No description available.

The global food supply is being stressed by climate change, a growing population, and harmful diseases. One risk to vital cereal crops such as wheat and barley is Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium graminearum. Ascospores of the fungus are released from perithecia on the residues of corn and small grains and can be transported long distances (>500 m) through the atmosphere. The overall objective of this work was to assess the influence of meteorological conditions and perithecial maturity on ascospore release. The research focuses on F. graminearum because of its damaging impact to staple crops and the global ubiquity of FHB. The first specific objective was to apply state-of-the-science techniques to identify causal meteorological variables of ascospore release. We analyzed field measurements of airborne ascospores against meteorological conditions at Virginia Tech's Kentland Farm, Blacksburg, Virginia, USA and used convergent cross mapping and multivariate state space reconstruction to identify significant causal agents within this complicated natural and dynamic system. We identified relative humidity, solar radiation, wind speed, and air temperature as predictors of ascospore release. Our second research objective was to understand the impact of varying meteorological conditions on ascospore release under controlled environmental conditions. We assessed ascospore release in a chamber with controlled temperature (15°C and 25°C) and relative humidity (60%, 75%, and 95%). Ascospores released from ascospore-producing structures (perithecia) were captured on microscope slides placed inside of 3D-printed ascospore discharge devices. Results showed the sensitivity of ascospore release to relative humidity and temperature, with cool temperature and high relative humidity resulting in greater quantities of ascospores released. Our third research objective was to determine the relationship between the maturity, the number of ascospores, and the hardness of perithecia. A mechanical compression testing instrument was used to investigate the hardness of perithecia at various stages of maturity, producing a mean perithecium compression constant quantifying the uniaxial compression force required to rupture a perithecium. Results indicated that old perithecia contain the greatest amount of ascospores and exhibit increased resiliency, requiring greater forces to rupture, compared to young perithecia. This research has illustrated the complexities of F. graminearum ascospore release by describing the impact of several meteorological conditions and perithecial maturity on the timing and quantity of released ascospores. Collectively, our results may inform wheat growers on the nature and timing of ascospore release, which could help inform FHB management decisions in the future. / Ph. D.

No description available.

Fusarium graminearum causa la fusariosi della spiga nei cereali a paglia. Il fungo produce sia conidi che ascospore sui residui della coltura precedente, le ascospore sono prodotte in periteci. La produzione e maturazione di periteci e ascospore in risposta a diverse condizioni di temperatura e umidità relativa sono state studiate. Dato che le condizioni atmosferiche influenzano anche l’umidità del substrato su cui l’inoculo è prodotto, la relazione tra i fattori atmosferici e l’umidità dei residui colturali di mais è stata esaminata. I fattori atmosferici influenzano anche il rilascio delle ascospore. L’effetto della temperatura è stato studiato in vitro. Mediante esperimenti in condizioni naturali, sono state definite regole per l’individuazione di condizioni favorevoli al rilascio di ascospore sulla base di pioggia e deficit di pressione di vapore. La distribuzione delle ascospore e dei conidi all’interno della vegetazione del frumento è quindi stata studiata mediante l’uso di captaspore passivi. Le ascospore possono essere rilasciate e depositarsi sulle spighe in condizioni non favorevoli per la germinazione. La germinazione di ascospore sottoposte a periodi asciutti di diversa durata, e a diverse condizioni di temperatura e umidità relativa durante il periodo asciutto, è stata studiata sia in vitro che in planta. / Fusarium graminearum causes Fusarium head blight of small-grain cereals. The fungus produces conidia and ascospores on the previous crop residues, ascospores are formed in perithecia. Production and maturation of perithecia and ascospores at several temperature and relative humidity conditions were studied. As environmental conditions also influence the moisture content of the substrate on which inoculum is produced, the relationship between environmental factors and moisture of maize residues was assessed. Environmental factors also influence ascospore discharge. The effect of temperature was studied in vitro. Experiments in natural condition allowed to define rules for conditions leading to ascospore discharge, based on rain and vapor pressure deficit. Once discharged, the distribution of ascospores and conidia in the wheat canopy was studied using passive spore traps. Ascospores can be discharged and deposit on wheat spikes also in conditions that are unfavorable for germination. Germination of ascospores incubated in dryness for periods of several length, in several condition of temperature and relative humidity during dryness, was studied both in vitro and in planta.

Gibberella zeae (anamorph Fusarium graminearum) is a homothallic ascomycete pathogen that is responsible for causing Fusarium head blight (FHB) of wheat and small grains. In addition to causing a reduction in yield, harvested grain is frequently contaminated with trichothecene mycotoxins that are harmful for human and animal health. Use of wheat varieties with resistance to FHB is an important strategy to lower its impact. In order to produce varieties with durable resistance, we must understand the origin and degree of genetic diversity present in the pathogen population. In my research, I focused my efforts on an investigation of the role of mating and sexual development in the generation of genotypic and phenotypic variability in G. zeae. The goal of one part of my work was to develop new genetic markers that can be used to monitor out-crossing and genetic diversity in the population. I also optimized gene deletion protocols for G. zeae so that I could produce mutant and control strains to address my research hypothesis that MAT genes play a direct role in pathogenicity. Application of novel repetitive RFLP probes to a group of G. zeae isolates originating from and near Kentucky revealed a surprisingly high degree of diversity in these local populations. Diversity between locations was greater than that within locations, suggesting the relative importance of local inoculum sources. The probes were also useful as genetic markers for segregation analysis. I crossed two genetically closely related, and commonly used, laboratory strains of G. zeae and found that this resulted in transgressive segregation for both aggressiveness and toxigenicity. I showed that the very high and very low levels of aggressiveness and toxigenicity in transgressive segregants are heritable. I also showed that selfing produced a higher degree of diversity in these traits among the progeny than was observed among conidial progeny. This suggests the presence of epigenetic factors that impact pathogenicity. Sexual behavior in G. zeae is under the control of MATing type genes. I deleted the complete MAT1 locus, and the MAT1-1-1, and MAT1-2-1 genes separately. Deletion of each of the targeted sequences produced the expected shifts in fertility phenotype. The mat1KO strains became asexual, while mat1-1-1KO and mat1-2-1KO strains shifted to obligate heterothallism. Deletion of the MAT1-1-1 and MAT1-2-1 genes had a negative effect on aggressiveness and mycotoxin production in planta, but deletion of the complete MAT1 locus had no effect. The set of mutant and ectopic control strains that I generated will be a useful asset that will be made available to the research community.

Master of Science / Department of Agronomy / Allan K. Fritz / Fusarium head blight (FHB), caused by Fusarium graminearum, is an important cereal disease in humid and semi-humid wheat growing regions. In recent FHB epidemics in the USA, FHB dramatically reduced wheat yields and grain quality due to mycotoxin contamination. Five types of FHB resistance have been reported, but resistance to disease spread within a spike (Type II) and low deoxynivalenol (DON) accumulation in infected kernels (Type III) have drawn the most attention. A Chinese Spring-Sumai3 chromosome 7A substitution line (CS-SM3-7ADSL) was reported to have a high level of Type II resistance, but quantitative trait locus (QTL) on chromosome 7A has never been mapped. To characterize QTL on chromosome 7A, we developed 191 Chinese Spring-Sumai3-7A chromosome recombinant inbred lines (CRIL) from a cross between Chinese Spring and CS-SM3-7ADSL and evaluated the CRIL in a greenhouse for both types of resistance in three experiments. Two major QTL with Sumai 3 (SM3) origin, conditioning Type II and Type III resistance were mapped in chromosomes 3BS and 7AC. QTL on chromosome 3BS corresponds to Fhb1, previously reported from SM3, whereas 7AC QTL, designated as Fhb5, is a novel QTL identified from SM3 in this study. Fhb5 explains 22% phenotypic variation for Type II resistance and 24% for Type III resistance. Marker Xwmc17 is the closest marker to Fhb5 for both types of resistance. Fhb1 and Fhb5 were additive and together explained 56% variation for Type II and 41% for Type III resistance and resulted in 66% reduction in FHB severity and 84% in DON content. Both QTL showed significant pleiotropy effects on Type II and Type III resistance, suggesting both types of resistance may be controlled by the same gene(s). Haplotype analysis of SM3’s parents revealed that Fhb5 originated from Funo, an Italian cultivar. A survey of worldwide germplasm collection of 400 accessions showed that Fhb5 is present mainly in Chinese cultivars, especially in Funo-related accessions. Further, Fhb5 is the second major QTL from SM3 and have potential to be used in improving wheat cultivars for both types of resistance.

Fusarium graminearum causes Fusarium Head Blight, (one of) the most destructive cereal diseases in Canada. Yield loss, quality degradation and mycotoxin production make Fusarium a multifaceted threat. Regulated production of reactive oxygen species by Nox enzymes is indispensable for fungal pathogenesis. F. graminearum Nox mutant ∆noxAB produced equivalent mycotoxin but caused reduced virulence than wild-type. We hypothesized that Nox mediated redox signaling may participate in F. graminearum pathogenicity. Two-DE and gel-free biotin affinity chromatography, followed by LC-MS/MS analysis were employed for a comparative redox-proteomics analysis between wild-type and ∆noxAB to identify proteins oxidized by Nox activity. Total 35 proteins, 10 by 2-DE and 29 by gel-free system, were identified. 34% proteins participated in fungal metabolism, 20% in electron transfer reactions and 9% were anti-oxidant proteins. The findings suggested that Nox mediated thiol-disulfide exchange in proteins provide a switch for redox-dependent regulation of metabolic and developmental processes during induction of FHB.

Fusarium head blight (FHB), a fungal disease caused principally by Fusarium graminearum, and barley yellow dwarf (BYD) caused by BYD luteoviruses are two serious fungal and viral diseases of wheat resulting in high economic losses annually. Wuhan, a Chinese wheat cultivar resistant to FHB, and Maringa, a Brazilian cultivar tolerant to BYDV were inter-crossed and crossed with Roblin, a Canada western red spring wheat susceptible to both FHB and BYDV, to determine the genetic basis of resistance/tolerance and to combine the two traits. Four hundred ninety nine F1-derived doubled haploid (DH) lines were generated from reciprocal crosses using corn pollen-mediated DH technology. The DH lines and the parents were evaluated for disease symptoms, reduction in height and spike mass for BYD and for disease incidence, disease severity and Fusarium-damaged kernels for FHB in field and controlled environments. A subset (20/150) of the best performing DH lines from Wuhan/Maringa populations for both BYD and FHB were further evaluated. Plants were point inoculated with F. graminearum in greenhouse experiments, and macroconidial spray inoculations and spread of corn inoculum were used in field environments to evaluate FHB. BYDV inoculations were performed by placing ten to fifteen viruliferous aphids (Rhopalosiphum padi infected with BYDV-PAV isolate 9301PAV), at the one to two leaf stage for both greenhouse and field trials. The studies showed that both FHB and BYDV are quantitatively inherited. Transgressive segregants were observed and the broad sense heritability was high (0.90 to 0.97) for all traits evaluated. Results from independent testing of diseases on Wuhan/ Maringa populations showed fourteen DH lines were as, or more resistant than Wuhan for FHB and Maringa for BYDV tolerance and have combined both BYDV tolerance and FHB resistance. Identifying such lines facilitates the pyramiding of independent genes to obtain adequate levels of enduring resistance. A further experiment was conducted on the 14 lines by inoculating them with BYDV and F. graminearum successively on the same plant. Six out of 14 selected DH lines demonstrated high resistance to FHB and tolerance to BYDV. These six lines can be used in FHB/BYDV resistance/tolerance breeding programs.

Fusarium graminearum, the causative agent of Fusarium head blight, is an economically important pathogen of wheat (Triticum aestivum). Breeding Fusarium head blight (FHB) resistant wheat requires knowledge of the underlying genetic control of FHB resistance. Genetic parameters for FHB resistance and five related traits were estimated in three populations at two locations and in two years. Moderate broad sense heritabilities for FHB severity and Fusarium damaged kernels (FDK) were observed. Incidence of FHB and the toxin deoxynivalenol (DON) accumulation had low to moderate broad sense heritabilities. Correlations between FDK and severity and FDK and DON were moderate to high in the three populations and do support indirect selection for FHB severity or DON based on FDK data alone, but it is important to be cautious in years with a high disease pressure when FHB resistance could be masked. A cycle of among-family and within-family selection cycle was conducted in 2003. Actual selection gain was higher than predicted gain based on variance components in 2003 in the within-family selection study. One population had also a strong response for low DON in the among-family selection study. The observed results suggest that selection for FHB resistant genotypes could be achieved with a recurrent selection scheme. Along with conventional breeding, molecular techniques are being used in breeding for FHB resistance. A first genotypic screening of the three populations showed Population 2 had the presence of a resistance allele form the resistant Chinese cultivar Sumai 3. Although Populations 1 and 3 did not have the resistance allele, the results suggest other sources of resistance might be present in these two populations.

Fusarium graminearum, the causative agent of Fusarium head blight, is an economically important pathogen of wheat (Triticum aestivum). Breeding Fusarium head blight (FHB) resistant wheat requires knowledge of the underlying genetic control of FHB resistance. Two nine-parent diallel analyses were completed in greenhouse and field environments. Combining abilities, variance component ratios, and narrow sense heritabilities for FHB resistance and deoxynivalenol levels were calculated. Significant general and specific combining ability effects were observed. Resistance to FHB seems to be mostly controlled by additive genetic effects with some dominance noted in the field. Resistance noted in the greenhouse environment may not hold up in the field. Genetic parameters for FHB resistance and four related traits were estimated in three populations. Moderate to high broad sense heritabilities for FHB severity and Fusarium damaged kernels (FDK) were observed. Incidence of FHB had low to moderate broad sense heritabilities. Correlations between FDK and severity and FDK and incidence were moderate and low, respectively, and do not support indirect selection for FHB severity or incidence based on FDK data alone. Substantial predicted gains from family selection were observed and therefore selection of FHB resistant wheat lines should be based on family means and not individual selection.