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Title: Field application of benzothiadiazole (BTH) to oats (Avena sativa): Effects on crown rust resistance and avenanthramide production

item Wise, Mitchell
item Vinje, Marcus
item CONLEY, SHAWN - University Of Wisconsin

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2016
Publication Date: 6/15/2016
Citation: Wise, M.L., Vinje, M.A., Conley, S. 2016. Field application of benzothiadiazole (BTH) to oats (Avena sativa): Effects on crown rust resistance and avenanthramide production. Crop Science. 56:1904–1913. doi: 10.2135/cropsci2015.11.0712.

Interpretive Summary: Oats produce at group of phytonutrients termed avenanthramides. These metabolites demonstrate several potentially beneficial effects in laboratory experiments to include: inhibiting inflammatory responses, up-regulating biological anti-oxidant systems, and inhibition of certain cancers. Biosynthesis of avenanthramides in the vegetative tissue of oat has also been correlated with resistance to crown rust infection. Unfortunately the production of avenanthramides in the oat crop is highly variable and appears to be strongly influenced by environmental conditions; crown rust infection appears to be a key factor. Chemical plant defense activators, such as benzothiadiazole (BTH), which act by eliciting a systemic acquired resistance response, were shown to up-regulate oat avenanthramide production in greenhouse experiments. These experiments were performed to determine if application of BTH, at rates approximating the manufacturer’s recommendations, could be effective in a field environment. The results show a clear reduction in crown rust incidence among the treated plants relative to the un-treated. In two of the cultivars there was also a dose response increase in avenanthramide content in the mature grain. Leaf avenanthramides also showed a small elevation of avenanthramide content relative to the un-treated controls at certain time points but there is also evidence that leaf avenanthramide levels are influenced by other, undiscerned, factors. The impact of this report is to illustrate that plant defense activators have potential to improve the value added characteristic of avenanthramide content in oat and to offer some protection against crown rust infections.

Technical Abstract: Plant defense activators such as benzothiadiazole (BTH) are known to elicit the biosynthesis of plant phytoalexins. In oat, BTH treatment was shown to up-regulate avenanthramide production in both the vegetative tissue and filling grain in greenhouse studies. Avenanthramides are phenolic antioxidants demonstrating several nutraceutical effects in laboratory experiments including: inhibition of nuclear factor kappa beta activation, suppression of the aberrant Wnt/beta-catenin signaling pathway in HeLa cells and activation of anti-oxidant response element (ARE) associated genes in vitro. Avenanthramides are also reported to function as phytoalexins in response to crown rust infection. Presented here are the results of application of BTH under field conditions. Field trials were conducted in 2013 using four application rates, approximating manufacturer’s recommendations, on two cultivars of oat and in 2014 using three application rates on four oat cultivars. The results showed a subtle but demonstrable effect of increased avenanthramide production in vegetative tissue, mature grain and enhanced resistance to crown rust infection. Gene expression of pathogenesis related protein-1 (PR-1), phenylalanine ammonia lyase (PAL) and hydroxycinnamoyl-CoA:hydroxyanthranilate hydroxycinnamoyl-CoA transferase (HHT) was also monitored by RT-qPCR. Both PR-1 and PAL expression were demonstrably up-regulated in the field trials, HHT was not. However, greenhouse experiments showed all three genes to be elicited with 68, 9, and 3 fold increases, respectively.