Influence of cowpea root powder and exudates on germination and radicle length in Striga hermothica, sorghum and pearl millet strains

The root parasitic weed Striga hermonthica constitutes a threat to cereals production in sub-Saharan Africa. Cowpea has been used as a rotational or a companion crop to combat the parasite on cereals with varying success. The present investigation was set to study the effects of root powder from 12 cowpea genotypes and root exudates from two genotypes on germination and radicle length in S. hermonthica, sorghum and millet strains. At 5 to 15 mg root powders from T198K-409-4 and T198K-317-2, the least and most active on S. hermonthica sorghum strain, induced 41-60 and 79-86% germination, respectively. Root powders from B301 and T100K-1263, the least and most active on the pearl millet strain induced 33-46 and 94-95%, germination, respectively. Maximum germination in response to root exudates of B301 and T100K-901-6, each applied at 5, 10 and 15 µl, was 54, 45 and 36% and 52, 43 and 31%, respectively for the sorghum strain and 43, 53 and 61% and 44, 49 and 53%, respectively for its pearl millet congener. B301and T100K-901-6 root exudates induced maximum germination at pH 10 and 7, respectively. Root powder reduced radicle length of both strains, while root exudates reduced radicle length of the sorghum strain, but increased that of its pearl millet congener. Employment of cowpea as a rotational or a companion crop to combat S. hermonthica on cereals implies rigorous selection through initial laboratory screening for stimulant production. Key words: Striga hermonthica strains, root powder, root exudates, germination, sorghum, pearl millet.