Ability of excised root and stem pieces of maize, cowpea and soybean to cause germination of Striga hermonthica seeds

High variation in results from Striga hermonthica experiments is common. The cut-root assay for in vitro screening of host and non-host plant cultivars for germination of S. hermonthica is particularly insensitive. In this study, some factors of the cut-root technique that could effect significant variation in germination percentage of a population of S. hermonthica seeds induced by the same crop cultivar were studied. It was found that excised pieces of both root and stem of maize (hybrid var 8338-1), cowpea (var IT81D-994) and soybean (var TGx 1448-2E) stimulated the germination of S. hermonthica seeds. Germination percentages obtained with maize and cowpea stem pieces were significantly higher than those produced by root pieces. Moistening filter paper on which conditioned Striga seeds were subjected to germination stimulants with 5 ml of distilled water resulted in significantly higher germination of the parasite's seeds induced by stimulants from both maize and soybean, than adding 3 ml of water, regardless of the plant part tested. Starting germination stimulant extraction immediately after cutting plant parts gave significantly higher germination percentage of S. hermonthica seeds than starting 3 h later, regardless of crop species and plant part tested. Conditioning S. hermonthica seeds and subsequent extraction of germination stimulant with non-sterile water generally resulted in higher germination percentage of S. hermonthica seeds than with sterile distilled water. These results are discussed and suggestions made about how to reduce variability of results of the cut-root method of in vitro assaying of germination stimulant production by hosts and trap crops of S. hermonthica. (C) 2003 Elsevier Science Ltd. All rights reserved.