Metabolic Profiling for Benzoxazinoids in Weed Suppressive and Early Vigour Wheat Genotypes

Replicated and randomized wheat (Triticum aestivum L.) cultivar trials were conducted in moderate to low rainfall zones at Wagga Wagga (572 mm) and Condobolin (449 mm) NSW, respectively in 2014-2016. At each experimental site, crop and/or weed growth were monitored at selected growth stages including tillering, vegetative, grain filling, harvest and after crop harvest. In addition, plant shoot and root tissues and rhizoplane, rhizosphere and bulk soil samples were collected for metabolomics profiling and biomass evaluation. Plant tissue samples were extracted in methanol using an automated Buchi high pressure extractor while soil samples were extracted over 24h using a rotary shaker. Extracts were filtered and specifically analyzed for numerous secondary metabolites or allelochemicals associated with weed suppression using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-ESI MS QToF, Agilent 6530). Benzoxazinoids (BXs) were profiled in negative ion mode and related microbially-produced metabolites (APO, AAPO, AAMPO) were profiled in positive ion mode. Metabolic profiling resulted in detection of up to 20 individual BXs including BX glycosides, lactones, hydroxamic acids and related microbial metabolites of interest. Both qualitative and quantitative differences in BXs were observed and were cultivar-, growth stage- and location-dependent. Plant part and rhizosphere location (distance from root) also impacted BX concentration. Microbially produced metabolites with phytotoxic activity were detected in rhizosphere soils. Metabolic profiling provided information regarding wheat metabolism, as well as the biosynthesis and release of metabolites associated with weed suppression in commercial wheat cultivars, in contrast to rye (Secale cereale L.) and a heritage wheat cultivar Federation, both recognized for their potent ability to suppress weeds. Certain wheat cultivars maintained high yield potential and were significantly more weed suppressive, depending on year and location, likely because of their vigorous early growth habit and canopy architecture as well as release of BX and related microbially produced metabolites into the rhizosphere over time.