TIME-BASED PHYTOTOXICITY CHANGE OF DECOMPOSING Arge-mone ochroleuca L. ON SELECTED VARIETIES OF SORGHUM (Sorghum bicolor (L.) Moench

Abstract

Allelopathic effects of plant litter have been extensively studied, but less attention has been given to the dynamics of phytotoxicity during the decomposition processes. Argemone ochroleuca, an invasive weed, suppresses neighboring crops by allelopathy. It is the most widespread weed in the temperate and subtropical African zones including Ethiopia. This study aimed to investigate the phytotoxicity of A. ochroleuca root and leaf suspensions on the S. bicolor varieties in labora-tory and greenhouse conditions. For allelopathic bioassay the 1st, 10th, 20th, and 30thdays aero-bically decomposed suspensions of leaves and roots were prepared in to 10, 20, and 30% con-centration levels in distilled water, while distilled water was used as a negative control to evalu-ate their impacts on germination parameters and early seedling growth of S. bicolor varieties. Varieties of sorghum named Melkam (M), Fedis (F), and Erer (E) were treated with equal amounts of 10, 20, and 30% (w/v) suspension in Petri dishes lined with Whatman no.1 filter pa-per and two Sorghum variety (M and F) in soil-filled pots under laboratory and greenhouse con-ditions, respectively. Treatments were laid out in a completely randomized design with three rep-lications and data were analyzed using the General linear model and one-way ANOVA. The re-sults showed that both the leaf and root suspenssions of A. ochroleuca contain allelochemicals and negatively impacted the measured parameters, with leaf suspension having higher negative impact than root suspenssions. Phytotoxicity of suspenssions peaked on the 10th day of decompo-sition, but decreased with increasing decomposition time. Germination parameters and seedling growth were significantly (P<0.01) affected by plant part, sampling day, suspension concentra-tion, Sorghum variety, and their interactions. The three S. bicolor varieties showed sensitivity differences to allelochemicals from A. ochroleuca with the M variety exhibiting a better toler-ance followed by F and E varieties. Thus, it can be concluded that A. ochroleu contains second-ary compounds that inhibit the germination and seedling growth of the tested S. bicolor varieties. Overall, this study revealed the dynamicity of toxicity with decomposition period.