Molecular and genomic insights into the pathogenicity of Sarocladium zeae causing maize stalk rot disease

Post-flowering stalk rot (PFSR) of maize has been traditionally associated with Fusarium verticillioides. Conversely, this study reveals Sarocladium zeae as a new phytopathogen responsible for the disease. This research was conducted to gain a comprehensive understanding of S. zeae by investigating its pathogenic mechanisms, profiling its metabolome, and deciphering its genomic characteristics. Maize stalks displaying stalk rot symptoms were collected from various regions of India. S. zeae was isolated and characterized using ITS and TEF-1α sequencing. Cultures of S. zeae exhibited slower growth on PDA medium compared to F. verticillioides, which dominated due to its rapid growth rate. Pathogenicity was confirmed through a toothpick inoculation assay. The symptoms induced by S. zeae was characterized by powdery, dry, pale brown-black discoloration, were distinct from the typical dark-brown lesions of Fusarium stalk rot. Enzymatic assays revealed increased activity of β-glucosidase, cellulase, and pectate lyase in infected stalks, while qPCR analysis showed the upregulation of endoglucanase and β-glucosidase genes in infected stalks underscored the critical roles of cellulase and β-glucosidase in pathogenicity Metagenomic analysis identified S. zeae as the predominant species in infected stalk samples. Genome assembly revealed the pathogen's complete genetic repertoire, including genes encoding effector proteins and CAZymes involved in cell wall degradation. Moreover, we have demonstrated that the S. zeae as a causal agent of maize stalk rot and further shedding light on its transition from an endophytic to a pathogenic lifestyle. Taken together, this research represents the first report to attribute maize stalk rot to S. zeae and to present its complete genome assembly, significantly advancing the understanding of its biology and pathogenic potential.