Studies On Screening Of Biocontrol Bacteria And Control Technologies Of Rice Bakanae Disease

Rice is one of the most important cereal crops in China.Every year,diseases of rice cause great yield losses,and pose a threat to food security of our country.Rice bakanae disease（RBD,Pathogen: Fusarium fujikuroi）of rice becomes more and more serious,however the control system of this disease can no longer meet the requirements of modern rice production.Currently,application of variety’s resistance,chemical control and biological control are three major measures for controlling many diseases.The control system was expected to be improved by several studies in our research,including biological control organisms isolating,screening,identifying and applying,assessing of variety resistance,and screening for effective fungicide.The results are as follows:1.A strain,which showed the most antagonistic effect against F.fujikuroi,the pathogen of RBD,was screened from 60 bacterial isolats from rhizosphere soil of rice.The strain,designated as H168,was finally identified as Bacillus velezensis by characteristics of culture,morphology,chemical sensitivity,nucleotide sequence and composition of fatty acid of cell wall.Strain H168 showed a lots of traits related to its abilities on biological control,such as great antagonistic effects,rapid growth on different media,maturely and stable biofilm,high production of cellulose,the ability to induce induced systematic resistance（ISR）of rice by adjusting the defense related enzymes,such as POD,CAT,SOD,PPO,and PAL,which showed great potential on biological control.H168 showed great control effects against rice bakanae disease in pot experiment.2.In this study,the resistance to RBD of 26 rice varieties were identified by seedling inoculation method.The result showed that only varieties of Huayou14,Qiuyoujinfeng,Y Liangyou 911,and Yuexiangzhan were resistant against RBD,and Yongyou 1540 and Chujing 2 were moderate resistant.Eleven varieties showed high and moderate susceptibility,which accounted for 42.3% of all tested varieties.No variety with high resistance was found in this study.3.Susceptibility of pathogens of RBD to 10 fungicides was evaluated by mycelial inhibition method.Among tested fungicides,prochloraz,tebuconazole and phenamacril showed the highest activity against the F.fujikuroi,whereas the fungicides of Qo Is showed the lower activities to F.fujikuroi.It was reported that fungicide-resistant of RBD pathogen to prochloraz occurred in the production practice,in this study,106 strains of F.fujikuroi were isolated in Fuyang,Zhejiang Province,and their susceptibility to prochloraz were evaluated to understand the resistance problem.The result showed that EC₅₀ of 85 strains of F.fujikuroi ranged from 0.012-0.620 mg/L,and among them the difference was as high as51 folds.The fungicide-resistant of the strains of RBD pathogens were not constant,and the level of fungicide-resistant could decreased with increasing of culturing generations,however,the decreasing rate of fungicide-resistant is quite slow.There is no cross resistance to RBD pathogen F.fujikuroi between prochloraz and azoxystrobin or carbendazim,but prochloraz showed cross resistance with tebuconazole.