The Life Cycle and Ultrastructure of the Host Response of the Smut Pathogen, Anthracocystis destruens, on Broomcorn Millet

Abstract

Broomcorn millet smut caused by the fungus Anthracocystis destruens is one of the most destructive diseases in broomcorn millet production. The life cycle of A. destruens and host defense responses against A. destruens remain elusive. Here we investigated the disease symptom development and the parasitic process of A. destruens as well as the ultrastructure of the host-pathogen interface. The results showed that there are four typical symptoms of broomcorn millet smut, which are blackfly, cluster leaves, hedgehog head and incomplete fruiting. A. destruens colonizes all tissues of broomcorn millet but only produces teliospores in the inflorescence. After infection, A. destruens proliferates in the host likely in a systemic manner. Ultrastructural study of the infected inflorescence showed that the pathogen grows intercellularly and intracellular within the host. The host active defense response against pathogen invasion, includes host secrets callose analogs and highly electron-dense deposits to prevent pathogen infection.