The relative phytotoxicity of sorgoleone as measured by seed germination
and seedling growth of
selected crop and weed species and inhibition of photosynthetic oxygen
evolution in atrazine-resistant
and -susceptible cell cultures of potato (Solanum
tuberosum L.) and common groundsel
(Senecio
vulgaris L.) were investigated. Relatively little or no
effect of sorgoleone was observed on radicle
elongation at concentrations less than 500 μM in Petri dish
bioassays. Sorgoleone was very
phytotoxic to large crabgrass (Digitatia sanguinalis), with
a GR50 of 10 μM for shoot growth in a
hydroponic culture bioassay. Inhibition of shoot and root growth
of velvetleaf (Abutilon theophrasti)
and barnyardgrass (Echinocloa crus-galli) was also observed
at higher concentrations ranging from
10 to 200 μM, but ivyleaf morningglory (Ipomea hederacea)
was tolerant. Sorgoleone inhibited
photosynthetic oxygen evolution in both susceptible and resistant cell
cultures of potato and common
groundsel, and the effect was similar to that of diuron, a strong
inhibitor of PS II electron transport.
Chlorophyll fluorescence response to sorgoleone in both resistant
and susceptible cell cultures was
nearly the same. Grain sorghum (Sorghum
bicolor L. Moench) genotypes varied considerably
in
the amount of sorgoleone produced. Root exudates generally
contained 85−90% pure sorgoleone
on the basis of HPLC analysis. These data indicate that sorgoleone
is phytotoxic at micromolar
concentrations, exhibits marked selectivity, and inhibits
photosynthetic electron transport similar
to diuron.
Keywords: Sorgoleone; bioassay; hydroponics; inhibition; phytotoxicity;
photosynthetic oxygen
evolution; electron transport; root exudate
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