The Microflora of Maize Grains as a Biological Barrier against the Late Wilt Causal Agent, Magnaporthiopsis maydis

Abstract

The maize pathogen Magnaporthiopsis maydis causes severe damage to commercial fields in the late growth stages. This late wilt disease has spread since its discovery (the 1980s) and is now common in most corn-growing areas in Israel. In some fields and sensitive plant species, the disease can affect 100% of the plants. The M. maydis pathogen has a hidden endophytic lifecycle (developed inside the plants with no visible symptoms) in resistant corn plants and secondary hosts, such as green foxtail and cotton. As such, it may also be opportunist and attack the host in exceptional cases when conditions encourage it. This work aims to study the pathogen’s interactions with maize endophytes (which may play a part in the plant’s resistance factors). For this purpose, 11 fungal and bacterial endophytes were isolated from six sweet and fodder corn cultivars with varying susceptibility to late wilt disease. Of these, five endophytes (four species of fungi and one species of bacteria) were selected based on their ability to repress the pathogen in a plate confrontation test. The selected isolates were applied in seed inoculation and tested in pots in a growth room with the Prelude maize cultivar (a late wilt-sensitive maize hybrid) infected with the M. maydis pathogen. This assay was accompanied by real-time qPCR that enables tracking the pathogen DNA inside the host roots. After 42 days, two of the endophytes, the Trichoderma asperellum, and Chaetomium subaffine fungi, significantly (p < 0.05) improved the infected plants’ growth indices. The fungal species T. asperellum, Chaetomium cochliodes, Penicillium citrinum, and the bacteria Bacillus subtilis treatments were able to reduce the M. maydis DNA in the host plant’s roots. Studying the maize endophytes’ role in restricting the invasion and devastating impact of M. maydis is an essential initial step towards developing new measures to control the disease. Such an environmentally friendly control interface will be based on strengthening the plants’ microbiome.