Studies On The Liquorice Leaf Spot For Alternaria

It is the first report about the largely occurrence of liquorice leaf spot caused by Alternaria azukiae in the Weiyuan region of Gansu Province in China.1.The major symptoms of the disease were described in detail. It initinally appears as circular,oblong, puce lesions with concentric lines in center on leaves,the biggest lesions can reach 6.0mm. Severely these lesions gradually turn black,connect each other and eventually lead to death of very diseased sites.The pathogenetic strain was isolated from diseased leaves of liquorice. Conidiophores are straight or curved,ramification or not ramification. Conidia have a layer similar to a beak,or no beak ,they are Lacking definite form,clavate,ovate or shuttle,brown or fuscous~brown,with 1～6 transverse and 0～4 longitudinal septa. In view of the morphological characteristic,the morphology is consistence, so it is confirmed the same species. The pathogen is identified as Alternaria azukiae.Alternaria azukiae not only infect liquorice,but also infect stramonium, duhuo,tengsanqi,and other Chinese traditional medicine.2. The results of the biological characteristics of the pathogen of liquorice leaf spot showed that temperature and pH affected the mycelium growth and sporulation of the fungus. The optimum growth and sporulation temperature was 30℃.The suitable pH was 8.The light time does not affected the mucelinm growth, but affected sporulation. light condition is good to sporulate. Both carbon sources and nitrogen source had an effect on the mycelium growth and sporulation. The growth of mycelia was the quickest with mannitol , and the number of sporulation was the largest with dextrose .So did the nitrogen sources. nitre was the most suitable for the growth of mycelia and sporulation. Alternaria azukiae grew faster on PDA.3. It is the first systematic research about the ocuurence of liquorice leaf spot. The result indicated that the primary infection sources mainly come from liquorice refuse in soil, secondly from infected seeds. The occurrence of the disease is closely correlated with weather conditions, site condition and the crop rotation.4. The more effective fungicides were chosed, such as 70%thiophanate methyl,mepiquat chloride,68.75%du bang yi bao. And the 68.75%du bang yi bao has the best bacteriostatic effect in them.The bottle green Trichoderma has the more bacteriostatic effect to Alternaria azukiae, and the effect is not reduce when the spore concentration changed.