Calonectria exiguispora N.Q. Pham, Marinc. & M.J. Wingf., 2022

Pham, Nam Q., Marincowitz, Seonju, Chen, ShuaiFei, Rodas, Carlos A. & Wingfield, Michael J., 2022, Soil-borne Calonectria (Hypocreales, Nectriaceae) associated with Eucalyptus plantations in Colombia, MycoKeys 94, pp. 17-35 : 17

Calonectria exiguispora N.Q. Pham, Marinc. & M.J. Wingf. sp. nov.

Figs 4 , 6A, B

Etymology.

“exiguus” (Latin) = small + “spora” (Latin) = spores, referring to the small macroconidia produced by this species.

Diagnosis.

Phylogenetically close to C. piauiensis and C. brassianae but differs in having smaller macroconidia.

Type.

Colombia: Risaralda, Quinchía. Soils in Eucalyptus plantation. August 2016. C.A. Rodas. (Holotype PRU(M) 4501, stored in a metabolically inactive state; ex - holotype CMW 49752 , CMW-IA 160). GenBank : OP796405 (ACT) ; OP822275 (CMDA) ; OP822382 (HIS3) ; OP822489 (RPB2) ; OP822168 (TEF1) ; OP822596 (TUB2) .

Description.

Sexual morph not observed. Conidiophores scarce on SNA, consisting of conidiogenous apparatus and stipes, branched or simple. Stipes infrequent, elongated, septate, 75-273 µm long, 2-5 µm wide near base, tapering towards apex, simple or occasionally dichotomously branched, mostly being part of conidiogenous apparatus; vesicles terminal, slightly inflate to ellipsoidal, 2-5 µm wide. Conidiogenous apparatus hyaline, simple or branched in 1-3 (-4) tiers, uncommonly developing from stipes; main axis upright, septate, 20-275 × 3-7 µm; branches doliiform to cylindrical, primary branches 8-39 × 3-7 µm, secondary branches 8-24 × 2-6 µm, tertiary branches 10-23 × 2-5 µm, quarternary branches 10-14 × 3-4 µm. Conidiogenous cells holoblastic, hyaline, discrete, cylindrical to tapered above, often constricted near base, with periclinal thickening, 8-20 × 3-5 (11.8 ± 2.71 × 3.2 ± 0.5) µm. Macroconidia hyaline, cylindrical, round at apex, 1-septate, septum sub-median or median, guttulate, 21-40 × 3-4 (30.9 ± 4.09 × 3.5 ± 0.23) µm. Chlamydospores present, scarce, in clumps or in chains. Mega - and microconidia not observed.

Colonies on 2% MEA in the dark for 6 d, white on surface, pale luteous in reverse, with moderate amount of aerial mycelium, with entire edges. Optimal growth temperature at 25 °C reaching 65.2 mm in 6 d, followed by 20 °C (57.3 mm), 15 °C (39.8 mm), 10 °C (19.7 mm), 5 °C (8.2 mm), no growth at 30 °C and 35 °C. Colonies kept at 30 °C and 35 °C being relocated to 25 °C for another 6 d revived (30 °C) and showed no growth (35 °C). Colonies on 2% MEA in the dark for 30 d, white to umber on surface, umber to dark brick in reverse, with flat mycelia.

Distribution.

Colombia.

Material examined.

Colombia: Risaralda, Quinchía. Soils in Eucalyptus sp. plantation. August 2016. C.A. Rodas. (PRU(M) 4502, stored in a metabolically inactive state; culture CMW 49753 , CMW-IA 161) .

Notes.

Calonectria exiguispora is a member of the C. candelabrum species complex ( Liu et al. 2020). It shares some characteristics with other species in the complex, such as 1-septate macroconidia and 'ellipsoidal to obpyriform’ shape vesicle. However, it can be distinguished from most species in the complex by its smaller conidial dimensions (21-40 × 3-4 µm, avg. 30.9 × 3.5 µm) except for C. brevistipitata (29-35 × 3-4 µm, avg. 31 × 3.5 µm, isolated from Mexican soil) and C. stipitate (27-37 × 3-6, avg. 32 × 4 µm, isolated from Colombian Eucalyptus sp.) ( Lombard et al. 2016). Nevertheless, these two species are distantly related to C. exiguispora (Fig. 3 ). Recently Liu et al. (2020) reduced C. stipitata to synonymy with C. spathulata , the conidial dimensions of which range from 48-100 × 4-6 µm (avg. 80 × 6 µm). They regarded the smaller conidial dimensions of C. " Calonectria stipitata " as representing intraspecific variation. Calonectria exiguispora is phylogenetically closely related to C. piauiensis and C. brassianae , which were isolated from soils associated with Eucalyptus brassiana trees in Brazil ( Alfenas et al. 2015). These two species, however, have much larger conidial dimensions: C. piauiensis (38-60 × 3-5 µm, avg. 49 × 4.5 µm) and C. brassianae (35-65 × 3-5 µm, avg. 53 × 4 µm) ( Alfenas et al. 2015). It can be differentiated from its most closely related species by sequences of ACT, CMDA, HIS3, RPB2, TEF1 and TUB2 gene regions.

Figures

Figure 3. Phylogenetic tree based on maximum likelihood (ML) analysis of a combined DNA data set of ACT, CMDA, HIS 3, RPB 2, TEF 1 and TUB 2 sequences for Calonectria spp. Bootstrap values ≥ 70 % for ML analyses and posterior probabilities values ≥ 0.90 obtained from Bayesian inference (BI) are indicated at the nodes as ML / BI. Bootstrap values <70 % or probabilities values <0.90 are marked with " * ", and nodes lacking the support values are marked with " - ". Isolates representing ex-type material are marked with " T ". Curvicladiella cignea (isolate CBS 109167 and CBS 109168) represents the outgroup.

Figure 4. Micrographs of Calonectria exiguispora sp. nov. (ex-holotype: CMW 49752 = CMW-IA 160). A conidiophores formed on SNA B stipes and vesicles C conidiogenous apparatus D chlamydospores E conidia (x 400) F conidia (x 1 000). Scale bars: 100 µm (A); 50 µm (D, E); 25 µm (C); 10 µm (B, F).

Figure 6. Culture morphology of Calonectria exiguispora (A-D) at 25 ° C and C. guahibo (E-H) at 30 ° C in the dark for 6 d (A, C, E, G) and 30 d (B, E, F, H) at its optimum temperature A, B CMW 49752 (ex-holotype) C, D CMW 49753 E, F CMW 49791 (ex-holotype) G, H CMW 49782.