| Abstract
| - Benzoxazinoids (Bx) are natural phytotoxins that function as chemical defense compounds in severalspecies. The release of Bx by intact plant roots associated these compounds with root allelopathy inTriticeae species; however, the significance of exudate concentrations of Bx for plant−plant interactionsis still a controversial question. A biological screening of 146 cultivars of four Triticeae species (Triticumaestivum L., Triticum durum Desf., Triticum spelta L., and Secale cereale L.) demonstrated a highcultivar dependence to suppress the root growth of Sinapis alba L. by root allelopathy in a dose−response bioassay. Only a few cultivars possessed a marked high or low allelopathic activity, wherebyhigh-performance liquid chromatography−diode array detection analysis of root exudates revealedthat these cultivars differed considerably in their ability to exude the two Bx aglucones, DIBOA [2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one] and DIMBOA [2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one]. The total amount of DIBOA and DIMBOA exuded showed a significant correlation to thegrowth inhibition in bioassay with a statistically estimated contribution to the overall allelopathiceffect of 48−72%. In a bioassay with pure phytotoxins, Bx concentrations consistent with theamounts quantified in the screening bioassay caused detrimental effects on S. alba and almostreproduced the statistically estimated contribution. The observed causal association between theallelopathic activity under laboratory conditions and the exudate concentrations of Bx suggests thatthis association might have implications for the interference of Triticeae species in natural plantcommunities. Keywords: Allelopathy; DIBOA; DIMBOA; root exudation; rye; wheat
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