Foliar selenium application reduces late blight severity and incidence in potato and acts as a pathogen growth inhibitor and elicitor of induced plant defence

Late blight caused by <i>Phytophthora infestans</i> is a serious threat to potato production. Currently, solutions to manage late blight in organic systems are scarce. This study was undertaken to evaluate the effect of selenium (Se) on plant emergence from seed pre-treated with Se and the seed decay pathogens <i>Pectobacterium carotovorum</i> ssp. <i>carotovorum</i> and <i>Fusarium sambucinum</i>, and on foliar potato late blight following inoculation with <i>P. infestans</i> and foliar treatment with Se. The potential modes of action of Se were also evaluated. Following inoculation of the seed decay pathogens on potato seed pre-treated with different rates of Se, plant emergence was not affected by Se treatment. By pre-treating potato seed with different Se rates, and applying different foliar Se rates on potato plants subsequently inoculated with the late blight pathogen in a greenhouse setting, we showed that foliar Se application alone or combined with Se seed treatment reduced the severity and incidence of late blight, and activated the production of secondary metabolites in potato leaves and tubers. Further, <i>in vitro</i> studies showed that Se directly inhibited the mycelial growth of <i>P. infestans</i> and other important plant pathogens, including <i>Fusarium graminearum</i> and <i>Sclerotinia sclerotiorum</i>. The data suggest that Se acts as an inducer of plant defences, while also inhibiting fungal growth. The study highlights the potential of Se for managing late blight, and suggests that its application could contribute to improving plant health in greenhouse production systems by helping to control diseases caused by <i>P. infestans, F. graminearum</i> and <i>S. sclerotiorum.</i>