| dc.description.abstract | Striga hermonthica (Del.) Benth. is a severe parasite on maize and
a limiting factor in achieving optimum maize yields in infested
areas in Africa. The parasite seeds are stimulated to germinate by
root exudates from host and non-host plants as well as by synthetic
germination stimulants. Objectives of these experiments were to
determine laboratory, screenhouse and field conditions for inducing
maximum germination of S. hermonthica seeds with extracts from
cultivars of cowpea (Vigna unguiculata (L) Walp.), cotton
(Gossypium spp.) and soybean (Glycine max. L.) plants, their
residues and a synthetic germination stimulant, GR 24.
Extracts of cowpea roots and S~lOOtS stimulated about 30 to 40% as
much germination as 10-2 mgL-1 GR 24. No differences were observed
among cowpea cuitivars in germination percent of S. hermonthica
seeds induced by the aqueous extracts. The population from Mokwa
responded most to the extracts. Increasing concentrations of both
whole cowpea plant extracts and GR 24 resul ted in increased S.
hermonthica seed germination upto 6.3mg plant tissue mL-1 of water
and 10-2 mgL -1 respectively, beyond which germination decreased.
Higher germination was recorded when incubation time of S.
hermonthica seeds with GR 24 at 30°C was increased from 24 to 48
hours in microtiter wells. Storing plant extracts at 7°C for 20
days did not reduce potency.
Germination of S. hermonthica seeds by cotton and cowpea plant
parts were dependent on the source of the stimulant, weight of
plant part and the distance of the parasite seeds from the source
of the stimulant. Germination of S. hermonthica seeds decreased
with increase in weight of plant part and period of time each
cultivar was grown. Cotton roots contained the most effective S.
hermonthica seed germination stimulant among the plant materials
tested. With both S. hermonthica and S. aspera, mixtures of cotton
extracts from different plant parts depressed germination of the
seeds below the average induced by individual extracts in the
mixture. Some extracts and mixtures were as effective as 10-2mgL-l
of GR 24.
DCM soluble extracts of cottoq and cowpea plant parts of different
ages separated by thin layer chromatography showed that the
extracts contained several similar compounds as shown by position
of relative fronts. DCM extracts of S. hermonthica seeds contained
similar compounds. Germination of S. hermonthica seeds by DCM
soluble extracts of cotton and cowpea roots increased with
increasing concentration from 0.1 to 0.5 % and 0.1 to 1.0 % for
cotton and cowpea respectively and then declined with further
increase in concentration.
Soybean extracts from TGX-1674-1F was as effective as 10-3 mgL'l GR
24 in inducing germination of S. hernJonthica seeds collected from
sorghum in Zaria, Mokwa and Abuja in 1991. Other very effective
cultivars were TGX-1660-18F and TGX-1674-8F from Zaria and Mokwa
respectively. Screenhouse experiments indicated that growing cotton
(Abuja Local) or cowpea (Tvx 3236) in S. hermonthica infested soil
the previous season significantly reduced parasitism on maize
planted the following season and increased yields. Unemerged
attached, emerged, total attached S. hermonthica and root dry
weight were positively correlated with symptom severity on maize.
All parameters were negatively correlated with grain weight, and
all, except stem dry weight were negatively correlated with harvest
index. Unemerged attached, emerged and total attached parasites on
each maize plant decreased with increasing length of cotton or
cowpea growth the previous season. No significant advantage was
obtained by addition of fresh cotton or cowpea mulch.
Pot experiments with crop residues indicated that at all incubation
periods of cowpea and soybean residues increasing weight of residue
delayed S. hermonthica emergence, reduced total number of parasites
attached per maize plant and increased plant height and total dry
matter yield of maize. At all residue levels, incubation period of
the parasite seeds and the residues for at least 7 days was
required to significantly reduce parasitism of S. hennonthica on
maize. Field experiments showed that all rotations significantly
reduced the number of attached parasites on maize plants and
increased grain yields the following season. Addition of residues
from Tvx 3236 reduced parasitism of the parasite on maize and
increased yields. | en |
