Phytotoxic Potential of the Crude Extract and Leaf Fractions of Machaerium hirtum on the Initial Growth of Euphorbia heterophylla And Ipomoea grandifolia

ABSTRACT: Allelopathy is the term used to define any process involving secondary metabolites produced by plants and microorganisms that influence growth and development of agrobiological systems. Currently, it is sought to find allelochemicals of interest and know how to apply them in bio-herbicides to combat weeds. In this study, the effects of the crude leaf extract and fractions of Machaerium hirtum (Vell.) Stellfeld were analyzed on Euphorbia heterophylla L. (wild poinsettia) and Ipomoea grandifolia (Dammer) O’Donell (morning glory), as well as the occurrence of morphoanatomical changes. For this, 0.04 g of the crude extract and fractions were solubilized and diluted (50 mL) to concentrations of 0.1, 0.2, 0.4, and 0.8 g L-1 (m/v). Initial growth tests were performed on Petri dishes containing two paper sheets and seedlings of weed species with the respective treatments, being maintained in a germination chamber for 48 hours at 25 oC. Distilled water was used as a control. Shoot and root length was assessed in the initial growth. The percentage of inhibition was calculated based on the values obtained in the initial growth bioassays. Morphologically altered wild poinsettia seedlings were fixed and sectioned transversely for anatomical analysis. The results indicated significant changes in length, being wild poinsettia seedlings more sensitive when compared to those of morning glory. Morphologically altered seedlings presented root necrosis as the most frequent symptom. Anatomically, parenchymatic cells of the hypocotyl and roots of wild poinsettia seedlings presented smaller and irregularly shaped cells when compared to the control, causing significant reductions in the measured parameters.