Doctor of Philosophy / Department of Agronomy / Guihua Bai / Growing resistant cultivars is an economically effective method to control wheat disease Fusarium head blight (FHB) caused by Fusarium graminearum. Ninety-five wheat lines mainly from China and Japan were evaluated for resistance to initial infection (type I), spread of symptoms within a spike (type II), and deoxynivalenol (DON) accumulation in infected grains (type III). Most of lines were resistant or moderately resistant, 15 lines had DON content lower than 2 ppm and six lines showed a high level of resistance for all the three types. Deoxynivalenol content was significantly correlated with type II, but not type I resistance. Fifty-nine of the ninety-five lines were evaluated for genetic diversity on the basis of amplified fragment length polymorphism (AFLP) and simple sequence repeats (SSRs). Genetic relationships among these lines were consistent with pedigrees and their geographic distribution. Chinese lines had broader genetic diversity than Japanese lines. Sumai 3 is a widely used Chinese variety for FHB-resistant breeding in the US and elsewhere. Haplotype patterns of the SSR markers linked to FHB resistance quantitative trait loci (QTL) on chromosomes 3BS, 5AS and 6BS of Sumai 3 indicated that only a few Sumai 3 derivatives carry all of these Sumai 3 QTL. SSR data also suggested that these QTL in Sumai 3 were derived from Chinese landrace Taiwan Xiaomai. Some highly resistant lines may carry novel QTL for FHB-resistance QTL, and need further investigation. A mapping population of 139 recombinant inbred lines derived from the cross of Wangshuibai (resistant Chinese landrace)/Wheaton (susceptible cultivar) was genotyped with more than 1300 SSR and AFLP markers. Five QTL for type I resistance were detected on chromosome arms 3BS, 4BS, 5DL, 3AS, and 5AS; seven QTL for type II resistance on 3BS, 1AL, 5AS, 5DL, 7AL, and 3DL; and seven QTL for type III resistance on 3BS, 5AS, 1AS, 5DL, 1BL, and 7AL. These QTL together explained 31.7%, 64%, and 52.8% of the phenotypic variation for FHB type I, II, and III resistance, respectively. QTL on 5AS, the distal end of 3BS, and 5DL contributed to all three types of resistance. FHB resistance QTL identified in Wangshuibai can be used in developing wheat cultivars with enhanced FHB resistance by pyramiding FHB resistance QTL from other sources.

Fusarium head blight (FHB) is a major challenge in global wheat production. In the United States, the disease is predominantly caused by the fungus Fusarium graminearum. Utilization of FHB-resistant wheat cultivars integrated with other measures such as fungicide application is the most effective approach for the management of this disease. This study aimed to 1) identify novel quantitative trait loci (QTL) for resistance to FHB in a Brazilian spring wheat cultivar ‘Surpresa’ through bi-parental mapping, 2) detect QTL for FHB resistance in a global panel of 233 spring wheat accessions by genome-wide association analysis (GWAS), and 3) localize genomic regions governing traits associated with virulence in Fusarium graminearum. Using phenotypic and genotypic data from 187 recombinant inbred lines derived from the cross between Surpresa and a susceptible spring wheat cultivar ‘Wheaton’, four QTL (Qfhb.ndwp-2AS, Qfhb.ndwp-2AL, Qfhb.ndwp-3B, and Qfhb.ndwp-4D) were mapped on chromosomes 2A, 3B, and 4D of Surpresa, respectively. Qfhb.ndwp-2AS, Qfhb.ndwp-2AL, and Qfhb.ndwp-3B were found to be novel based on physical locations of the markers tightly linked to these QTL. Two significant marker-trait associations (Qfhb.ndwp-3A and Qfhb.ndwp-2BL) were detected by GWAS of 233 spring wheat accessions, which conferred type II and type III FHB resistance and mapped on chromosomes 3A and 2B, respectively. Both QTL were novel based on the physical locations of tightly linked markers. GWAS of virulence and fungicide sensitivity using 183 F. graminearum isolates collected from North Dakota identified two significant marker-trait associations in chromosomes 1 and 3 for virulence, and two for fungicide sensitivity. The genes associated with virulence that were detected in this study were not previously reported. Identification of these novel genes in metabolic pathways of F. graminearum could help to develop new strategies for the management FHB.

La fusariose est une des maladies les plus importantes altérant le blé en Bourgogne. L’espèce fongique Fusarium graminearum est l’un des agents principaux de la maladie. L’interaction hôte-pathogène peut entrainer la production de mycotoxines toxiques pour l’homme et l’animal.La seule alternative pour prévenir le développement de la maladie est de contrôler l’inoculum primaire dans son habitat naturel : les adventices, le sol et les résidus de culture. En raison de la tendance à la réduction du travail du sol, une attention particulière doit être portée au rôle des résidus de culture dans la survie et le développement de F. graminearum. Dans ce travail de thèse, deux approches ont été choisies pour mieux comprendre le développement saprotrophe du champignon et ses conséquences. La première, à travers un essai en champ dans le contexte pédoclimatique Bourguignon, avait pour but de définir la part relative des différentes sources d’inoculum dans le développement de la fusariose et l’accumulation des mycotoxines dans les grains. Cet essai devait en outre permettre de déterminer si des indicateurs précoces du développement de la maladie sur épi et de l’accumulation de mycotoxines pouvaient être identifiés. La seconde, à travers un essai en microcosmes, avait pour but de suivre le développement de F. graminearum dans le sol et les résidus.Ce travail a permis de souligner l’importance de la gestion des résidus de culture dans le développement de la fusariose du blé. Favoriser une décomposition biologique rapide des résidus de culture et/ou introduire des cultures intermédiaires assainissantes constituent des perspectives de recherche sur lesquelles doivent porter nos efforts / Fusarium Head Blight (FHB), mainly caused by the fungal species Fusarium graminearum, is one of the most important disease altering wheat crops in Burgundy. Moreover the plant-pathogen interaction leads to the production of mycotoxins potentially toxic for humans and animals.The only alternative to date to prevent the development of the disease is to control the saprotrophic development of F. graminearum in its natural habitat, i.e. weeds, soil and crops residues. Due to the trend of reduced tillage, special attention should be paid to the role of crop residues in the survival and development of F. graminearum.Two approaches were chosen to better understand the saprotrophic development of F. graminearum and its consequences towards FHB. i) The first through a field experiment in the Burgundian pedoclimatic context aimed at defining the relative importance of the different sources of inoculum in the development of FHB and the accumulation of mycotoxins in grains. The field experiment was also to determine whether early indicators of disease development on ears and accumulation of mycotoxins could be identified. ii) The second, through test microcosms, was to follow the development of F. graminearum in the soil and crop residues.This work highlighted the importance of crop residues management in the development of FHB and gave new understanding about the survival of the fungus on these residues. Improve the biological decomposition of crop residues at the soil surface or/and using suppressive intermediate crops could be the next prospective to investigate to limit the soil inoculum potential of saprotrophic F. graminearum