Inhibitory Effect Of Two Endophytic Strains Against Sclerotinia Sclerotiorum On Oilseed Rape

Sclerotinia rot, caused by Sclerotinia sclerotiorum, is a disease of rape worldwide and cancause serious damage to the yield of oilseed rape （from10%to80%） and oil quality at everyproducing arears of rape. Although breeding resistance rape is the most effective way tocontrol Sclerotinia rot, it is hindered due to the lack of resistant germplasm among oilseedrape varieties to the pathogen, and the resistance is not always consistent year to year.Chemical and cultivating control measures have been the main ways to control Sclerotinia rot,such as procymidone, carbendazim and crop rotation. However, cultivating control measuresdo not work very well because of the lack of labor and cultivation measures. As for chemicalcontrol measures, the main problems with them includes the huge cost and environmentaldestroy they induced, and the resistant isolates have been discovered in many fields. So noneof these measures have been controlled the disease effectively in oilseed rape and canolaproduction. Biocontrol has been another way proven to be effectively against pathogens.There have been more than40kinds of microorganisms used as biocontrol agents to inhibitthe Sclerotinia sclerotiorum, such as coniothyrium minitans, and trichoderma viride.Endophytes, living asymptomatically within plant tissues, have been detected in almost allplants species studied. However, use of plant endophytes against Sclerotinia sclerotiorum israre, and most of the studies have just focus on the efficacies in vitro and greenhouse. Inpreliminary studies, we have screened two endophytic strains that can be inhibited the growthof hyphae of Sclerotinia sclerotiorumt. Therefore, the objectives of this study were to test theeffecacies of the two endophytic strains in greenhouse and fields, and develop a kind of newbiological agents to suppress the sclerotinia rot.1. The two endophytic strains suppressed the growth of hyphae and the germination ofsclerotinia significantly. The best control effect was achieved by spraying the cell-free filtrateand cell suspension at the same time as inoculation, and there were no significant differencesbetween the efficacy of cell-free filtrate and cell suspensions. The germination of seedsshowed that both of the endophytic strains were safe to the plant and environment. In the fieldexperiments, the efficacy of applying EDR4to rape plants twice at the flowering stagereached58%and decreased gradually with the dilution.2. Scanning electron microscopy revealed that endophytic strains could suppress the growth of hyphae significantly, and cause leakage of hyphal cytoplasm and irregular swellingof top hyphal. The ultrastructure of mycelial cell was investigated under transimissionelectronic microscopy. The results showed that endophytic strains caused increasing ofvacuole in the cytoplasm, disordered of the orgarelles, rupture of the cell wall, and leakage ofthe cytoplasma. The biomass of hyphal has been reduced, and the formation of infectioncushions has been delayed and the infection of hypha has been suppressed after spraying theculture of endophytic strains on the leaves.3. A kind of biological agents has been developed which contains the bacteria EDR4.The quantity was8.1×10⁸CFU·g^-1and the diameters of inhibitated zones reached18mm11weeks after storage. The best efficacy was62%achieved at spraying the biological agentdiluent1day before inoculation, was equal to the efficacy of spraying culture of EDR4. In thefield experiments, the best efficacy,57%, was achieved at spraying biological agent A to rapeplants twice at the flowering stage.