Cytospora azadirachtae Mahadevak., Josna & Maharachch., 2024

Cytospora azadirachtae Mahadevak., Josna & Maharachch. sp. nov. FIGURE 2 View FIGURE 2 & 3 View FIGURE 3

MycoBank no.: MB 849769

Etymology: azadirachtae (Lat.) : named to represent the host genus ( Azadirachta ) from which it was obtained.

Pathogenic on the neem twigs (associated with dieback symptoms) of Azadirachta indica ( Meliaceae ). Asexual morph: Conidiomata pycnidial (4−7 mm), immersed in host tissue, solitary, erumpent, aggregated with white to yellow conidial mass. Conidiophores hyaline, unbranched or occasionally branched at the bases, formed from the innermost layer of the pycnidial wall, embedded in a gelatinous layer. Conidiogenous cells cylindrical to clavate, straight, (5.4–)6.2–8.5(–8.9) × (1.0–)1.4–1.5(–1.9) µm, enteroblastic, phialidic, subcylindrical to cylindrical, tapering towards apices. Conidia (4.2–)4.5–5.2(–5.7) × (1.0–)1.2–1.5(–1.7) µm, hyaline, unicellular, elongate-allantoid, guttulate, smooth, thin-walled. Sexual morph: Undetermined.

Cultural characteristics: Colonies on PDA medium reaching 70 mm diam in 7 days at 28°C. The surface is dense, flat, fluffy mycelium with a uniform texture, whitish to pale, while the reverse is yellowish to pale and becomes buff towards the centre. Conidiomata pycnidial, solitary or aggregated, half-immersed, pale brown to dark brown or black.

Material examined: INDIA, Karnataka, Mysuru, Doddamaragowdanahalli, Mysore, on infected twigs of Azadirachta indica ( Meliaceae ), 15 April 2022, S. Mahadevakumar & M. Mahesh (holotype, KFRI-MH 1532), extype KFRIMCC1532.

Notes: —Considering a MegaBLAST search of NCBI’s GenBank nucleotide database, the nearest hits using the ITS sequence of Cytospora heveae ( MFLUCC 17-0358, GenBank OL 780505; Identities = 546/580 (94%), 13 gaps (2%)), C. pingbianensis (strain MFLUCC:18-1204, GenBank MK 912135, Identities = 540/571 (95%), 15 gaps (2%)), C. thailandica (strain MFLUCC:17-0262, GenBank MG 975776, Identities = 527/555 (95%)), eight gaps (1%), C. pavettae ( CBS 145562, GenBank MK 876386, Identities = 533/568 (94%), 18 gaps (3%)), and C. brevispora ( CBS 116811, GenBank KY 051786, Identities = 510/539 (95%), 15 gaps (2%)). The tub2 gene sequence shared the highest similarity to Cytospora phitsanuloensis (strain MFLUCC 21-0046, GenBank MZ 451172; Identities = 423/429 (98.6 %) three gaps (0 %)), C. tamaricicola (strain CFCC 50508, GenBank MH 933588; Identities = 396/450 (88.22 %) ten gaps (2 %)), C. platycladi (strain CFCC 50504, GenBank MH 933581; Identities = 392/448 (87.50 %) 11 gaps (2 %)), C. pavettae (culture CBS:145562, GenBank MK 876503; Identities = 362/419 (86.40 %) 12 gaps (2 %)), C. shoreae (strain MFLUCC 21-0047, GenBank MZ 451170; Identities = 373/442 (84 %) 14 gaps (3 %)), and C. chiangmaiensis (strain MFLUCC 21-0049, GenBank MZ 451169; Identities = 332/398 (83 %) 17 gaps (2 %)).

Further, the tef -1α gene sequence had the highest similarity to Cytospora platycladi (strain CFCC 50504, GenBank MH 933516; Identities = 515/608 (84.7 %), 28 gaps (4 %)), C. tamaricicola (strain CFCC 50508, GenBank MH 933523; Identities = 505/603 (83.7 %), 36 gaps (5 %)), C. pavettae (culture CBS:145562, GenBank MK 876497; Identities = 465/553 (84.09 %), 21 gaps (3 %)), C. phitsanulokensis (isolate MFLUCC 21-0046, GenBank MZ 451164; Identities = 269/315 (96.2 %), six gaps (3 %)), and. C. haidianensis (strain CFCC 54057 T, GenBank MT 363998; Identities = 271/319 (84.93 %), 12 gaps (3 %)). Cytospora azadirachtae is isolated for the first time from neem tree twigs and is showing dieback symptoms. The symptoms include necrotic lesions on the necrotic twigs, under the bark and dieback.

Considering the phylogenetic analysis, C. azadirachtae is closely related to C. shoreae ( MFLUCC 21-0049). They can be distinguished on ITS, tub 2 and tef -1α sequence data and have a distinct conidial shape. Cytospora rhizophorae differ from C. azadirachtae because they have shorter conidia and condiogenous cells. Further, C. rhizophorae is halotolerant, saprobic and shows host-specificity usually associated with Rhizophora sp. ( R. mangle and R. mucronata ). Similarly, C. shoreae differs from C. azadirachtae in larger flask-shaped conidiomata and larger conidia. Morphologically, the shape of the conidia closely resembles that of C. hippophaicola , but the sequence didn’t share any relatedness. Further, however, C. azadirachtae is distinct among all the known Cytospora species in having curved conidia with guttules. Based on multi-locus sequence and phylogenetic analysis, the canker and dieback disease symptoms, the present collection has been introduced as a new species.