Morphological and Molecular Characterization of Septoria nodorum Causing Septoria Nodorum Blotch on Wheat

Abstract

Septoria nodorum blotch, incited by Septoria nodorum (Berk.) Berk. (anamorph: Stagonospora nodorum, Ascomycota: Dothideomycetes), represents one of the most economically consequential foliar diseases of wheat (Triticum aestivum L.) in temperate and semi-arid cereal-growing regions worldwide, inducing characteristic necrotic leaf blotches with dark pycnidia embedded within lesion centers that collectively compromise photosynthetic capacity, precipitate premature senescence, and substantially reduce grain yield and milling quality under conditions of high inoculum pressure and favorable environmental conditions. Although S. nodorum has been recognized as a primary wheat pathogen for over a century, contemporary integrative characterization combining comprehensive morphological reassessment with multilocus molecular phylogenetics across diverse pathogen populations from geographically distinct wheat production regions remains essential for resolving cryptic species complexes, detecting virulence-associated genetic variation, and establishing reliable diagnostic frameworks supporting resistance breeding initiatives and fungicide stewardship programs. This study conducted detailed morphological and molecular characterization of S. nodorum isolates recovered from wheat plants displaying characteristic Septoria nodorum blotch symptoms across surveyed production fields spanning multiple geographic regions and agro-climatic zones. Symptomatic leaf tissues were systematically collected, and fungal isolates were established through standard single-spore isolation procedures maintained on potato dextrose agar. Morphological characterization encompassed colony pigmentation and growth rate, pycnidial structure and arrangement, conidial dimensions, septation patterns, conidial mucoid appendages, and sporulating structure morphology examined under light microscopy and scanning electron microscopy at standardized magnifications. Pathogenicity of representative isolates was confirmed through spray inoculation of susceptible wheat cultivars under controlled greenhouse conditions with documented disease severity and lesion formation characteristics consistent with Koch's postulates.