHB was associated with two-row spike, purple lemma, long glume awn, tall stature, and resistance to lodging, but it was not associated with long rachilla hairs, rough lemma awn, or heading date. Two-row spike was associated with tall stature and resistance to lodging. These associations as well as its spike characteristics helped reduce FHB infection and DON accumulation in two-row lines compared with six-row lines. The association between long glume awn and FHB resistance could be due to genetic linkages. Therefore, trait associations should be taken into consideration when breeding for FHB resistance and interpreting data from FHB experiments.     

Evaluation of type I fusarium head blight resistance of wheat using non-deoxynivalenol-producing fungi

A series of experiments was conducted to determine whether type I resistance (resistance to initial infection) to fusarium head blight (FHB) in wheat could be assessed using fungal species/isolates that do not produce deoxynivalenol (DON), a mycotoxin critical to the spread of Fusarium graminearum in the wheat spike. It was shown that, while the non-toxin-producing species Microdochium nivale and M. majus could infect following spray inoculation of wheat spikes, they were unable to spread within the spike following point inoculation. However, although these species might reveal type I resistance, they are not highly pathogenic towards wheat. A nivalenol (NIV)-producing isolate of F. graminearum caused high levels of disease following spray inoculation, but spread only very slowly within the spike and rarely induced bleaching above the point of inoculation. It is proposed that spray inoculation with an appropriate, aggressive, non-DON-producing FHB pathogen may be used to characterize type I resistance to complement point inoculation with a DON-producing isolate to assess type II resistance (resistance to spread within the spike).     

Genetic architecture of adult plant resistance to leaf rust in a wheat association mapping panel

Leaf rust caused by Puccina triticina is one of the most destructive fungal diseases of wheat (Triticum aestivum). Adult plant resistance (APR) is an effective strategy to achieve long‐term protection from the disease. In this study, findings are reported from a genome‐wide association study (GWAS) using a panel of 96 wheat cultivars genotyped with 874 Diversity Arrays Technology (DArT) markers and tested for adult leaf rust response in six field trials. A total of 13 quantitative trait loci (QTL) conferring APR to leaf rust were identified on chromosome arms 1BL, 1DS, 2AS, 2BL, 2DS, 3BS, 3BL, 4AL, 6BS (two), 7DS, 5BL/7BS and 6AL/6BS. Of these, seven QTLs mapped close to known resistance genes and QTLs, while the remaining six are novel and can be used as additional sources of resistance. Accessions with a greater number of combined QTLs for APR showed lower levels of disease severity, demonstrating additive and significant pyramiding effects. All QTLs had stable main effects and they did not exhibit a significant interaction with the experiments. These findings could help to achieve adequate levels of durable resistance through marker‐assisted selection and pyramiding resistance QTLs in local germplasm.     

Investigation into components of partial disease resistance,determined <Emphasis Type="Italic">in vitro</Emphasis>, and the concept of types of resistance to <Emphasis Type="Italic">Fusarium</Emphasis> head blight (FHB) in wheat

This work presents an analysis of the relationship between components of partial disease resistance (PDR) detected using in vitro detached leaf and seed germination assays, inoculated with Microdochium majus, and Fusarium head blight (FHB) resistance to Fusarium graminearum assessed using point inoculation, termed Type II resistance. Relationships between in vitro-determined PDR components and FHB resistance using techniques which inoculate the wheat spike uniformly, termed Type I resistance (incidence and severity), have been reported previously. In this study shorter incubation periods, longer latent periods and shorter lesion lengths in the detached leaf assay and higher germination rates in the seed germination assay were related to greater FHB resistance measured by single point inoculation (Type II), collectively explaining 54% of the variation. Overall the relationships observed for Type II FHB resistance were similar to previous findings for Type I resistances. However, the relative magnitude of effects of the individual PDR components determined in vitro varied between FHB disease resistance parameters. Resistance in seed germination and latent period in the detached leaf assay were more strongly related to resistance assessed by point inoculation (Type II) and severity-Type I as opposed to incubation period which was most strongly related to disease incidence-Type I. The results provide evidence that individual components of partial disease resistance differentially affect aspects of FHB disease progression in the wheat spike. This work supports the view that the current model of types of resistance is an oversimplification of the interacting mechanisms underlying expression of FHB resistance.     

The Brachypodium distachyon UGT Bradi5gUGT03300 confers type II fusarium head blight resistance in wheat

Fusarium head blight (FHB), caused by fungi belonging to the Fusarium genus, is a widespread disease of wheat (Triticum aestivum) and other small-grain cereal crops. The main causal agent of FHB, Fusarium graminearum, produces mycotoxins mainly belonging to type B trichothecenes, such as deoxynivalenol (DON), that can negatively affect humans, animals and plants. DON detoxification, mainly through glucosylation into DON-3-O-glucose, has been correlated with resistance to FHB. A UDP-glucosyltransferase from the model cereal species Brachypodium distachyon has been shown to confer resistance both to initial infection and to spike colonization (type I and type II resistances, respectively). Here, the functional characterization of transgenic wheat lines expressing the Bradi5g03300 UGT gene are described. The results show that, following inoculation with the fungal pathogen, these lines exhibit a high level of type II resistance and a strong reduction of mycotoxin content. In contrast, type I resistance was only weakly observed, although previously seen in B. distachyon, suggesting the involvement of additional host-specific characteristics in type I resistance. This study contributes to the understanding of the functional relationship between DON glucosylation and FHB resistance in wheat.     

抗赤霉病普通小麦-大赖草易位系T5AS/5LrL的分子细胞遗传学鉴定

 大赖草作为小麦野生近缘植物,对赤霉病表现较好的抗性, 将其赤霉病抗性基因转入普通小麦, 对创新小麦赤霉病抗性种质有重要意义。本研究在获得抗赤霉病普通小麦-大赖草异附加系基础上, 采用1200R ⁶⁰Co-γ射线处理小麦-大赖草二体附加系 DA5Lr花粉, 授予已去雄的普通小麦中国春,对其后代(M1)种子根尖细胞有丝分裂中期染色体进行GISH分析,获得了1株具有1条普通小麦-大赖草易位染色体的植株,让其自交,对自交后代中具有2条易位染色体植株的花粉母细胞减数分裂中期I进行观察,发现2条易位染色体形成了稳定的环状二价体,表明该植株为纯合体。利用顺序GISH-双色FISH分析,结合小麦D组专化探针Oligo-pAs1-2和B组专化探针Oligo-pSc119.2-2,进一步鉴定出该普通小麦-大赖草易位系为T5AS/5LrL,且筛选出了可追踪该易位系的3个EST-STS分子标记BE591127 、BQ168298和BE591737。赤霉病抗性鉴定结果表明,易位系T5AS/5LrL连续3年的病小穗率分别为7.69%、10.29%和8.66%,显著低于感病品种中国春和绵阳85-45。该易位系的育成为小麦赤霉病抗病性遗改良提供了新种质。     

Quantitative trait Loci mapping for adult-plant resistance to powdery mildew in bread wheat

ABSTRACT Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major disease to wheat (Triticum aestivum) worldwide. Use of adult-plant resistance (APR) is an effective method to develop wheat cultivars with durable resistance to powdery mildew. In the present study, 432 molecular markers were used to map quantitative trait loci (QTL) for APR to powdery mildew in a doubled haploid (DH) population with 107 lines derived from the cross Fukuho-komugi x Oligoculm. Field trials were conducted in Beijing and Anyang, China during 2003-2004 and 2004-2005 cropping seasons, respectively. The DH lines were planted in a randomized complete block design with three replicates. Artificial inoculation was carried out in Beijing with highly virulent isolate E20 of B. graminis f. sp. tritici and the powdery mildew severity on penultimate leaf was evaluated four times, and the maximum disease severity (MDS) on penultimate leaf was investigated in Anyang under natural inoculation in May 2004 and 2005. The heritability of resistance to powdery mildew for MDS in 2 years and two locations ranged from 0.82 to 0.93, while the heritability for area under the disease progress curve was between 0.84 and 0.91. With the method of composite interval mapping, four QTL for APR to powdery mildew were detected on chromosomes 1AS, 2BL, 4BL, and 7DS, explaining 5.7 to 26.6% of the phenotypic variance. Three QTL on chromosomes 1AS, 2BL, and 7DS were derived from the female, Fukuho-komugi, while the one on chromosome 4BL was from the male, Oligoculm. The QTL on chromosome 1AS showed high genetic effect on powdery mildew resistance, accounting for 19.5 to 26.6% of phenotypic variance across two environments. The QTL on 7DS associated with the locus Lr34/Yr18, flanked by microsatellite Xgwm295.1 and Ltn (leaf tip necrosis). These results will benefit for improving powdery mildew resistance in wheat breeding programs.     

Comparison of spray and point inoculation to assess resistance to fusarium head blight in a multienvironment wheat trial

ABSTRACT Fusarium head blight (FHB, scab), caused by Fusarium graminearum or F. culmorum, results in yield and quality reductions and accumulation of mycotoxins. Two inoculation methods are commonly used. Spraying a spore suspension on the head (spray inoculation) will detect resistance to initial infection (type I) and to disease spread within the spike (type II). Injecting a spore suspension into individual florets (point inoculation) will detect type II resistance only. To analyze the association of spray and point inoculation, 20 elite winter wheat cultivars from Romania, Germany, and Switzerland were inoculated in factorial field experiments in seven environments (location x year combinations) in Germany and Romania. Response to FHB was assessed by the percentage of visually infected spikelets and head weight relative to the noninoculated control. Point and spray inoculations resulted in a mean disease severity varying from 52 to 63%. Significant (P = 0.01) genotypic variation was found within and across the environments. Genotype-environment interaction was important also. Estimates of entry-mean heritability were higher for spray than for point inoculation as assessed by percent infected spikelets (0.81 versus 0.77) and relative head weight (0.77 versus 0.52). Significant (P = 0.01) interaction was found between inoculation methods. Consequently, coefficients of phenotypic correlation between both methods were low to medium for percent infected spikelets (0.40, P > 0.1) and relative head weight (0.52, P = 0.05). We conclude that the application of both inoculation methods should provide additional information for selection and scientific studies. Spray inoculation, however, is less laborious for large-scale routine screening of breeding materials.     

Mapping of QTL lengthening the latent period of Puccinia striiformis in winter wheat at the tillering growth stage

The winter wheat lines Luke and AQ24788-83 are respectively susceptible and slow-rusting at tillering stage to yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici (Pst). A mapping population consisting of 206 recombinant inbred lines was developed from the cross Luke?×?AQ24788-83. These lines were evaluated at the tillering stage in the field trials for infection type (IT) and disease incidence (DI) and in greenhouse trials for IT and latent period (LP). A significant negative correlation was found between LP and DI. A genetic map with 473 marker loci was constructed and used for identifying QTL associated with LP and IT. Two QTL, QYr.cau-1BS and QYr.cau-5AS, were mapped on 1BS and 5AS respectively, explaining collectively up to 46.4 % of LP phenotypic variance. QYr.cau-5AS was clearly distinct, in terms of mapping position, from all six yellow rust resistance genes/QTL previously reported on 5A. QYr.cau-1BS could not be spatially differentiated from three (i.e. YrAlp, Yr15, and YrH52) of the six genes/QTL known on 1BS and centromere-vicinity regions, but was determined to be different from these three genes based on phenotype. The two QTL identified here, therefore, are likely to be novel to the currently known Pst resistance genes/QTL. A minor QTL on 3AL was detected to be associated with both IT and LP. Expression of quantitative resistance at early wheat growth stages and usefulness of the QTL are discussed for the wheat-Pst system.     

Comparative Quantitative Trait Loci Mapping of Partial Resistance to Puccinia sorghi Across Four Populations of European Flint Maize

ABSTRACT We mapped and characterized quantitative trait loci (QTL) for partial resistance to Puccinia sorghi and investigated consistency across different European flint maize populations. Four independent populations, containing 280 F(3) lines (AxB(I)), 120 F(5) lines (AxB(II)), 131 F(4) lines (AxC), and 133 F(4) lines (CxD) were produced from four European elite flint inbreds (A, B, C, and D) and genotyped at 89, 151, 104, and 122 restriction fragment length polymorphism marker loci, respectively. All F(n) lines were evaluated in field trials with two replications in three or five (AxB(I)) environments. Genotypic variance was highly significant for rust ratings in all populations, and heritabilities exceeded 0.64. Between 4 and 13 QTL were detected in individual populations using composite interval mapping, explaining between 33 and 71% of the phenotypic variance. Twenty QTL were distributed over all ten chromosomes, without preference to chromosomes 3, 4, 6, and 10, which harbor qualitatively acting Rp loci. In most cases, gene action was additive or partially dominant. Four pairs of QTL displayed significant digenic epistatic interactions, and QTL-environment interactions were observed frequently. Approximately half of the QTL were consistent between AxB(I) and AxB(II) or AxC and CxD; fewer were consistent between AxB(I) and AxC or CxD. In European flint maize germ plasm, conventional selection for partial rust resistance seems to be more promising than marker-assisted selection.     

A novel QTL on chromosome 5AL of Yangmai 158 increases resistance to Fusarium head blight in wheat

Fusarium head blight (FHB) of wheat is a destructive fungal disease worldwide and has become more severe over the last two decades. Development of FHB resistant wheat varieties is the most effective way to manage FHB. The middle and lower reaches of the Yangtze River are the traditional FHB epidemic areas in China. The landraces and germplasms with resistance to FHB originating from this region were used to identity FHB resistance quantitative trait loci (QTLs). Yangmai 158 and Ningmai 9 are the most popular varieties for commercial wheat production in this region and both have moderate FHB resistance. A high-density genetic map was constructed using 282 recombinant inbred lines (RILs) from a cross between Ningmai 9 and Yangmai 158. Ten QTLs related to Type II FHB resistance were identified, and QFhb-3B.1 and QFhb-5A were stably detected across all environments. Based on position alignment, QFhb-3B.1 from Ningmai 9 is likely to be Fhb1 and QFhb-5A from Yangmai 158 is a novel QTL not previously described. A competitive allele-specific PCR (KASP) marker closely linked to QFhb-5A was developed and could be used for marker-assisted selection. Distribution of QFhb-5A was tested with numerous accessions from a widespread core collection. The results suggest that QFhb-5A has undergone both natural and artificial selection. Some RILs with both Fhb1 and QFhb-5A presented better FHB resistance than the parents and could be used in FHB resistance breeding.     

Effects of plant height on type I and type II resistance to fusarium head blight in wheat

By carefully separating type I and type II resistances, the possible effects of plant height on fusarium head blight (FHB) resistance in wheat were assessed using near‐isogenic lines (NILs) for several different reduced‐height (Rht) genes. Tall isolines all gave better type I resistance than their respective dwarf counterparts when assessed at their natural heights. These differences largely disappeared when the dwarf isolines were physically raised so that their spikes were positioned at the same height as those of their respective tall counterparts. The effects of plant height on type II resistance was less clear. For those NIL pairs which showed significant differences, it was the dwarf isolines which gave better resistance. As the Rht genes involved in these NILs locate at different genomic regions, the differences in FHB between the dwarf and tall isolines are unlikely to be the result of linkages between each of the different Rht loci with a beneficial or a deleterious gene affecting type I or type II resistance. Rather, the different FHB resistances are probably caused by direct or indirect effects of height difference per se, and microclimate may have contributed to the better type I resistance of the tall plants. Thus, caution should be exercised when attempting to exploit any of the FHB resistant loci co‐located with Rht genes.