Graphilbum niveum R.L. Chang & X.Y. Zhang, 2021

Chang, Runlei, Zhang, Xiuyu, Si, Hongli, Zhao, Guoyan, Yuan, Xiaowen, Liu, Tengteng, Bose, Tanay & Dai, Meixue, 2021, Ophiostomatoid species associated with pine trees (Pinus spp.) infested by Cryphalus piceae from eastern China, including five new species, MycoKeys 83, pp. 181-208 : 181

4. Graphilbum niveum R.L. Chang & X.Y. Zhang sp. nov.

Fig. 12

Holotype.

China. Shandong province: Zhujiajuan village, Huancui District, Weihai City, from Cryphalus piceae on Pinus thunbergii , 10 Oct. 2019, R. L. Chang (HMAS 350268-holotype; SNM145 = CGMCC3.20423- ex-holotype culture).

Additional cultures checked.

China. Shandong province: Laojiangou village, Laoshan District, Qingdao City, from the gallery of Cryphalus piceae on Pinus densiflora , 2, Aug. 2020, R. L. Chang (SNM100).

Etymology.

The name refers to the white mycelia that appear on the MEA after 14 days.

Diagnosis.

Graphilbum niveum differs from the closely related species Gr. crescericum by its shorter conidiophore and conidia.

Description.

Sexual morph is unknown. Asexual state hyalorhinocladiella-like: the conidiophores directly arising from the vegetative hyphae, or produce 1-3 branches, which then branch irregularly and form conidiogenous cells at their apices, measuring (14.0-) 21.7-36.7 (-56.0) μm (Fig. 12c-e ); conidiogenous cell hyaline, discrete, measuring (6.2-)8.4-13.8 (-18.7) μm × (0.7-) 0.9-1.3 (-1.8) μm (Fig. 12c -e ); conidia hyaline, smooth, unicellular oblong to ovoid, with rounded ends, measuring (2.2-) 2.6-3.4 (-4.1) × (0.8-) 1.0-1.6 (-1.8) μm (Fig. 12b-e ).

Culture characteristics.

Colonies at first translucent to light brown in color on MEA (7 days). Thereafter, turning white in colour after 14 days (Fig. 12a ). Mycelia are partially submerged in the agar. The optimal temperature for growth is 25 °C, reaching 61.0 mm diam in 8 days. The growth is relatively slower at 5 and 35 °C, reaching 2.7 mm and 9.1 mm diam in 8 days, respectively.

Distribution.

Currently known from Qingdao and Weihai City in Shandong Province, China.

Note.

Phylogenetic analyses based on each ITS, EF, and CAL tree shows that Gr. niveum is phylogenetically close to Gr. crescericum (Figs 3 - 5 ). In the ITS tree (Fig. 3 ), Gr. niveum clustered with Gr. crescericum whereas they a distinct clade in the EF and CAL trees (Figs 4 and 5 ). In both these species, the asexual structure is hyalorhinocladiella-like. Nonetheless, the conidiophore of Gr. niveum is shorter than Gr. crescericum (14.0-56.0 vs. 16.3-69.9 μm) ( Romón et al. 2014b). Additionally, the conidia of Gr. niveum and Gr. crescericum are similar in shape, but differ in sizes. The conidia of Gr. niveum (2.2-4.1 × 0.8-1.8 µm) are substantially smaller than those of Gr. crescericum (4.4-6.2 × 1.7-3.3 μm). Furthermore, the colony color of Gr. niveum is light brown at first, whereas that of Gr. crescericum is white ( Romón et al. 2014b).

Graphilbum niveum emerged as a sister to Gr. kesiyae in the BT tree. This is because sequences for the BT gene region were unavailable for Gr. crescericum . Graphilbum kesiyae has both pesotum-like and hyalorhinocladiella-like asexual states, whereas Gr. niveum exclusively has the latter one. Furthermore, Gr. niveum 's conidiogenous cells and conidia are smaller than those of Gr. kesiyae ( Chang et al. 2017).

Figures

Figure 3. Maximum likelihood phylogeny of Graphilbum using complete ITS region. The isolates recovered in this study are highlighted in color and in bold font. ML and MP bootstrap support values ≥ 75 are indicated at the nodes as ML / MP. Bold branches indicate posterior probabilities values ≥ 0.9. T indicates ex-type cultures.

Figure 4. Maximum likelihood phylogeny of Graphilbum using partial BT and partial CAL gene regions. The isolates recovered in this study are highlighted in color and in bold font. ML and MP bootstrap support values ≥ 75 are indicated at the nodes as ML / MP. Bold branches indicate posterior probabilities values ≥ 0.9. T indicates ex-type cultures.

Figure 5. Maximum likelihood phylogeny of Graphilbum using partial EF gene region. The isolates recovered in this study are highlighted in color and in bold font. ML and MP bootstrap support values ≥ 75 are indicated at the nodes as ML / MP. Bold branches indicate posterior probabilities values ≥ 0.9. T indicates ex-type cultures.

Figure 12. Morphological characters of asexual structures of Graphilbum niveum sp. nov. a left: seven-day-old culture on MEA; right: twenty-day-old culture on MEA b Conidia c-e conidiophores and conidia. - Scale bars: 10 μm.