Effects Of Seedborne Fungi On The Quality Of Perennial Ryegrass (Lolium Perenne L.) Seeds

This research was conducted to isolate and identify the fungi from 20 cultivars of perennial ryegrass (Lolium perenne L.) seeds (including herbage and turf types), study the effects of seedborne fungi on the germination and seedling growth, reveal the mechanism of how to the fungi having the adverse effects on the seeds, and study the ideal sterilization conditions of the seedborne fungi. The results indicated that:1. Twenty seed samples of perennial ryegrass cultivars produced in different countries were analyzed to determine the species and location of seedborne fungi. Fifty-two species belonging to 36 genera were identified from seed without surface sterilization and thirty-three species belonging to 20 genera were identified from surface sterilized seeds. Surface sterilization could reduce the fungal species and mean percentage recovery of fungi, for mean percent infection, it had different effects according to seed samples.2. Most fungi were located in the endosperm followed by the pericarp and the embryo by using component plating method. Alternaria tenuissima was isolated from sterilized and unsterilized seeds and located in coat and endosperm, indicating that this fungus was of seed-borne nature and this was the first report on seedborne fungi from the perennial ryegrass seeds.3. The effects of seedborne fungi on the germination and seedling vigor index of seeds inoculated with spore suspension were also studied using the standard blotter method and the paper towel method. Seeds inoculated with Acremonium sp. showed significantly increase in percentage germination (P<0.05), seedling vigor index insignificantly increase. About 13 species including Cladosporium spp., most of Alternaria alternata and A. tenuissima had no significant effect on these indexes compared to control (P>0.05). Other fungi had adverse effects on seed germination and seedling vigor (P<0.05). When 18 fungi tested were inoculated to seeds of different cultivars, all could inhibit the germination, delay the time to achieve 50% germination and reduce the shoot and root length resulting in vigor index lower than their corresponding control, especially Fusarium avenaceum, F. semitectum, F. culmorum, Marielliottia biseptata, Bipolaris sorokiniana and Trichothecium roseum. When the seeds inoculated with the culture filtrates of seedborne fungi, it drew a similar conclusion.4. Seeds inoculated with spore suspension of seedborne fungi were used to measure physiological and biochemical indexes in order to know how fungi had adverse effects on the seed quality. The relative conductivity and respiration rate showed significantly increase, the contents of total sugars and reducing sugars were decreased, the contents of soluble sugars, soluble protein, free amino acids and malonaldehyde (MDA) were increased significantly, the activities of α -amylase, superoxide dismutase (SOD) and phenylalanine ammonia-lyase (PAL) showed significantly reduction, and the content of chlorophyll a, chlorophyll b and the ratio of a/b in the seedling shoots were decreased compared to their corresponding control (P<0.05). The respiration rate, contents of soluble sugars, soluble protein, free amino acids and MDA and the activities of α -amylase, SOD and PAL in seeds inoculated with different fungi had different changes when the inoculation time changes.5. Hot water treatments were used to sterilize the seedborne fungi. Seeds soaking the water at 45℃ for 20 min could significantly reduce the mean percent infection and the mean frequency recovery of fungi without decreasing the percentage germination.6. Fungicides tested could inhibit the mycelial growth of seedborne fungi such as B. sorokiniana, F. avenaceum, M. biseptata and T. roseum in different concentrations. When soaking the seeds inoculated with seedborne fungi for 45 min in all kinds of fungicidal suspension, the fungicide Kairun at the concentration of 0.2 mg/ml, Cuibei at 0.3 mg/ml and F518 at 0.2mg/ml were most effective on sterilizing the tested fungi and making percentage germination increase. For fungic...