Studies On Genetic Diversity Of Sporisorium Scitamineum And The Physiological Differencesfrom Interaction Between S. Scitamineum And Sugarcane

Sugarcane smut disease, caused by Sporisorium scitamineum, was one of the most prevalent fungal diseases of sugarcane worldwide.At present, the main sugarcane cultivars are commonly infected by smut in C hina, leading to considerable economic damage.Breeding smut-resistant sugarcane varieties was the most efficient method for control sugarcane smut. However, the S. scitamineum physiological races werestill obscure, caused breeding blindness and effect is not obvious. The molecular genetic diversity and genetic structure of 90mating-type isolates of S. scitamineum,collected from sugarcane growing regions in Southern China, was studied by using the ISSR（Inter-simple sequence repeat） molecular marker and SCo T（Start codon tar geted polymorphism） molecular marker technology. And investigated the changes of defensive enzyme activities in sugarcane infected by S. scitamineum isolates originated from different molecular genetic groups to figure out the differentiation of S. scitamineum, and for identification on physiological races provides a new idea. The mainresults of this study are as follows:（1） The best SCo T-PCR reaction system for S. scitamineumwasestablished, of which the total 25μL reaction mixture contained 12.5 ng template DN A, 0.17 mmol/L d NTPs, 0.46 μmol/L primer, 1.7 mmol/L Mg²⁺, 0.85 U r Taq DNA polymerase and 1×Buffer(Mg²⁺ free).（2）Fifteen ISSR polymorphism primers andfourteen SCo T polymorphism primers were screened. A total of 162 bands were amplified using 15 ISSR primers, of which 115 bands were polymorphic with the polymorphic rate was 71.0%, and at an average of 10. 8 bands per primer. The polymorphism information content（PIC） ranging from 0.12⁰.92 with average 0.82. A total of 135 bands were amplified using 14 SCo T primers, of which 98 bands were polymorphic with the polymorphic rate was72.6%, and at an average of 9.6 bands per primer. The polymorphism information content（PIC） ranging from 0.65⁰.91 with average 0.82. The results suggested that ISSR and SCo T were applicable in the genetic diversity analysis of S. scitamineum.（3） The Jaccard′s genetic similarity coefficient based on ISSR, SCo T and ISSR+SCo T markers of 90 S. scitamineumwere from 0.522 to 0.981, 0.573 to 0.942 and 0.586⁰.946,respectively. Based on ISSR+SCo T markers, the highest genetic similarity was found in the isolates No.39 and No.41, which both from Tianyang district of Guangxi province, whereas the lowest genetic similarity was observed between the isolates No.71 and No.86. The No.71 was collected from Liucheng district of Guangxi province and the No.86 was from Lincang district of Yunnan province. The total gene diversity（ Ht） and Genetic diversity within populations（Hs） were estimated to be 0.245 and 0.169, respectively. Genetic differentiation coefficient of the total population（Gst） and gene flow（Nm） was estimated to be 0.309 and 1.117, indicating that a high degree of genetic differentiation in total population（Gst>0.15）, of which 30.9% variation from between subpopulations and 69.1% variation from within the subpopulations.（4） There is significant correlation（r=0.838） between ISSR marker and SCo T marker based on Mantel correspondence test.The UPGMA cluster and PCA analysis based on ISSR and SCo T marker data sets were similar, which indicated that the isolates of S. scitamineumcollected from same province or same producing district tend to be cluster in the same group. But the isolates of S. scitamineumcollected from Leizhou（Guangdong province）, Hepu（Guangxi province） and Danzhou（Hainan province） were always clustered together, whereas the isolates of S. scitamineumcollected from Wengyuan and Leizhou, both of which belong to Guangdong province but not same district, were not clustered in the same group. The molecular genetic diversity of S. scitamineum tends to be associated with their geographical origins, rather than ther host origins.（5）The activities of SOD, POD and CAT existed 2 peak values, PPO of resistant variety Q171 and PAL of susceptible variety ROC22 also existed 2 peak values.Peak Ⅰ appeared in the first day, peak Ⅱ appeared in the third to fifth days after inoculation. During the peak Ⅱ, activities of five defensive enzymes mentioned above were higher in sugarcane plants inoculated by five isolates of S. scitamineum than those in the corresponding non- inoculated controls. However,peak II values and occurrence time of the SOD, POD and PAL showed significant difference among five isolates. Especially, occurrence time was earlier 1-2 days than other four isolates in peak Ⅱ of isolate No. 89 and its value also showed significant difference from other isolates. It was initially considered that the isolate No. 89 may be represent a new physiological race which was different from other four isolates.