High Diversity of Cytospora Associated With Canker and Dieback of Rosaceae in China, With 10 New Species Described

Abstract

Cytospora canker is a destructive disease of numerous hosts and causes serious economic losses with a worldwide distribution. Identification of Cytospora species is difficult due to insufficient phylogenetic understanding and overlapped morphological characteristics. In this study, we provide an assessment of 23 Cytospora spp., which covered nine genera of Rosaceae, and focus on 13 species associated with symptomatic branch or twig canker and dieback disease in China. Through morphological observation and multilocus phylogeny of internal transcribed spacer (ITS), large nuclear ribosomal RNA subunit (LSU), actin (act), RNA polymerase II subunit (rpb2), translation elongation factor 1-α (tef1-α), and beta-tubulin (tub2) gene regions, the results indicate 13 distinct lineages with high branch support. These include 10 new Cytospora species, i.e., C. cinnamomea, C. cotoneastricola, C. mali-spectabilis, C. ochracea, C. olivacea, C. pruni-mume, C. rosicola, C. sorbina, C. tibetensis, and C. xinjiangensis and three known taxa including Cytospora erumpens, C. leucostoma, and C. parasitica. This study provides an initial understanding of the taxonomy of Cytospora associated with canker and dieback disease of Rosaceae in China.

Keywords: 10 new taxa; Cytosporaceae; Diaporthales; phylogeny; taxonomy.

FIGURE 1

Disease symptoms associated with Cytospora species. (A,B) Rosa sp. (C) Prunus serrulata. (D,E) Spiraea salicifolia.

FIGURE 2

Disease symptoms associated with Cytospora species on Malus sp. (A) Death of the apple trees caused by Cytospora in the orchards. (B,C) Conidiomata on a naturally infected stem in the field.

FIGURE 3

Phylogram of Cytospora based on combined internal transcribed spacer (ITS), large nuclear ribosomal RNA subunit (LSU), actin (act), RNA polymerase II subunit (rpb2), translation elongation factor 1-α (tef1-α), and beta-tubulin (tub2) genes. Maximum parsimony (MP) and maximum likelihood (ML) bootstrap support values above 70% are shown at the first and second positions. Thickened branches represent posterior probabilities above 0.95 from Bayesian inference (BI). Ex-type strains are in bold. Strains in current study are in blue. All the Cytospora species listed from Rosaceae plants in China are marked with *.

FIGURE 4

Morphology of Cytospora cinnamomea from Prunus armeniaca (CF 20197654). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on potato dextrose agar (PDA) for 2 weeks. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 5

Morphology of Cytospora cotoneastricola from Cotoneaster sp. (CF 20197031). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. Bars: (B–D) = 500 μm; (E,F) = 10 μm.

FIGURE 6

Morphology of Cytospora mali-spectabilis from Malus spectabilis ‘Royalty’ (CF 20197665). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E,F) = 10 μm.

FIGURE 7

Morphology of Cytospora ochracea from Cotoneaster sp. (CF 20197684). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E,F) = 10 μm.

FIGURE 8

Morphology of Cytospora olivacea from Sorbus tianschanica (CF 20197670). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 9

Morphology of Cytospora parasitica from Malus pumila (CF 20197714). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 10

Morphology of Cytospora pruni-mume from Prunus mume (CF 20197515). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 11

Morphology of Cytospora rosicola from Rosa sp. (CF 20197024). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 12

Morphology of Cytospora sorbina from Sorbus tianschanica (CF 20197660). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F,G) Conidia. Bars: (B–D) = 500 μm; (E) = 10 μm; (F,G) = 5 μm.

FIGURE 13

Morphology of Cytospora tibetensis from Cotoneaster sp. (CF 20197032). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.

FIGURE 14

Morphology of Cytospora xinjiangensis from Rosa sp. (CF 20197520). (A,B) Habit of conidiomata on twig. (C) Transverse section of conidioma. (D) Longitudinal section through conidioma. (E) Conidiophores and conidiogenous cells. (F) Conidia. (G) Colonies on PDA for 2 weeks. Bars: (B–D) = 500 μm; (E) = 10 μm; (F) = 5 μm.