Ravenelia xanthophloeae Ebinghaus, W. Maier & Begerow

Ebinghaus, Malte, Maier, Wolfgang, Wingfield, Michael J. & Begerow, Dominik, 2018, New host associations and a novel species for the gall-inducing acacia rust genus Ravenelia in South Africa, MycoKeys 43, pp. 1-21 : 9-10

Ravenelia xanthophloeae Ebinghaus, W. Maier & Begerow sp. nov. Figure 4 A–H

Type.

South Africa, KwaZulu-Natal, 29°38'21.6"S; 31°05'27.3"E, on leaves and gall-transformed inflorescences of Vachellia xanthophloea (Benth.) P.J.H. Hurter ( Fabaceae : Mimosoideae), 16 June 2012, M. Ebinghaus ME188, (holotype: PREM61213); South Africa, Mpumalanga, 25°46'52.5"S; 31°03'10.7"E, on leaves of Vachellia xanthophloea (Benth.) P.J.H. Hurter ( Fabaceae : Mimosoideae), 3 July 2012, M. Ebinghaus ME174, (paratype: PREM61215); South Africa, Mpumalanga, 25°26'10.0"S; 31°57'48.6"E, on leaves of Vachellia xanthophloea (Benth.) P.J.H. Hurter ( Fabaceae : Mimosoideae), 9 April 2013, M. Ebinghaus ME248, (paratype: PREM61000)

Etymology.

The name refers to the host tree, Vachellia xanthophloea .

Description.

Spermogonia not found. Aecia on rust-induced galls, which are formed instead of inflorescences. Aeciospores globose to sub-globose, often angular, yellowish-transparent in light microscopy, light brown when dry (19.0)21.0-24.0(28.5) × (14.5)18.0-20(21.5) μm, cell wall (1.0 –)2.0(– 3.0) μm thick, densely verrucose, germ pores numerous, scattered (Figure 4C). Peridia and peridial cells could not be described because only disintegrated aecia were present in the dried herbarium material.

Uredinia amphigenous on leaves, but mostly on the abaxial side of the leaflets, scattered or in small groups, minute, 0.1-0.2 mm, erumpent and surrounded by the torn epidermis; ellipsoidal to roundish, light-brown to blackish; paraphyses numerous, scattered within sorus; capitate, thickened end ovoidal, about 19-20 × 11-13 μm, cell wall 2-3 μm, light-brown, smooth; urediniospores ovoidal to broadly ellipsoidal or sometimes subglobose, (18)23-26(38) × (13)16-20(25) μm, spore wall evenly 1.5-2.0 μm thick with densely echinulate aculei (Figure 4D), germ pores 5-6, subequatorial to equatorial (Figure 4E).

Telia replacing the uredinia; teliospores often irregularly shaped from top view; single probasidial cells distinctly arched upwards (Figure 4 F–H), orange-brown to pale brown, teliospore surface in general smooth but with single and irregularly arranged small verrucae, (Figure 4 F–I); teliospores varying in size from (40)65-75(84) μm in diameter with mostly 4-5 probasidial cells in a cross-section, rarely 3 or 6 cells; central cells in two layers, 32-40 μm in lateral view; marginal cells in a single layer, (19)22-28(33) μm in lateral view and (12)18-25(29) μm from above; upper cellwall (2)3-4(6) μm thick; verrucose ornamentations (0.5)1-2(3) μm in height (Figure 4F, H), rarely with protuberances of up to 7 μm in height; cysts smooth and hyaline, of variable number but often appear in same number as marginal probasidial cells, swelling in water but only slightly in lactophenol, pedicels compound, not persisting.

Notes.

In South Africa, R. macowaniana , R. glabra Kalchbr. & Cooke and R. deformans (Maublanc) Dietel are the only known species that exhibit two-layered probasidial cells and smooth teliospores. While the first character is shared by R. xanthophloeae , the teliospore surface bears small and irregularly arranged small warts clearly visible in SEM (Fig. 4F). However, these can easily be overlooked in light microscopy (Fig. 4H) and could potentially lead to misidentification. Specifically, R. macowaniana differs from R. xanthophloeae in the overall size of its teliospores (Table 2; Figure 4K) and the urediniospores have four equatorial germ pores whereas those of R. xanthophloeae have five to six equatorial germ pores. The teliospores of the microcyclic R. glabra Kalchbr. & Cooke are about twice the size (120-160 μm) of those of R. xanthophloeae and its oblong urediniospores are significantly larger (32-48 × 14-21 μm). This rust has also been reported only from Calpurnia sylvatica (Burch.) E. Mey ( Fabaceae ) ( Doidge 1927). The demicyclic R. deformans (Maublanc) Dietel was synonymised with the neotropical R. hieronymi Speg. based on nearly identical morphology and congruent life cycle characteristics ( Hernandez and Hennen 2003; Hennen et al. 2005) but conspecificity of these two rust fungi is doubtful as they infect distinct host species and occur each on different continents. However, both species produce aecia that induce malformations in young branches, which is a characteristic similar to the newly described R. xanthophloeae . With a size of 60-120 µm and 75-120 µm, respectively, the teliospores of R. deformans and R. hieronymi are, however, on average significantly larger and develop intermingled with the aecia ( Doidge 1927), while R. xanthophloeae is macrocyclic and aecia, uredinia and telia are produced in spatially separated sori.

The teliospores of R. xanthophloeae may also be confused with those of R. natalensis Syd., P. Syd & Pole-Evans, but they are significantly smaller in size (30-50 μm diam.) and possess extraordinarily long and persistent pedicels (up to 110 μm; Sydow 1912, Fig. 4I). In R. natalensis , the aparaphysate uredinia and telia are confluent and cover large areas on the branches of the host ( Sydow and Sydow 1912; own observations), while the specimens of R. xanthophloeae examined in this study have minute uredinia with numerous paraphyses and telia not exceeding 200 μm in diameter.

New host records.

Morphological and molecular phylogenetic analyses based on nrITS and nrLSU data confirmed new host records for R. macowaniana and R. evansii that will be reported in the following section. An emended species decription for R. evansii is also provided.