Morpho-cultural and molecular characterization based on multigene phylogeny of Colletotrichum truncatum associated with leaf blight of linseed (Linum usitatissimum L.)

Abstract

Linseed, is an vital oilseed and imperative medicinal crop growing during the rabi season in the northern and mid regions of India, along with the northeastern districts of Karnataka. During the recent field surveys conducted in the 2023–24 and 2024–25 rabi seasons, characteristic leaf blight symptoms were observed with a severity ranging from 9.23 % to 23.33 %. Symptomatic leaf samples were collected and the pathogen was isolated on PDA. The colony initially appeared greyish white and later turned dark gray. The spores were generally falcate, unicellular, and hyaline. The identity of the pathogen as Colletotrichum truncatum was recognized based on the morpho-cultural observations. Further, identification was confirmed by molecular identification which was performed by amplifying and sequencing the ITS-rDNA region, along with TUB2, CAL, and GAPDH genes, using specific primers targeting the gDNA of two fungal isolates. The BLASTn analysis showed that the sequences of the ITS region, along with TUB2, CAL, and GAPDH, exhibited significant similarity with the reference sequences of C. truncatum. The multigene phylogenetic analysis performed, using the ITS-TUB2-CAL-GAPDH sequence alignment, revealed that the sequences obtained in the present study were closely aligned with respective reference sequences, thus, confirming the identity phylogenetically. Further pathogenicity tests were performed by applying the conidial suspension of C. truncatum onto the leaves of a 45-day-old linseed plant. Characteristic leaf blight symptoms developed within 8–10 days of post-inoculation, and the same pathogen was subsequently re-isolated and identified microscopically. To the best of our knowledge, this is the first report of Colletotrichum truncatum associated with leaf blight of linseed from India.