Studies On Bionomics Comparison Of Different Strains Of Sclerotinia Sclerotiorum And Methods For Identification Of Resistance In Rapeseed

Sclerotia was collected from the infected stem of Brassica napobrassica in suburbs of Ya—an, Leshan, Mianyang, Mianzhu, Yibin and Chengdu of Sichuan province. They were Sclerotinia sclerotiorum by purification and identification, and been reserved by cultivation on PDA medium.Comparison of bionomics among the strains of S. sclerotorium from different districts was made. The rerults indicated that the hypha of the strain Mianzhu grew the fastest and those of Leshan were much slower at the different temperature. The strain Mianyang produced sclerotia quickly and strain Yibin were the most slow. The faster growth of hypha was and the more quickly sclerotia formed, however, the converse was not so sure. In different pH treatments, Sclerotinia sclerotiorum for Ya-an was acid tolerance, for Mianyang was alkali tolerance, and for Mianzhu was strongly tolerant to the acid and alkali.The pathogenicity of Sclerotinia sclerotiorum collected from six districts had not obvious differentiation. The optimum temperatures of hypha growth and sclerotia formed were 25℃, and optimum temperature range of hypha growth was 20℃-25℃, forming sclerotium was 20℃-30℃. The optimum pH range of hypha growth was pH4-pH7, the more suitable medium for the hyphal growth was wheat bran medium, next was PDA.The fungicide test in the lab indicated that Topsin-M was most efficiante to inhibit hypha growth, the EC₅₀ was 4.6, the next was Fernasan. The effect of Carbendazol, Chlororthalonil or Dasheng M-45 was not so good.The seven methods reported for identification of resistance to Sclerotinia sclerotiorum were compared with two susceptible and two resistant rapeseed varieties under the same conditions. The results indicated that the method of dipping root( or leaf) into oxalic acid solution was not suitable for resistance identification of Brassica rapa L. It suggested that the resistance identification be done during flowering period and seedling identification was used only as supplement method because the resistance to S. sclerotiorum was different at the different growth stages. In three inoculation methods of inoculating infected wheat grain to leaf axil,mycelium agar disk to leaf axil and infected toothpick to stem, the disease severity in the varieties tested were toothpicks > wheat grains > agar disks. The results of the three methods were significantly correlated with field inoculation identification (r>0.800). The three methods during flowering period could well react varieties' resistance and susceptibility. Especially, the correlation between toothpick inoculation and field inoculation was highly significant (r=0.9140). According to the results above, 44 breeding materials which were provided by the Rapeseed Research Center of Sichuan Agriculture University, were tested with the toothpick method. The results showed that there were 12 high resistant materials, of which the resistance of 5 materials was much higher than control variety, the resistant rates were all above 0.55.The determination of enzymatic activity showed that POD and SOD(in 18 hours) were positive correlation with variety resistance in not innoculation rapes, however, while rapes were innoculation, SOD and PAL of the varieties were related positively to the resistance, and the enzymatic activity of resistant variety rised much faster and higher. The activity of defensive enzymes was quite different between innoculation and not inoculation rapes. The results suggested it was one of the physiology and biochemistry mechanisms of rapeseed variety resistance to S.sclerotiorum.