Characterization and Identification of the Causal Agent of White Rust in Stevia (Stevia rebaudiana B.)

Abstract

In the Callejón de Huaylas, stevia cultivation is still in its early stages and is affected by a disease known as “white rust,” the pathogen of which is still unknown; in order to identify it, observations and microscopic analyses of its structures were conducted, determining that the sporangiophores measure between 37.5 and 50 μm long by 10 to 15 μm wide, the sporangia between 17.5 and 22 μm by 17.5 and 25 μm, and the oospores have a diameter between 42.5 and 57.5 μm. Additionally, the pathogen’s specificity was evaluated by inoculating six host species susceptible to other white rust species: Raphanus raphanistrum L., Helianthus annuus L., Ipomoea purpurea (L.) Roth, Spinacia oleracea L., Brassica oleracea L., and Physalis peruviana L., using Stevia rebaudiana B. as a control. Both in the laboratory and under field conditions with high humidity, the disease did not manifest in any of the six species; it infected only stevia under field conditions. The morphometric data and pathogenicity tests, when compared with the specialized literature, allow us to conclude that the pathogen belongs to the genus Pustula. Given the high specificity characteristic of species in the family Albuginaceae, the agent was identified as Pustula sp.