Abstract:

This experiment investigated the cytological mechanism of Trifolium repens and powdery mildew interaction， clarified the classification status of powdery mildew infecting T. repens， and provided information for breeding disease-resistant clover varieties and scientifically directed prevention and control of forage fungal pathogens. Optical and electron microscopy methods were used to observe the changes to cellular physiological characteristics caused by pathogens invading T. repens. The pathogen was identified as Erysiphe pisi based on traditional observation of morphological characteristics and sequence analysis of rDNA-ITS （ribosomal RNA internal transcribed spacer）. The water agar slide method was used to observe conidial germination characteristics of E. pisi. The results showed that E. pisi directly invaded the epidermal cells of T. repens at the junction of epidermal cells and stomatal guard cells， resulting in degradation and darkening of color in the cell wall tissue of at the location where the hypha invaded the cell wall. A large quantity of cell wall deposits were produced inside the corresponding cells. After the cell wall was no longer intact， the stomatal channel deformed to cause plasma membrane separation of the guard cells. The haustorium that invaded the epidermal cell was surrounded by the host plasma membrane to form an interface. The chloroplasts in the palisade tissue cells swelled， changing from elliptical to nearly spherical and clustering， starch grains were changed in shape from elongated to elliptical， and osmophilic particle numbers increased. The conidia inoculated on the leaf germinated and grew primary bud tubes within 4 hours post-inoculation （hpi）， formed mature appressoria in 10 hpi， formed infection pegs after 12 hpi， and secondary hyphae formed after 48 hpi. Germ tubes of abundant branches differentiated into hyphae and produced mature conidiospore after 96 hpi. At the same time leaves showed symptoms， the conidiophore differentiated into 2 to 3 conidia at 144 hpi， the top matured first， and the powder layer was expanded to 2/3 of the leaf at 168 hpi； at 240 hpi， the area of the powder layer had covered more than 90% of the leaf， and the powder layer was thick and its leaves were curled. The pathogen E. pisi grows best at 25 °C and pH 7.0， and light conditions are conducive to spore germination.

Key words: Trifolium repens, powdery mildew, ultrastructure, pathogen identification, biological characteristic