Taxonomy, Host Associations, and Life Cycles of Four Rust Fungi Associated with Prunus spp. in Korea

Abstract

Rust fungi associated with Prunus spp. in Korea have been reported under different genera, yet their taxonomy, host associations, and life cycles have remained insufficiently clarified. In this study, rust specimens collected from Prunus species and their putative alternate hosts were examined using morphological observations and molecular phylogenetic analyses based on internal transcribed spacer (ITS) and large subunit (LSU) rDNA sequences. Four species belonging to three genera were identified: Blastospora makinoi, Blastospora radiata, Leucotelium semiaquilegiae, and Tranzschelia discolor. Blastospora radiata and L. semiaquilegiae are newly recorded in Korea. In addition, Prunus salicina and Semiaquilegia adoxoides are reported for the first time in Korea as hosts of rust fungi. Field investigations combined with sequence data clarified the heteroecious life cycles of Blastospora and Leucotelium species in Korea, confirming host alternation between Prunus spp. and alternate hosts including Se. adoxoides and Smilax spp. Historical records of rust fungi on Prunus in South Korea were taxonomically reassessed in light of these results. The congruence between molecular phylogenies and morphological characteristics provides an updated taxonomic framework for rust fungi associated with economically important Prunus species.

1. Introduction

The genus Prunus L. (Rosaceae) includes economically important fruit crops, such as almond, apricot, cherry, peach, plum, as well as numerous ornamental and wild species widely distributed in temperate regions. The fruits of Prunus are drupes with a single hard-coated seed and contain polyphenols, which significantly relax blood vessels and improve endothelial function [1,2]. Especially, peach (Prunus persica (L.) Batsch) is rich in phenolics, carotenoids, and vitamins and is widely consumed worldwide [3]. Although global peach and nectarine production reached 27.1 million metric tons in 2023 [4], production has declined in many countries since 2013 [5]. Fungal diseases are major factors affecting peach cultivation. Rust disease on Prunus spp. may cause premature defoliation and reduce fruit quality and yield, thereby affecting agricultural production and ornamental value [6]. Despite their economic importance, the taxonomy, diversity, and life cycles of rust fungi associated with Prunus remain unresolved in many countries, including Korea.

Rust fungi (Pucciniales) include about 7000 species and represent the largest group of plant-pathogenic Basidiomycota [7]. They are characterized by complex life cycles that may produce up to five spore stages [8]. Many species are heteroecious, alternating between unrelated host plants, which complicates their identification based solely on morphology and host association. Reliable species identification therefore requires an integrated approach combining morphology, host association, and molecular phylogenetic data.

In East Asia, rust fungi associated with Prunus have been placed in several genera, including Caeoma Link, Blastospora Dietel, Leucotelium Tranzschel, and Tranzschelia Arthur [9,10]. Species of Blastospora alternate between Prunus (aecial host) and Smilax L. (telial host) [11–13], whereas Leucotelium species typically alternate between Ranunculaceae (aecial host) and Prunus (telial host) [14,15]. Tranzschelia discolor (Fuckel) Tranzschel & M.A. Litv. has been widely reported on Anemone L. (aecial host) and Prunus (telial host) worldwide [16], but in some (sub)tropical countries, it has been suggested to overwinter without an alternate host [17,18]. Recent molecular studies have clarified generic concepts and nomenclature of Prunus-associated rust fungi [13,19], but regional confirmations using DNA sequence data remain limited.

In Korea, rust fungi on Prunus have been recorded under three different genera, Blastospora, Caeoma, and Tranzschelia [10]. However, their host–fungus associations remain unclarified, and some Prunus hosts (e.g., P. mume (Siebold) Siebold & Zucc.) have been attributed to different rust taxa [13]. In addition, Prunus salicina Lindl. and Semiaquilegia adoxoides (DC.) Makino have not been documented previously in Korea as hosts of rust fungi. These issues highlight the need for an updated taxonomic account based on integrative evidence.

The present study aims to clarify the taxonomy and diversity of rust fungi associated with Prunus spp., to document previously unreported rust species and host plants, and to complete their life cycles in South Korea through integrating field observations with morphological and molecular phylogenetic analyses based on the internal transcribed spacer (ITS) and large subunit (LSU) rDNA sequences.

2. Materials and methods

2.1. Collection of rust samples

Rust-infected samples of Prunus spp. were collected at various sites in Korea between 1994 and 2026. As several rust fungi associated with Prunus are known to be heteroecious, field surveys also targeted potential alternate hosts, including Smilax spp. (Smilacaceae) and Se. adoxoides (Ranunculaceae), growing near infected Prunus trees. All collected samples were air-dried and preserved as herbarium specimens. A total of 25 specimens were deposited in the Kunsan National University Herbarium (KSNUH) and the Korea University Herbarium (KUS-F). Detailed information on host plant, locality, year of collection, and GenBank accession numbers is provided in Table 1.

Table 1.

Information on rust samples used in this study.

Rust species	Host	Herbarium no.	DNA no.	Geographic origin	Year	GenBank no.
						ITS/LSU
Blastospora makinoi	Smilax sieboldii var. inermis	KUS-F30338	PR23	Gimcheon	2017	PZ296738/PZ296760
Blastospora radiata	Prunus sp.	KUS-F12797	PR12	Chuncheon	1994	PZ296729/PZ296750
B. radiata	Smilax nipponica	KUS-F16243	PR17	Gangneung	1999	–/PZ296754
B. radiata	Sm. nipponica	KUS-F17752	PR18	Gangneung	2000	PZ296733/PZ296755
B. radiata	Sm. nipponica	KUS-F19685	PR19	Pyeongchang	2003	PZ296734/PZ296756
B. radiata	Sm. nipponica	KUS-F24623	PR20	Goesan	2009	PZ296735/PZ296757
B. radiata	Sm. nipponica	KUS-F24745	PR21	Yangpyeong	2009	PZ296736/PZ296758
B. radiata	Sm. nipponica	KUS-F25313	PR22	Yangpyeong	2010	PZ296737/PZ296759
B. radiata	Sm. nipponica	KUS-F32364	PR24	Yangpyeong	2021	PZ296739/PZ296761
B. radiata	Sm. nipponica	KSNUH2824	PR30	Sangju	2023	PZ451477/PZ440650
B. radiata	Sm. nipponica	KSNUH2825	PR31	Gimcheon	2025	PZ451478/PZ440651
Leucotelium semiaquilegiae	Semiaquilegia adoxoides	KSNUH00075	PR01	Seogwipo	2017	PZ296719/PZ296740
L. semiaquilegiae	Se. adoxoides	KSNUH00089	PR02	Seogwipo	2017	PZ296720/PZ296741
L. semiaquilegiae	Se. adoxoides	KUS-F30879	PR03	Naju	2019	PZ296721/PZ296742
L. semiaquilegiae	Se. adoxoides	KUS-F32737	PR04	Buan	2022	PZ296722/PZ296743
L. semiaquilegiae	Se. adoxoides	KSNUH2241	PR14	Buan	2024	PZ296730/PZ296751
L. semiaquilegiae	Se. adoxoides	KSNUH2242	PR15	Buan	2024	PZ296731/PZ296752
L. semiaquilegiae	Se. adoxoides	KSNUH2243	PR16	Jangseong	2024	PZ296732/PZ296753
L. semiaquilegiae	Se. adoxoides	KSNUH2723	PR29	Jeju	2026	PZ451476/PZ440649
L. semiaquilegiae	Prunus persica	KUS-F29421	PR08	Jeju	2016	PZ296726/PZ296747
L. semiaquilegiae	Prunus salicina	KUS-F22133	PR10	Chuncheon	2006	PZ296727/PZ296748
L. semiaquilegiae	P. salicina	KUS-F30984	PR11	Chuncheon	2019	PZ296728/PZ296749
Tranzschelia discolor	P. persica	KUS-F30220	PR05	Jeju	2017	PZ296723/PZ296744
T. discolor	P. persica	KUS-F30251	PR06	Jeju	2017	PZ296724/PZ296745
T. discolor	P. persica	KUS-F30409	PR07	Jeju	2017	PZ296725/PZ296746

2.2. Morphological analysis

Symptoms and sori were examined under a stereomicroscope (M205C; Leica, Wetzlar, Germany) equipped with a digital camera (Dhyana 400DC; Tucsen, Fuzhou, China). For observation of spermogonia and internal tissue structures, cryosections were prepared using a cryostat (CM1860; Leica). Small pieces of infected leaf tissue were placed on specimen disks and embedded in frozen section compound. After freezing at low temperature, the specimens were mounted onto the specimen holder and sectioned at a thickness of 50 µm. Sections were mounted on glass slides and examined under a differential interference contrast (DIC) microscope (Axio Imager 2 + Axiocam 512 color; Carl Zeiss, Oberkochen, Germany). For morphological observation, sori (aecia, uredinia, and telia) and spores (aeciospores, urediniospores, and teliospores) were mounted in lactic acid on glass slides, gently heated, and examined using a DIC microscope. Measurements of at least 30 structures per structure type (sori and spores) were taken to determine size ranges and averages. Surface ornamentation of rust structures was examined with a scanning electron microscope (SEM; S-4800 + EDS; Hitachi, Tokyo, Japan). Samples were mounted on aluminum stubs, sputter-coated with platinum, and observed at 3–5 kV.

2.3. Molecular phylogenetic analysis

Genomic DNA was extracted from rust-infected leaves using the MagListo 5 M Plant Genomic DNA Extraction Kit (Bioneer, Daejeon, Korea). The ITS region was amplified using the primer set ITS5u/ITS4rust [20,21], and LSU was amplified using LRust1R/LRust3 [21]. For some specimens, the primer pair Rust2inv/LR6 was additionally used to obtain longer LSU fragments [22,23]. PCR products were purified with the AccuPrep^® PCR/Gel Purification Kit (Bioneer) and bidirectionally sequenced by a DNA sequencing service (Macrogen, Seoul, Korea). Sequences were assembled and edited using DNASTAR Lasergene v7.1 (DNASTAR Inc., Madison, USA) and aligned with reference sequences retrieved from GenBank (NCBI). Phylogenetic trees were constructed with the maximum likelihood (ML) method based on the Tamura 3-parameter model in MEGA 7 [24]. The robustness of phylogenetic relationships was evaluated by bootstrap analysis with 1000 replicates.

3. Results

3.1. Molecular phylogenetic analysis

ML phylogenetic analyses based on ITS and LSU rDNA sequences produced congruent tree topologies and consistently resolved three well-supported genera comprising four species associated with Prunus spp. in Korea: Blastospora, Leucotelium, and Tranzschelia (Figures 1 and 2). All major clades received high bootstrap support values (above 87%) in both phylogenetic trees, although there were weak supports (60–70%) for two Blastospora species.

Figure 1.

Maximum likelihood tree of Prunus-associated rust species based on the ITS rDNA sequences. Bootstrap values higher than 60% are given above branches. The Korean specimens are shown in bold.

Figure 2.

Maximum likelihood tree of Prunus-associated rust species based on the larger subunit rDNA sequences. Bootstrap values higher than 60% are given above branches. The Korean specimens are shown in bold.

The Blastospora clade comprised two species-level lineages corresponding to Blastospora makinoi (Kusano) Jing X. Ji, Okane & Kakish. and Blastospora radiata (Shirai) Jing X. Ji, Okane & Kakish. Korean specimens grouped with reference sequences of both species from Japan and China. The sequences of B. makinoi exhibited five nucleotide differences (ITS: 4, LSU: 1) from B. radiata. Among B. radiata samples, the sequences from Japan and Korea exhibited two nucleotide variations in ITS and one in LSU. Leucotelium semiaquilegiae (Dietel) Kakish., K. Hosaka & Hosoya formed a monophyletic clade, including Korean samples from Se. adoxoides, P. persica, and P. salicina, together with a Japanese Prunus sample. Korean specimens identified as T. discolor clustered within a globally distributed clade containing sequences from Brazil, China, Iran, New Zealand, Oman, Taiwan, and the USA, originating from various Prunus species.

3.2. Morphology

Morphological characteristics observed in Korean specimens supported the recognition of three genera: Blastospora, Leucotelium, and Tranzschelia (Figures 3–6). Species of Blastospora produced yellow aecia on Prunus, with uredinia and telia on Smilax. Aeciospores were ornamented, urediniospores globose to subglobose and echinulate, and teliospores one-celled with thin, smooth walls. B. makinoi was characterized by verrucose aeciospores and rounded telia, whereas B. radiata showed completely echinulate urediniospores and telia distinctly confined by leaf veins.

Figure 3.

Blastospora makinoi on Prunus mume and Smilax sieboldii var. inermis. (A) Symptoms of flower bud on P. mume. (B–D) Field symptoms on Sm. sieboldii var. inermis. (E,F) Aecia under a SEM. (G) Telia on the leaf surface. (H–J) Aeciospores under a DIC microscopy (H) and SEM (I,J). (K,L) Urediniospores under a DIC microscope (K) and SEM (L). (M,N) Teliospores under a DIC microscope (M) and SEM (N).

Figure 4.

Blastospora radiata on Prunus sp. and Smilax nipponica. (A) Dried infected leaf on Prunus sp. (B) Close-up of aecia on the lower surface. (C) Aecium under a SEM. (D) Field symptoms on Sm. nipponica. (E–G) Aeciospores under a DIC microscope (E) and SEM (F,G). (H) Uredinia and urediniospores under SEM. (I) Telia on the leaf surface. (J) Teliospores under SEM. (K,L) Urediniospores under a DIC microscopy (K) and SEM (L). (M,N) Teliospores under a DIC microscopy (M) and SEM (N).

Figure 5.

Leucotelium semiaquilegiae on Semiaquilegia adoxoides, Prunus persica, and P. salicina. (A–C) Field symptoms of leaves on Se. adoxoides. (D) Close-up of aecia on the leaf surface. (E) Aecium under DIC microscopy. (F) Aecium under a SEM. (G–I) Aeciospores under a DIC microscope (G,H) and SEM (I). (J,K) Uredinial symptoms on P. persica. (L) Uredinia under SEM on P. persica. (M–O) Uredinial symptoms on P. salicina. (P–R) Urediniospores under a DIC microscope (P,Q). and SEM (R).

Figure 6.

Tranzschelia discolor on Prunus persica. (A,B) Symptoms appeared on the lower leaf surface. (C,D) Close-up of uredinia. (E) Uredinium under a SEM. (F–H) Urediniospores under a DIC microscope (F,G) and SEM (H).

Leucotelium semiaquilegiae was distinguished by hypophyllous, aecidium-type aecia. Aeciospores were verrucose and subglobose to oblong, and uredinia produced reddish brown, echinulate urediniospores. However, in T. discolor, uredinia were only hypophyllous, and urediniospores were ellipsoid to obovoid, echinulate, with the apex nearly smooth. Detailed measurements are provided in the Taxonomy section.

3.3. Host associations and life cycles

Field surveys combined with ITS and LSU sequence data enabled documentation of heteroecious life cycles in three species (Figure 7). In Blastospora, Prunus spp. served as the aecial host and Smilax spp. served as the telial host. For B. makinoi, specimens collected from P. mume and Sm. sieboldii var. inermis Nakai were placed within the same phylogenetic clade, supporting host alternation between these species. Similarly, B. radiata appears to complete its life cycle between Prunus sp. and Sm. nipponica Miq., with specimens from both hosts forming a single clade in the phylogenetic analyses.

Figure 7.

Life cycles of four rust species (Blastospora makinoi, B. radiata, Leucotelium semiaquilegiae, and Tranzschelia discolor) associated with Prunus spp. and their alternate hosts in South Korea.

Leucotelium semiaquilegiae was documented on Se. adoxoides and P. persica and P. salicina. Specimens from these hosts clustered together in a well-supported monophyletic clade, supporting a heteroecious life cycle alternating between Ranunculaceae and Prunus. In Korea, only the uredinial stage of T. discolor was observed on P. persica, and neither telia nor alternate hosts were discovered. The heteroecious life cycles of Blastospora and Leucotelium species are confirmed here for the first time in Korea.

4. Taxonomy

Blastospora makinoi (Kusano) Jing X. Ji, Okane & Kakish., Mycologia 115 (4): 566 (2023) [MB 846304] (Figure 3).

Description: Aecia densely covering flower buds, yellow, compact, and conspicuous. Aeciospores verrucose, ovoid to ellipsoid. Urediniospores of the uredo-type, globose, (20.7–)24.5–28.9(–31.8) × (19.6–)22.7–27.1(–29.4) μm (av. 26.7 × 24.9 μm), with a colorless, echinulate wall, of 1.39–1.81 μm thick. Telia hypophyllous, powdery, often covering nearly the entire leaf surface, yellowish orange to orange. Teliospores 1-celled, oblong to ovoid, subglobose to ellipsoid, (46.9–)50.0–55.3(–58.3) × (34.3–)36.8–41.5(–44.7) μm (av. 52.7 × 39.1 μm), with a thin, smooth wall.

Host plants in Korea: Spermogonia and aecia on Prunus mume (Rosaceae); uredinia and telia on Smilax sieboldii var. inermis (Smilacaceae).

Note: Two species of Blastospora, B. makinoi and B. radiata, have been reported on Prunus spp. from East Asia [9]. Ono [12] noted that the two species are distinguishable by spore ornamentation and soral configuration: B. radiata has completely echinulate urediniospores, aciculate aeciospores, and telia distinctly confined by leaf veins, whereas B. makinoi shows verrucose aeciospores and round-shaped telia [11,12,25]. The Korean specimens from P. mume and Sm. sieboldii var. inermis match B. makinoi in having verrucose aeciospores and rounded telia. Their ITS/LSU sequences place them within the B. makinoi clade. However, the ventrally smooth area on urediniospores reported in some descriptions [11] was not clearly observed in the present study. In Korea, this species has previously been reported as Caeoma makinoi Kusano on P. armeniaca L. [10,26]. and P. mume [27], but the telial host had not been reported (Table 2). Therefore, the heteroecious life cycle alternating between P. mume and Sm. sieboldii var. inermis is confirmed here based on field observations and ITS and LSU phylogeny. Global host plants of B. makinoi are summarized in Table 3.

Table 2.

Identification of rust fungi affecting Prunus species and alternate host plants in Korea.

Host plants	Previous study [reference]	Present study
Prunus sp.	–	Blastospora radiata
P. armeniaca	Caeoma makinoi [10,26]	–
P. japonica var. nakaii	Tranzschelia pruni-spinosae [30] (now, a synonym of T. discolor)	–
P. mume	C. makinoi [27]	B. makinoi
P. mume	T. japonica [10,34]	–
P. persica	–	Leucotelium semiaquilegiae
P. persica	T. discolor [31]	T. discolor
P. salicina	–	L. semiaquilegiae
Semiaquilegia adoxoides	–	L. semiaquilegiae
Smilax china	Puccinia caricis-blepharicarpae [10,35]	–
Sm. china	P. citrina [36]	–
Sm. nipponica	Blastospora itoana [28]	B. radiata
Sm. sieboldii	P. smilacis-sempervirentis [36]	–
Sm. sieboldii var. inermis	–	B. makinoi

Table 3.

Global host plants and distribution of four rust fungi (Blastospora makinoi, B. radiata, Leucotelium semiaquilegiae, and Tranzschelia discolor) examined in this study.

Rust species	Host plant	Distribution [reference]
Blastospora radiata
=B. itoana	Prunus grayana	Japan [37]
	P. jamasakura	Japan [37]
	P. maximowiczii	Japan [38]
	P. mume	Japan [38]
	P. sargentii	Japan [38]
	*P. donarium var. sachalinensis (=P. sargentii)	Japan [38]
	*P. pseudocerasus (=P. sargentii)	Japan [38]
	Smilax aspera	Nepal [39]
	Sm. cocculoides	China [40]
	Sm. discotis	China [41]
	*Sm. glaucophylla (=Sm. elegans)	Nepal [39]
	Sm. herbacea	Japan [38]
	Sm. maximowiczii	USSR [42]
	Sm. menispermoidea	China [41], Himalaya [43], Japan [38], Taiwan [44]
	Sm. Nipponica	Japan [45], Korea [28]
	*Sm. herbacea var. japonica (=Sm. nipponica)	Japan [38]
	Sm. oldhamii	Japan [37]
	*Sm. menispermoidea var. randaiensis (=Sm. pygmaea)	Taiwan [44]
	Sm. randaiensis	China [46], Taiwan [47]
	Sm. sieboldii	Japan [38]
	Sm. stans	China [48]
=Caeoma radiatum	P. conradinae	China [46]
	P. grayana	Japan [12]
	*P. serrulata var. spontanea (=P. jamasakura)	Japan [45]
Blastospora makinoi
=B. smilacis	P. armeniaca	Japan [37]
	P. mume	Japan [37]
	P. tomentosa	China [48]
	Sm. sieboldii	Japan [23,37]
=C. makinoi	P. armeniaca	Korea [10,26]
	*P. ansu (=P. armeniaca)	Japan [45]
	P. cerasus	China [46]
	P. grayana	Japan [45]
	P. mandshurica	China [46]
	P. mume	China [46], Japan [45]
	P. tomentosa	China [46]
Leucotelium semiaquilegiae
=L. pruni-persicae	Aquilegia pubiflora	Pakistan [29]
	P. amygdalus	Pakistan [29]
	P. mume	Japan [14,45]
	P. persica	China [46], Japan [14,45]
	Pulsatilla chinensis	China [46]
	Se. adoxoides	China [41]
	*Aq. adoxoides (=Se. adoxoides)	Japan [14,37]
=Puccinia pruni-persicae	P. persica	Taiwan [49]
=Sorataea pruni-persicae	P. mume	Japan [38]
	P. persica	Japan [38], Taiwan [50]
Tranzschelia discolor
=P. discolor	Anemone coronaria	United States [51]
=T. discolor	An. blanda	Greece [52]
	*An. apennina subsp. blanda (=An. blanda)	Bulgaria
	An. coronaria	Bulgaria [53], Canada [54], Greece [16,52], Israel [55], New Zealand [56,57], Spain [58], Turkey [59], United Kingdom [60], United States [61]
	An. hortensis	Greece [52]
	*An. fulgens (=An. hortensis)	United Kingdom [60], United States [62]
	*An. pavonina (=An. hortensis)	Bulgaria [53], Greece [52]
	Anemone sp.	Canada [62], Norway [63]
	Chrysobalanus icaco	United States [64]
	P. americana	Argentina [65], Brazil [66], New Zealand [67], Turkey [68], United Kingdom [60], United States [69]
	P. amygdalus	Australia [70], South Africa [71], Spain [58], United States [61], Uruguay [72]
	*Amygdalus communis (=P. amygdalus)	Algeria [73], Bulgaria [53], Israel [55], Ukraine [74]
	*P. dulcis (=P. amygdalus)	Australia [75], Greece [52], Iran [76], New Zealand [56,57], South Africa [77], United States [51,78]
	P. andersonii	United States [62]
	P. angustifolia	United States [69]
	P. armeniaca	Argentina [62,72], Australia [79], Brazil [62], Bulgaria [80], Chile [81], China [46], Denmark [82], Ecuador [62], Greece [52], Israel [55], Mexico [83], New Zealand [56,57], Norway [63], South Africa [71], Spain [58], United States [78]
	*Armeniaca vulgaris (=P. armeniaca)	Algeria [73], Bulgaria [53], Czech Republic [84]
	P. avium	Australia [75], Bulgaria [80], New Zealand [56,57], United States [62,85]
	*Cerasus avium (=P. avium)	Bulgaria [53]
	P. buergeriana	Japan [38,86]
	P. cerasifera	Australia [75], Bulgaria [53], Czech Republic [84], Israel [55], New Zealand [56,57], United States [87]
	*P. divaricate (=P. cerasifera)	Turkey [68]
	*P. pissardii (=P. cerasifera)	Argentina [72]
	P. cerasus	Brazil [66], Bulgaria [80], Israel [55], United States [87]
	*Ce. vulgaris (=P. cerasus)	Bulgaria [53]
	P. davidiana	United States [61]
	P. domestica	Argentina [65,72], Australia [79], Azores [86], Belgium [88], Brazil [66], Bulgaria [53], Canada [54], Chile [81], Czech Republic [84], Denmark [82], Germany [89], Iran [23], Israel [55], Madeira Islands [86], New Zealand [56,57], Spain [86,90], United Kingdom [60], United States [61], USSR [42]
	*Ce. erythrocarpa (=P. erythrocarpa)	Israel [55]
	P. fasciculata	United States [62]
	P. fenzliana	United States [62]
	P. hortulana	United States [61]
	P. insititia	Algeria [73], Czech Republic [84], Germany [82], Norway [91]
	*P. domestica subsp. insititia (=P. insititia)	Bulgaria [53], United Kingdom [60]
	*P. domestica subsp. Italica (=P. insititia)	Belgium [88]
	P. japonica	Korea [30]
	P. mahaleb	Greece [52], United States [87]
	*Ce. mahaleb (=P. mahaleb)	Bulgaria [53]
	P. mexicana	United States [61]
	P. munsoniana	United States [69]
	P. persica	Argentina [62,72], Australia [79,92], Azores [86], Brazil [93,94], Bulgaria [80], Cape Verde [95], Chile [81], China [46,96], Colombia [97,98], Costa Rica [99], Denmark [82], Greece [100], Israel [55], Japan [37], Korea [31], Madeira Islands [101], Mexico [83,102], New Zealand [56,57], Norway [63], Oman [103], Pakistan [104], Panama [105], South Africa [71], Spain [86,90], Taiwan [44], United Kingdom [60], United States [106], Vietnam [107]
	*Am. persica (=P. persica)	Colombia [98]
	*Persica vulgaris (=P. persica)	Bulgaria [53], Iran [108]
	P. pumila	United States [61]
	P. salicina	Australia [79], China [46], Japan [37], New Zealand [56,57], South Africa [71], United States [51]
	*P. communis (=Prunus sp.)	Spain [109], United States [62]
	P. spinosa	Bulgaria [53], Turkey [68]
	P. subcordata	United States [51]
	*P. communis var. tangutica (=P. tangutica)	United States [62]
	P. tenella	Denmark [82], Norway [63]
	*Am. nana (=P. tenella)	Czech Republic
	P. triloba	Denmark [82], Norway [63]
	P. virginiana	United States [110]
=T. pruni-spinosae var. discolor	P. americana	Brazil [111]
	P. cerasifera	Turkey [112]
	P. cerasus	Brazil [111]
	P. domestica	Brazil [94]
	P. persica	Brazil [111], Hong Kong [113]

*Synonyms; accepted names are given in parentheses.

Blastospora radiata (Shirai) Jing X. Ji, Okane & Kakish., Mycologia 115 (4): 566 (2023) [MB 846305] (Figure 4).

Description: Aecia densely clustered, yellow, epiphyllous. Aeciospores echinulate, subglobose to broadly ellipsoid, sometimes obovoid, (21.3–)23.0–26.9(–29.7) × (16.7–)19.6–24.7(–29.7) μm (av. 25.0 × 22.2 μm). Urediniospores globose, echinulate, (21.4–)23.3–25.8(–26.9) × (20.7–)22.5–24.9(–26.1) μm (av. 24.5 × 23.7 μm), with a hyaline wall of 1.45–1.85 μm thick. Telia hypophyllous, vein-limited, scattered, angular to irregular, powdery, yellow to yellowish orange. Teliospores 1-celled, subglobose to obovoid, (38.8–)44.8–54.0(–61.0) × (28.4–)38.1–45.7(–49.0) μm (av. 49.4 × 41.9 μm), with a thin, smooth wall.

Host plants in Korea: Spermogonia and aecia on Prunus sp. (Rosaceae); uredinia and telia on Smilax nipponica (Smilacaceae).

Note: The Korean specimens exhibited echinulate aeciospores and more distinctively echinulate urediniospores, and vein-limited telia. These morphological characteristics were consistent with previous descriptions of B. radiata [12]. Previously, Blastospora itoana Togashi & Onuma was described as the teleomorph of Caeoma radiatum Shirai and was later treated as a synonym of B. radiata [12,13]. Prunus spp. and Smilax spp. have been recorded as its hosts in China, Japan, Nepal, Taiwan, the Himalaya, and USSR [9] (Table 3). Previously, B. itoana was reported on Sm. nipponica in Korea [28], but the record remained uncertain due to the lack of detailed description and no preserved specimen. The present study provides voucher-based morphology and ITS and LSU sequence data, supporting the occurrence of B. radiata in Korea and documents its heteroecious life cycle between Prunus sp. and Sm. nipponica.

Leucotelium semiaquilegiae (Dietel) Kakish., K. Hosaka & Hosoya, Bull. Natl. Sci. Mus., Tokyo, B. 49 (4): 138 (2023) [MB 849095] (Figure 5).

Description: Aecia aecidium-type, hypophyllous, peridiate, cupulate, yellowish orange to reddish brown, 91–132 μm in diameter (av. 109.8 μm). Aeciospores verrucose, subglobose to oblong, (16.4–)17.6–19.0(–19.5) × (15.4–)15.9–17.5(–19.1) μm (av. 18.3 × 16.7 μm), with a colorless wall. Uredinia hypophyllous, scattered or densely clustered, cinnamon brown. Urediniospores of the uredo-type, reddish brown to light brown, echinulate, obovoid, (18.5–)20.3–24.8(–27.3) × (15.1–)16.4–18.3(–19.1) μm (av. 22.6 × 17.4 μm).

Host plants in Korea: Spermogonia and aecia on Semiaquilegia adoxoides (Ranunculaceae); uredinia and telia on Prunus persica and P. salicina (Rosaceae).

Note: The Korean specimens produced aeciospores of 18–19 × 16–18 μm and urediniospores of 20–25 × 16–18 μm. Urediniospore measurements are consistent with the previous ones of L. semiaquilegiae [14,29], whereas the aeciospores are slightly smaller than those previously reported (19–24 × 15–20 μm) recorded in Pakistan [29]. This species has been recorded on P. persica and Se. adoxoides in East Asia [9], with additional host records summarized in Table 3. This is the first study reporting L. semiaquilegiae in Korea, and Se. adoxoides and P. salicina are newly documented hosts of rust fungi in Korea. The heteroecious life cycle alternating between Se. adoxoides (aecial host) and P. persica and P. salicina (telial host) is confirmed based on field survey, morphological and molecular evidence.

Tranzschelia discolor (Fuckel) Tranzschel & M.A. Litv., J. Bot. (Desvaux): 248 (1939) [MB 251863] (Figure 6).

Description: Uredinia hypophyllous, densely clustered, cinnamon to reddish brown. Urediniospores echinulate, orange brown to light brown, ellipsoid to obovoid, (26.4–)27.2–33.8(–39.3) × (13.3–)14.3–16.4(–17.5) μm (av. 30.5 × 15.4 μm).

Host plants in Korea: Uredinia on Prunus persica (Rosaceae).

Note: T. discolor has been reported on P. japonica var. nakaii (H.Lév.) Rehder [30] and P. persica in Korea [31]. The Korean specimens examined here agree morphologically with published descriptions [31–33] and are placed within the global T. discolor clade in ITS and LSU trees. No alternate hosts were detected during either previous studies or the present study in Korea. Anemone spp. which are distributed in Korea and have been reported as alternate host plants of this species in several countries (Table 3), were also investigated. However, no evidence of an association with T. discolor was found in Korea.

5. Discussion

Rust fungi associated with Prunus in Korea have been recorded in limited taxonomic accounts (Table 2), and most previous identifications were based primarily on morphology and host association [10,26,27,30,31,34]. Given the morphological similarities of rust taxa and the complexity of heteroecious life cycles, such records require verification using molecular data. In the present study, ITS and LSU phylogenies were combined with detailed morphological observations and host data to clarify the taxonomic status of four rust species associated with Prunus in Korea.

The taxonomic history of these fungi reflects long-standing difficulties in rust classification. Aecidium semiaquilegiae Dietel was originally described as the anamorph of Leucotelium pruni-persicae (Hori) Tranzschel and later treated as L. semiaquilegiae [14,19]. Likewise, as Caeoma makinoi was demonstrated to present the aecial stage of Blastospora smilacis Dietel, the name B. makinoi was formally adopted under the Shenzhen Code [11,13]. Recent molecular studies in Japan and China have clarified generic boundaries within these rust fungi and the distinct host-alternation systems of Blastospora and Leucotelium [11,12,14]. The Korean specimens examined in this study are well congruent with those East Asian lineages.

As many rust fungi require two unrelated hosts to complete their life cycles, understanding these cycles is essential for assessing risk and epidemiology, particularly in economically important crops [7,8]. The present study confirms host alternation in Blastospora and Leucotelium species, strengthening the biological interpretation of these rust systems in temperate fruit trees. Recent integrated studies in East Asia have indicated the value of combining molecular phylogenetics and field data to resolve rust life cycles in woody crops. For example, the heteroecious cycle of Nyssopsora cedrelae (Hori) Tranzschel alternating on Aralia elata (Miq.) Seem., an economically important tree species, and Toona sinensis (Juss.) M. Roem. was clarified using multilocus sequence analyses and pathogenicity assay [114].

For T. discolor, Anemone spp. have been reported as alternate hosts in several regions outside East Asia (Table 3) [9]. Ellison et al. [17] showed that urediniospores of T. discolor can overwinter on infected leaf litter and infect Prunus spp. the following spring in New South Wales, Australia, and the species has been suggested to overwinter as mycelia in twig infections, forming twig cankers that serve as sources of urediniospores in California, USA [18]. Given that neither the present study nor previous observation [31] detected telia on infected leaves [31] in South Korea and that this species was only found on the southern island of South Korea, a similar overwintering mechanism may contribute to the survival of this species without any alternate host in Korea.

The distribution of alternate hosts represents a key ecological determinant of heteroecious rust fungi, because shifts in alternate host distribution may influence the establishment, persistence, and spread. Climate change can further shape rust epidemiology by altering temperature regimes, precipitation patterns, host phenology, and the distribution ranges of alternate hosts [7]. In Korea, ecological modeling has demonstrated that northward expansion of Corydalis incisa (Thunb.) Pers. under climate change is associated with increased risk of rust disease on Wisteria floribunda (Willd.) DC., an economically important ornamental vine [115]. Similarly, Se. adoxoides, an aecial host of L. semiaquilegiae in Japan [14] and Korea, is recognized as a climate-sensitive biological indicator species [116], and its recent expansion in Korea [117] provides ecological context for the occurrence of L. semiaquilegiae on Prunus cultivations. More broadly, increasing incidence of subtropical rust pathogens such as Puccinia polysora Underw. in the Korean Peninsula further illustrates how environmental change may facilitate the establishment and persistence of rust fungi beyond their previously recognized distribution ranges [118]. These climate-driven shifts in alternate host distribution may therefore influence the long-term dynamics of heteroecious rust fungi associated with Prunus in Korea.

The present study refines the taxonomy of rust fungi infecting Prunus in Korea through integrated morphological and molecular evidence and documents their host associations. It clarifies species boundaries and heteroecious life cycles, providing a systematic foundation for future ecological, epidemiological, and phytosanitary research under ongoing climate and environmental change.

Funding Statement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2026-25486323) and the Animal and Plant Quarantine Agency (I-1543086-2025-28-01 and Z-1543086-2025-28-01), Korea.

Disclosure statement

No potential conflict of interest was reported by the authors.