Allelopathic Activity of a Novel Compound, Two Known Sesquiterpenes, and a C13 Nor-Isopenoid from the Leave of Croton oblongifolius Roxb. for Weed Control

Abstract

Investigation of allelopathic substances from herbal plants may lead to the development of allelochemical-based natural herbicides. Croton oblongifolius (Roxb.) is a well-known herbal plant with a long history of being used for traditional medicines and for being the source of a diverse range of bioactive compounds. This plant has been reported to have allelopathic potential; however, its allelopathic-related substances have not yet been described. Therefore, we conducted this investigation to explore the allelopathic substances from the leaves of C. oblongifolius. Aqueous methanol extracts of C. oblongifolius leaves exhibited significant growth inhibitory potential against four test plants (monocot barnyard grass and timothy, and dicot cress and lettuce). The leaf extracts were purified in various chromatographic steps and yielded four active compounds identified as (3R,6R,7E)-3-hydroxy-4-7-megastigmadien-9-one (I), 2-hydroxy alpinolide (a novel compound) (II), alpinolide (III), and epialpinolide (IV) via an analysis of the spectral data. These identified compounds significantly restricted the seedling growth of cress. The concentration necessary for 50% growth reduction of the cress seedlings varied from 0.15 to 0.24 mM for (3R,6R,7E)-3-hydroxy-4-7-megastigmadien-9-one, 0.04 to 0.11 mM for 2-hydroxy alpinolide, 0.07 to 0.12 mM for alpinolide, and 0.09 to 0.16 mM for epialpinolide. Therefore, the leaf extracts of C. oblongifolius and the characterized compounds have the potential to be used as weed-suppressive resources for natural weed control.

Allelopathy and Identification of Five Allelochemicals in the Leaves of the Aromatic Medicinal Tree Aegle marmelos (L.) Correa

“…Additionally, the different I 50 values of the A. marmelos extracts for the hypocotyl/coleoptile and root growth of L. sativum , L. sativa , M. sativa , E. crusgalli , L. multiflorum , and P. pretense indicate that the inhibitory effect of the extracts depends on the six examined plant species ( Table 1 ). Similar results of dose- and species-dependent allelopathic properties have been documented by other researchers [ 36 , 37 , 38 ]. The growth inhibitory activity of the A. marmelos extracts against the six plant species investigated in this study indicates that these extracts may involve active compounds that have growth-suppressive properties.…”

Allelopathic Activity of a Novel Compound and Two Known Sesquiterpene from Croton oblongifolius Roxb.

“…These growth-inhibitory effects are in agreement with the findings from our earlier investigation. In our earlier study, we found that C. oblongifolius extracts inhibited the growth of four plants (two dicots, L. sativum and L. sativa, and two monocots, E. crusgalli and P. pratense) [39]. Additionally, the IC50 values of the extracts used against the hypocotyls/coleoptiles and roots of M. sativa and L. multiflorum (in this present research)…”

“…Based on the IC 50 results, the root growth of the two plant species in the current study and the four plant species in the prior study [39] showed greater susceptibility to the C. oblongifolius leaf extracts than the hypocotyl/coleoptile growth. Roots are more susceptible to plant extracts than hypocotyls or coleoptiles, because they come into direct contact with the allelochemicals during germination [49,50].…”

“…Nonetheless, there is little information on the allelopathic potential and allelochemicals of C. oblongifolius. In our earlier research, C. oblongifolius extracts significantly restricted the growth of four plants (Lactuca sativa, Lepidium sativum, Phleum pratense, and Echinochloa crusgalli), and we also identified one C 13 nor-isopenoid and three sesquiterpenes in the leaf extracts [39]. Moreover, we previously observed that one other fraction of C. oblongifolius leaf extracts was strongly allelopathic, suggesting that other constituents of interest remain to be identified.…”

“…The ethyl acetate (EtOAc) fraction exhibited more inhibitory activity than the aqueous fraction in partition [39]. Therefore, EtOAc was chosen for a subsequent isolation step and loaded onto a silica gel column, resulting nine fractions (Figure 3).…”