Neofusicoccum cryptomeriae sp. nov. and N. parvum Cause Stem Basal Canker of Cryptomeria japonica in China

Abstract

Cryptomeria japonica D. Don is a coniferous tree species widely grown in southern China for its high ornamental value. Recently, during disease surveys in China, a symptom of dieback occurred on C. japonica in Nanjing, Jiangsu Province, China. A total of 130 trees were surveyed and more than 90% showed the same symptom. The crowns of affected trees were brown when viewing from a distance, and the bark showed no difference from the healthy ones. In this study, 157 isolates were isolated from the 3 affected plants of C. japonica, and based on the living culture on PDA, the fungal isolates were preliminarily divided into 6 groups. Thirteen representative isolates were selected for the pathogenicity test, and seven of them showed obvious pathogenicity on C. japonica, causing stem basal canker. These isolates were identified based on comparisons of the DNA sequences of the internal transcribed spacer regions (ITS), partial translation elongation factor 1-alpha (tef1), β-tubulin (tub2), and DNA-directed RNA polymerase II subunit (rpb2) and combined with their morphological characteristics. Results showed that these seven isolates belong to two taxa in Neofusicoccum, including a species new to science. The new species, Neofusicoccum cryptomeriae, was hereby described and illustrated. The other species was N. parvum. Both species were pathogens of stem basal canker of Cryptomeria japonica.

Keywords: Cryptomeria japonica; Neofusicoccum; multi-locus phylogeny; new disease.

Figure 1

Symptoms of stem basal canker disease on C. japonica in the field. (A,B) Aerial view. (C,D) Stem basal canker of C. japonica. (E–G) Lesions on the phloem of the tree trunk. (H) Lesions on the phloem of the tree root. Scale bars: (G,H) = 5 cm.

Figure 2

Symptoms caused by fungal isolates in this study 20 days after inoculation. (A) Control, G4, G11, G18, G23, G74, and C7, showing the absence of lesion development on C. japonica. G1, G2, G15, and G92, showing the lesion development on C. japonica. (B–H) Lesions produced on C. japonica by isolates (B) G1, (C) G2, (D) G15, (E) G16, (F) G24, (G) G91, and (H) G92.

Figure 3

Phylogenetic relationship of Neofusicoccum cryptomeriae and N. parvum with closely related taxa derived from a maximum likelihood (ML) analysis and Bayesian Inference using combined ITS, tef1, tub2, and rpb2 sequence alignment, with Botryosphaeria dothidea (CBS 115476) as the outgroup. Maximum likelihood bootstrap support values (ML ≥ 50) and Bayesian posterior probability (PP ≥ 0.90) are shown at the nodes (ML/PP). Ex-type strains are marked in bold, the species are delimited with colored blocks, and isolates in this study are marked in red.

Figure 4

Pairwise homoplasy index (PHI) test of Neofusicoccum cryptomeriae and closely related N. sinense, N. brasiliense, and N. kwambonambiense using both LogDet transformation and splits decomposition. PHI test results (Φ_w) < 0.05 indicate significant recombination within the dataset.

Figure 5

Morphology of Neofusicoccum cryptomeriae (G24). (A) Five-day-old front and back view culture on PDA. (B,C) Conidioma formed on pine needle culture. (D) Conidiophores, conidiogenous cells, and developing conidia. (E) Conidiogenous cells. (F) Conidia with 1 septum (indicated by arrow). (G) Conidia. Scale bars: (B,C) = 500 μm; (D–G) = 10 μm.

Figure 6

Morphology of Neofusicoccum parvum (G15). (A) Five-day-old front and back view culture on PDA. (B) Conidioma formed on pine needle culture. (C) Conidiogenous cells and developing conidia. (D) Hyaline conidia. (E) Brown, septate conidia (indicated by arrow). Scale bars: (B) = 200 μm; (C–E) = 10 μm.