Cabbage plants defend themselves against herbivores and pathogens by deploying a defensive mechanism called the mustard oil bomb: when the plant tissue is damaged, toxic isothiocyanates are formed and can effectively fend off attackers. Researchers at the Max Planck Institute for Chemical Ecology and the University of Pretoria have now been able to show in a new study that this defense is also effective to some extent against the widespread and detrimental fungus Sclerotinia sclerotiorum. However, the pathogen uses at least two different detoxification mechanisms that enable the fungus to successfully spread on plants defended in this way. The metabolic products thus formed are non-toxic to the fungus, allowing it to grow on these plants.
Sclerotinia sclerotiorum is a devastating fungal pathogen that can infect more than 400 different plant species. The main symptom of the disease called Sclerotinia wilt or white mold is wilting. Visible are also the white, cotton-like fungal spores that overgrow plant leaves and stalks. In agriculture, rapeseed cultivation is particularly at risk. The plant disease can affect other members of the cabbage family, and also potatoes, legumes and strawberries.
Scientists at the Max Planck Institute for Chemical Ecology in Jena have long been studying the glucosinolates and isothiocyanates that constitute the special defense mechanism of cabbage family plants, which include rapeseed, radishes and mustard. "We wanted to find out how successful plant pathogens overcome the plant defense and colonize these plants. We therefore asked ourselves whether widespread fungal pathogens have strategies to adapt to the chemical defenses of plants of the cabbage family," Jingyuan Chen, the first author of the study, explains.