Studies Of Genetic Diversity On Ustilaginaoidea Virens From Indica Rice Areas In Sichuan Province And Control Techniques To Rice False Smut

Rice false smut(RFS) is a worldwide fungal disease in rice,caused by Ustilaginoidea virens(Cooke) Takahashi,which threaten the panicles of rice and further,produced rice fade balls.Not only it reduced rice yield,but also impacted rice quality,furiously.RFS brought on serious economic loss and became another obstruction against high quality and high yield.In addition,U.virens can produce a toxin of C₉H₆O₇,which lead to abnormality of human and brute.So it become very important on rice production and foodstuff safety that controlling appearance and development of RFS.Sichuan is an important indica rice production-area in China,which possesses more about 2000 thousand hm²,and it has multiform environments.RFS has become one of important diseases on rice product in recent years especially.RFS became serious in indica rice area of Sichuan,about 261.8 thousand hm²,indeed seriousest in part area,actual loss is 14.8 thousand ton in 2005.U.virens of indica rice area in Sichuan is complex,and its genetic background is unclear,at present there was no study on genome of U.virens, variety and entironment in indica rice area of Sichuan.Be to research the relationship between the genetic diversity of Ustilaginoidea virens and the ecological distribution and the host cultivars deeply.In the present study,the genetic diversity of the 60 Ustilaginoidea virens isolates,which collected from 6 indica rice production regions in Sichuan province in 2006 or 2007,have been investigated by ERIC-PCR(Enterobacterial Repetitive Intergenic Consensus-Polymerase Chain Reaction). Using the ERIC primers,the polymorphic bands ranging from 5 to 20 of each examined isolate were detected.According to cluster analysis of UPGMA,11 clusters(L1 to L11) were formed based on the boundary level of 0.75 average distances;and clusters of L1,L4 and L5 were predominant groups and there also exist some subordinate and special groups. The results of similarity analysis indicated that the U.virens isolates collected from the similar regions possessed the considerable stability in DNA composition,while the isolates which collected from the different regions showed some regionalism in different degrees; and there exist low degree of correlation between rice varieties and genetic diversity of the different strains.At present,the main strategies of control techniques to RFS are selecting the resistant varieties,with the procedures of chemical control and biological perspectives.Breeding and using resistant varieties not only of achieved high yield and quality,but also is the best way to against RFS.In the present study,the integrative strategy against RFS was explored according to these three aspects described above.The distribution characteristic of RFS in the field experiment was investigated and the resistance abilities of rice varieties against U.virens were evaluated.The results showed that this disease occurred on the middle and lower locations of the spikelets predominately, and few were investigated on the upper spikelets.The prevalence cultivars used in Sichuan Province possessed the resistance ability to RFS in different degrees,but the whole capacity for resistance to this disease is poor,and the order of the ability of resistant of these variations was conventional varieties＞hybrid combinations and precocious varieties＞moderate＞late varieties.Chemical control:By six fungicides against Ustilaginoidea virens,their toxicities were tested in vitro.The results showed that Jinggangmycin A and Diniconazole had good effects against U.virens,and their 50%effective concentration(EC₅₀)values were 22.07μg/ml and 90.16μg/ml,respectively.Then used the way of growth inhibition to test toxicity of the mixture of Jinggangmycin A and Diniconazole determined by the different concentration and different ratios against U.virens,and evaluated their effects of synergy according to the method of Wadley.The results showed that the mixtures had greatest synergistic interaction and their SR values were 1.8124 and 1.9052,respectively,when Jinggangmycin A and Diniconazole were mixed by 3:1 and 5:1.The efficacies of 7 fungicides,including 30%Aimiao emulsifiable solution and so on,were detected in field to direct how to control it.The results indicated that the efficacies of 7 fungicides on RFS before 5～7 days spraying in crevasse was better than those of beginning tasseling.The efficacies of 30%Aimiao emulsifiable solution with 15ml/667m2 and 20%jingangmycin water-soluble powder with on U.virens were ideal and about 70%.However,the efficacy of 50%carbendazim wettable powder was lowest and only about 30%and significant with other treatments.So 30%Aimiao emulsifiable solution and 20%jingangmycin water-soluble powder can be applied to control U.virens in rice production.Biological control:By Bacillus subtilis Xi-55 against Ustilaginoidea virens,its antagonistic activity was tested in vitro.Its inhibition rate,deformation effect,and effect on spore germination of Xi-55 with strong antagonistic effect and its growth-promoting effect on rice were studied.The results showed that the average inhibition rate of the metabolites of Xi-55 against U.virens was 54.64%.The average inhibition rate against spore germination of U.virens was 69.33%,while the growth-promoting effect on rice of Xi-55 was opposite.