Pathogen Identification Of Rice Stem Rot Type-white Head And Fungicide Screening

In2011, a wide incidence of white head occurred on the maternal parent Y58S of hybrid rice-Y liangyou NO.1in the seed production fields in Wuyang town, Suining county of Shaoyang city in Hunan province. After preliminary examination, it showed to be caused by Fusarium spp.The samples were collected from different sites in the province, to certify the symptom of white head, pathogenic species, biological characteristics and fungicides toxicity determination in laboratory. The following results were obtained.1. The pathogen of rice stem rot type-white head from Suining is Fusarium graminearum. Pick mould surface with white or light pink layer from Suning rice brown rot stem in microscopy. Typical Fusarium large sickle-shaped conidia are found, mostly5compartment, separated clearly, the top cell beak, slightly curved. By isolated and cultured, mycelium is wool-like, vigorous growth, white to purple. Colony-Central produces yellow mycelium and mycelium is colony-purple mycelium on the back. Reproduce the symptoms of stem rot by inoculated. ITS-rDNA sequence analysis show that pathogenic bacteria is the pathogen of wheat scab caused by F. graminearum.2. Only2species of Fusarium did cause stem rot type-white head from isolation and identification of5species of Fusarium on rice.77Fusarium isolates were collected from Wuyang Town(Shaoyang City), Longfu Town and Beisheng Town(Liuyang City), ChaLing(Zhuzhou City) and Hanshou County(Changde City), which included21of F. graminearum,16of Fusarium culmorumhas,11of Fusarium equiseti,7of Fusarium oxysporum and5of Gibberella fujikuroi. Others were Fusarium spp. After an inoculation of CLA3(F. graminearum) and D4(F. equiseti) on healthy rice, stem rot type-white head was reproduced while the other strains caused no symptom. This confirmed that CLA3and D4were the pathogen of white head. At present, white head caused by Fusarium infecting stem has not been reported in the country. F. graminearum and F. equiseti are the pathogen of wheat scab and their damage are not reported on rice in hunan.3. F. graminearum is stronger pathogenicity than F. equiseti. The two stem rot strains were inoculated by injection into3indica cultivars and3japonica cultivars. The result showed that japonica rice got infected more easily than indica rice. And the later spray inoculation on japonica rice showed that CLA3is more virulent than D4.4. Biological characteristics of stem rot Fusarium strains were tested. Both CLA3and D4grew among pH3-11. For mycelium growth of CLA3and D4, the optimum pH was7. The range of temperature was22-31℃. However, the optimum temperature of CLA3was25℃. The optimum temperature of D4was28℃. Dark treatment was most beneficial to the growth of hypha for both strains. For CLA3, the optimum carbon source was mannitol and for the D4the optimum carbon source was maltose. The optimum nitrogen source was KNO4for both strains.5. Difenoconazole and Prochloraz gave best efficacy. Antibacterial test results showed that, for CLA3, Difenoconazole and Prochloraz had the best inhibition with EC50of0.383mg-L"1and0.285mg·L-1respectively). Thiophanate-Methyl (EC50=94.088mg·L-1) and Azoxystrobin (EC50=78.726mg·L-1) were the worst. For D4Difenoconazole (EC50=0.613mg·L-1) and Prochloraz (EC50=1.477mg·L-1) also performed best. Azoxystrobin (EC50=175.800mg·L-1)had little effect.