Caracterización morfológica, patogénica y molecular del agente causal de la roya blanca en girasol (Helianthus annuus L.)

Abstract

White rust (Pústula helianthicola) of sunflower, discovered in Argentina in 1940, is characterized by the production of pustules on the leaves, with yellow pustules on the adaxial surface and white pustules on the abaxial surface, leading to necrosis of the plant, which affects the yield and quality of the flower head. The objective of the present work was to characterize morphologically, pathogenically and molecularly the causal agent of white rust in sunflower. For the morphological characterization, the sunflower crop was established in a field with a history of white rust, and from the vegetative growth of the crop, the different symptoms and signs were recorded, and later the diameter of pustules, sporangia, oospores and zoospores were observed under the microscope. For pathogenic characterization, healthy leaves of different sunflower varieties (Vincent's Choice, Sunbright Hybrid and Sunrich Orange) were inoculated with a suspension of 104 spores obtained from white rust pustules. For molecular characterization, PCR-amplified fragments of the COX2 (cytochrome C oxidase) gene HelF3/R2 specific for white rust were detected. For the first time in Ecuador, sunflower leaves were described presenting as a symptom the appearance of yellowish pustules in the form of blisters on the adaxial surface of the leaf and later as a sign the appearance of white pustules on the abaxial surface of the leaves, which contained the spores that will spread the disease. The average value of the diameter of the pustules of the sunflower samples with white rust was 29.24 μm. Sporangia reached an average value of 14.81 μm. Zoospores showed an average value of 9.9 μm. Oospores reached an average of 17.6 μm. Hyphae were not found and therefore have no measurements. Inoculation of healthy leaves of different varieties showed that there are significant differences between varieties, detailing that the Vincent's Choice variety is the most susceptible to white rust and the Sunrich Orange variety is the most resistant. Of the sunflower samples with white rust analyzed, the COX2 (cytochrome C oxidase) HelF3/R2 gene was detected in the Montalvo parish of the Tungurahua Province.