Induction Of Sunflower Resistance By Elicitor IR-18 And Its Synergistic Effect On Alleviation Of Orobanche Cumana Infection

Orobanche cumana?sunflower broomrape?is a root holoparasitic angiosperm which can attach to sunflower root and absorb water and nutrients from sunflower,resulting in retarded growth of sunflower or even death of the crop.Study on the interaction between O.cumana and sunflower will help us understand the parasitic characteristics of O.cumana and the resistance mechanism of sunflower,helping to reduce O.cumana hazards.In this paper,exogenous regulators such as new elicitor were used to induce resistance against O.cumana and reduce the hazards,which showed good application potential.In this paper,a new elicitor,IR-18,was investigated to find out how it induces resistance against O.cumana in a sensitive sunflower cultivar?X3939?.The main research results are as follows:1.The range of optimal dilution ratio,spraying period and times of application of IR-18 were defined.The results showed that the sunflower was harmed under spraying of 500×diluent,the spraying of 1500×diluent was not efficient and the spraying of1000×diluent could not only avoid phytotoxicity but also inhibit the development of O.cumana.Spraying IR-18 diluent at 2-leaf stage has a good effect and most of O.cumana could develop normally on the IR-18 diluent treated sunflower at the stage behind 4-leaf.Generally,the best outcome could be seen under 1000×diluent treatment at the 2-leaf and 4-leaf stages,and compared with the control group,sunflower plant height,shoot fresh weight,shoot dry weight and root dry weight increased by 73.68%,274.37%,182.69%and 300%,respectively,and O.cumana dry weight decreased by67.61%.At the same time,spraying IR-18 at 2-leaf and 4-leaf stages both was better than a single spray at either stage.2.Chlorophyll fluorescence,histochemical staining,physiological and biochemical reaction were used to identify sunflower resistance induced by treatment of 1000×IR-18 diluent at 2-leaf stage.Compared with control group,the net photosynthetic rate increased significantly,indicating IR-18 diluent maintains the normal photosynthesis of sunflower.The cortex cells in the contact area of sunflower root and O.cumana increased greatly,which prevented O.cumana from connecting with the central cylinder.There was a large accumulation of H₂O₂ and MDA in O.cumana,and the activity of three antioxidant enzyme,CAT,APX and POD,increased significantly,possibly resulting in oxidative burst in O.cumana.These results indicated that the elicitor IR-18 activated the defense response in sunflower and alleviated the infection of O.cumana.3.The role of biochar in improving the application effect of elicitor was identified.The effect of IR-18 was affected by different inoculation density,being severely inhibited when the density was high.Biochar can reduce the content of O.cumana in the soil,resulting in reducation of number of O.cumana on sunflower roots.At the same time,the advantages and disadvantages of the three application methods of IR-18,foliage spray,seed soaking and pregermination were clarified.The results showed foliage spray is the best method to promote the growth of sunflower and inhibit the growth of O.cumana.In addition,pregermination significantly increased the plant height of sunflower,and significantly reduced the number of attachment and dry weight of O.cumana.