Research On The Beneficial Effects Of Sclerotinia Sclerotiorum On Non-host Wheat

Sclerotinia sclerotiorum(Lib.)de Bary is a notorious necrotrophic fungal plant pathogen that destroys many important economic crops and vegetable crops and leads to huge economic losses worldwide.It has a wide host range and is known to attack over 400 species and subspecies of plants distributed in 75 families.Wheat(Triticum aestivum L.)was recorded as a host of S.sclerotiorum;while it is actually a non-host and has been used in rotation with rapeseed and other host crops.In previous research,we found that S.sclerotiorum could be detected in wheat seedlings and seeds with a high ratio.In this research,the endophytic growth of S.sclerotiorum was confirmed and the potential effects on wheat were investigated.The main results obtained are presented as follows:1.S.sclerotiorum could grow in wheat endophytically.Both mycovirus-mediated hypovirulent strains DT-8,SCH941,AH98,T1-1-20 and virus free strain DT-8VF of S.sclerotiorum were proved to grow endophytically in root and stem through PCR amplification,Laser Scanning Confocal Microscope(LSCM),Transmission electron microscope(TEM),Scanning electron microscope(SEM),Immune-colloidal gold technology(ICGT)and Fluorescence in Situ Hybridization(FISH)techniques.The intracellular hyphae could enter into neighboring cells by breaking plant cell walls,and the membrane-like structure was formed to surround the fungal cell wall closely.In addition,we also found that both virulent strain DT-8VF and hypovirulent strain DT-8 could grow endophytically in the roots of rice,barley,oat,and maize.2.The endophytic growth of S.sclerotiorum increased resistance of wheat,rice and barley.Fourteen days after inoculation with conidial suspension(10~5/m L)of F.graminearum strain PH-1,the percent of the infected spikelet in S.sclerotiorum-treated wheat was 25.5±6.34%,while it was 38.8±7.34%in the non-treated control.Field experiments with artificial inoculation in E-zhou in 2017and 2018 also confirmed that the percent of the infected spikelet of Fusarium head blight(FHB)in wheat treated with strain DT-8 was reduced by 53.5±2.7%and49.6±2.9%,respectively,compared with the control.Field experiments at E-zhou,Xiangyang,and Jingmen of Hubei province in 2018 showed that treatment with strain DT-8 reduced the natural incidence rate of FHB by 39.72±5.80%,54.91±4.11%,and58.79±3.53%,respectively.The DON content in the diseased spikelet of wheat treated was not significantly different from the non-treated control.Taken together,the treatment of strain DT-8 could increase significantly the resistance to FHB.Furthermore,the incidence of wheat stripe rust was investigated under natural conditions in E-zhou(winter wheat)and Tianzhu County(spring wheat),the results showed that the disease index of stripe rust decreased by 73.4%and 57.4%in wheat treated with strain DT-8,respectively,compared to the non-treated control.Meanwhile,the control effect of stalk rot in wheat treated with strain DT-8 was 45%in the greenhouse in 2017.Therefore,the endophytic growth of S.sclerotiorum increased resistance of wheat to Fusarium head blight,stripe rust,and stalk rot diseases.In addition,we also found that both S.sclerotiorum-treated barley and rice demonstrated strong resistance against the rice blast fungus.3.The endophytic growth of S.sclerotiorum promotes the growth of wheat.Wheat seed was prepared by inoculating with hyphal fragments of hypovirulent strain DT-8 and planted in soil from the field.The average plant height,the length,width,and thickness of flag leaves,the content of N,P,chlorophyll and photosynthetic rate of flag leaves,the content of IAA in wheat spike and root activity were examined.The results showed that all the data were significantly larger than the non-treated control.Among them,the chlorophyll content,photosynthetic rate,the content of N and P of wheat flag leaf treated with DT-8 strain were increased by 51.56%,7.65%,27.3%,and 4.54%,respectively.The root activity,IAA content of spike and 1000-grain weight in wheat treated with strain DT-8 were increased by 65.74%,3 times,and5.83%,respectively.In order to confirm the result,the experiments were performed in nature fields located at E-Zhou in 2016,Minqin County and Tianzhu County of Gansu Province at early summer of 2017,E-Zhou City,and two additional fields located at Jingmen City and Xiangyang City of Hubei Province in late autumn of 2017.The wheat yields were significantly increased by 4%to 18%in 2017 and 2018.4.The mechanism in resistance and growth promotion of wheat by endophytic growth of S.sclerotiorum.RNA-Seq analyses of spikes and flag leave demonstrated that endophytic growth of S.sclerotiorum activated the expression of genes involved in defense responses(innate immunity,systemic induction resistance,plant hormones pathway,calcium signaling pathway,MAPK signaling pathway,and wax biosynthesis metabolism).At the same time genes related to chlorophyll,chloroplast,photosynthetic system,carbon metabolism pathway,nitrogen metabolism pathway,starch and sucrose pathway and rhythm were also activated in wheat plant treated with strain DT-8.The differentiated expressed genes may account for the resistance and growth promotion of wheat.In brief,S.sclerotiorum could grow endophytically in wheat.The endophytic growth of S.sclerotiorum could not only increase the resistance of wheat to Fusarium head blight,stripe rust,and stalk rot diseases but also promotes the growth of wheat,maybe by activating expression of defense-related genes and genes involved in chlorophyll,chloroplast,photosynthetic system,etc.The findings indicate that fungal pathogens may play multiple roles in the natural ecosystem.