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Induction of apoptosis in the anthracnose fungi by Bacillus subtilis

Tzu-Pi Huang: Department of Plant Pathology, National Chung Hsing University

<div>Anthracnose on passion fruits caused by <em>Colletotrichum</em> species is a destructive disease hindering the production. The main objectives are to select and identify native antagonistic microorganisms against anthracnose fungi on passion fruits; to exploit their potential application in disease control and growth promotion; and to investigate the putative control mechanisms. The strain 151B1 isolated from rhizosphere soils in Taichung city, Taiwan was classified as the <em>Bacillus subtilis </em>based on the analysis of 16S rRNA sequences, DNA polymorphism, physiology and biochemistry tests and by Biolog System III. <em>B. subtilis</em> 151B1 showed inhibitory effect on mycelial growth and conidial germination of <em>Colletotrichum</em> sp. N-PF1. Application of <em>B. subtilis </em>151B1 culture broth increased survival rates of passion fruit cuttings with or without inoculation of anthracnose fungi compared to the water and medium controls. It also enhanced the plant height, numbers of leaves, nodes, leaf width, and shoot fresh weights of passion fruit seedlings compared to the controls. Treatment of culture filtrates from strain 151B1 resulted in cell death and chromatin fragmentation, and caused reduction in mitochondrial membrane potential and energy metabolism of <em>Colletotrichum</em> sp. N-PF1, suggesting its function in triggering apoptotic-like cell death. In conclusion, <em>B. subtilis </em>151B1 is a potential biocontrol agent for anthracnose disease of passion fruits. Our findings also suggested that aberrant hyphal morphology and inhibition of spore germination of anthracnose fungi caused by culture filtrates of <em>B. subtilis</em> 151B1 may in part attribute to their ability in triggering program cell death of the fungi.</div>