Crude Extracts and Secondary Metabolites of Epichloë bromicola against Phytophthora infestans.

Potato late blight caused by Phytophthora infestans is still one of the main factors limiting potato production. Epichloë spp. can provide host plants with various resistances, which makes them show great potential in the biological control of diseases. In this study, we explored the potential biological activity of crude extracts of 20 strains of Epichloë bromicola to control P. infestans. The crude extracts of strains 1 and 8 showed significant antifungal activity with an inhibition rate of 88 % and 81 %, respectively, and showed different effects on the mycelium morphology of P. infestans observed by scanning electron microscopy. Moreover, the two crude extracts demonstrated an interesting therapeutic and protective effect on potato late blight, and none of the extracts had an adverse effect against zebrafish embryos. A total of 13 metabolites were isolated from the crude extract of strain 8, and these tested compounds showed a weak antifungal effect and the inhibition rate was less than 80 %. These findings suggested that strains 1 and 8 have potential for biocontrol of late potato blight.

Antifungal, Repellency, and Insecticidal Activities of Cymbopogon distans and Ruta graveolens Essential Oils and Their Main Chemical Constituents.

Essential oils produced by Cymbopogon distans and Ruta graveolens with a similar Chinese name could be explained as book fragrance in the Chinese idiom 'shu xiang men di', namely, a wealthy intellectual family according to ancient Chinese. Therefore, volatile oils from these two plants and their main compounds were tested to explore their antifungal, repellent, and insecticide actions. In this study, the essential olis (EO) of C. distans exhibited significant antifungal activity against Rhizopus stolonifera (97 %), Mucor racemosus (97 %), and Trichoderma viride (84 %); its main compounds exhibit interesting activity, such as methyleugenol (87 %) and elemicine (85 %) against T. viride and butyl hydroxytoluene against M. racemosus (90 %) and R. stolonifera (95 %). The EO of R. graveolens and other major chemical constituents showed weak inhibitory effects against other fungi (Aspergillus flavus and Fusarium oxysporum). Then, EO (C. distans and R. graveolens) and its main compounds exhibited obvious repellent activity (more than 85 %) at a concentration of 16 nL/cm2 , which was consistent with the repellency of the positive control (DEET). In terms of insecticidal activity, the mortality of C. distans volatile oil against R. padi (56.4 %) was lower than that of R. graveolens volatile oil (92.4 %), and all compounds showed weak lethal effects. These results provide a natural substance for controlling fungi and insects when storing books and that can be used as a biological pesticide for industrial production. Through our study, the book fragrance in the Chinese idiom 'shu xiang men di' was speculated to be the EO odor of C. distans.

Isolation and identification of Tussilago farfara leaf spot caused by Alternaria alternata in China.

Tussilago farfara is of vital medical value. A new leaf spot disease was observed on T. farfara leaves, in Dingxi, Gansu Province, China, in October 2019. In order to research the pathogen, the diseased samples were collected for isolation and identification. The isolate KD3 was verified by pathogenicity test, as the pathogen causing the T. farfara leaf spot disease. Its morphological characteristics were consistent with Alternaria alternata, the colony color gray-green with concentric rings, conidia fusiform and pear-shaped, brown, with 1-7 septa and 0-3 longitudinal septa, conidia size (19. 62-44.49) µm × (6.97-10.53) µm, beak length (1.35-10.03) µm × (1.01-3.63) µm, and the spore phenotype was a dwarf tree-like chain of short conidia. Multilocus sequences analysis manifested that the internal transcribed spacer (ITS), Alternaria major allergen (Alta1), and Calcium barine (CAL) sequences of strain KD3 were most closely to A. alternata (A23), with the homology of 99.47%, 99.56% and 98.28%, respectively. Based on morphological and molecular characteristics, strain KD3 was identified as A. alternata. OA was the optimal medium for its growth and PCA medium was the optimal for sporulation. This is the first report of A. alternata causing T. farfara leaf spots in China.