Title : Report of pathogen identification and preliminary control technology on fruit rot and leaves blight on Macadamia ternifolia
Abstract:
Macadamia is native to Australia with important nutritional and economic value. After being introduced in my country, it has been planted in Yunnan, Guangxi and other places on a large scale. In this study, samples of macadamia fruit rot and leaf blight fungal diseases were collected from Yingjiang County, southern Yunnan Province. Part of the fungal strains were isolated, and the pathogens were verified by Koch's postulates. The identification of pathogen species is carried out through the observation of the morphological characteristics of pathogens and the phylogenetic analysis based on multiple genes. On the basis of observing the biological characteristics of pathogens, the study conducted biological and chemical control of pathogens experiments. The main findings are as follows: Isolation, purification and pathogenicity determination of the pathogens of macadamia fruit rot and leaf blight: The tissue separation method was used to separate, purify and determine the pathogenicity of macadamia fruit rot and leaf blight. A total of 20 fungi were isolated from the diseased fruits of macadamia fruit rot. After Koch's postulates experiment, Lasiodiplodia pseudotheobromae was identified as the pathogen of the disease. A total of 24 fungi were isolated from diseased leaves of macadamia leaf blight. After Koch's postulates experiment, Beltrania pseudorhombica was identified as the pathogen of the disease.
Identification of the types of pathogens: Colonies of L. pseudotheobromae which grew on PDA were regularly round, and reached an average 60 mm after 3 days in the dark at 25°C.The conidia are produced in the conidiomata. Aerial mycelia were dense, felted, and grey-white at early stage. With age, the color darkened and became pale olivaceous grey to olivaceous grey. Mature conidia were brownish, longitudinally, striate, 1-septate and thickened wall. The fungal taxonomy was further analyzed under molecular identification. The internal transcribed spacer (ITS) region, and translation elongation factor 1-α (tef1-α) of the fungal isolates. These characteristics were in accordance with the morphological and molecular identification of L. pseudotheobromae. Colonies of B. pseudorhombica which grew on PDA were regularly slowly at the beginning. The colonies showed a fluffy spreading type, the color darkened and became pale olivaceous grey to olivaceous grey. Mature conidia went from green-yellow to brownish, solitary, biconical, with short appendage filaments connecting the tail, without septum. The fungal taxonomy was further analyzed under molecular identification. These characteristics were in accordance with the morphological and molecular identification of B. pseudorhombica.
Biological control and chemical control: biocontrol fungus (SMEL1) and biocontrol bacteria (B. velezensis) YCEB-20 had an inhibition effect on the mycelial growth, appressorium formation and maturation of the pathogens of macadamia fruit rot and leaf blight. The results of the susceptibility test of the L. pseudotheobromae and B. pseudorhombica to six chemical agents showed that the agents had different effects on the growth of the hyphae and spore germination of the two pathogenic fungi. The above research provides a certain reference for the prevention and control of macadamia fruit rot and leaf blight.
