First Report of Leaf Spot on Taraxacum mongolicum Caused by Alternaria solani in China.

Taraxacum mongolicum is a perennial herbaceous plant in the family Asteraceae, with a high edible and medicinal value and is widely planted in China. In August 2022, leaf spots were found on T. mongolicum in Tianjiazhai Town, Xining City, Qinghai Province, China (36°27'17.65″N, 101°47'19.65E, elevation: 2,408 m). The plants exhibited round or irregular brown spots, and the centers of some of the spots were gray (Fig. S1A). An investigation was performed over a hectare area, and the incidence of leaf spot reached 15%-30%, seriously affecting the quality and yield of T. mongolicum. Eleven T. mongolicum leaf spot samples were collected. To isolate the pathogenic fungus, approximately 0.5 cm×0.5 cm pieces of tissues were obtained using sterile scissors from the junction of infected and healthy tissues. The symptomatic leaves were surface-disinfected with 3% NaClO for 1.5 min and washed three times with sterile water. The disinfected pieces were dried and placed on water agar plates in an incubator for 2 days at 25°C. Subsequently, the leaf surface exhibited conidiophores and conidia. Eleven isolates were obtained by single spore isolation. The sparse aerial mycelia were dark grey to black brown in color on potato dextrose agar (PDA) (Fig. S2A), and produced dark, multi-septate conidia with 7-11 transverse septa and 1-2 longitudinal septa (Fig. S2C). Conidia with one or two beaks were long-ovoid, with an average length and width of 103.4 × 21.2 µm, and 80.7 × 3.9 µm of the beaks. One hundred and ten conidia were measured. The identification of 11 isolates was confirmed by multilocus sequence analyses of the internal transcribed spacer of ribosomal DNA (rDNA ITS) (White et al. 1990), and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (Xu et al. 2022), actin (ACT) (Yang et al. 2020), histone 3 (HIS3) (Zheng et al. 2015), translation elongation factor 1-α (TEF1-α) (Carbone. 1999), and the second largest subunit of RNA polymerase II (RPB2) (Liu et al. 1999) genes. The sequences of all the isolates were deposited in Genbank (NCBI Accession Nos. ITS: OR105029-OR105039, ACT: OR135220-OR135230, GAPDH: OR135231-OR135241, HIS3: OR122992-OR123002, TEF1-α: PP055972-PP055982, and RPB2: PP055983-PP055993), and the sequence similarity of ITS, ACT, GAPDH, HIS3，TEF1-α and RPB2 were 100%, 98%, 100%, 99%, 100%, and 99% to the sequences of Alternaria solani, respectively. Combined sequences of ITS, GAPDH, TEF1-α, and RPB2 genes were concatenated and a maximum parsimony tree was constructed with PAUP* v. 4.0 alpha. The results indicated that 11 isolates were clustered together with A. solani (Fig. S2D). Therefore, 11 isolates were identified as A. solani based on their morphological and molecular characteristics. Eleven isolates were inoculated on their host to perform Koch's postulates. The isolates were grown on PDA for six days. Healthy one month old T. mongolicum seedlings were planted in 10 cm flowerpots (Fig. S1B) or the seedlings were moved to Petri dish (Fig. S1C), and their leaves were inoculated with 5 mL of hyphae suspension by smearing method. In addition, seedlings of the same age were treated with sterile water to serve as the control. The inoculated seedlings were moved into an artificial climatic box at 25℃, relative humidity was 70%, with 12 h light/12 h dark condition. Totally 80 seedlings were inoculated with isolates and 15 were used as the control. After 7 days, similar symptoms were observed on the plants inoculated with isolates, while control plants did not produce symptoms. The assays were conducted three times. Furthermore, isolates were re-isolated from the symptomatic leaves, and the colonial morphology was the same as the original isolates (Fig S2 A and B). The recovered isolates were identified as A. solani by amplifying and sequencing a portion of the HIS3 gene. Alternaria solani has been previously reported to cause early blight of potato and other Solanum crops (van der Waals et al. 2004; Zheng et al. 2015). To our knowledge, this is the first report of A. solani causing leaf spot of T. mongolicum in China. This disease must be considered in management practices, and our finding provided a basis for disease prevention and management.

Analysis of Pyricularia oryzae and P. grisea from Different Hosts Based on Multilocus Phylogeny and Pathogenicity Associated with Host Preference in China.

Pyricularia oryzae and P. grisea are important agents of major diseases on a wide range of gramineous hosts. Whereas P. oryzae is the most important pathogen causing outbreaks of rice blast, P. grisea is mainly a pathogen of crabgrass. In this study, 103 P. oryzae and 20 P. grisea isolates were collected from seven species of plants, and we analyzed their phylogeny, pathogenicity, and relationship with host preferences to investigate the differences among them from different hosts. Based on phylogenetic analysis of multilocus sequences, 16 isolates from crabgrass and four isolates from green bristlegrass were identified as P. grisea and another 103 isolates from crabgrass, green bristlegrass, goose grass, foxtail millet, wild millet, rice, and sedge belonged to P. oryzae. Results of pathogenicity tests by artificial inoculation demonstrated that six of 10 P. oryzae isolates from rice and three of 44 P. oryzae isolates from green bristlegrass showed cross-infectivity on green bristlegrass and rice, respectively. Taken together, our results demonstrated that isolates from green bristlegrass and crabgrass consist of both P. oryzae and P. grisea and that P. oryzae isolates showed cross-infectivity between rice and green bristlegrass, suggesting that host shifts may occur for P. oryzae and P. grisea.

Non-targeted metabolomics analysis reveals the mechanism of arbuscular mycorrhizal symbiosis regulating the cold-resistance of Elymus nutans.

Elymus nutans is a perennial grass of the Gramineae family. Due to its cold-resistance and nutrition deficiency tolerance, it has been applied to the ecological restoration of degraded alpine grassland on the Qinghai-Tibet Plateau. As an important symbiotic microorganism, arbuscular mycorrhizal fungi (AMF) have been proven to have great potential in promoting the growth and stress resistance of Gramineae grasses. However, the response mechanism of the AMF needs to be clarified. Therefore, in this study, Rhizophagus irregularis was used to explore the mechanism regulating cold resistance of E. nutans. Based on pot experiments and metabolomics, the effects of R. irregularis were investigated on the activities of antioxidant enzyme and metabolites in the roots of E. nutans under cold stress (15/10°C, 16/8 h, day/night). The results showed that lipids and lipid molecules are the highest proportion of metabolites, accounting for 14.26% of the total metabolites. The inoculation with R. irregularis had no significant effects on the activities of antioxidant enzyme in the roots of E. nutans at room temperature. However, it can significantly change the levels of some lipids and other metabolites in the roots. Under cold stress, the antioxidant enzyme activities and the levels of some metabolites in the roots of E. nutans were significantly changed. Meanwhile, most of these metabolites were enriched in the pathways related to plant metabolism. According to the correlation analysis, the activities of antioxidant enzyme were closely related to the levels of some metabolites, such as flavonoids and lipids. In conclusion, AMF may regulate the cold-resistance of Gramineae grasses by affecting plant metabolism, antioxidant enzyme activities and antioxidant-related metabolites like flavonoids and lipids. These results can provide some basis for studying the molecular mechanism of AMF regulating stress resistance of Gramineae grasses.

Complete mitochondrial genome of Polyphylla gracilicornis (Coleoptera：Scarabaeoidea).

Polyphylla gracilicornis is one of the important underground pest species that damage agricultural and forestry plants and often requires chemical control during outbreak. Here, we determined the complete mitochondrial genome sequence of P. gracilicornis (GenBank accession no. MW143080) using Illumina NovaSe Sequencing System with a read length of 150 bp. The complete mitogenome consists of a 16,793 bp circular DNA molecule and the overall base composition was 36.97% A, 31.95% T, 10.41% G and 20.67% C. The full mitochondrial genome contains 38 sequence elements: 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and a putative control region (CR). All protein-coding genes of P. gracilicornis have the typical ATN (Met) start codons and typical TAN stop codons. Phylogenetic analysis revealed that P. gracilicornis clustered into a clade with homologous species with high bootstrap support.