Effect of selected soybean accessions on germination and attachment of Striga hermonthica on maize

Abstract

Production of maize in Western Kenya is adversely affected by Striga hermonthica, a hemiparastic weed that produces numerous seeds that remain dormant in the soil for even more than 20years. These characteristics coupled with continuous cereal cropping have contributed to the high level of Striga seeds in the soil and the accompanying maize yield losses. Integrating legumes as intercrops is one way of reducing density of S. hermonthica in the soil and improving the livelihood of subsistence farming communities. Legume species and varieties however vary in their ability to stimulate suicidal germination of S. hermonthica seeds. A study was conducted to select soybean (Glycine max) accessions with high ability to stimulate germination of S. hermonthica seeds (from Western Kenya) and to determine the effect of selected soybean accessions on the Striga attachment and emergence on associated maize. The cut-root technique was used in-vitro to screen 32 soybean accessions in the laboratory at icipe-Mbita. Desmodium, Mucuna and maize varieties: Nyamula, KSTP94 and WH502 were used as checks while strigol (Nijimegen 1_) and distilled water were used as positive and negative controls, respectively. Plants were grown in plastic pots containing sterilized sand for 21 days to provide roots for the experiments. The cut roots were arranged in a Completely Randomized Design (CRD) with three replications. Fourteen soybean accession (selected from the cut-root experiment), Desmodium and Mucuna were then grown in association with maize variety WH502 in pots inoculated with Striga seeds in screen house in a CRD with three replications. Four soybean accessions (selected from the cut-root experiment) were grown in association with maize variety WH502 in a field at Nyabeda for two seasons in Randomly Complete Block Design (RCBD). Results showed a significant variation among soybean accessions in the ability to induce germination of Striga. The relative germination of Striga seed by soybean accessions ranged from 8% to 66% compared to 60%, 66% and 70% for Desmodium, Mucuna and synthetic germination stimulant Nijmegen 1®, respectively. Accessions TGX1448-2E, Tgm 1576, TGX1876-4E and Tgm1039 had the highest relative germination induction percentages. Most accessions that stimulated high germination of Striga seeds also increased the Striga attachment by 6% to 95%. Desmodium resulted in low Striga attachment on the associated maize. Accessions TGX 1831-32E, Tgm944, Tgm 1419 and Namsoy4m had high stimulation but low attachment hence making them potentially important trap crops. In the field experiment, maize grown in association with legumes had low Striga counts and high grain yield compared to maize grown in pure stand. This led to the conclusion that some soybean accessions could be used to control Striga