Aspergillus terreus Inhibits Growth and Induces Morphological Abnormalities in Pythium aphanidermatum and Suppresses Pythium-Induced Damping-Off of Cucumber

Abstract

The study investigated the efficacy of two isolates of <i>Aspergillus terreus</i> (65P and 9F) on the growth, morphology and pathogenicity of <i>Pythium aphanidermatum</i> on cucumber. <i>In vitro</i> tests showed that the two isolates inhibited the growth of <i>P. aphanidermatum</i> in culture. Investigating <i>P. aphanidermatum</i> hyphae close to the inhibition zone showed that the hyphae showed abnormal growth and loss of internal content. Treating <i>P. aphanidermatum</i> with the culture filtrate (CF) of <i>A. terreus</i> resulted in significant rise in cellular leakage of <i>P. aphanidermatum</i> mycelium. Testing glucanase enzyme activity by both <i>A. terreus</i> isolates showed a significant increase in glucanase activity. This suggests that the cell walls of <i>Pythium</i>, which consist of glucan, are affected by the glucanase enzyme produced by <i>A. terreus</i>. In addition, Aspergillus isolates produced siderephore, which is suggested to be involved in inhibition of <i>Pythium</i> growth. Also, the CFs of 65P and 9F isolates significantly reduced spore production by <i>P. aphanidermatum</i> compared to the control (<i>P</i> < 0.05). In bioassay tests, the two isolates of <i>A. terreus</i> increased the survival rate of cucumber seedlings from 10 to 20% in the control seedlings treated with <i>P. aphanidermatum</i> to 38-39% when the biocontrol agents were used. No disease symptoms were observed on cucumber seedlings only treated with the isolates 65P and 9F of <i>A. terreus</i>. In addition, the <i>A. terreus</i> isolates did not have any negative effects on the growth of cucumber seedlings. This study shows that isolates of <i>A. terreus</i> can help suppress <i>Pythium</i>-induced damping-off of cucumber, which is suggested to be through the effect of <i>A. terreus</i> and its glucanase enzyme on <i>P. aphanidermatum</i> mycelium.