|
Allelochemical
mechanisms of Striga hermonthica
suppression by Desmodium uncinatum
J.A. Pickett,
Z.R. Khan, A. Hassanali, W. Overholt, T.M. Khamis, A.M. Hooper,
L.J. Wadhams
& C.M. Woodcock
During investigations into the control of insect
damage to maize crops in subsistence farming in Kenya, which involved
intercropping with repellent plants, the fodder legumes silverleaf (Desmodium
uncinatum) and greenleaf (D.
intortum) were also found to reduce dramatically the infestation of
maize by parasitic witchweeds such as Striga
hermonthica. This
effect was confirmed by further field testing and shown to be
significantly greater than that observed with other legumes, e.g.
cowpea, as were the concomitant yield increases. The mechanism was
investigated, and although soil shading and addition of nitrogen
fertiliser showed some benefits against S.
hermonthica infestation, a putative allelopathic mechanism for D.
uncinatum was also observed. In screenhouse studies, a highly
significant reduction in S. hermonthica infestation was obtained when an aqueous solution,
eluting from pots in which D.
uncinatum plants were growing, was used to irrigate pots of maize
planted in soil seeded with high levels of S.
hermonthica. Growth of
the parasitic weed was almost completely suppressed, whereas extensive
infestation occurred with the control eluate. Laboratory investigations
into the allelopathic effect of
D. uncinatum, using samples of
water-soluble chemical components exuded from cleaned roots,
demonstrated that this involved a germination stimulant for S.
hermonthica and also an inhibitor for haustorial development.
|
