A major gene underlying quantitative resistance of barley against Pyrenophora graminea, a seedborne pathogen causing leaf stripe, was mapped with molecular markers in a barley doubled haploid (DH) population derived from the cross 'Proctor' x 'Nudinka'. This quantitative trait locus (QTL) accounts for r (2)= 58.5% and was mapped on barley chromosome 1, tightly linked to the "naked" gene. A second resistance QTL accounting for 29.3% of the variation in the trait was identified on the P arm of barley chromosome 2. Another two minor QTLs were detected by further analysis. None of the QTLs was found in the barley chromosome 2 "Vada" region studied by Giese et al. (1993).

Septoria speckled leaf blotch (SSLB), incited by Septoria passerinii, has reemerged as one of the most serious foliar diseases of barley (Hordeum vulgare) in the Upper Midwest region of the United States over the last decade. The most cost-effective and environmentally safe method of preventing SSLB epidemics is through the use of resistant cultivars. Thus, the objective of this study was to investigate sources of resistance to S. passerinii in barley and to determine the reliability of greenhouse seedling tests for predicting the adult-plant reaction in the field. From a preliminary greenhouse screening of over 250 barley accessions, 78 lines were selected and subsequently evaluated at the seedling (greenhouse) and adult-plant (field) stages for reaction to S. passerinii. All of the major malting (cultivars grown in or recommended for the Upper Midwest region of the United States were highly susceptible. Highly significant correlations were detected between the infection response of seedlings in the greenhouse and adult plants in the field. Twenty-nine accessions exhibited resistance at both the seedling and adult-plant stages. The resistant accessions identified in this study were from geographically diverse regions and will be valuable in developing barley cultivars with diverse and broad-based resistance to SSLB.Key words: resistance to disease, Hordeum vulgare, Septoria passerinii, septoria speckled leaf blotch.Résumé : Depuis une dizaine d'années, les taches septoriennes (TS), causées par le Septoria passerinii, sont réapparues en tant qu'une des plus importantes maladies foliaires de l'orge (Hordeum vulgare) dans le Haut Midwest des États-Unis. La méthode la plus rentable et respectueuse de l'environnement pour prévenir les épidémies de TS est l'utilisation de cultivars résistants. Ainsi, l'objectif de la présente étude était de rechercher dans l'orge des sources de résistance au S. passerinii et de déterminer la fiabilité des tests effectués en serre sur des semis pour prédire la réaction des plantes adultes au champ. À partir d'une sélection préliminaire en serre sur plus de 250 obtentions d'orge, 78 lignées furent sélectionnées et évaluées par la suite aux stade semis (en serre) et plante adulte (au champ) pour leur réaction au S. passerinii. Tous les principaux cultivars cultivés ou recommandés pour le Haut Midwest des États-Unis, qu'ils soient destinés à l'industrie brassicole (, furent très sensibles. Des corrélations très significatives furent trouvées entre la réponse des semis à l'infection en serre et celle des plants adultes au champ. Vingt-neuf obtentions ont manifesté de la résistance aux stades semis et plant adulte. Les obtentions résistantes identifiées dans la présente étude provenaient de régions géographiques diverses et seront précieuses pour le développement de cultivars d'orge possédant de la résistance diversifiée et générale contre les TS.

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Pyrenophora graminea is a seed‐borne pathogen and is the causal agent of the barley leaf stripe disease. Our aim is to study the genetic basis of barley resistance to leaf stripe. A qualitatively acting resistance factor has been identified in the cultivar ‘Vada’ and the partial resistance of the cultivar ‘Proctor’ to a P. graminea isolate has been demonstrated to be dominated by a major quantitative trait locus (QTL), mapped on barley chromosome 1. Map colinearity between the leaf stripe ‘Proctor’ resistance QTLs,‘Vada’ resistance to leaf stripe, and other disease resistance loci have been investigated in this work using molecular markers. Moreover, since inoculation of barley rootlets by the fungus had been shown to induce the accumulation of several PR (pathogen‐related) mRNA families, seven barley PR genes have been mapped as RFLPs, and one assigned to a chromosome arm via ditelosomic analysis to verify possible map associations with resistance QTLs. This work discusses the genetic relationships between the known leaf stripe resistance loci, resistance loci towards other seed‐borne pathogens and defence gene loci.

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, has become one of the most serious diseases of barley in the Upper Midwest region of the USA. The recombinant line 36L5 derived from a backcross of the susceptible barley cultivar ÔEmirÕ and a resistant Hordeum bulbosum parent Cb2920/4/Colch was found to be resistant to S. passerinii. Two doubled haploids derived from 36L5 were backcrossed to cv. ÔEmirÕ to obtain two BCF 2 populations for determining the inheritance of resistance to S. passerinii. BCF 2 progeny and BCF 2:3 families were evaluated at the seedling stage in the greenhouse for reaction to S. passerinii. BCF 2 progeny and BCF 2:3 families from both crosses segregated 3 : 1 (resistant : susceptible), and 1 : 2 : 1 (resistant : segregating : susceptible), respectively, indicating that the H. bulbosum-derived SSLB resistance is conferred by a single dominant gene. The H. bulbosum introgressions were positioned on chromosome 4HL by genomic and fluorescent in situ hybridizations (GISH and FISH, respectively) and by Southern hybridization with the rye repetitive sequence pSc119.2. These findings indicate that SSLB resistance in H. bulbosum has the potential to be transferred and utilized in barley breeding programs.