Alternaria longiformis N. Bessadat & P. Simoneau, 2025

Alternaria longiformis N. Bessadat & P. Simoneau sp. nov.

Fig. 5 View Figure 5

Etymology.

Name refers to conidial shape and size, which is longer than other species within the section Embellisioides .

Type.

Algeria • Mostaganem, Hassi Mamache on infected leaves of Solanum lycopersicum . 22 May, 2015, N. Bessadat, ( INH 001055 About INH , holotype), preserved in a metabolically inactive state via deep freezing at INH herbarium, France, using the COMIC technical platform, ex-type culture ( CBS 149901 View Materials , NB 354) .

Description.

On PCA, attaining 69 mm diam., colony wooly, loose, with aerial branched subhyaline hyphae and 2–3 pairs of moderately defined concentric rings of growth and sporulation. During an initial 5–7 d of growth, colony producing only minor sporulation near the agar surface. At the same time, abundant, long, suberected aerial hyphae arising throughout light-deprived parts of the colony. The tip and some branches of these slender aerial axes enlarging into well-defined conidiophores with few lateral branches, mostly near the hyphal apex, from a simple and short conidiophore bear 2–4 conidia (Fig. 5 A, B View Figure 5 ), yielding to an open layer of sporulation in the surface of the colony. Sporulation pattern forming compact, small clumps of conidia. Conidiophores septate, simple or sparingly branched, straight to slightly curved, pale to medium brown, with series of 2–6 (– 14), geniculate, sympodial conidiogenous sites. Primary conidiophores of short length, 15–20 × 4–7 µm, cylindrical, 0–3 - septate, produced from fertile hyphae, commonly becoming 35–80 (– 170) µm long with 4–9 transverse septa. Each conidiophore bearing a single conidium, rarely a chain of 2 conidia in undisturbed young colonies. Conidiogenous cells terminal or intercalary, solitary or proliferating sympodially (Fig. 5 B View Figure 5 ). Seldom production of secondary conidiophores from primary conidia forming short 5–23 (– 41) × 3.5–7.5 µm, 0–3 - septate, cylindrical or angular complexity structure at the apex leading to false conidia chains upon the aging parts of the colony. Mature conidia with 4–7 transverse septa, 31–60 × 10–18 µm, oblong, ellipsoid, or subcylindrical, broadly rounded at the base with a bluntly rounded apical cell (Fig. 5 C, D View Figure 5 ). Conidia at full development tapering gradually from narrowly ovoid into narrowly cylindrical, 56–90 (– 100) × 12.5–17 µm, always rounded at base tapering towards apex with 8–11 (– 15) transverse septa (Fig. 5 E View Figure 5 ). A few submedian cells increasing in width and producing thin longitudinal and oblique septa. Abundant juvenile conidia, 5–20 × 2.5–12.5 µm, spherical to ovoid at the center of the colony at 14 d, formed through extension of secondary conidiophores and usually 1–2 - celled. Fully developed conidia mostly equilateral until enlargement of a few body cells and their secondary internal septation cells introducing minor degree of curvature. Conidia slightly, to distinctly constricting at their 1–3 transverse septa, contrastingly darker than others. One to two longitudinal septa very pale inserted in 1–3 first transverse segments. Conidia color pale to medium yellow, appearing quite smooth, thin-walled due to a lack of ornamentation on the surface. Conidium germination after 24 h usually bipolar but not conspicuous from a non-polar cell. Conidiophores emerging from the surface of dead infected plants brown, scattered, with 1–3 (– 6) conidiogenous loci, 25–67 (– 100) µm long and 3.8–6 (– 7.5) μm thick (Fig. 5 F View Figure 5 ). Most conidia with 8–10 (– 11) transverse septa, 44–55 (– 59) × 8–10 µm.

Culture characteristics after 7 days — Colonies color and aspect the holotype strain on PDA (Fig. 5 G View Figure 5 ), PCA (Fig. 5 H View Figure 5 ), MEA (Fig. 5 I View Figure 5 ), and OA (Fig. 5 J View Figure 5 ) are provided in Table 2 View Table 2 . This strain grows over a wide range of temperatures with varying growth rates. Among the different temperature and culture media, the best mycelial growth occurs between 20–25 ° C on PDA. On all media, the strain grows slowly below 4 ° C, moderately at 16 ° C and 30 ° C, rapidly between 20–25 ° C, and does not grow well at a temperature of 35 ° C. Mycelial growth was inhibited at 40 ° C.

Additional isolate examined.

Algeria • Mascara City, Tizi province , from leaves of Daucus carota . 21 December, 2020, N. Bessadat, ( CBS 149905 View Materials , preserved in a metabolically inactive state in the Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands). Living culture NB 930 .

Notes.

Phylogenetic analyses indicated that Alternaria longiformis sp. nov. fell in an individual branch close to A. lolii (ex-type, CBS 115266 ). Between this species and A. lolii , there were 4 / 464 differences in ITS, 3 / 529 in gpd, 15 / 833 in rpb 2, and 8 / 199 in tef 1. Isolates of Alternaria longiformis sp. nov. are morphologically similar to A. lolii ( Bessadat et al. 2021) . Conidia of both species are quite similar in shape but different in size (Table 3 View Table 3 ), and primary conidiophores are geniculate but slightly different in size (25–150 × 3–5 in A. lolii and 35–170 × 4–7 μm in A. longiformis ). These two species can be distinguished mainly by their sporulation patterns, the presence / absence of cellular knots, and the abundance of secondary conidiophores. Alternaria lolii was reported to produce distinctive submerged knots of hyphal cells and emergent rhizoidal branches ( Simmons 2004). This species produces rarely chlamydospores (Table 3 View Table 3 ). None of these structures were observed on the two A. longiformis sp. nov. isolates. Further, branching through secondary conidiophores is conspicuous in A. lolii , which is not in A. longiformis sp. nov. Other species belonging to the same section, such as A. proteae , A. novae – zelandiae, and A. hyacinthi , form multi-geniculate conidiophores ( Hoog and Muller 1973; Simmons 1990) and shorter conidia compared to A. longiformis sp. nov. (Table 3 View Table 3 ). Alternaria planifunda and A. tumida were reported to produce conspicuous chlamydospores and smaller, solitary conidia ( Simmons 1983), making them distinct from the new species (20–28 × 10–13 and 35–42 × 13–18 vs. 40–97 × 10–25, respectively).