Light and electron microscopy studies elucidating mechanisms of tomato leaf infection by Pseudocercospora fuligena

Authors: MERSHA, ZELALEM - Virginia State University; Birru, Girma; HAU, BERNHARD - Leibniz University

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2022
Publication Date: 4/1/2023
Citation: Mersha, Z., Birru, G.A., Hau, B. 2023. Light and electron microscopy studies elucidating mechanisms of tomato leaf infection by Pseudocercospora fuligena. Plant Pathology. 39(2):181-190. https://doi.org/10.5423/PPJ.OA.06.2022.0082.
DOI: https://doi.org/10.5423/PPJ.OA.06.2022.0082

Interpretive Summary: This study has found results ranging from descriptions of macroscopic to microscopic characterizations of P. fuligena, the causative agent of BLM. Stomatal penetration and egress as well as progression of the latent infection are very informative for designing disease management strategies.

Technical Abstract: The fungal pathogen Pseudocercospora fuligena, mainly known to affect tomatoes in tropics and subtropics, has been recently reported from temperate climates including the U.S.A. Because of this expanded horizon and its consequential impact, first draft genome of the pathogen has been published. In this study, aspects related to the identification, characterization and infection mechanisms of an isolate of Pseudocercospora fuligena from Thailand and the leaf mold disease it causes were investigated. Macroscopically, indistinct effuse patches appeared on both sides of tomato leaves. Amphigenous fructification and prolific production of fuliginous lesions predominantly on abaxial side and, as infection progresses, also on the adaxial side were peculiar features of the disease. Microscopically, fascicles of conidiophores measuring 11–128 µm in length x 3.5–9 µm in width consisting of conidia with up to 12 septations were observed. In situ, blocked stomatal aperture area of 154, 401 and 2043 µm2 were measured 7, 12 and 17 days after inoculation, respectively. Direct transfer of conidia from profusely sporulating lesions was found to be the easiest and quickest method of isolation for in-vitro studies. This pathogen grew well on ten artificial culture media in this study but sporulated better on tomato oatmeal agar and carrot leaf decoction agar, both supplemented with CaCO3. Stomatal penetration and egress of P. fuligena were studied on cleared as well as intact leaves using light and scanning electron microscopy. Pathogenesis studies on artificially inoculated leaves revealed prevalence of primary and secondary infection hyphae. Outcomes of the study could provide hints management strategies targeting the pathogen.