Study On Isolation, Identification And Biological Characteristics Of A Pathogenic Strain Alternaria Sp. WH56 Against Water Hyacinth

Rapid spread of Water Hyacinth (Eichhornia crassipes) caused serious environmental problems, which was recognized throughout the world. Currently, controlling Water Hyacinth with pathogens gained more and more attention.An Alternaria strain WH56, with high pathogenicity against Water Hyacinth was isolated from naturally diseased Water Hyacinth collected from Zhejiang province. On the basis of determining the pathogenicity of WH56 against Water Hyacinth, biological characteristics of the strain were studied. And the genetic relationship between WH56 and Alternaria eichhorniae, an internationally recognized potent pathogen against Water Hyacinth, was further analysed at the molecular level. Five representative sequences of Alternaria sp.WH56 and Alternaria eichhornaria including the ITS region,eg gene,ssu region,hk gene and gpd gene were sequenced and blasted with other signed Alternaria species on Genbank. The results were as follows: The diseaed ratings of Alternaria sp.WH56 was 100%; the diseased indexes were 46.47%, 75.38%, 85.71% and 100% after 7 days, 14 days, 21 days and 28 days respectively.Conidiophores of Alternaria sp.WH56 were light brown, septate, curved and rarely branched measuring 53.4 to 96.7μm long and 3.8 to 6.2μm wide. Conidia developed singly at the blown-out ends of each conidiophore and rarely appeared in chains of 2-3. The Conidia were obclavate, dark olive brown with 2-5 transverse and 1-4 longitudinal septa, dictyospores to nearly ovoid and measured 35.26 to 55.5μm (average 43.8μm) long and 9.7 to 18.0 (average 13.3μm)μm wide.The colony of Alternaria sp.WH56 was red by the excretion of a red hydrosoluble pigment. The colony of Alternaria sp.WH56 growed best and presented dark red on PDA under the light treatment of alternation illumination and darkness while the colony growed better and presented proper red on PDA under all illumination. All darkness did not benefit colony growth and excretion of the red pigment of Alternaria sp.WH56. The optimum temperature for colony longtime growth was found to be 25℃. The thermal death point of Alternaria sp.WH56 was 56℃for 10 minutes. At the condition of neutral pH or alkalescence, the best colony growth was obtained. The fitting carbon and nitrogen source were glucose and sodium nitrate respectively. Alternaria sp.WH56 presented varying morphological characteristics on different media tested, and the colonies grothed best on PDA, PDAY and MDYEA.Five phylogenetic trees were generated from the aligned ITS region,eg gene,ssu region,hk gene and gpd gene sequences. The treeing analyses showed that Alternaria sp.WH56 presented highly homologous with Alternaria eichhornaria, and the sequence similarities were 100%(449/449bp), 99.06%(420/424bp), 99.43%(524/527bp), 98.36%(1322/1344bp) and 100%(524/524bp) respectively.Biological characteristics of WH56 and phylogenetic tree analyses indicated that Alternaria sp.WH56 could be basically identified as Alternaria eichhornaria.The results listed above indicated that Alternaria sp.WH56, isolated from this study, possessed the great potential to be developed into the fungal herbicide against Water Hyacinth. This research had positive significances for the biological control of exotic plants.