The effect of cocultivation of Fusarium, Alternaria, and Pseudomonas on the mycotoxin production and growth

Mycotoxigenic fungal pathogens Fusarium and Alternaria are a leading cause for loss in cereal production. During their growth in wheat-ears, they oppose bacterial antagonists such as Pseudomonas. Studies on these groups’ interactions often neglect the infection process’s temporal aspect and the associated priority effects. Here, we focus on how the first colonizer affects the subsequent ones. In a climatic chamber experiment, wheat-ears were sprayed successively with a pair of the strains A. tenuissima At625, F. graminearum Fg23, or Pseudomonas simiae Ps9. Over three weeks, microbial abundances and mycotoxin concentrations were analyzed and visualized via Self Organizing Map with Sammon Mapping (SOM-SM). All three strains revealed different characteristics and strategies to deal with co-inoculation: Fusarium, as the first colonizer, suppressed the establishment of Alternaria and Pseudomonas. Nevertheless, primary inoculation of Alternaria reduced all of the Fusarium toxins and stopped Pseudomonas from establishing. Pseudomonas showed priority effects in delaying and blocking the production of the fungal mycotoxins. The SOM-SM analysis visualized the competitive strengths: Fg23 ranked first, At625 second, Ps9 third. Our findings of species-specific priority effects in a natural environment and the role of the mycotoxins involved are relevant for developing biocontrol applications.