Stemphylium Wallr., Flora Cryptogamica Germaniae 2: 300 (1833)


Stemphylium mainly comprises saprobes or weak plant pathogens (Woudenberg et al. 2017). However, some species are primary pathogens causing leaf blight on various crops, resulting in yield and economic losses (Hanse et al. 2015; Brahmanage et al. 2018). The asexual morph is a dematiaceous hyphomycete while the sexual morph was previously defined as Pleospora sensu stricto (Inderbitzin et al. 2009; Woudenberg et al. 2017). Rossman et al. (2015) recommended the use of Stemphylium over Pleospora which has been followed by various authors (Hongsanan et al. 2017, 2020; Wijayawardene et al. 2018, 2020). Stemphylium is one of the most important moulds human allergens in the USA (Gutiérrez-Rodríguez et al. 2011). Brahmanage et al. (2018) discussed the pathogenicity, disease severity, distribution and molecular phylogenetic affinities of pathogenic isolates of Stemphylium.

Stemphylium leaf blight caused by S. versicarum was identified as an emerging disease in New York, USA. Sharma et al. (2020b) provided two genome resources for two S. versicarum isolates from leaf blight of onion. Genomic data allows for an understanding of the population biology, fungicide resistance, as well as development of control strategies against the disease. Pathogenesis related 511 secreted proteins were predicted from S. lycopersici by Zeng et al. (2018) which helps in understanding the roles of proteins in host penetration and tissue necrosis. Stemphylium loti secretes Tenuazonic acid, inhibiting the plant plasma membrane H+-ATPase, which results in membrane potential depolarization and eventually necrosis (Bjørk et al. 2019). Su et al. (2019) fine-mapped the tomato grey spot resistance gene Sm, in a 185kb region through a map-based cloning strategy. Leach et al. (2020) identified a relationship between thrips (Thrips tabaci) and S. vesicarium in the development of Stemphylium leaf blight in onion.

Classification – Ascomycota, Pezizomycotina, Dothideomycetes, Pleosporomycetidae, Pleosporales, Pleosporaceae

Type species Stemphylium botryosum Wallr.

Distribution – worldwide

Disease symptoms – Gray spot, Stemphylium leaf blight (Leaf spot, defoliation, curling and bending of the leaf margins and stems)

             Initial symptoms of the leaves are small, irregular, brown spots. Generally, the spots gradually lighten and eventually become greyish as they become necrotic and dry. When severe, yellow spots can be seen throughout all leaves of the plant and the heavily infected leaves die (Basallote-Ureba et al. 1999, Crous et al. 2016; Brahamanage et al. 2018).

Hosts – Species are pathogenic on a wide range of hosts including Amaryllidaceae, Asparagaceae, Fabaceae, Malvaceae, Poaceae, Rosaceae and Solanaceae


Pathogen biology, disease cycle and epidemiology

Species can survive as saprobes on crop residues, soil, plant debris and on many alternative hosts and ascospores become the primary inocula in the following season. Once the disease is established during favourable conditions, conidial production in primary lesions may occur, dispersing spores to healthy plants by wind and rain splashing. Environmental factors such as temperature and moisture are key factors in disease development. Seedlings of plants can transmit the diseases if they become infected in the nursery (Basallote-Ureba et al. 1998, 1999; Boshuizen et al. 2004; Zheng et al. 2010; Blancard 2012). However, to date, diseases and epidemiology such as factors affecting the disease development, interactions with different hosts and genetics of host resistance are poorly studied (Das et al. 2019).


Morphological based identification and diversity

Species can be distinguished from other hyphomycetes in Pleosporaceae forming phaeodictyospores, based on percurrent proliferation of its conidiophores and apically swollen conidiogenous cells (Köhl et al. 2009). Simmons (1967) established criteria for morphological identification of various Stemphylium species and introduced Pleospora herbarum as the sexual morph of the type species Stemphylium botryosum. However, Simmons (1985) subsequently reclassified and reported Pleospora tarda as the sexual morph of Stemphylium botryosum and Pleospora herbarum as the sexual morph of Stemphylium herbarum (Moslemi et al. 2017). Morphological features, such as size and time of pseudothecial maturation, conidiophores and conidia and ascospore shape and size can be considered as important characteristics in species identification (Câmara et al. 2002; Fig. 1).

Köhl et al. (2009) and Woudenberg et al. (2017) pointed out that the lack of (ex-) type material of species and morphology-based species identifications without molecular evidence make it difficult in determining correct species nomenclature. Therefore, relying on morphological characters alone in identifying species is not recommended.

Fig. 1 Stemphylium sp. a. Ascomata on host b. Vertical section through an ascoma c. immature and mature asci d. Pseudoparaphyses e. Ascospores f. Ascospores in Indian ink. Scale bars: b = 50 μm, c-f = 10 μm.

Molecular based identification and diversity

ITS (rDNA) and glyceraldehyde-3-phosphate dehydrogenase (gapdh) sequences were used by Câmara et al. (2002) to confirm the monophyly of Stemphylium. In the extensive study of 110 Stemphylium strains from various hosts and DNA sequence data of ITS, gapdh and tef1 loci and the intergenic spacer between vmaA and vpsA, Inderbitzin et al. (2009) identified 23 representatives derived from type strains, while 40 strains remained unnamed. Woudenberg et al. (2017) revised the genus and accepted 28 species, synonymizing 22 names and proposing two new combinations based on combined analyses of the ITS, gapdh and cmdA gene regions. Marin-Felix et al. (2019) introduced three new species (S. rombundicum, S. truncatulae and S. waikerieanum), while Brahmanage et al. (2018) introduced S. dianthi based on multi loci phylogeny. In this study, we reconstruct the phylogeny based on combined ITS, gapdh and cmdA sequence data (Fig. 2).

Recommended genetic marker (genus level) – ITS

Recommended genetic markers (species level)cmdA, gapdh

Accepted number of species – There are 207 epithets listed in Index Fungorum, however only 32 species have DNA sequence data (Table 1).

References –Simmons 1967, Köhl et al. 2009 (morphology); Câmara et al. 2002, Inderbitzin et al. 2009, Moslemi et al. 2017, Woudenberg et al. 2017, Brahmanage et al. 2019, Marin-Felix et al. 2019 (morphology and phylogeny)


Table 1 DNA barcodes available for Stemphylium. Ex-type/ex-epitype/ex-neotype/ex-lectotype strains are in bold and marked with an asterisk (*). Voucher strains are also in bold. Species confirmed with pathogenicity studies are marked with #.

Species name Isolate/specimen no ITS gapdh cmdA
Stemphylium amaranthi CBS 124746* KU850505 KU850652 KU850793
S. armeriae CBS 338.73 KU850511 KU850658 KU850799
S. astragali # CBS 116583* KU850512 KU850659 KU850800
S. beticola# CBS 141024* KU850520 KU850667 KU850808
S. botryosum# CBS 714.68* KC584238 AF443881 KU850826
S. callistephi CBS 527.50* KU850539 KU850686 KU850828
S. canadense CBS 116602* KU850641 KU850782 KU850932
S. chrysanthemicola# CBS 117255* KU850640 KU850781 KU850931
S. dianthi MFLU 19-0556* MK500718 MK500734
S. drummondii CBS 346.83* GQ395365 KU850687 KU850829
S. eturmiunum# CBS 109845* KU850541 KU850689 KU850831
S. gracilariae CBS 482.90* KU850549 AF443883 KU850839
S. halophilum CBS 337.73* KU850553 KU850700 KU850843
S. ixeridis CBS 124748* KU850590 KU850737 KU850881
S. lancipes CBS 133314* KU850596 KU850742 KU850887
S. loti CBS 407.54* KU850597 KU850743 KU850888
S. lucomagnoense CBS 116601* KU850629 KU850770 KU850920
S. lycii CBS 125241* KU850602 KU850748 KU850893
S. lycopersici CBS 122639* KU850611 KU850756 KU850902
S. majusculum CBS 717.68* KU850618 AF443891 KU850909
S. novae-zelandiae CBS 138295* KU850631 KU850772 KU850922
S. paludiscirpi CBS 109842* KU850620 KU850762 KU850911
S. rombundicum BRIP 27486* MK336819 MK336865 MK336842
S. sarciniforme CBS 110049* KU850591 KU850738 KU850882
S. simmonsii# CBS 133518* KU850637 KU850778 KU850928
S. solani# CBS 116586* KU850627 KU850768 KU850918
S. symphyti CBS 115268* KU850643 KU850784 KU850934
S. trifolii CBS 116580* KU850647 KU850788 KU850938
S. triglochinicola CBS 718.68* KU850648 KU850789 KU850939
S. truncatulae BRIP 14850* MK336815 MK336861 MK336838
S. vesicarium# CBS 715.68* KU850565 KU850712 KU850855
S. waikerieanum VPRI 21969* MK336832 MK336878 MK336855

Fig. 2 Phylogram generated from MP analysis based on combined sequences of ITS, gapdh and cmdA sequences of all species of Stemphylium. Related sequences were obtained from GenBank. Thirty three taxa are included in the analyses, which comprise 1936 characters including gaps, of which 1355 characters are constant, 271characters are parsimony-uninformative and 310 characters parsimony-informative. The parsimony analysis of the data matrix resulted in the maximum of four equally most parsimonious trees with a length of 1112 steps (CI = 0.660, RI=0.721, RC = 0.476, HI = 0.340) in the first tree. Single gene analyses were carried out and compared with each species, to compare the topology of the tree and clade stability. The tree was rooted with Alternaria abundance (CBS 534.83). MP bootstrap support value ≥50% and BYPP ≥0.9 are shown respectively near the nodes. Ex-type strains are in bold.

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