Cultivars Resistance Assay for Maize Late Wilt Disease

SIMPLE SUMMARY: Maize late wilt disease (LWD) is considered the most severe corn disease in Israel and Egypt and a significant threat in other countries. The utilization of disease-resistant maize cultivars is currently our best LWD control method. Here we evaluated the predictive ability of a rapid test to examine the susceptibility/tolerance of corn varieties to the disease. The fastest assay is based on the sensitivity of corn seeds to metabolites secreted by the pathogen. However, it is only reliable in detecting highly resistant or extremely susceptible maize varieties. To identify LWD immunity of mildly tolerant hybrid plants, a full-season pot assay in the open air, under field conditions, is needed. New detection methods, including aerial visible dehydration symptom monitoring and real-time PCR-based tracking of M. maydis DNA inside the plants’ tissues, were evaluated here and proved to provide a great advantage. No complete overlap exists between the fungal DNA amount and the severity of symptoms. Such a correlation exists in high sensitivity or resistance cases but not in intermediate situations. Still, the valuation of the pathogen’s establishment in asymptomatic corn hybrids is a powerful means to predict each maize variety’s LWD immunity. ABSTRACT: Magnaporthiopsis maydis late wilt disease (LWD) in corn is considered to be the most severe in Israel and Egypt and poses a significant threat in other countries. Research efforts extending over a period of five decades led to the development of chemical, biological, agrotechnical, physical (solar disinfection) and other means for controlling late wilt disease. Today, some applications can reduce damage even in severe cases. However, cultivating disease-resistant maize varieties is the primary means for reducing the disease’s impact. The current work uses a rapid (six days) laboratory seedling pathogenicity test and a full-season open encloser semi-field conditioned pots assay (101 days) to classify maize varieties according to their LWD resistance. To better evaluate differences between the cultivars, a real-time based molecular assay was applied to track the pathogen’s presence in the plants’ tissues, and visible light aerial imaging was used in parallel. The findings show that in cases of extreme sensitivity or tolerance (for example, in the highly susceptible Megaton cultivar (cv.) or the resistant Hatai cv.), a similarity in the results exists between the different methods. Thus, a reliable estimate of the varieties’ sensitivity can be obtained in a seed assay without the need for a test carried out throughout an entire growing season. At the same time, in most situations of partial or reduced LWD sensitivity/resistance, there is no match between the various tests, and only the entire growing season can provide the most reliable results. Tracking the amount of M. maydis DNA in the plants’ bodies is a precise, sensitive scientific tool of great importance for studying the development of the disease and the factors affecting it. Yet, no complete overlap exists between the fungal DNA amount and symptom severity. Such a correlation exists in high sensitivity or resistance cases but not in intermediate situations. Still, the valuation of the pathogen’s establishment in asymptomatic corn hybrids can indicate the degree of LWD immunity and the chance of susceptibility development.