Natural uptake of anti-oomycetes Trichoderma produced secondary metabolites from pearl millet seedlings ? A new mechanism of biological control of downy mildew disease

The present study aims to analyze the pearl millet (PM) seedlings ability to uptake anti-oomycetes secondary metabolites (SMs) produced by Trichoderma and their subsequent involvement in downy mildew (DM) disease suppression. SMs from potent Trichoderma spp. were extracted and studied for their anti-mildew and zoospor-angiosporicidal properties in PM infected with Sclerospora graminicola. Varying degree of inhibition was recorded against sporangiophore development on the infected abaxial leaf surface and zoosporangiosporicidal activity by SMs. T. asperellum (DL-81) recorded higher anti-mildew activity and 83% of zoosporangiosporicidal activity. Xylem exudates collected from decapitated PM seedlings pretreated with SMs as soil drench also recorded similar activities. Similarly, xylem exudates collected from T. atroviride (MH-50), T. asperellum (DL-81), T. virens (MP-60) and treated seedlings recorded 42%, 40% and 36% of zoosporangiospricidal activity, respectively. Under greenhouse conditions, seed, soil drench and foliar spray treatment with crude SMs showed the reduction in diseases incidence. Least disease incidence of 14.6% was recorded with T. asperellum (DL-81)-SMs soil drench followed by T. virens (MP-60)-SMs soil drench treatment (15.5%). Supporting to our laboratory and greenhouse studies, UPLC-MS/MS analysis of SMs from culture filtrates and xylem exudates of selected Trichoderma revealed the presence of several compounds, which were previously reported as antimicrobial in nature. A novel biocontrol mechanism through which the PM can uptake some anti-oomycetes compounds from rhizosphere and suppress the DM severity is discussed in this study.