Morpho-Molecular Characterization and Technique for Induction of Growth, Sporulation in Cercospora longipes Causing...

A significant outbreak of brown spot disease caused by Cercospora longipes E. J. Butler has recently been observed in sugarcane growing regions of India. Cercosporoid fungi grow slowly and sporulate sparsely, making their isolation challenging. In vitro studies were conducted to standardize the isolation technique and optimize the media and culture conditions for growth and sporulation. The causal organism was isolated from brown spot-infected leaves. After 14 days of incubation on PDA, the mycelium exhibited a light yellow-green coloration with dark brown-greenish-black pigmentation. The phylogenetic analysis of ITS region, 18S rRNA, actin, and β-tubulin genes, revealed that Cercospora IISRBCCBP01 isolate form distinct branch, from closely related C. nicotianae, C. kikuchi and C. armoraciae. The morphological characteristics also support this finding, and thus, it was identified as Cercospora longipes. Pathogenicity tests were conducted based on Koch's postulates. Among the fourteen-host plant extract agar media tested, highest growth and conidial production was observed on 25% fresh leaf (FL) + 20% V8 agar media, at a temperature of 25 ℃ and a slightly acidic pH. Continuous light or dark photoperiods induced higher sporulation and growth than alternating light periods. These findings provide a reliable method for isolation and cultivation of this pathogen, while also offering foundational molecular data for future investigations.