Crown Rot Resistance Research Articles

The non-gibberellic acid-responsive semi-dwarfing gene uzu affects Fusarium crown rot resistance in barley

BackgroundStudies in Arabidopsis show that DELLA genes may differentially affect responses to biotrophic and necrophic pathogens. A recent report based on the study of DELLA-producing reduced height (Rht) genes in wheat and barley also hypothesized that DELLA genes likely increased susceptibility to necrotrophs but increased resistance to biotrophs.ResultsEffects of uzu, a non-GA (gibberellic acid)-responsive semi-dwarfing gene, on Fusarium crown rot (FCR) resistance in barley were investigated. Fifteen pairs of near isogenic lines for this gene were generated and assessed under two different temperature regimes. Similar to its impacts on plant height, the semi-dwarfing gene uzu also showed larger effects on FCR severity in the high temperature regime when compared with that in the low temperature regime.ConclusionsResults from this study add to the growing evidence showing that the effects of plant height on Fusarium resistances are unlikely related to DELLA genes but due to direct or indirect effects of height difference per se. The interaction between these two characteristics highlights the importance of understanding relationships between resistance and other traits of agronomic importance as the value of a resistance gene could be compromised if it dramatically affects plant development and morphology.

Major QTL for Fusarium crown rot resistance in a barley landrace

Fusarium crown rot (FCR) is a serious cereal disease in semi-arid regions worldwide. In assisting the effort of breeding cultivars with enhanced resistance, we identified several barley genotypes with high levels of FCR resistance. One of these genotypes, AWCS079 which is a barley landrace originating from Japan, was investigated by developing and assessing three populations of recombinant inbred lines. Two QTL, one located on the long arm of chromosome 1H (designated as Qcrs.cpi-1H) and the other on 3HL (designated as Qcrs.cpi-3H), were found to be responsible for the FCR resistance of this genotype. Qcrs.cpi-1H is novel as no other FCR loci have been reported on this chromosome arm. Qcrs.cpi-3H co-located with a reduced height (Rht) locus and the effectiveness of the former was significantly affected by the latter. The total phenotypic variance explained by these two QTL was over 60%. Significant effects were detected for each of the QTL in each of the three populations assessed. The existence of these loci with major effects should not only facilitate breeding and exploitation of FCR-resistant barley cultivars but also their further characterization based on fine mapping and map-based gene cloning.

A novel and major quantitative trait locus for fusarium crown rot resistance in a genotype of Wild Barley (Hordeum spontaneum L.).

Fusarium crown rot (FCR), caused by various Fusarium species, is a destructive disease of cereal crops in semiarid regions worldwide. As part of our contribution to the development of Fusarium resistant cultivars, we identified several novel sources of resistance by systematically assessing barley genotypes representing different geographical origins and plant types. One of these sources of resistance was investigated in this study by generating and analysing two populations of recombinant inbred lines. A major locus conferring FCR resistance, designated as Qcrs.cpi-4H, was detected in one of the populations (mapping population) and the effects of the QTL was confirmed in the other population. The QTL was mapped to the distal end of chromosome arm 4HL and it is effective against both of the Fusarium isolates tested, one F. pseudograminearum and the other F. graminearum. The QTL explains up to 45.3% of the phenotypic variance. As distinct from an earlier report which demonstrated co-locations of loci conferring FCR resistance and plant height in barley, a correlation between these two traits was not detected in the mapping population. However, as observed in a screen of random genotypes, an association between FCR resistance and plant growth rate was detected and a QTL controlling the latter was detected near the Qcrs.cpi-4H locus in the mapping population. Existing data indicate that, although growth rate may affect FCR resistance, different genes at this locus are likely involved in controlling these two traits.

Introgression of hexaploid sources of crown rot resistance into durum wheat

Triticum turgidum ssp. durum (tetraploid durum) germplasm is very susceptible to crown rot, caused by the fungus Fusarium pseudograminearum. Screening activities to date have failed to identify even moderately susceptible lines. In contrast partial resistance to this disease has been identified in a number of Triticum aestivum (hexaploid wheat) lines, including 2-49 and Sunco. This study describes the successful introgression of partial crown rot resistance from each of these two hexaploid wheat lines into a durum wheat background. Durum backcross populations were produced from two 2-49/durum F6 lines which did not contain any D-genome chromosomes and which had crown rot scores similar to 2-49. F2 progeny of these backcross populations included lines with field based resistance to crown rot superior to that of the parent hexaploid wheat.

Potential Sources of Resistance in U.S. Cucumis melo PIs to Crown Rot Caused by Phytophthora capsici

Phytophthora capsici is an aggressive pathogen that is distributed worldwide with a broad host range infecting solanaceous, fabaceous, and cucurbitaceous crops. Over the past two decades, increased incidence of Phytophthora blight, particularly in eastern states, has threatened production of many vegetable crops. Cucumis melo L. (honeydew and muskmelon), although especially susceptible to fruit rot, is also highly susceptible to crown rot. Currently, little is known about host resistance to P. capsici in C. melo. To assess crown rot resistance in C. melo seedlings, 308 U.S. PIs, and two commercial cultivars (Athena and Dinero) were grown under greenhouse conditions. Seedlings with three to four true leaves were inoculated with a five-isolate zoospore suspension (1 × 104 zoospores per seedling) at the crown and monitored for 6 weeks. All the susceptible control plants of Athena died within 7 days post-inoculation. The majority of the PIs (281 of 308) were highly susceptible to crown rot and succumbed to the disease rapidly and had less than 20% of the plants survive. Several PIs (PI 181748, PI 182964, and PI 273438) succumbed to crown rot earlier than the susceptible melon cultivars. Eighty-seven PIs selected on the basis of the first screen were re-evaluated and of these PIs, 44 were less susceptible than cultivars Athena and Dinero. Twenty-five of the 87 PIs were evaluated again and of these six PI, greater than 80% of the plants survived in the two evaluations. Disease development was significantly slower on these PIs compared with the susceptible checks. High levels of resistance in S1 plants of PI 420180, PI 176936, and PI 176940 were observed, which suggests that development of resistant germplasm for use in breeding programs can be accomplished. Further screening and careful selection within each of these PIs can provide a framework for the development of resistant germplasm for use in breeding programs.

Development and Validation of Markers Closely Linked to Crown Rot Resistance in Wheat and Barley

Crown rot (CR), caused by various Fusarium species, is a chronic cereal disease in Australia and many other parts of the world. As part of our objective of improving the efficiency of breeding CR resistant wheat and barley varieties, we have been searching for novel sources of resistance and identifying new genes conferring CR resistance in the two crops. This paper reports on the development of more closely linked markers and validation of the effects of the previously identified wheat 3B CR QTL and the barley 3H major CR locus using four wheat and three barley validation populations. With an effect varied from 36.7 to 59.4% in wheat and 29.4 to 55.2% in barley, the validation experiments demonstrated that both of the 3B and 3H CR locus have a stable and significant effect in reducing CR severity at different genetic backgrounds. The huge effect of a single QTL as the CR loci detected in this study warrant a significant value of incorporating these two genes in wheat and barley breeding. The possible homoeologous relationship between these two major CR loci is preliminarily investigated by comparative mapping the two genomic regions and it warrants further investigation.

The homoeologous regions on long arms of group 3 chromosomes in wheat and barley harbour major crown rot resistance loci

Crown rot (CR), caused by various Fusarium species, has become an important cereal disease worldwide and growing resistant varieties is an essential strategy to reduce the $A80 mil annual loss from CR in Australia. To facilitate the breeding of resistant varieties, we have screened 2514 wheat and 1059 barley genotypes and identified several lines with high levels of CR resistance in each crop. Initially focused on two wheat and one barley resistance sources, we have identified major QTL with unprecedented magnitudes. Two wheat QTL explain between 35% (LOD 7.6) and 49% (LOD 10.8) and the barley QTL explains up to 63% (LOD 14.8) of the phenotypic variance. One of the wheat QTL has been further assessed in four validation populations, and the presence of this QTL alone reduces CR severity by 33% on average. Surprisingly, all of the three major CR QTL are located in similar regions on the long arms of the homoeologous group 3 chromosomes, the two wheat QTL on 3BL and the barley QTL on 3HL. The possible homoeologous relationship between the 3BL wheat QTL and the 3HL barley QTL warrants further investigation. Relative rearrangements between 3H and 3B chromosomes are unknown, although the relative distances between the different QTL and the centromeres seem to be different. Compared with the barley QTL, the 3BL wheat QTL seems to be more distally located. However genetic distance can be affected by many factors including the use of different populations, thus the differences in genetic distances between the two different genera may have only limited value. The physical map of wheat chromosome 3B, which was recently made available as the first such resources for wheat, would make such a study much easier. Results will be presented on the detection, genetic analysis and mapping of these new sources of CR resistance.

English

  Fusarium crown and root rot of tomato (Solanum lycopersicum) is the disease caused by the fungal pathogen Fusarium oxysporum f.sp. radicis-lycopersici(FORL). The most effective way to control this disease is to plant resistant varieties. Markers tightly linked to Fusarium crown and root rot could be used in breeding programs to introgress crown rot resistance into new varieties. In this study, we converted the random amplified polymorphic DNA (RAPD) marker UBC#116, linked to the Fusarium crown and root rot resistance gene (Frl), into a co-dominant sequence characterized amplified region (SCAR) marker. A fragment of about 480 bp, linked to the Frl gene, was polymerase chain reaction (PCR) amplified with the use of the UBC#116 primers, cloned and sequenced. A pair of primers were designed and PCR amplification was performed to develop a new SCAR marker for the Frl gene. The new marker was applied for the analysis of 96 tomato genotypes. The RAPD marker UBC#116 was also used and it revealed that the markers were equivalent to each other. However, the development of the new co-dominant SCAR marker has made marker-assisted selection (MAS) more practical, rapid and efficient.   Key words: Fusarium oxysporum f. sp. radicis-lycopersicum (FORL), marker-assisted selection (MAS), Solanum lycopersicum, breeding.

Enhancing Fusarium crown rot resistance of durum wheat by introgressing chromosome segments from hexaploid wheat

Compared with hexaploid wheat, tetraploid durum is more susceptible to Fusarium crown rot (FCR) infection. The feasibility of enhancing FCR resistance in durum wheat by introgressing chromosome segments of hexaploid wheat was investigated by generating and analysing a backcross population derived from a susceptible durum wheat variety ‘Bellaroi’ (recurrent parent) and a resistant hexaploid genotype ‘CSCR6’ (donor parent). Together with a few scattered segments on various chromosomes, segments of a large section of the donor chromosome 6B showed a significant effect in enhancing FCR resistance in the durum background. However, a known major locus on the donor 3BL conferring high level of resistance to FCR in hexaploid wheat failed to provide any improvement in resistance than that of the genome average once it was introduced into the durum wheat. A small proportion of the backcross population gave similar resistance to the bread wheat variety ‘Kennedy’, a level of FCR resistance acceptable to durum growers. These lines share a 4B segment from the hexaploid donor, although the segment was not among those with the largest individual effect across the whole population. These results show that it is feasible to improve FCR resistance of durum wheat by exploiting hexaploid chromosome segments, although resistance loci of the hexaploid wheat may not function properly in durum backgrounds.

Screening of Cucurbita moschata Duchesne Germplasm for Crown Rot Resistance to Floridian Isolates of Phytophthora capsici Leonian

Phytophthora capsici causes seedling death, crown and root rot, fruit rot, and foliar blight on squash and pumpkins (Cucurbita spp. L.). A total of 119 C. moschata accessions, from 39 geographic locations throughout the world, and a highly susceptible butternut squash cultivar, Butterbush, were inoculated with a suspension of three highly virulent P. capsici isolates from Florida to identify resistance to crown rot. Mean disease rating (DR) of the C. moschata collection ranged from 1.4 to 5 (0 to 5 scale with 0 resistant and 5 susceptible). Potential resistant and tolerant individuals were identified in the C. moschata collection. A set of 18 PIs from the original screen were rescreened for crown rot resistance. This rescreen produced similar results as the original screen (r = 0.55, P = 0.01). The accessions PI 176531, PI 458740, PI 442266, PI 442262, and PI 634693 were identified with lowest rates of crown infection with a mean DR less than 1.0 and/or individuals with DR = 0. Further selections from these accessions could be made to develop Cucurbita breeding lines and cultivars with resistance to crown rot caused by P. capsici.

Development of near-isogenic lines for a major QTL on 3BL conferring Fusarium crown rot resistance in hexaploid wheat

By essentially fixing the genetic background, near-isogenic lines (NILs) are ideal for studies of the function of specific loci. We report in this paper the development of NILs for a major QTL located on the long arm of chromosome 3B conferring Fusarium crown rot (FCR) resistance in hexaploid wheat. These NILs were generated based on the method of the heterogeneous inbred family analysis. 13 heterozygous lines were initially selected from three segregating populations using a single SSR marker linked with the major FCR QTL. The two isolines for each of the putative NILs obtained showed no obvious morphological differences, but differences among the NIL pairs were large. Significant differences in FCR resistance between the isolines were detected for nine of the 13 putative NIL pairs. The presence of the FCR allele from the resistant parent reduced FCR severity by 29.3–63.9% with an average of 45.2% across these NILs. These NILs will be invaluable in further characterising this major FCR locus, in studying the mechanism of FCR resistance and in investigating possible interactions between FCR resistance and other traits of agronomic importance.

Different genes can be responsible for crown rot resistance at different developmental stages of wheat and barley

Crown rot, caused by several Fusarium species, is one of the most damaging diseases in wheat and barley. Growing resistant varieties has long been recognised as an integral part in effectively managing the disease. One of the factors hindering the progress of breeding for crown rot resistance is the lack of a reliable and high throughput bioassay that allows rapid and accurate assessment of large numbers of genotypes so that highly susceptible materials can be quickly rejected and potentially resistant lines identified for more focused further assessments. We developed a method which, by growing several inoculated seedlings wrapped in a single piece of moist paper towel, offers significant advantages over all of the existing methods. The new soil-less assay takes only about two weeks, requires very little space, and removes variability associated with the use of soil/potting mixes. Results from the new assay are highly reproducible and agree well with known field performances of different varieties. However, mapping studies conducted using the new soil-less assay did not detect all of the quantitative trait loci found with a soil-based assay. These results show that, although different resistance genes may all contribute to the performance of a variety, caution should be used when comparing results from different assays.

Pyramiding QTL increases seedling resistance to crown rot (Fusarium pseudograminearum) of wheat (Triticum aestivum)

Crown rot of wheat (Triticum aestivum), predominantly caused by the fungus Fusarium pseudograminearum, has become an increasingly important disease constraint in many winter cereal production regions in Australia. Our group has previously identified a range of quantitative trait loci (QTL) for partial resistance to crown rot in various bread wheat sources. Here, we report on work that has assessed the effectiveness of pyramiding QTL to improve resistance to crown rot. Two doubled haploid populations were analysed--one from a cross between two previously characterised sources of partial seedling resistance (2-49 and W21MMT70; n = 208) and one from a cross between 2-49 and the commercial variety Sunco, a source of adult field resistance (n = 134). Both populations were phenotyped for seedling resistance to crown rot. Microsatellite and DArT markers were used to construct whole genome linkage maps for use in composite interval mapping (CIM) to identify QTL. Three QTL were detected in both trials conducted on the 2-49/W21MMT70 population. These were located on chromosomes 1D (QCr.usq-1D.1), 3B (QCr.usq-3B.1) and 7A. QCr.usq-1D.1 and the previously undetected 7A QTL were inherited from 2-49. QCr.usq-3B.1, inherited from W21MMT70, was the most significant of the QTL, explaining up to 40.5% of the phenotypic variance. Three QTL were identified in multiple trials of the Sunco/2-49 population. These were located on chromosomes 1D (QCr.usq-1D.1), 2B (QCr.usq-2B.2) and 4B (QCr.usq-4B.1). Only QCr.usq-2B.2 was inherited from Sunco. QCr.usq-4B.1 was the most significant of these QTL, explaining up to 19.1% of the phenotypic variance. In the 2-49/W21MMT70 population, several DH lines performed significantly better than either parent, with the best recording an average disease severity rating of only 3.8% of that scored by the susceptible check cultivar Puseas. These lines represent a new level of seedling crown rot resistance in wheat.

Resistance of Pepper to Phytophthora Crown, Root, and Fruit Rot Is Affected by Isolate Virulence.

Greenhouse and laboratory experiments were conducted to determine the virulence of four Phytophthora capsici isolates from Michigan to 31 bell and hot pepper cultivars and breeding lines. Resistance to crown and root rot was assessed following the inoculation of soilless media with P. capsici-infested millet seed. In a detached fruit assay, fruit rot resistance was evaluated following inoculation with zoospore suspensions of 1.75 × 106 zoospores/ml. The four isolates differed in virulence to pepper lines screened for crown and root rot resistance and were considered to be four different physiological races. The pepper lines CM334, NY07-8001, NY07-8006, and NY07-8007 were resistant to the isolates tested. None of the commercial cultivars were resistant to P. capsici isolate 12889, but several cultivars were resistant to the other isolates screened. The isolates varied in their ability to cause infection on the fruits of the different cultivars. Overall, pepper fruit were more susceptible to P. capsici than the roots and crowns. Management of Phytophthora crown and root rot of pepper can be improved through the use of resistant cultivars. However, since isolate virulence affects resistance, cultivar resistance will need to be utilized on a local scale accordingly.

Identification and validation of a major QTL conferring crown rot resistance in hexaploid wheat

Crown rot (CR), caused by various Fusarium species, is a chronic wheat disease in Australia. As part of our objective of improving the efficiency of breeding CR resistant wheat varieties, we have been searching for novel sources of resistance. This paper reports on the genetic control of one of these newly identified resistant genotypes, 'CSCR6'. A population derived from a cross between CSCR6 and an Australian variety 'Lang' was analyzed using two Fusarium isolates belonging to two different species, one Fusarium pseudograminearum and the other Fusarium graminearum. The two isolates detected QTL with the same chromosomal locations and comparable magnitudes, indicating that CR resistance is not species-specific. The resistant allele of one of the QTL was derived from 'CSCR6'. This QTL, designated as Qcrs.cpi-3B, was located on the long arm of chromosome 3B and explains up to 48.8% of the phenotypic variance based on interval mapping analysis. Another QTL, with resistant allele from the variety 'Lang', was located on chromosome 4B. This QTL explained up to 22.8% of the phenotypic variance. A strong interaction between Qcsr.cpi-3B and Qcsr.cpi-4B was detected, reducing the maximum effect of Qcrs.cpi-3B to 43.1%. The effects of Qcrs.cpi-3B were further validated in four additional populations and the presence of this single QTL reduced CR severity by up to 42.1%. The fact that significant effects of Qcrs.cpi-3B were detected across all trials with different genetic backgrounds and with the use of isolates belonging to two different Fusarium species make it an ideal target for breeding programs as well as for further characterization of the gene(s) involved in its resistance.

Inheritance of Resistance to Crown Rot Caused by Phytophthora capsici in Cucurbita

The various disease syndromes caused by Phytopthora capsici Leonian can be devastating to squash (Cucurbita spp.) production areas of the United States. In some growing seasons, yield loss has been reported up to 100%. A recently developed University of Florida Cucurbita breeding line, #394-1-27-12, resistant to the crown rot syndrome of P. capsici, was used to determine the inheritance of resistance to this disease. Data from F1, F2, and backcross progeny from crosses of a P. capsici-susceptible butternut-type winter squash (C. moschata) with #394-1-27-12 indicated that resistance is conferred by three dominant genes. The introgression of P. capsici crown rot resistance from #394-1-27-12 into morphologically diverse domesticates within Cucurbita will aid in the management of this economically important pathogen.

A major QTL conferring crown rot resistance in barley and its association with plant height

Crown rot (CR) is one of the most destructive diseases of barley and wheat. Fusarium species causing CR survive in crop residue and a growing acceptance of stubble retention practices has exacerbated disease severity and yield loss. Growing resistant cultivars has long been recognised as the most effective way to reduce CR damage but these are not available in barley. In a routine screening of germplasm, a barley landrace from China gave the best CR resistance among the genotypes tested. Using a doubled haploid population derived from this landrace crossed to Franklin, we demonstrate that the CR resistance of TX9425 was conditioned by a major QTL. The QTL, designated as Qcrs.cpi-3H, was mapped near the centromere on the long arm of chromosome 3H. Its effect is highly significant, accounting for up to 63.3% of the phenotypic variation with a LOD value of 14.8. The location of Qcrs.cpi-3H was coincident with a major QTL conferring plant height (PH) and the effect of PH on CR reaction was also highly significant. When the effect of PH was accounted for by covariance analysis, the Qcrs.cpi-3H QTL remained highly significant, accounting for over 40% of the phenotypic variation. The existence of such a major QTL implies that breeding barley cultivars with enhanced CR resistance should be feasible.

A Simple Method for the Assessment of Crown Rot Disease Severity in Wheat Seedlings Inoculated with Fusarium pseudograminearum

AbstractCrown rot caused by Fusarium pseudograminearum (teleomorph: Gibberella coronicola) is a serious disease of wheat. A simple and reliable method for assessing this disease would enhance our capacity in identifying resistance sources and developing resistant wheat cultivars. In searching for such a method, several inoculation techniques were tested. One technique, soaking 1‐ to 4‐day old seedlings in fungal spore suspension, produced consistent and severe crown rot symptoms. Glasshouse testing of several wheat genotypes using this method produced results that agreed well with previously established field ratings for crown rot disease, suggesting that this assay can be conveniently employed for screening of wheat genotypes for crown rot resistance.

Identification of novel QTL for resistance to crown rot in the doubled haploid wheat population ‘W21MMT70’ × ‘Mendos’

AbstractCrown rot (causal agent Fusarium pseudograminearum) is a fungal disease of major significance to wheat cultivation in Australia. A doubled haploid wheat population was produced from a cross between line ‘W21MMT70’, which displays partial seedling and adult plant (field) resistance to crown rot, and ‘Mendos’, which is moderately susceptible in seedling tests but partially resistant in field trials. Bulked segregant analysis (BSA) based on seedling trial data did not reveal markers for crown rot resistance. A framework map was produced consisting of 128 microsatellite markers, four phenotypic markers, and one sequence tagged site marker. To this map 331 previously screened AFLP markers were then added. Three quantitative trait loci (QTL) were identified with composite interval mapping across all of the three seedling trials conducted. These QTL are located on chromosomes 2B, 2D and 5D. The 2D and 5D QTL are inherited from the line ‘W21MMT70’, whereas the 2B QTL is inherited from ‘Mendos’. These loci are different from those associated with crown rot resistance in other wheat populations that have been examined, and may represent an opportunity for pyramiding QTL to provide more durable resistance to crown rot.

A high‐throughput glasshouse bioassay to detect crown rot resistance in wheat germplasm

A high‐throughput and reliable seedling bioassay to screen wheat germplasm for crown rot resistance was developed. Single wheat seedlings were grown in square seedling punnets in a glasshouse and inoculated with a monoconidial Fusarium pseudograminearum isolate 10 days after emergence. The punnets were laid horizontally on their side and a 10‐µL inoculum droplet placed on the stem base. Seedlings were incubated at near‐saturated relative humidity, and crown rot severity was assessed 35 days after inoculation. Studies on the duration of incubation period, inoculum concentration and temperature were carried out to optimize these parameters. Seedling growth at 25/15(±5)°C in a glasshouse and 48‐h incubation at near‐saturated RH in darkness gave the best results. When crown rot resistance rankings of 16 Australian cultivars from the bioassay were compared with their field performance, Spearman's rank correlation coefficient was highly significant. This indicated that the seedling bioassay mimicked field resistance to crown rot in adult plants. A bootstrap resampling analysis showed little or no improvement in the coefficient of variation with an increasing number of replications, indicating a high level of precision and reproducibility. By detecting small but consistent differences in crown rot severity, the bioassay proved effective in large‐scale screening for partial resistance: already over 1400 wheat genotypes have been screened. The high degree of precision makes this an invaluable tool in the understanding of pathogen aggressiveness, host specialization and parasitic fitness.