First Report of <i>Colletotrichum gloeosporioides</i> Causing Blight of Foxtail Palm ( <i>Wodyetia bifurcata</i> ) in India

Foxtail palm (Wodyetia bifurcata L.) is an elegant palm species native to Australia and is a member of Arecaceae family. The robust trunk and bushy leaves of foxtail palm are highly prized attributes (Farid et al., 2018). The current study is to identify the causal agent responsible for the blight disease in foxtail palms. Blight affected palm leaves showing characteristics symptoms were collected from gardens of College of Horticulture, Hiriyur, Karnataka and the symptoms appeared as circular, brown, water-soaked necrotic lesions surrounded by a chlorotic halo that then turned brown or black to give blighted appearance. The associated pathogen was isolated by standard tissue isolation technique, Petrini et al. (1992) on PDA media amended with streptomycin (40 mg L−1), incubated at 27±1 ℃ for 7-10 days. Further, single spore isolation (Chomnunti et al., 2011) was done to obtain the pure culture of the pathogen. On PDA the fungus produced cottony, dull white to salmon buff mycelium with concentric rings turning orange on maturity. Microscopic observations revealed hyaline, aseptate, cylindrical or slightly dumbell shaped conidia with rounded ends and two oil globules, measuring 35.30 - 34.00 µm * 12.70 -11.1 µm. Based on these observed characters the pathogen was identified as C. gloeosporioides. To validate Koch’s postulates, pathogenicity test was assayed by detached leaf technique using the pin prick method developed by Cao et al., (2020). The pathogenicity test confirmed blight symptoms on inoculated leaves, showing small brown spots with yellow halo after 5 days of post-inoculation (dpi), which gradually increased 15 dpi. Control leaves remained symptomless. The induced symptoms resembled those on naturally infected leaves. Furthermore, the same fungus was re-isolated and has similar characteristics of original culture. Total genomic DNA was extracted from Colletotrichum using the standard method developed by Murray et al. (1980). The obtained DNA was subjected for amplification where, the rDNA internal transcribed spacer (ITS) and Col region were amplified using ITS1/ITS4 primers along with Colletotrichum specific primers col1/col2 and amplified products were sent for sequencing (BIOKART India Pvt. Ltd, Bengaluru, Karnataka, India). The nucleotide sequences were deposited in GenBank with accession number OR029273 and OR755655 respectively. BLAST searches revealed a sequence homology of 98 % with C. gloeosporioides, confirming its identity. Phylogenetic tree constructed revealed that sequence of C. gloeosporioides showed 93% homology with other ITS sequences of C. gloeosporioides and 89% homology with other Colletotrichum sp. This analysis presented compelling evidence supporting the association of C. gloeosporioides with blight disease in foxtail palms. The emergence of C. gloeosporioides on foxtail palm may be linked to the widespread cultivation of Arecanut in the malnad regions susceptible to Colletotrichum species, this might have contributed to the shift of pathogen on foxtail palm trees. Therefore, this pathogen poses a serious threat to the ornamental value of foxtail palms, demanding prompt development of effective control strategies.