Systemic protection against pearl millet downy mildew disease induced by cell wall glucan elicitors from Trichoderma hamatum UOM 13

The obligate oomycete Sclerospora graminicola (Sacc.) Schroet, is the incitant of downy mildew disease, which is the main constraint in pearl millet production worldwide. Different elicitors from Trichoderma hamatum UOM 13, e.g. mycelial extract and cell wall glucans, were assessed for their resistance elicitation efficiency and the possible underlying mechanisms. Both mycelial extract and cell wall glucans of T. hamatum UOM 13 positively influenced seed quality parameters of pearl millet, significantly enhanced seed germination and seedling vigor in comparison to the untreated control. Seed priming with cell wall glucan elicitors of T. hamatum UOM 13 suppressed downy mildew on susceptible pearl millet seedlings under greenhouse conditions by induction of systemic host resistance. Of the different elicitor delivery methods tested, transplant root dip was more effective than seed treatment and foliar spray. A combination of transplant root dip + seed treatment + foliar spray was significantly more effective than the single delivery methods. The induced resistance corresponded to up regulation of genes of important defense proteins upon pathogen inoculation. Transcripts of genes of defense enzymes glucanase, phenylalanine ammonia lyase, peroxidase and polyphenoloxidase were significantly increased due to the T. hamatum UOM elicitor effect. Expression of hydroxyproline-rich glycoprotein genes, known to play an important role in cell wall cross-linking, were also up regulated in response to T. hamatum UOM cell wall glucan treatment. This study emphasizes the role of T. hamatum UOM as a potential elicitor of downy mildew resistance in pearl millet and presents novel insights into the involvement of important defense proteins mediating such as resistance trigger.