Effects Of Two Kinds Of Triazole Fungicides On The Morphology And Ultrastructure Of Valsa Mali

Apple canker disease,caused by Valsa mali,often lead to apple stem rot.However,when severely infected,the whole tree can be blasted.Due to unidentified on the pathogenic process and epidemical regularity,the apple production has seriously occurred and harmful without effected management.Valsa mali is a weak parasite,with a latent period,could be long hidden in the xylem,the internal absorption fungicide is also difficult to achieve,so that the disease is difficult to cure.At present,the method of the prevention and control of the disease on the production mainly adopts the lesion curettage method combined with chemical control,but the control effect is very poor and time-consuming work.Therefore,to find the fungicide which could deeply prevent V.mali is an urgent problem to be solved.A large number of studies have shown that triazole fungicides,difenoconazole and tebuconazole could inhibit the growth of the pathogen hyphae,spore germination,and effective cure scab.Some studies have shown that triazole fungicides could cause abnormal situation of mycelium and cell structure of hyphae abnormalities.Therefore,this study reveals the mechanism of these two fungicides by light microscopy and electron microscopy,which provides an important theoretical basis for more direct and effective control of apple tree rot.The results of this experiment are as follows:1.Microscopic observation showed that two fungicides could inhibit spore germination and inhibit the elongation of germ tube,so that the germ tube could not invade the host normally,but it did not affect the swelling of spores.2.Hyphae still infected hosts after treated apple branches with two fungicides,but hyphae mainly colonization between epidermis and hyphae after callus with difenoconazole treated,hyphae expanded faster with tebuconazole treated,mainly in the cortex of colonization.3.The observation of electron microscopic discovered that,The two fungicides could induce morphological and ultrastructural changes of hyphae.The morphological changes were mainly that: the growth of apical hyphae was inhibited and the top expanded into a sphere with rough surfaces,hyphae were irregularly swelled and excessively branched,hyphal cell walls ruptured,and someones even had the protoplasm extravasation,and the part of hyphae was swollen,and the new hyphae was abnormality.The main ultrastructural changes were that,the hyphal cell walls were irregularly thickened,the number of mitochondria in cytoplasm increased and its morphology was abnormally thickened,its membrane was irregularly thickened and malformed,the number of nuclei increased and the nucleolus gradually spread,and there was extracellular deep staining maybe caused by cytoplasm leakage material.At the moment,the cell had some septum and the part of the septum was irregularly thickened and malformed,and could not even develop into a complete diaphragm.In addition,the vacuolization of mycelial cell was very serious,some intracellular organelles were disorganized until disappeared completely,the cytoplasms were necrosis.It was worthy of being mentioned that there was a discovery: a daughter hypha was formed within the original degenerated hypha.However,The cell walls were irregularly thickened,and the cytoplasms of the daughter hyphae with disorganized organelles were necrosis,the original degenerated hypha cell walls were disappeared.Difenoconazole could lead to hyphal cell wall degradation,extracellular substances appear darker,cytoplasmic consolidation is not serious.However the whole cell wall was thickened and no degradation with tebuconazole,no granular material was found outside the cells,cytoplasmic consolidation is serious and can lead to cell necrosis.