The parasitism of Striga hermonthica Benth. on Sorghum spp. under irrigation: I. Preliminary results and the effect of heavy and light irrigation on Striga attack

Investigations were carried out at the Gezira Research Farm in the Anglo‐Egyptian Sudan. The greater majority of the seeds of Striga hermonthica can only be germinated by excretions from roots of certain plants not all of which can act as hosts for this parasite. Unless it becomes attached to a host plant, the Striga seedling dies. The growing of those plants whose roots can stimulate the germination of Striga seed but cannot be parasitized by it, may be a means of ridding infested land of this parasite. Green ovaries picked from flowering plants produce viable seeds if left to dry. Sorghum is sown in the field during the rainy season, viz. June to October: the earlier the sowing date within this period the greater is the Striga attack. In the field Striga seeds are distributed in the soil to a depth of at least 15 in. When Striga seeds are evenly distributed through the soil, the number of Striga seedlings attached to a sorghum root is proportional to the root's development. Size of sorghum seed has no effect on the root size of a sorghum plant and consequently no effect on the degree of parasitism. The effect of severe Striga attack on the sorghum plant is to produce a reduction of about 60% in leaf and root weight. No reduction of Striga attack is obtained when various micro‐elements are coated on sorghum seeds before sowing. Field and laboratory experiments show that light irrigation of the sorghum crop during the normal sowing period increases the Striga attack and heavy irrigation decreases it. This result was not obtained in laboratory experiments when sorghum was sown out of season. Striga attack is lessened when conditions favouring growth of the sorghum crop are improved.