Histopathological investigation of varietal responses to Cercospora beticola infection process on sugar beet leaves

Authors: BHUIYAN, ZIAUR - North Dakota State University; SOLANKI, SOLANKI - South Dakota State University; LUIS, DEL RIO MENDOZA - North Dakota State University; BOROWICZ, PAUL - North Dakota State University; Lakshman, Dilip; QI, AIMING - University Of Hertfordshire; AMEEN, GAZALA - South Dakota State University; KHAN, MOHAMED - South Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2023
Publication Date: 6/17/2023
Citation: Bhuiyan, Z., Solanki, S., Luis, D., Borowicz, P., Lakshman, D.K., Qi, A., Ameen, G., Khan, M. 2023. Histopathological investigation of varietal responses to Cercospora beticola infection process on sugar beet leaves. Plant Disease. https://doi.org/10.1094/PDIS-03-23-0562-RE.
DOI: https://doi.org/10.1094/PDIS-03-23-0562-RE

Interpretive Summary: Cercospora leaf spot (CLS) of sugar beet caused by the fungal pathogen Cercospora beticola is a major constraint to yield worldwide. A better understanding of the infection process is essential to develop better management practices. However, limited reports are available to understand the histological process of disease development by this pathogen. Therefore, we investigated the mechanism of infection in both susceptible and disease-tolerant sugar beet varieties by advanced microscopic techniques. C. beticola biomass accumulation, percentage leaf cell death, and disease severity were all significantly greater in the susceptible variety compared to the resistant variety. Overall, this study highlighted the C. beticola infection process as well as a possible mechanism of resistance during host-pathogen interactions. The results of this investigation will be useful to mycologists, plant pathologists, and extension workers to develop better management practices for the disease.

Technical Abstract: Cercospora leaf spot (CLS) is the most destructive foliar disease in sugar beet (Beta vulgaris). It is caused by Cercospora beticola Sacc., a fungal pathogen that produces toxins and enzymes which affects membrane permeability and cause cell death during infection. In spite of its importance, little is known about the initial stages of leaf infection by C. beticola. Therefore, we investigated the temporal progression of C. beticola on leaf tissues of susceptible and resistant sugar beet varieties using confocal microscopy. Inoculated leaf samples were collected at 12-h intervals between 0 and 120-hours post inoculation (hpi), and stored in DAB (3,3'-Diaminobenzidine) solution until processed. Samples were stained with Alexa Fluor 488 dye to visualize fungal structures with a confocal laser scanning microscope. Fungal biomass accumulation, reactive oxygen species (ROS) production, and the area under disease progress curve for both susceptible and resistant varieties were evaluated to compare the host response to C. beticola inoculation. Upon DAB staining, no ROS production was found on any cultivar until 36-hpi. C. beticola biomass accumulation, percentage leaf cell death and disease severity were all significantly greater in the susceptible variety compared to the resistant variety (P<0.05). Conidia penetrated directly through stomata between 48- to 60-hpi and produced appressoria on stomatal guard cells at 60- to 72-hpi in susceptible and resistant varieties, respectively. Penetration of hyphae inside the parenchymatous tissues varied in accordance with time post-inoculation and varietal genotypes. Overall, this study documented the early stages of infection in sugar beet leaf by C. beticola.