Possible Role of Glandular Trichome Exudates in Interference by Velvetleaf (Abutilon theophrasti)

Abstract

The glandular trichomes on velvetleaf (Abutilon theophrastiMedic. # ABUTH) stems and petioles exude liquid globules which are phytotoxic in petri plate bioassays. Because the exudate is easily removed with water, it was hypothesized that it may be washed from velvetleaf stems and petioles into the surrounding soil environment where it may exert allelopathic influences. Field and greenhouse studies attempted to separate the influence of exudates from other mechanisms of interference by removing exudates from some velvetleaf plants and not from others. Velvetleaf trichome exudates did not increase interference by velvetleaf in either field or greenhouse studies. A velvetleaf accession from Rosemount, MN, produced 1.4 times more exudate/stem dry weight than another accession from Stoneville, MS. However, the MS exudate was about 1.4 times more toxic in petri plate assays when compared to the MN exudate. Although greenhouse-grown plants had approximately 3.3 times more exudate/stem dry weight than field-grown plants, the field exudate was 1.6 times more toxic. The activity of velvetleaf exudates was also assayed in autoclaved and nonautoclaved soil. Although active in autoclaved soil, extract activity was lost at all but the highest dosage when the soil was not autoclaved. Microorganisms appear to rapidly detoxify the velvetleaf toxin(s) and may reduce or eliminate its impact in the field.