19 Sep Venturia
Venturia Sacc., Syll. fung. (Abellini) 1: 586 (1882)
The genus Venturia was introduced by Saccardo (1882), for V. inaequalis (Cooke) G. Winter. Most of the species in this genus are notable plant pathogens, e.g. apple scab (V. inaequalis), pear scab (V. pyrina Aderh.), poplar shoot blight (V. populina (Vuill.) Fabric.), and stone fruit scab or freckle (V. carpophil E.E. Fisher). The taxonomic concept of Venturia was adopted by Sivanesan (1977). Molecular evidence indicated that Venturia is a genus within Venturiales, Dothideomycetes (Zhang et al. 2011; Hyde et al. 2013).
Classification – Dothideomycetes, Pleosporomycetidae, Venturiales, Venturiaceae
Type species – Venturia inaequalis (Cooke) G. Winter, in Thümen, Mycoth. Univ., cent. 3: no. 261 (1875)
Distribution – Worldwide
Disease Symptoms – Leaf blight/spot, Scab
Symptoms are more noticeable on leaves and fruits. Nearly circular, velvety, olive-green spots on both sides of the leaves appear in early spring. The spots eventually turn dark green to brown and the leaves will turn yellow and fall. Lesions on the leaves and fruit are “scabby” in appearance, with a distinct margin. The earliest noticeable symptom on fruit is water-soaked areas which develop into velvety, green to olive-brown lesions (Vaillancourt and Hartman 2000).
Hosts – broad host range including genera Acer, Achilea, Alchemilla, Allium, Alnus, Betula, Epilobium, Malus, Pandanus, Persea, Pinus, Populus, Prunus, Quercus and Salix (Farr and Rossman 2018).
Morphological based identification and diversity
Species of Venturia are parasitic or endophytic on leaves, bark and wood, immersed and becoming erumpent, black, globose ascomata, with papillate, ostiolate, bitunicate, oblong to obclavate asci, with or without short and thick pedicel, with an ocular chamber, uniseriate, ellipsoidal, broadly rounded ends, hyaline to pale brown, 1-septate ascospores, with upper cell shorter than the lower one (Wu et al. 2011; Hyde et al. 2013). The asexual morph of this genus was found as two genera, Pollaccia E. Bald. & Cif. and Spilocaea Fr. (Barr 1968; Sivanesan 1984; Crous et al. 2007). Seifert and Gams (2011) synonymized Spilocaea under Fusicladium Bonord., however, Zhang et al. (2011) indicated that the type species of Spilocaea (S. pomi Fr.) is the asexual morph of Venturia based on molecular analyses. Therefore, Spilocaea was synonymized under Venturia based on the number of its epithets being higher than Spilocaea (Index Fungorum 2018). Currently, about 180 species are listed in Index Fungorum (2018), but many of them lack clear description and illustration. There ais little sequence data for Venturia available in GenBank when compared with the number of species listed in Index Fungorum (2018). Fresh collections and molecular data are needed to clarify relationships between species (Zhang et al. 2011; Hyde et al. 2013).
The species are distinguished by hosts, disease symptoms, the morphology of ascomata, number of ascospores in the ascus, and shape and colour of ascospores. However, most species have unclear descriptions. Thus, it is difficult to compare unknown/newly collected Venturia species with described species. Molecular analysis is an important method for identifying species in Venturia, but not many species have such data.
Molecular based identification and diversity
Sequence data has been provided from both sexual and asexual morphs (Crous et al. 2007; Zhang et al. 2011). In phylogenetic trees, Venturia was placed in a monophyletic clade of Venturiaceae, which is a sister group to Symphoventuriaceae (Zhang et al. 2011; Hyde et al. 2013). It is closely related to Microthyriales with Phaeotrichaceae as a sister clade (Schoch et al. 2009; Wu et al. 2011; Hyde et al. 2013, Liu et al. 2017). We update the phylogenetic relationship of Venturia species by analysing the concatenated alignment of SSU, LSU and ITS sequence data. Based on this phylogenetic tree, the placement of species within this genus are not different from previous studies. Only a few species are confidently identified and established due to little sequence data from Venturia species available in GenBank.
Recommended genetic markers (genus level) – LSU, SSU
Recommended genetic markers (species level) – ITS
Accepted number of species: There are 276 species epithets in Index Fungorum (2018) under this genus. However, only around 20 species are confirmed by sequence data (Hyde et al. 2013; Ibrahim et al. 2016; Zhang et al. 2016).
References: Crous et al. 2007, Zhang et al. 2011 (morphology, phylogeny), Carisse et al. 2010 (life cycle and disease management), Machouart et al. 2014 (Phylogeny), Zhang et al. 2016 (Phylogeny)
Table Venturia. Details of the isolates used in the phylogenetic analyses. Ex-type (ex-epitype) strains are in bold and marked with an * and voucher strains are in bold
|Sympoventuria capensis||CPC 12840||DQ885904||DQ885904||–||–||–||–|
|V. anemones||CBS 370.55||EU035447||EU035447||KF853965||–||KF808264||–|
|V. atriseda||CBS 371.55||EU035448||EU035448||–||–||–||–|
|V. aucupariae||CBS 363.35||EU035450||EU035450|
|V. catenospora||BJFU 140822-1||KU220966||KU220964||–||–||–||–|
|V. catenospora||CBS 447.91||EU035427||EU035427||KF853957||–||KF808256||–|
|V. chinensis||BJFU 140826-17||KP689595||KP689596||–||–||–||–|
|V. chlorospora||CBS 470.61||EU035454||EU035454||–||–||–||–|
|V. chlorospora||CBS 466.61||EU035453||EU035453||–||–||–||–|
|V. ditricha||CBS 118894||EU035456||EU035456||KF853970||–||KF808270||–|
|V. fuliginosa||BJFU 140827.14||KU220967||KU220965||–||–||–||–|
|V. helvetica||CBS 474.61||EU035458||EU035458||KF853974||–||KF808274||–|
|V. inaequalis||CBS 309.31||EU035437||EU035437||–||–||–||–|
|V. inaequalis||CBS 476.61||GU456336||EU282478||GU456288||–||–||–|
|V. inopina||MYA 2852||–||AY177406||–||–||–||–|
|V. lonicerae||CBS 445.54||EU035461||EU035461||–||–||–||–|
|V. macularis||CBS 477.61||EU035462||EU035462||KF853977||–||KF808277||–|
|V. martianoffianum||BJFC 150828_1||KU985140||KU985131|
|V. minuta||CBS 478.61||EU035464||EU035464||KF853980||–||KF808280||–|
|V. phaeosepta||BJFC 140520_1||KU985142||KU985133|
|V. populina||CBS 256.38||GU323212||EU035467||–||–||–||GU296206|
|V. saliciperda||CBS 480.61||EU035471||EU035471||–||–||–|
|V. tremulae||CBS 112625||EU035438||EU035438||–||–||–|
|V. tremulae var. tremulae||CBS 257.38||EU035475||EU035475||–||–||–||–|
|V. viennotii||CBS 690.85||EU035476||EU035476||–||–||–||–|
Fig. Phylogenetic tree generated by maximum likelihood analysis of combined ITS and LSU sequence data of Venturia species. Sequences were obtained from GenBank. Thirty-two strains are included in the analyses, which comprise 1380 characters including gaps. Single gene analyses were carried out to compare the topology of the tree and clade stability. The tree was rooted with Sympoventuria capensis (CPC 12840). Tree topology of the Bayesian analysis was similar to the RAxML. The best scoring RAxML tree with a final likelihood value of -4376.419190 is presented. The matrix had 261 distinct alignment patterns, with 15.44% of undetermined characters or gaps. Estimated base frequencies were as follows; A = 0.237094, C = 0.259593, G = 0.296334, T = 0.206979; substitution rates AC = 1.996953, AG = 2.270150, AT = 1.867221, CG = 0.763559, CT = 10.363584, GT = 1.000000; gamma distribution shape parameter α = 0.419710. RAxML and Bayesian posterior probabilities value ≥70% (BT) and 0.9 (PP) are shown respectively near the nodes. The scale bar indicates 0.2 changes. The ex-type strains are in bold.