Natural products for the control of Phytophthora infestans and Phytophthora capsici

The genus Phytophthora includes phytopathogens of relevant socio-economic importance. Among these, the species Phytophthora infestans and Phytophthora capsici threat several crops and, in particular, Solanaceae and cucurbits. In order to support the searching for sustainable means for the management of plant diseases, this study evaluated several safe natural products (botanicals, inorganics, and vitamins) for the control of P. infestans and P. capsici. In vitro tests on P. infestans highlighted that Tagetes minuta-, Lavandula angustifolia- and ascorbic acid-based formulas, at the highest concentration, were the most effectives; they determined 91.1, 91.3 and 100.0% of radial growth inhibition and 21.3, 6.0 and 9.3% of sporangial germination, respectively; the negative control (Cuprostar–copper-based formula) totally inhibited the mycelial growth and determined the 18.0% of sporangial germination. Among products tested in vitro on P. capsici the most effectives were Armicarb 85 (a potassium hydrogen carbonate-based formula) and ascorbic acid; at the highest concentration they determined the total inhibition of mycelial growth and the 28.0 and 19.3% of sporangia germination, respectively; the Abies sibirica-based formula also significantly affected P. capsici, determining the 97.6% of radial growth inhibition and 38.0% of sporangia germination; the negative control (Cupravit Blu 35–copper-based formula) totally inhibited the mycelial growth and determined the 27.7% of sporangial germination. Natural products were also tested in vivo on artificially P. infestans-infested tomato plants; results highlighted a significant reduction of disease severity by treatments with Tagetes minuta, Lavandula angustifolia and Adigor formulation (a rapeseed oil-based formulation) at the concentrations of 1.0, 0.5 and 0.5%, respectively. In conclusion, this study provided new evidence supporting the employment of safe natural products for the management of Phytophthora diseases.