Melampsora salicis-michelsonii C. M. Tian & L. L. Wang, 2020

Wang, Li-Li, Li, Ke-Mei, Liu, Yun & Tian, Cheng-Ming, 2020, Melampsora salicis-michelsonii sp. nov. on Salix michelsonii and Melampsora salicis-cavaleriei on Salix serrulatifolia from China, Phytotaxa 435 (4), pp. 280-292 : 284-290

Melampsora salicis-michelsonii C. M. Tian & L. L. Wang , sp. nov. FIGURE 2

MycoBank no.:—MB 834617

Diagnosis:— Melampsora salicis-michelsonii differs from the known Melampsora species on Salix in having uredinia and telia amphigenous usually grouped, and the paraphyses with thickened apex.

Type:— CHINA. Xinjiang Uygur Autonomous Region:Altay Prefecture, Jimuai County, II, III on Salix michelsonii Goerz ex Nasarow , 6 August 2013, coll. L.L. Wang, Y, Yu & H. Wang (Holotype: HMAAC4039).

Etymology:—Named after the host species, Salix michelsonii , of the type specimen.

Spermogonia and aecia unknown. Uredinia amphigenous to mainly hypophyllous, yellow, grouped, 0.1–0.8 mm ( Figs. 2A, 2B, 2C ). Urediniospores globoid to ellipsoid, 15–22 × 13–17 μm, wall 1.8–2.5 μm thick ( Fig. 2D ), echinulate spines 1.47–1.91 μm apart ( Fig. 2I ), 3–6 germ pores, scattered ( Fig. 2E ). Paraphyses capitate, clavate occasionally, intermixed with urediniospores ( Fig. 2H ), 37–77 × 11–22 μm, with thickened apical wall up to 6.5 μm sometimes ( Fig. 2F ). Telia amphigenous to mainly epiphyllous, 0.1–0.4 mm, scattered or aggregated, reddish brown. Subepidermal teliospores 29–46 × 8–16 μm, with evenly thickened wall 1 μm ( Fig. 2G ).

Other specimens examined:— CHINA, Xinjiang Uygur Autonomous Region: Altay Prefecture, Jimuai County, II, III on S. michelsonii , 6 August 2013, coll. L.L. Wang, Y, Yu & H. Wang (HMAAC4040, 4041).

Host/distribution:—Leaves of S. michelsonii from China.

Notes:—The habitat was special and the specimens were collected in an arid and less rainy desert areas. The host plant, S. michelsonii , is a kind of psammophyte shrub, which has not been reported to be infected by any rust fungus previously. Melampsora salicis-michelsonii was distinguishable on the basis of phylogenetic analysis ( Fig. 1 ) and morphological characteristics ( Table 2). Phylogenetically, it was distinct from other Melampsora species in clustering in a well-supported clade ( Fig. 1 ), and morphologically, different from its close species, M. arctica , M. iranica , M. ribesii-purpureae and M. salicis-purpureae in paraphyses, teliospores and the colonized position of uredinia and telia. The host plant, S. michelsonii is new for the genus Melampsora .

Specimens on S. serrulatifolia

(1) Results of morphological observation and phylogenetic analysis

Specimens on S. serrulatifolia (HMAAC4043, 4044) had yellow-orange uredinia on adaxial leaf surface, scattered ( Fig. 3B ). The urediniospores were ellipsoid to clavate, sometimes pyriform, with scattered germ pores and evenly echinulate spines on the surface. The capitate paraphyses were intermixed with urediniospores in the uredinia ( Figs. 3D–3F, 3H, 3I ). The telia, brown spots on the leaves, were epiphyllous and scattered or aggregated. The teliospores were subepidermal and did not have apparently thickened apical walls ( Fig. 3G ).

The phylogenetic tree indicated that the samples on S. serrulatifolia (HMAAC4043, 4044) clustered in a distinct clade with high support values of 96/0.98 (ML/BI).

(2) Reasons of species identification

In previous study, Melampsora salicis-cavaleriei on S. cavaleriei H. Lév was the sole Melampsora taxon on Salix that had epiphyllous uredinia and telia to date ( Tai 1979, Zhao 2013b). In this study, the rust fungus on Salix serrulatifolia (HMAAC4043, 4044) had epiphyllous uredinia and telia, corresponding with the previous descriptions of M. salicis-cavaleriei ( Tai 1979, Zhao 2013b) ( Table 3). Phylogenetically, due to absence of ITS and LSU reference sequences of M. salicis-cavaleriei in GenBank, it couldn’t prove the relation between the examined specimens and M. salicis-cavaleriei . However, the phylogenetic tree indicated that the two examined specimens were distinct from the rest Melampsora species in a distinct clade with high support values ( Fig. 1 ). Hence, the rust fungus on S. serrulatifolia was identified as M. salicis-cavaleriei .

(3) Description of species

Figures

FIGURE 1. Phylogram of combined genes of rDNA ITS and LSU based on ML and Bayesian analysis. Melampsora laricis-populina was used as outgroup. Type specimens are indicated by (T).

FIGURE 2. Morphology of Melampsora salicis-michelsonii (HMAAC4039, holotype). A: Habit of sori on leaves. B: Telia (T) and Uredinia (U) on the epiphyllous surface.C: Telia (T) and Uredinia (U) on the hypophyllous surface.D:Globoid and ellipsoid urediniospores observed by LM. E: Scattered germ pores on the urediniospores (red arrows). F: Capitate paraphyses with evenly thickened apex. G: Subepidermal teliospores without thickened apical wall.H: Uredinia observed by SEM, abundant intermixed paraphyses. I: Urediniospores with echinulate spines observed by SEM. Bars: B, C = 1 mm; D−G = 10 μm; H = 20 μm; I = 5 μm.

FIGURE 3. Morphology of Melampsora salicis-cavaleriei (HMAAC4043).A: Habit of sori on leaves. B: Uredinia (U) on the epiphyllous surface. C: Telia (T) on the epiphyllous surface. D: Obovoid and ellipsoid urediniospores observed by LM. E: Scattered germ pores on the urediniospores (red arrows). F: Capitate paraphyses with evenly thickened apex. G: Subepidermal teliospores without thickened apical wall. H: Uredinia observed by SEM, abundant intermixed paraphyses. I: Urediniospores with echinulate spines observed by SEM. Bars: B, C = 1 mm; D−G = 10 μm; H = 50 μm; I = 2 μm.