In: Sydowia 74, (2022): 277-286; ISSN 0082-0598, DOI 10.12905/0380.sydowia74-2021-0277, Published online on January 21, 2022

An assay for the quantification of pathogenicity and
virulence of two strains of Podosphaera xanthii
(Erysiphaceae) on different hosts from digital images

Rosario Gregorio-Cipriano, Efraín De Luna & Dolores González*

Red de Biodiversidad y Sistemática, Instituto de Ecología, A.C., Xalapa, México
Carretera Antigua a Coatepec No. 351, Col. El Haya, Xalapa 91073, Veracruz, México

*e-mail: dolores.gonzalez@inecol.mx

Gregorio-Cipriano R., De Luna E. & González D. (2022) An assay for the quantification of pathogenicity and virulence of two
strains of Podosphaera xanthii (Erysiphaceae) on different hosts from digital images. – Sydowia 74: 277–285.
The predominant species of powdery mildew in the Cucurbitaceae is Podosphaera xanthii. However, there is little information
on the epidemiology of this disease in Mexico despite its importance. As a first assay, we explore the applicability of a quantitative
technique to estimate differences in the severity of disease caused by P. xanthii on leaves of Cucurbitaceae. We obtained
two samples from different hosts: cultivated (Cucurbita pepo) and wild (C. radicans) cucurbits. Conidia were inoculated onto the
leaves of growing plants of seven cucurbit species. We used the ImageJ program to quantify the infected area for each leaf as the
sum of several polygons. The severity of the infection was calculated as the percentage of the infected foliar area. The two inocula
of P. xanthii were pathogenic in five of seven inoculated cucurbits. Our analyses of variance to compare the variation of the
percentage values among susceptible hosts revealed different levels of severity. This result indicates that this is a promising
method to quantitatively compare differences in disease severity of different strains or hosts of powdery mildews.

Keywords: cucurbits, image analysis, infection percentage, powdery mildew, Ascomycota.