Submitted to: Wheat: Science and Trade
Publication Type: Book / Chapter
Publication Acceptance Date: 3/20/2009
Publication Date: 7/15/2009
Citation: Marshall, D.S. 2009. Diseases which challenge global wheat production - powdery mildew, leaf, and head blights. Wheat: Science and Trade. 7:155-170. Interpretive Summary: 1) Conservation tillage practices have provided wheat producers with many crop production benefits, but have resulted in exacerbating residue-borne pathogens. 2) Not only does wheat residue increase the quantity of primary inoculum available to infect subsequent wheat crops, it also serves as the primary means for powdery mildew, leaf blight, and head blight pathogens to complete their life cycle, thereby increasing variability in the pathogen populations. 3) Crop diversity and host plant resistance when used together are the two primary methods of managing residue-borne diseases of wheat. Emphasis must be placed on methods of identifying and incorporating durable host plant resistance that does not encourage resistance breaking variability in the pathogen populations.
Technical Abstract: A common thread to each of these diseases is the ability of the causal fungi to survive and undergo sexual recombination on wheat residue. When infested residue is not brought into contact with soil, it can serve as a safe harbor for the pathogen to survive between crops. Moreover, it allows the pathogen to complete its life cycle, thus increasing genetic variability and potentially new virulence combinations. Increased amounts of wheat residue on the soil surface increases the likelihood of pathogens surviving on the residue, thereby providing a source of inoculum that otherwise may have been eliminated or minimized by tillage This does not mean that increased residue will inevitably lead to greater disease. Disease incidence and severity depend on many factors including a virulent pathogen, a susceptible host, and environmental conditions conducive for infection, growth, reproduction, and spread of the pathogen. In addition, the level of disease on the residue crop, how the residue was handled (if at all), and the nutritional status of the previous and subsequent crop all influence pathogen growth and development on the residue Interestingly, combine harvesters may contribute to the dispersal of residue-inhabiting pathogens by moving pathogen spores from ground level up into atmospheric wind currents. Thus, the widespread adoption of reduced and no-till residue management aids in the survival, increase, and genetic variability of potentially damaging residue inhabiting fungi. This has caused some shifts and could possibly cause even greater changes in global wheat research priorities. Emphasis must be placed on coupling crop diversification strategies with host resistance in order to minimize these important diseases.