Eukaryotic Soilborne Plant Pathogens: Interactions With Their Hosts and Biocontrol

Soilborne diseases caused by soilborne plant pathogens are a serious threat to crops worldwide as host resistance is often unavailable and chemical control is ineffective. The hallmark of eukaryotic soilborne plant pathogens is the formation of resting structures in the soil and plant debris. Resting structures, known as sclerotia, survive in the soil for many years in absence of a host, and are able to withstand adverse environmental conditions such as chemical treatments, radiation, and extreme temperatures. When conditions become favorable, sclerotia germinate and start a new disease cycle. The most common soilborne diseases are initiated in below ground plant tissues and include root and crown rot, damping-off of seedlings, and vascular wilts. Eukaryotic soilborne pathogens belong to different groups of microorganisms including fungi, oomycetes, and rhizaria. The most important genera are Fusarium, Rhizoctonia, Sclerotinia and Verticillium that are fungi, Phytophthora, Pythium and Aphanomyces that are oomycetes, and the rhizaria Plasmodiophora brassicae and Spongospora subterranea. Soilborne plant pathogens have developed a variety of interactions with their hosts, from biotrophism and hemibiotrophism to necrotrophism, and produce an arsenal of effector proteins to evade plant immunity and establish successful infections.

Since soil fumigation using methyl bromide has been banned, infestation by soilborne pathogens has increased sharply. Application of chemical pesticides to soil is controversial due to the perceived detrimental impacts on human health and the environment. There is therefore a need for alternative management options including biocontrol. Different fungi have shown promising results, including Trichoderma species and Clonostachys rosea. These biocontrol agents produce toxins and cell wall degrading enzymes and show high tolerance to chemical compounds, usually by overexpression of ABC and MFS transporters. Many aspects of the infection biology of soilborne plant pathogens still remains to be elucidated. The scope of this topic is to collect the recent scientific achievements on the interaction of soilborne pathogens and their hosts, including effector proteins secreted by the pathogens, host immune responses, and interactions with biological control agents.

Authors are welcome to submit their research or review articles in the following and related areas:

• Identification and role of effectors in the soilborne pathogen infection process
• Plant defense responses against these pathogens
• Role of secondary metabolites in plant-pathogen interactions
• Interactions between soilborne pathogens and biocontrol agents