(Schizaphis graminum). High levels of DIBOA
(28mmol/kg fresh weight) were reported in Elymus
arizonicus (Scribner & Smith) Gould (Arizona wheat-
grass). Arizona wheatgrass is suggested to be the most
promising genus for breeding programs. Hydroxamic
acids are non-volatile compounds and released into the
environment by root exudation (Niemeyer and Perez,
1995). Barnes and Putnam (1983, 1986) reported that
spring-sown rye suppressed the weed biomass by 93%
when compared to rye-free plots. Interestingly, suppres-
sion of weeds such as wild oat was observed with rye
cultivars and not with wheat or oat cultivars (Niemeyer
and Perez, 1995). Niemeyer and Perez (1995) concluded
that high amounts of hydroxamic acids in the roots
should not be the criterion for the selection of
allelopathic varieties. Root exudates are key to crop
allelopathy. Root content is of little value as exudation