Morphopathological and Molecular Morphometric Characterization of Waitea circinata var. prodigus Causing a Novel Sheath Spot Disease of Maize in India

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 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, whereas infected upper leaves remained on the stem. The pathogen was isolated, characterized morphologically, pathologically, and molecularly, and identified as Waitea circinata var. prodigus, a basidiomycete known to cause basal leaf blight of seashore paspalum. The internal transcribed spacer (ITS) sequence 2 (ITS2) of rDNA from MBSS isolates formed a well supported Glade with known W. circinata var. prodigus 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-CBCs, 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 necessitate further investigations of pathogen identification and disease management.

Automated summary

Maize brown sheath spot (MBSS) is a newly discovered disease on maize in India. It is caused by a fungus called Waitea circinata var. prodigus, which is known to cause basal leaf blight of seashore paspalum. The symptoms of MBSS are discrete lesions on the sheaths of maize plants. Further investigations are needed to understand the geographical distribution and potential impacts of MBSS on the maize crop in India.