Impact of Kenaf (Hibiscus cannabinus L.) Leaf, Bark, and Core Extracts on Germination of Five Plant Species

Abstract

The chemical interaction between plants, which is referred to as allelopathy, may result in the inhibition of plant growth and development. The objective of this research was to determine the impact of kenaf (Hibiscus cannabinus L.) plant extracts on the seed germination of five plant species. Four concentrations (0, 16.7, 33.3 and 66.7 g/L) of kenaf leaf, bark, and core extracts were applied to the germination medium of redroot pigweed (Amaranthus retroflexus L.), green bean (Phaseolus vulgaris L.), tomato (Solanum lycopersicum Mill.), cucumber (Cucumis sativus L.), and Italian ryegrass (Lolium multiflorum Lam.) seeds. The treated seeds were placed in a non-illuminated incubator at 27 o C. Germination was recorded after 7 days in the incubator. Seed germination decreased with increasing extract concentration for all the plant species tested, except for green bean. Tomato, cucumber, Italian ryegrass, and redroot pigweed followed similar trends in their responses to the extract source (kenaf bark, core, and leaves) and the impact of extract concentration. The research demonstrated that kenaf leaf extracts were allelopathic by reducing seed germination for tomato, cucumber, Italian ryegrass and redroot pigweed. Sensitivity to the allelopathic impact of the kenaf leaf extracts from highest to lowest was Italian ryegrass > tomato > redroot pigweed > cucumber > green bean, with reductions in percentage germination of 79% (Italian ryegrass), 78% (tomato), 53% (redroot pigweed), 40% (cucumber), and 0% (green bean). Future research should pursue cultural practices to utilize these natural allelopathic materials to benefit crop production and limit weed competition, assess the impact of kenaf extracts on post-germination growth, and isolate the active ingredients in the kenaf leaf extracts that are allelopathic.

Kenaf (Hibiscus cannabinus L.) Impact on Post-Germination Seedling Growth

“…Although there is not a clear trend between experiments, all experiments for each of the extract sources produced accelerated hypocotyl growth for green bean plants. These results are consistent with earlier research by Russo et al (1997b) and Webber et al (2015) who observed little or no detrimental impact of kenaf extract concentrations on green bean germination. Also, as reported by Webber et al (2015), there was a slight beneficial impact of the kenaf bark and leaf extracts on seed germination, which is consistent with a potential benefit to post-germination growth of the green bean hypocotyl.…”

“…These results are consistent with Webber et al (2015), who reported that tomato seed germination decreased as extract concentration increased for different sources of kenaf plant extracts. The core extracts was the least impactful on post-germination growth, while leaf extracts were the most detrimental on hypocotyl and radicle growth, and root numbers (Table 5).…”

“…Unlike hypocotyl length, green bean radicle lengths were not significantly affected by either source of the kenaf extract or by extract concentration (Tables 2). These results are consistent with Russo et al (1997b) and Webber et al (2015) who determined that of the five seed types evaluated, green bean was the least detrimentally impacted by kenaf extracts. X Means in a column within a main effect (kenaf plant part, extract concentration, and experiment) followed by the same lower case letter are not significantly different at P ≤ 0.05, ANOVA.…”

“…These results are consistent with earlier research by Russo et al (1997b) who reported that green bean germination was the least detrimentally impacted when exposed to whole plant kenaf extracts compared to the same plant species. Webber et al (2015) also reported mixed results concerning the impact of different kenaf plant extracts on green bean germination, indicating that the core extracts actually increased germination and the extract concentration did not produce a clear trend. Perhaps a higher concentration of the kenaf extracts might produce a clearer trend to determine if the material is consistently beneficial or detrimental.…”

“…Jalali et al (2013) determined that aqueous leaf extracts of the common mallow (Malva sylvestris) also exhibited allelopathic activity decreasing the germination and seedling growth of blanket flower (Gaillardia pulchella), plumed cockscomb (Celosia argentea), and sweet William (Dianthus barbatus). Webber et al (2015) when examining the impact of different concentrations of kenaf bark, core, and leaf extracts, determined that the kenaf leaf extracts were allelopathic, reducing seed germination of tomato, cucumber, Italian ryegrass and redroot pigweed.…”