Myceliogenic Germination And Infection Characteristics Of Sclerotinia Sclerotiorum

In recent years,the sclerotinia rot of oilseed rape at seedling stage,which might be caused by mycelial germination of sclerotia was found in Sichuan and Hubei Provinces.In order to gain a better understanding of the mechanism of sclerotinia rot,a series of studies related to myceliogenic germination were carried out.Rapid water uptake was observed in sclerotia during the first 1hr and sclerotia were saturated in approximately 2 hr.After saturated,sclerotia had doubled in weight.Just like Sclerotinia minor and Sclerotium rolfsii,saturated sclerotia of Sclerotinia sclerotiorum geminated myceliogenically within 4 days of incubation without exogenous nutrients at 25?.And almost all of these sclerotium germinated myceliogenically within 11 days of incubation.In the early stage of mycelial germination,the protein bodies of cortical cells did not decrease.Sclerotia could not germinate myceliogenically on dry soil while the high soil moisture was favorable for mycelial germination.Dry and wet alternation inhibits mycelial germination of sclerotia.There was little effect of maturity stage of sclerotia on myceliogenic germination,and the young sclerotia germinated faster than the old ones.Sclerotia could germinate myceliogenically at 10.0-30.0?,and rapidly germinated at 20.0-27.5?.The germination rate of sclerotia decreases with the pH increasing and the germination rate is the highest when the pH value is 3 on the fourth day.In addition,Sclerotia could germinate carpogenically after the myceliogenic germination,but the number of apothecia produced less.In the presence of exogenous nutrition,the number of branches of mycelium increased.Mycelium were stained for nuclei lipid bodies and glycogen.In the absence of nutritional conditions,hyphae still have energy substances.The germinated sclerotia in water and on the PDA were placed on the leaves of healthy rape in vitro,the incidence of rape leaves was less than 5% for germinated sclerotia in water,and the incidence of rape leaves is more than 55% for germinated sclerotia in water.Similarly,the the incidence of sclerotia germinated in water is also much lower than the incidence of sclerotia germinated on the PDA when the sclerotia placed at the base of the stem.The pathogenicity of S.sclerotiorum to the base of stem and the stem was stronger.Sclerotia could germinate myceliogenically and infect rapeseed seedlings with disease incidence of 5.00-11.7%.In this paper,eight AQPs genes were identified,and the expression levels of AQP2,AQP4,AQP5 and AQP7 increased gradually during the mycelium germination.The expression of PKS1 and YG1 in melanin synthesis was down-regulated during mycelial germination,the expression of THNR1 was up-regulated at 3d and 6d.The Ss-oah1 was up-regulated only at 3d,which may be involved in mycelial germination.The cell wall degrading enzymes cwde1,cwde6 and cwde10 were up-regulated expressed and the expression levels increased gradually during mycelial germination.