Double trouble or a blessing in disguise? Co-infection of potato with the causal agents of late and early blight

The simultaneous occurrence of multiple diseases is an understudied area in plant pathology; however, studies of animal and human diseases have shown that the presence of multiple pathogens can impact virulence, and the course of disease development. Furthermore, they also present an important driver of epidemiological dynamics. Global potato production is plagued by multiple pathogens, amongst which are Phytophthora infestans and Alternaria solani, the causal agents of potato late and early blight respectively. Both these pathogens have different lifestyles and are successful pathogens of potato, but despite observations of both pathogens infecting potato simultaneously in field conditions, the tripartite interactions between potato and these two pathogens are so far, poorly understood. Here we studied the interaction of A. solani and P. infestans first in vitro and subsequently in planta both in laboratory and field settings. We found that A. solani can inhibit P. infestans both in terms of growth in vitro and infection of potato, both in laboratory experiments and in an agriculturally relevant field setting.