Background

Maize is one of the most important staple food crops and energy plants worldwide. It has been becoming the No.1 crop species in China and worldwide regarding both yield and planting areas since 2012. However, corn stalk rot has become one of the most destructive diseases, which normally lead to significant yield loss and quality reduction of maize extensively (Oerke, 2006). The pathogens causing corn stalk rot mainly include the soil-borne fungal species, such as Fusarium graminearum, F. verticillioides, Colletotrichum graminicola, Pythium aphanidermatum, and Pectobacterium chrysanthemi. Infection of maize by F. graminearum (teleomorph Gibberella zeae Schw. Petch) normally causes Gibberella stalk rot with reddish-pink discoloration inside the stalk, and Gibberella ear rot with carcinogenic mycotoxins deoxynivalenol (DON) and zearalenone produced in mature corn kernels that are harmful to human and animals (Mesterhazy et al., 2012). Moreover, F. graminearum is also the major causal agent infecting other small grain cereal crops, such as wheat, leading to the well-known Fusarium head blight (FHB), which is one of the most serious diseases impacting wheat production in China and is endemic in many wheat-producing countries (Walter et al., 2010; Ma et al., 2017). F. verticillioides [=F. moniliforme J. Sheld.(sexual stage: G. moniliformis Wineland)], on the other hand, predominantly infect maize, resulting in Fusarium stalk rot and Fusarium ear rot, and producing Fumonisins, another type of mycotoxins in maize kernels (Presello et al., 2008). Thus, the increasing prevalence of mycotoxins produced by Fusarium spp., along with their direct impact on yield losses in many cereal-growing regions worldwide, has become one of the major concerns of much research.

In recent years, due to the rapid development and application of mechanization, the harvesting technology of corn grain by machines puts forward a high requirement of disease resistance to corn stalk rot. Currently, the field assay for identifying stalk rot resistance using adult plants is largely relying on large population, yet time-consuming, labor costs, and often influenced by environmental conditions. Therefore, a rapid, reliable and large-scale method for screening disease resistant lines and identifying the resistance to corn stalk rot is extremely in urgent, which can provide a great convenience for the researchers to rapidly excavate the elite genetic resources of maize. We have previously deployed a seedling assay to identify the resistance of maize lines to stalk rot caused by F. verticillioides (Gao et al., 2007). Here, we describe the detailed procedures of modified protocol of a seedling assay, which can be applied to evaluate the stalk rot not only caused by Fusarium spp., but also other fungal pathogens, such as C. graminicola.