Morphopathological and molecular morphometric characterization of Waitea circinata var. prodigus causing a novel sheath spot disease of maize in India

Authors: SINGH, VIMLA - Haryana Agricultural University; Lakshman, Dilip; Roberts, Daniel; HOODA, KARAMBIR - National Bureau Of Plant Genetic Resources; GOGOI, ROBIN - Indian Agricultural Research Institute

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2021
Publication Date: 7/14/2021
Citation: Singh, V., Lakshman, D.K., Roberts, D.P., Hooda, K.S., Gogoi, R. 2021. Morphopathological and molecular morphometric characterization of Waitea circinata var. prodigus causing a novel sheath spot disease of maize in India. Plant Disease. 106:526-534. https://doi.org/10.1094/PDIS-05-21-0951-RE.
DOI: https://doi.org/10.1094/PDIS-05-21-0951-RE

Interpretive Summary: Maize is the third leading cereal crop of the world after rice and wheat. A new maize sheath brown spot disease (MBSS) was discovered in India and the pathogen was identified as Waitea circinata var. prodigus (Wcp), which is a Rhizoctonia-like soilborne fungus. The same pathogen (Wcp) also causes basal leaf blight of turf grasses in the United States. We have characterized the fungus at the morphological, molecular and pathological levels and described the implications of the findings on disease management of maize. This is also the first report, to date, of this new disease on maize. This information will be useful for plant pathologists and agricultural extension agents.

Technical Abstract: Maize brown sheath spot (MBSS), a new disease of maize, was discovered while surveying for maize leaf and sheath blight diseases in the Indian states of Assam, Jharkhand, Meghalaya, Manipur, and Odisha. Maize is the third most important cereal after rice and wheat in India. Unlike banded leaf and sheath blight (BLSB) disease caused by Rhizoctonia solani, MBSS symptoms on maize were discrete and limited to sheaths only. Symptoms of MBSS in the field were initially water soaked necrotic lesions of 1 to 2 cm in diameter on the lowermost leaf sheaths, which then progressed to the upper sheaths. Lesions coalesced and covered approximately 2 to 5% of the sheath area. Infected dried lower leaves were shed while infected upper leaves remained on the stem. The pathogen was isolated, characterized morphologically, pathologically, and molecularly, and identified as Waitea circinata var. prodigus (Wcp); a basidiomycete known to cause basal leaf blight of seashore paspalum. The internal transcribed spacer sequence 2 (ITS2) of rDNA from MBSS isolates formed a well-supported clade with known Wcp isolates. Molecular morphometric analysis of the ITS2 regions of the five known varieties of W. circinata detected distinguishing variations in GC content, compensatory base changes (CBCs), hemi-compensatory base changes (hCBCs), indels, and altered base-pairing of helices. Variation in these characteristics may indicate that varieties are distinct biological species within W. circinata sensu lato. The geographical distribution and potential impacts of MBSS on the maize crop in India necessitates further investigations on pathogen identification and disease management.