Aerial dispersion of smut spores during peanut harvest.

Abstract Peanut smut ( Thecaphora frezii ) is one of the most important peanut diseases in Argentinian peanut production. This soil-borne pathogen transforms kernels into spore masses. Spore liberation from broken infected pods during the harvest process is supposed to be the main mechanism of inoculum spread, with the subsequent spread among fields. However, we are unaware of any published study on the role of wind in the spread of smut spores. Therefore, we conducted an observational study where spore traps were distributed at harvest around six fields placed at 100, 200, 300, and 400 m away from each field's centroid in four cardinal directions. Three time slices were sampled: from the beginning of harvest to 90-, 180-, and 270-minutes during harvest. Wind speed and direction were recorded at each trap. A generalised additive model was fitted to describe the spore spread. Modelling the dispersion shows that the spread is influenced by wind direction, and the smut intensity present at the harvested field. Additionally, spore size and proportion of different smut spore types were assessed (from a single unit spore to a 5-multinuclear propagule). No statistical differences were observed in the proportion of the spore types trapped. However, the spores' spread decreased over distances from the harvested area. This work led us to understand one fundamental component of the peanut smut cycle and epidemiology, which is, to design management strategies, such as avoiding harvest on windy days.