Eucalyptus is one of the three fast-growing tree species in China, and as one of the four pillars of Guangxi’s forestry economy, it has important economic, social and ecological values. With the expansion of planting area, the change of ecological environment and poor management, the occurrence of Eucalyptus leaf diseases is becoming more and more serious, which affects the growth of Eucalyptus and restricts the healthy development of Eucalyptus industry. Eucalyptus grows rapidly, leaf diseases are difficult to detect in the early stage, and after the disaster, the leaves are lost in a large area, the plant growth cycle is shortened, and the growth is slow, causing significant economic losses. In order to identify the diseases pathogenic fungi, enriching the biological control resources of Eucalyptus leaf diseases and formulate a reasonable disease control plan.

Based on the Koch rule to determine the pathogenicity, identify the pathogenic fungi, use morphological characteristics and rDNA-ITS sequence analysis to identify the pathogenic fungi, and use the plate confrontation method to screen the pathogenic antagonistic bacteria from the surface of Eucalyptus leaves, and identify them, and the evaluation of the control efficacy of biocontrol bacteria was also carried out, so as to provide a basis for the biological control of the Eucalyptus leaf diseases.

The results showed that four pathogenic fungi were isolated from the leaves of eucalyptus trees in Da Gui Shan Stateowned forest farm, namely F202310093, F202310094, F202310095 and F202310096, and the leaf disease symptoms caused by them were consistent with the onset symptoms of forest disease. Combined with morphological characteristics and rDNA-ITS sequence analysis, the four fungi were Colletotrichum fructicola, C. cliviicola, C. siemese and Coniella quercicola. The strains B2311001 with obvious antagonism to the above four pathogenic fungi were screened and identified as Bacillus subtillis by plate confrontation method which identified as Bacillus subtilis by morphological and 16s rDNA sequence analysis. The control effect of antagonistic bacteria was better than that of azoxystrobin, and the potted control effect against C. fructicola was 84.01%, followed by C. siemese with 83.67%, and the lowest control effect was Coniella quercicola, with an interforest control effect of 81.33%. C. cliviicola and C. siamense was first reported as a pathogenic fungi of Eucalyptus leaves disease.

In this study, the antagonistic bacteria of eucalyptus leaf pathogens were screened, and the biocontrol resources of Eucalyptus leaf diseases were enriched, and a theoretical basis was provided for the biological control of Eucalyptus leaf diseases.