Germination, attachment to host root and growth of
Striga hermonthica (Del.) Benth. seeds and seedlings
were studied in in vitro co-culture w ith
Sorghum bicolor (L.) Moench and in pot experiments. Two
varieties, the resistant Framida and the susceptible CK-60B, were used.
Histological, morphological and physiological studies revealed the key stages
of resistance mechanisms involved. Resistance of Framida to
Striga does not occur at the germination or the
attachment stages, since its roots do not support fewer
Striga than does CK-60B. As Framida roots support the
lowest number of young Striga stems with scale leaves,
its resistance appears to occur during the establishment of a functional
haustorium. Metabolite uptake by the haustorium and growth rate of the young
parasite were lower on Framida roots than on CK-60B roots, even when similarly
developed haustoria were compared. Furthermore, at a later stage of
infestation, significant accumulation of a coloured material likely to be rich
in phenolic compounds was observed in and around Framida conductive tissues,
but not CK-60B tissues. These features indicate the involvement of at least
three steps in development of resistance in Framida roots: the first is linked
to a partial inhibition of development of the young haustorium; the second
could play a role in the physiological events that decrease nutrient
translocation towards the haustoria; and the last seems to be associated with
the accumulation of a coloured phenolic-like material.
Impact of nitrate supply in C and N assimilation in the parasitic plant Striga hermonthica (Del.) Benth (Scrophulariaceae) and its host Sorghum bicolor L.
