Abstract:

Incidence of the disease and the rate of pathogen carried and substances including phenolic compounds, soluble sugar, and starch in fruits of Chinese Chestnut were tested regularly during the development of chestnut fruits and post harvest storage period. The variation of viability and the related physiological index of seeds in the process of water loss, and the effects of those variation on the activity of pathogens inside the seeds were also tested. The content of phenolic compound in involucre, style, pericarp and seedcoat of chestnut fruit reached 1 mg·g ^-1 of fresh weight, exceeded the concentration of 0 5 mg·g ^-1 , which was proved to be the concentration for markedly inhibiting the mycelial growth of the pathogens in vitro. Pathogens were isolated from the tissue of involucre, style, pericarp and seedcoat but no symptoms appeared. This indicated that high contents of phenolic compounds in chestnut fruit contributed to the latent infection of the pathogens of Chinese Chestnut seed rot. On maturation of chestnut seeds, the content of phenolic compounds in pericarp decreased sharply and reduced the inhibiting effects to the pathogens inside. As the water content of seeds decreased the seed germination index declined, and the content of malondialdehyde (MDA) increased steadily, and the relative conductivity of soaking solution, in which the Chinese Chestnut seeds soaked, were increased markedly. When the rate of water loss exceeded ten percent, the germination rate of seeds started to decline, and the activities of free-radical scavenging enzymes (superoxide dismutase and peroxidase) decreased markedly,and the seed rot was induced. The fact that the critical moisture content for pathogenesis was close to the moisture content, when the germination rate of seeds started to decline, indicated that the water loss in seed reduced the resistance of seed. Accompanied by starch hydrolysis and the quantity of soluble sugar increasing, the pathogens relieved from latent infection and caused the seed rot.

Key words: Chinese Chestnut seed rot, Latent infection, Phenolic compound, Soluble sugar, Pathogenesis