Study On Scrophulariae Leaf Spot Caused By Septoria Scrophulariae

Scrophulariae grayana as an important traditional herbal, its has a wide range of applications in traditional Chinese medicine, the current production has a large-scale cultivation. Septoria scrophulariae West, the causal agent of Figwort leaf spot is the most destructive foliar disease of Figwort Root. The biological characteristics of the pathogen was studied first and systematically. The results are as follows:1. The biological characteristics of the Septoria scrophulariaeThe temperature rage for mycelium growth and sporulation was 10 to 30℃, the optimum temperature was 20 to 25℃, the most suitable pH value was 6 to 7, the pathogen could grow and sporulate well on 10% of the host juice + PDA, soluble starch and maltose are the most favorable to mycelial growth, sucrose and maltose are the most conducive to sporulation, organic nitrogen is more conducive than the inorganic nitrogen to mycelium growth and sporulation. The light treatment hadn't remarkable effect on the mycelium growth and sprulation. Conidia germinated at 10 to 35℃,with optimum temperature was 20 to 25℃. Conidia were able to germinate in sterile deionized water but at a low percentage, sugar and host juice stimulated conidial germination of the pathogen. The maximum rate of spore germination was in 20 % of the host juice. The lowest relative humidity of germination was 93 % ,and the maximum rate of spore germination was in water. The optimum pH value for sporulation was 5-7. The light hadn't substantial effect on spore germination. The lethal temperature of conidia was 55℃(10min).2. The infection process of Septoria scrophulariaeInfection process to Scrophulariae grayana by Septoria scrophulariae was studied. Results showed that conidia germinated at the leaves surface after inoculating for six hours, conidia germ tube from the one side, on two sides or the middle, tube extended,then formed the non-branched hypha, hypha was the infection structure of S. scrophulariae. The pathogen was able to penetrate host through two paths such as stomata and epidermis after inoculation.3. The infection conditions of Septoria scrophulariaeThe infection of Scrophulariae grayana by Septoria scrophulariae could be occured at 10 to30℃, the incubation period was the shortest(9d) and the optimum temperature of infection was 25℃. The wetness period rage for infecting leaf of Scrophulariae grayana by Septoria scrophulariae was 12-72 hour, the optimum wetness period was 24-72 hour. The Septoria scrophulariae infected the basal leaves firstly, the spreaded to the upper leaves. Old leaves had more conducive to the infection.4. The infection sources and diesease dynamics of Scrophulariae leaf spot in fieldThe infection sources of Scrophulariae leaf spot were the mycelium and conidia in pycnidia, the pathogen overwinter on the disease leaves and in the field in form of the mycelium. The following year in spring, the pathogen encountered rain, the conidia were released, then caused primary infection. The diseased began to appear in early March, the strain rate and the diseased leaves rate were 5 % and 6.06 %. From March to May the expansion of the disease from the lower leaves to the upper leaves and nearby plants. Because of the temperature riseing fast and rainwater is more, the strain rate, the diseased leaves rate and the index of disease increased significantly. The strain rate, the diseased leaves rate and the index of disease were 38%,32.29% and 26.11. From July to October, the Scrophulariae ground part growth is slowing, the new leaves is less, the disease developed rapidly because of the hot and humid weather conditions, so the strain rate, the diseased leaves rate and the index of disease reached to 100%,79.89% and 62.07.5. The fungicides screening in laboratoryThe five fungicides were tested in laboratory to determine the effect on the mycelical growth and germination of conidia. The results showed that Thiophanate-methyl, carbendazim, mancozeb and chlorothalonil were good fungicides on the inhibition of the mycelial growth and the germination of conidia. Triadimefon were bad fungicides on the inhibition of the mycelial growth and the germination of conidia.