Alternaria alternata, the Causal Agent of a New Needle Blight Disease on Pinus bungeana.

Pinus bungeana, an endangered and native coniferous tree species in China, has considerable timber and horticulture value. However, little is known about needle diseases in P. bungeana. A needle blight of P. bungeana has been observed in Hebei Province, China. P. bungeana inoculated with mycelial plugs of fungal isolates presented symptoms similar to those observed under field conditions. Ten virulent fungal isolates were identified as a small-spored Alternaria species based on morphological observations. Maximum likelihood and Bayesian phylogenetic analyses carried out with multilocus sequence typing of eight regions (SSU, LSU, ITS, gapdh, tef1, Alt a 1, endoPG, OPA10-2) assigned the pathogen to Alternaria alternata. This is the first report of A. alternata causing needle blight on P. bungeana in China.

Cyclocarya paliurus Reprograms the Flavonoid Biosynthesis Pathway Against Colletotrichum fructicola.

Cyclocarya paliurus is an endemic Chinese tree species with considerable medicinal, timber, and horticultural value. The anthracnose disease of C. paliurus is caused by the fungal pathogen Colletotrichum fructicola, which results in great losses in yield and quality. Here, resistance evaluation of six cultivars of C. paliurus exhibited varying degrees of resistance to C. fructicola infection, where Wufeng was the most resistant and Jinggangshan was the most susceptive. Physiological measurements and histochemical staining assays showed that the Wufeng cultivar exhibits intense reactive oxygen species accumulation and defense capabilities. A multiomics approach using RNA sequencing and metabolome analyses showed that resistance in C. paliurus (Wufeng) is related to early induction of reprogramming of the flavonoid biosynthesis pathway. In vitro antifungal assays revealed that the flavonoid extracts from resistant cultivars strongly inhibited C. fructicola hyphal growth than susceptible cultivars. Relative gene expression analysis further demonstrated the pivotal antifungal role of C. paliurus flavonoids in targeting Colletotrichum appressorium formation. Together, these results represent a novel resistance mechanism of C. paliurus against anthracnose through the reprogramming of flavonoids, which will lay a foundation for breeding anthracnose-resistant varieties and the application of flavonoid extraction of C. paliurus as a natural antifungal treatment.

Stem Canker on Cyclocarya paliurus Is Caused by Botryosphaeria dothidea.

Cyclocarya paliurus, an important endangered plant in China, has considerable medicinal, timber, and horticultural value. However, little is known about diseases that affect its health. In recent years, stem canker diseases on C. paliurus have been observed frequently in newly established nurseries in Jiangsu Province, China. Symptomatic trees showed elliptical, sunken lesions on the bark, with internal discoloration, leading to enlarging cankers with delineated margins. Pathogenicity tests with fungi isolated from symptomatic samples reproduced typical canker symptoms on both detached branches and potted plants of C. paliurus. Moreover, conidia from pycnidia of isolate ZB-23 could also cause stem canker on C. paliurus. Through combined morphological observation and DNA sequences of ITS region, ß-tubulin, and translation elongation factor 1-α genes, the pathogen was identified as Botryosphaeria dothidea. Multigene maximum likelihood and maximum parsimony phylogenetic analyses further supported the identification of the pathogen. To our knowledge, this is the first report of B. dothidea causing stem canker on C. paliurus in China.

Etiology of Cyclocarya paliurus Anthracnose in Jiangsu Province, China.

Cyclocarya paliurus is an extremely valuable and multifunctional tree species whose leaves have traditionally been used in used in medicine or as a medicinal tea in China. In recent years, anthracnose has been frequently observed on young leaves of C. paliurus in several nurseries located in Jiangsu Province, resulting in great yield and quality losses. To date, no information is available about the prevalence of C. paliurus anthracnose in China. The main purpose of the present study was to characterize the etiology of C. paliurus anthracnose. Phylogenetic analysis of the eight-loci concatenated dataset revealed that all 44 single-spore Colletotrichum isolates belonged to three species in the Colletotrichum gloeosporioides species complex, namely, Colletotrichum aenigma, Colletotrichum fructicola, and C. gloeosporioides sensu stricto. Phenotypic features, including the colony appearance and the morphology of conidia, appressoria, and ascospores, were consistent with the phylogenetic grouping. Virulence tests validated that the three Colletotrichum species could cause typical symptoms of anthracnose on C. paliurus leaves, similar to those observed in the field. The optimum mycelial growth temperature ranged from 25 to 30°C for all representative isolates, while C. gloeosporioides s. s. isolates exhibited greater tolerance to high temperature (40°C). Fungicide sensitivity assays indicated that all three Colletotrichum species were sensitive to tetramycin, which may be a potential alternative for the management of C. paliurus anthracnose. To our knowledge, this study provides the first report of C. aenigma, C. fructicola, and C. gloeosporioides s. s. causing C. paliurus anthracnose in China as well as in the world.