Seiridium (Sporocadaceae): an important genus of plant pathogenic fungi

Abstract

The genus Seiridium includes multiple plant pathogenic fungi well-known as causal organisms of cankers on Cupressaceae. Taxonomically, the status of several species has been a topic of debate, as the phylogeny of the genus remains unresolved and authentic ex-type cultures are mostly absent. In the present study, a large collection of Seiridium cultures and specimens from the CBS and IMI collections was investigated morphologically and phylogenetically to resolve the taxonomy of the genus. These investigations included the type material of the most important Cupressaceae pathogens, Seiridium cardinale, S. cupressi and S. unicorne. We constructed a phylogeny of Seiridium based on four loci, namely the ITS rDNA region, and partial translation elongation factor 1-alpha (TEF), β-tubulin (TUB) and RNA polymerase II core subunit (RPB2). Based on these results we were able to confirm that S. unicorne and S. cupressi represent different species. In addition, five new Seiridium species were described, S. cupressi was lectotypified and epitypes were selected for S. cupressi and S. eucalypti.

Keywords: Cupressus; appendage-bearing conidia; canker pathogen; pestalotioid fungi; systematics.

Fig. 1

The best Maximum Likelihood tree (lnL = -15056.777813) from the multi-gene alignment (with the 4 loci ITS, RPB2, TUB and TEF) for the Seiridium acquired and sequenced in this study. Nodes are labelled with bootstrap values from RAxML/Bayesian posterior probabilities/Parsimony bootstrap values. Nodes receiving below 50 bootstrap values and 0.5 probability values are not labelled. Grey highlighted names indicate groups containing specimens that were part of the original description of S. cupressi (Guba 1961). Clades 2, 5, 7, 9 and 11 represent new lineages described here as the novel species Seiridium neocupressi, S. cancrinum, S. spyridicola, S. kenyanum and S. kartense. Ex-type culture, ex-epitype culture, ex-generic type culture and reference strains are denoted behind strain numbers with ^T, ^ET, ^GT and ^R, respectively.

Fig. 2

The best Maximum Likelihood trees from single-locus alignments. Nodes are labelled with bootstrap values from RAxML/Bayesian posterior probabilities/Parsimony bootstrap values. Nodes receiving below 50 bootstrap values and 0.5 probability values are not labelled. Clade numbers and colours, indicating monophyletic lineages, correspond to the combined phylogeny in Fig. 1: a. The best Maximum Likelihood tree for the ITS alignment including 616 positions (lnL = -2040.052011); b. the best Maximum Likelihood tree for the RPB2 alignment including 803 positions (lnL = -3938.132103); c. the best Maximum Likelihood tree for the TEF alignment including 634 positions (lnL = -3885.959255); d. the best Maximum Likelihood tree for the TUB alignment including 810 positions (lnL = -4789.464706).

Fig. 3

Boxplots reflecting the distribution of variance in conidial measurements in micrometres as acquired from living culture material on SNA (in white) or from herbarium material (in grey). The boxes show the first and third quartiles. Lower and upper whiskers extend from the boxes to the extreme values or 1.5 times the inter quartile range when the extreme values are outside this range, in which case outlying values are indicated by black dots. Strains are ordered by clade as in Fig. 1 and in the background coloured accordingly to the clade colours in Fig. 1: a. Conidial length; b. conidial width; c. length of basal appendage; d. length of apical appendage.

Fig. 4

Seiridium cancrinum sp. nov. (IMI 52256, holotype). a. Herbarium specimen; b. conidiogenous cells and conidia; c. conidia. — Scale bars: b–c = 10 μm.

Fig. 5

Seiridium cardinale (CBS 909.85, reference strain). a–d. Colony morphology in 90 mm Petri dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e. conidioma on PDA partially immersed in agar; f. sporodochia on SNA immersed in agar; g. conidia; h–i. conidiophores; j–k. conidiogenous cells. — Scale bars: e–f = 100 μm; g–k = 10 μm.

Fig. 6

Seiridium cardinale (IMI 75045 isotype of Coryneum cardinale). a. Herbarium specimen; b–c. conidiomata and conidia in vivo; d. conidia in vitro. — Scale bars: b–c = 20 μm; d = 10 μm.

Fig. 7

Seiridium cupressi (IMI 52254, lectotype of Cryptostictis cupressi). a. Herbarium specimen; b–c. conidiogenous cells and conidia; d. conidia. — Scale bars: b–d = 10 μm.

Fig. 8

Rhynchosphaeria cupressi (IMI 40096). a–b. Herbarium specimen; c. ascomata; d. ascoma with asci; e–j. paraphyses and asci. — Scale bars: d–j = 20 μm.

Fig. 9

Seiridium eucalypti (CBS 343.97, culture ex-epitype). a–d. Colony morphology in 90 mm dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e–g. sporodochia on SNA; h. conidia; i–j. conidiophores; k. conidiophore; l. conidiogenous cell. — Scale bars: e–g = 100 μm; h–l = 10 μm.

Fig. 10

Seiridium kartense sp. nov. (CBS 142629, culture ex-holotype). a–d. Colony morphology in 90 mm dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e. sporodochia on SNA immersed in agar; f. sporodochia on SNA erumpent from agar; g. conidia; h–i. conidiophores; j. polyblastic conidiogenesis; k. conidiogenous cell proliferating percurrently showing multiple collarettes. — Scale bars: e–f = 100 μm; g–k = 10 μm.

Fig. 11

Seiridium kenyanum (IMI 52257, holotype). a. Herbarium specimen; b–c. conidia. — Scale bars: b–c = 10 μm.

Fig. 12

Seiridium neocupressi sp. nov. (CBS 142625, culture ex-holotype). a–d. Colony morphology in 90 mm dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e. conidioma on PDA; f–g. sporodochia on SNA immersed in agar; h. conidia; i. conidiophores and paraphyses-like structures; j. microconidia (spermatia) on PDA; k–l. conidiophores. — Scale bars: e–g = 100 μm; h–l = 10 μm.

Fig. 13

Seiridium spyridicola sp. nov. (CBS 142628, culture ex-holotype). a–d. Colony morphology in 90 mm dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e–f. sporodochia on SNA immersed in agar; g. conidia; h–j. conidiophores; k. conidiogenous cell. — Scale bars: e–f = 100 μm; g–k= 10 μm.

Fig. 14

Seiridium unicorne (CBS 538.82, reference strain). a–d. Colony morphology in 90 mm dishes after 2 wk at 22 °C on PDA, CMA, MEA, SNA, respectively; e. conidioma on PDA erumpent from agar partially covered with mycelium; f–g. sporodochia on SNA erumpent from agar; h. conidia; i–j. conidiophores produced from sporodochia; k. conidiophore; l. conidiogenous cells — Scale bars: e–g = 100 μm; h–l = 10 μm.

Fig. 15

Seiridium unicorne (IMI 5816, holotype of Pestalozzia unicornis). a. Herbarium specimen; b. conidiomata and conidia in vivo; c–f. conidiogenous cells and conidia in vitro. — Scale bars: b = 20 μm; c–f = 10 μm.