BREEDING WHEAT AND RYE FOR RESISTANCE TO FUSARIUM DISEASES

Fusarium culmorum and F. graminearum Groups 1 and 2 cause seedling bli ght, crown rot, foot rot and head blight in wheat and rye that may aff ect grain yield and quality for baking and feeding. This review starts with an analysis of Fusarium populations with regard to their genetic variation for aggressiveness, mycotoxin production, and isolate-by-ho st genotype interaction. To assess resistance in the different host gr owth stages, quantitative inoculation and disease assessment technique s are necessary. Based on estimated population parameters, breeding st rategies are reviewed to improve Fusarium resistance in wheat and rye. Epidemiological and toxicological aspects of Fusarium resistance that are important for resistance breeding are discussed. F. culmorum and F. graminearum display large genetic Variation for aggressiveness in i solate collections and in naturally occurring populations. The product ion of mycotoxins, especially deoxynivalenol and its derivatives, is a common trait in these populations. Significant isolate-by-host genoty pe interactions were not found across environments in wheat and rye. A rtificial infections in the field are indispensable for improving Fusa rium crown rot, foot rot and head blight resistance in wheat and rye. For a reliable disease assessment of large populations, disease severi ty ratings were found to be the most convenient. The differentiation o f host resistance is greatly influenced by an array of nongenetic fact ors (macro-environment, microclimate, host growth stage, host organ) t hat show significant interactions with host genotype. Selection for en vironmentally stable resistance has to be performed in several environ ments under a maximum array of different infection levels. Selection i n early growth stages or on one plant organ does not in most cases all ow prediction of resistance in adult-plant stages or another plant org an. Significant genetic variation for resistance exists for all Fusari um-incited diseases in breeding populations of wheat and rye. The path o-systems studied displayed a prevalence of additive gene action with no consistent specific combining ability effects and thus rapid progre ss can be expected from recurrent selection. In wheat, intensive testi ng of parental genotypes allows good prediction of the mean head bligh t resistance after crossing. Subsequent selection during selfing gener ations enables the use of transgression towards resistance. In hybrid breeding of winter rye, the close correlation between foot rot resista nce of inbred lines and their GCA effects implies that selection based on the lines per se should be highly effective. This is not valid for F. culmorum head blight of winter rye caused by a greater susceptibil ity of the inbred lines compared to their crosses. For both foot rot a nd head blight resistance, a high correlation between the resistance t o F. graminearum and F. culmorum was found in wheat and rye. Mycotoxin accumulation occurs to a great extent in naturally and artificially i nfected plant stands. The correlation between resistance traits and my cotoxin contents are medium and highly dependent on the environment. F urther experiments are needed to clarify whether greater resistance wi ll lead to a correlated reduction of the mycotoxin content of the grai ns under natural infection.