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Much effort has been directed at identifying sources of resistance to Fusarium head blight (FHB) in wheat. We sought to identify molecular markers for what we hypothesized was a new major FHB resistance locus originating from the wheat cultivar 'Freedom' and introgressed into the susceptible wheat cultivar 'USU-Apogee'. An [F.sub.2:3] mapping population from a cross between Apogee and A30, its BC4 near-isoline exhibiting improved FHB resistance, was evaluated for resistance. The distribution of FHB resistance in the population approximated a 1:3 moderately resistant : moderately susceptible + susceptible ratio. Separate disease evaluations established that A30 accumulated less deoxynivalenol and yielded a greater proportion of sound grain than Apogee. Molecular mapping revealed that the FHB resistance of A30 is associated with molecular markers on chromosome arm 3DL that exhibit a null phenotype in A30 but are present in both Apogee and Freedom, indicating a spontaneous deletion occurred during the development of A30. Aneuploid analysis revealed that the size of the deleted segment is approximately 19% of the arm's length. Our results suggest that the deleted interval of chromosome arm 3DL in Apogee may harbor FHB susceptibility genes that promote disease spread in infected spikes, and that their elimination increases FHB resistance in a novel manner. Keywords: Fusarium, susceptibility, breeding, genetics, mapping. Des efforts considerables ont ete consacres a l'identification de sources de resistance a la fusariose de l'epi (FHB) chez le ble. Les auteurs ont cherche a identifier des marqueurs moleculaires associes a un presume nouveau gene de resistance majeur provenant du cultivar de ble 'Freedom'. Parallelement, ce gene a ete introgresse dans le cultivar de ble sensible 'USU-Apogee'. Une population de cartographie [F.sub.2:3] derivee d'un croisement entre Apogee et A30, une lignee BC4 quasi-isogenique affichant une resistance accrue a la FHB, a ete evaluee pour la resistance. La distribution de la resistance a la FHB au sein de la population s'approchait d'un ratio 1:3 (moderement resistants : moderement sensibles + sensibles). Des evaluations distinctes de la maladie ont montre que la lignee A30 accumulait moins de desoxynivalenol et produisait une plus grande proportion de grains sains que le cultivar Apogee. La cartographie genetique a revele que la resistance a la FHB chez A30 est associee a des marqueurs moleculaires sur le bras chromosomique 3DL qui presentent un phenotype nul chez A30, mais qui sont presents tant chez Apogee que chez Freedom. Cela suggere qu'une deletion spontanee serait survenue au cours du developpement de la lignee A30. Une analyse de l'aneuplo'idie a revele que le segment manquant representerait environ 19 % de la taille de ce bras. Ces resultats suggerent que cet intervalle du bras chromosomique 3DL chez Apogee porterait des genes de sensibilite a la FHB qui favoriseraient la propagation de la maladie sur des epis infectes et que leur elimination accroit la resistance a la FHB d'une maniere inedite. [Traduit par la Redaction] Mots-cles : Fusarium, sensibilite, amelioration genetique, genetique, cartographie., Introduction The disease Fusarium head blight (FHB), caused by members of the fungal genus Fusarium, reduces yields and erodes grain quality in wheat and other small grains. The principal species [...]

Fusarium Head Blight (FHB), caused by Fusarium graminearum Schwabe [(teleomorph Giberella Zeae (Schwein.)], has been a major disease problem of barley (Hordeum vulgare L.) in the U.S. Midwest since 1993. It can make a potentially profitable barley crop unusable for malting, and substantially reduce its value as a feed grain. The main cause of economic loss in malting barley is the presence of deoxynivalenol (DON) or vomitoxin, a mycotoxin produced by the fungus. The objective of this research was to investigate the inheritance of resistance to FHB by the estimation of heritability through components of variance in multiple environments. Four populations resulting from crosses between putative resistant and susceptible parents were evaluated in inoculated and mist irrigated nurseries at three locations in Minnesota from 1995 to 1997 and China in 1997. On the basis of multiple environment data, estimates of heritability for FHB ranged from 0.48 to 0.76. Heritability estimates from individual environments for FHB ranged from low to high; these estimates were likely inflated by genotype x environment (G x E) interaction. Resistance levels approximating that of the resistant parent were recovered in most populations and one transgressive resistant line was found in Population 3. Transgressive segregates toward susceptibility were found in Populations 2, 3, and 4 for FHB. The heritability estimates were somewhat encouraging, as they indicated that moderate genetic gain can be expected when selecting for FHB resistance in a breeding program. However, a strong message was conveyed in the variable response of the parents and the ever present G x E interaction that FHB resistance breeding represents an unusually large challenge., FUSARIUM HEAD BLIGHT has become the most devastating and economically important disease of malting barley and wheat (Triticum aestivum L.) in the U.S. upper Midwest. FHB of barley, also called [...]

Kernel color and grain protein concentration (GPC) are two of the most important attributes of barley (Hordeum vulgate L.) grain intended for use in malting and brewing. Grain with protein levels that are too low or high or that have dark kernel color, which may result from the disease complex of kernel discoloration (KD), is unacceptable for the malting and brewing industries. The purpose of this study was to use molecular markers to map quantitative trait loci (QTLs) for KD and GPC in two recombinant inbred line (RIL) populations. One population was created by means of the high GPC and KD resistant cultivar Chevron. The other population was created from a KD resistant cultivar MNBrite that was derived from Chevron through eight generations of crossing and selection for bright kernels. The traits KD and GPC were evaluated in four and three environments, respectively, using the Chevron population and six environments using the MNBrite population. GPC and KD score were negatively correlated in both populations. A revised genetic map for the Chevron/M69 population, with an additional 45 simple sequence repeat (SSR) markers, was used to identify nine QTLs associated with KD on chromosomes 1(7H), 2(2H), 4(4H), 6(6H), and 7(5H), including two major QTLs on chromosome 6(6H). A single QTL for GPC identified in the Chevron mapping population, accounting for over 55% of the phenotypic variation, was located on chromosome 6(6H) and was coincident with one of the two major QTLs for KD. In this region, the Chevron allele increased GPC and decreased KD score. In the MNBrite mapping population, the same region of chromosome 6(6H) was mapped with SSR markers, and QTL analysis verified that this region was associated with both KD and GPC, indicating that MNBrite inherited this region of chromosome 6(6H) from Chevron. The results of this study suggest that if GPC and KD are controlled by tightly linked genes, then it should be possible to use SSR markers to identify recombinants in this region of chromosome 6(6H) and break the linkage to allow selection for KD resistance without high GPC. Alternatively, if GPC and KD are conditioned by the same gene, then it should he possible to select for KID resistance from Chevron by means of SSR markers and to use phenotypic selection to introgress other genes to reduce GPC to acceptable levels., KERNEL COLOR AND GPC are two of the most important selection criteria for determining whether barley grain is of sufficient quality for malting and brewing. Kernel color is negatively affected [...]