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Maize is a globally important staple that is used as food for human and animal consumption, fuel, and other industrial applications. Pathogens affect all stages of the plant life cycle and every plant organ, and lead to significant yield losses. An integrated strategy incorporating cultural and chemical management practices, as well as development of resistant plant varieties, is needed to prevent yield losses due to plant diseases. Large numbers of breeding material must be screened to develop pathogen-resistant maize varieties. Inoculation methods must be high-throughput to accommodate the large screening experiments. Additionally, there needs to be an extensive understanding of the plant–pathogen interaction to use a targeted biotechnology-based approach, which takes advantage of knowledge of the system to engineer resistance. To evaluate germplasm for breeding and biotechnology approaches, inoculation methods must replicate natural infection, and disease severity must be rated consistently to accurately screen germplasm or gather data on pathogens of interest. Here, we review inoculation and rating methods for Gibberella ear rot, seedling blight caused byGlobisporangium ultimumvar.ultimum, and Goss's wilt that are efficient and high-throughput. We also introduce fluorescence microscopy techniques for leaf samples infected withExserohilum turcicum, the causal agent of northern corn leaf blight. These pathogens all cause significant yield losses, and in particular, Gibberella ear rot is associated with the accumulation of harmful mycotoxins. Understanding how pathogens cause disease and how plants defend against attack is a major goal of maize pathology studies and critical for developing integrated management strategies. 

Maize significantly contributes to food and fuel production. Yields can be reduced due to foliar diseases, which reduce photosynthetic leaf area. The bacterial foliar disease Goss's wilt (caused byClavibacter nebraskensis) can cause significant yield losses in susceptible maize varieties.C. nebraskensiscan infect leaves through wounds and colonize the vascular tissue of the leaf. We present a protocol that replicates this process with the use of a “clapper” with pins on one end to create wounds and a sponge soaked in inoculum on the other end, which allows for efficient field inoculations of maize leaves. Disease severity is then rated on a percentage scale multiple times over the season to generate an area under disease progress curve (AUDPC). Genetic host resistance is one of the most effective forms of foliar disease control in maize, as there are few effective forms of chemical control for bacterial diseases that affect maize. Screening for resistance in diverse germplasm, or for fine mapping a specific resistance gene, requires inoculating large populations in the field for obtaining phenotypic data. Our high-throughput protocol allows for large-scale disease evaluations and is useful for finding forms of genetic resistance or to understand plant–pathogen interactions of bacterial foliar pathogens. 

Maize is an important food and fuel crop globally. Ear rots, caused by fungal pathogens, are some of the most detrimental maize diseases, due to reduced grain yield and the production of harmful mycotoxins. Mycotoxins are naturally occurring toxins produced by certain fungal species that can cause acute and chronic health issues in humans and animals that consume mycotoxin-contaminated grain. Pathogens can infect the developing ear through silks, or through wounds in the ears produced by pests. Plants naturally develop genetic resistance to pathogens. The maize genes involved in resistance to the pathogen may be different, depending on whether the ear was infected via silks or wounds. To differentiate between these two forms of resistance, natural infections can be reproduced by injecting inoculum through the silk channel, or by producing wounds using a needle, and introducing inoculum directly onto developing ears. Our protocol describes a technique used to inoculate developing maize ears withFusarium graminearum, one of the fungal species that causes ear rot. We describe both silk channel and side needle inoculation techniques. Our protocol uses a backpack inoculator for both methods of infection, allowing for high-throughput inoculations, which are necessary for large field experiments. After harvest, the ears are visually rated on a percentage of disease scale. The protocol results in quantitative data that can be used for research on elucidating genetic resistance to fungal pathogens to assist breeding selections, and to understand plant–pathogen interactions of ear rots in maize. 

Maize is a globally important grain crop that is important for food and fuel. Northern corn leaf blight, caused byExserohilum turcicum, is an important fungal foliar disease of maize that is highly prevalent and causes yield losses globally. Microscopy can be used to visualize plant–fungal interactions on a cellular level, which enables pathology and genetics studies. Host resistance and isolate aggressiveness can be characterized at different stages of disease development, which enables a more detailed understanding of the pathogenesis process and host–pathogen interactions. Our protocol outlines an efficient, cost-effective method for stainingE. turcicumtissue on inoculated maize leaves and visualizing samples using a compound fluorescence microscope. This protocol uses KOH treatment followed by aniline blue staining, which stains glucans present in plant and fungal cell walls, and samples are visualized using fluorescence microscopy. Quantitative data about fungal structures including the conidia, hyphal structures, and appressoria, the structures formed to push through the plant leaf surface after conidia have germinated, can be obtained from the images generated using this technique. Visualization of these structures can help pathologists understand plant–pathogen interactions for maize andE. turcicum. This method has advantages over other methods because the stain is less toxic than other available stains, samples can be processed in a more high-throughput manner than other protocols, and the required supplies are relatively inexpensive.