Identification of Two Fungal Pathogens Responsible for Liriodendron chinense × tulipifera Black Spot and Screening of Trichoderma sp. for Disease Control.

Liriodendron chinense × tulipifera black spot is a newly discovered disease that causes yellowing and early shedding of leaves, affecting the growth of Liriodendron trees, and significantly reducing their ornamental value as a garden species. The pathogen responsible for this disease, and how it can be prevented and controlled, are not clear. In this study, the occurrence of this disease was first investigated according to Koch's postulates, and the primary pathogens causing Liriodendron black spot were determined to be Colletotrichum gloeosporioides and Alternaria alternata . Biocontrol strains antagonistic to these two pathogens were then screened from the leaf microorganisms of L . chinense × tulipifera , and a preliminary investigation of the biological control of Liriodendron black spot was performed. Through the screening of antagonistic microorganisms on the leaf surface of L . chinense × tulipifera , the strain Trichoderma koningiopsis T2, which displayed strong antagonism against C . gloeosporioides and A . alternata , was obtained. The T2 strain could inhibit the growth of the two pathogens via three mechanisms: hyperparasitism, volatile and nonvolatile metabolite production, and environmental acidification. The biocontrol experiments in the greenhouse and field showed that initial spraying with a T . koningiopsis T2 spore suspension followed by the two pathogens resulted in the lowest disease incidence. These results confirmed the black spot pathogens of L . chinense × tulipifera , clarified the antagonistic mechanism of T . koningiopsis T2 against the two pathogens, and provided a theoretical basis and technical support for the biological control of the disease.