Myrislignan, a Growth Inhibitor from the Roots of Citronella grass

A phytotoxic compound was isolated from the root extracts of Cymbopogon nardus by bioassay-guided purification and characterized to be myrislignan. Myrislignan significantly inhibited seedling growth of cress at a concentration greater than 100 μM (p < 0.05). The concentrations required for 50% growth inhibition of myrislignan on hypocotyl and root growth of cress were 429 μM and 517 μM, respectively. The inhibition on seedling growth indicated that myrislignan had a phytotoxic activity and may contribute to the phytotoxic effect of C. nardus.

Phytotoxicity and Benzoxazinone Concentration in Field Grown Cereal Rye (Secale cerealeL.)

Winter rye (Secale cerealeL.) is used as a cover crop because of the weed suppression potential of its mulch. To gain insight into the more effective use of rye as a cover crop we assessed changes in benzoxazinone (BX) levels in rye shoot tissue over the growing season. Four rye varieties were planted in the fall and samples harvested at intervals the following spring. Two different measures of phytotoxic compound content were taken. Seed germination bioassays were used as an estimate of total phytotoxic potential. Dilutions of shoot extracts were tested using two indicator species to compare the relative toxicity of tissue. In addition, BX (DIBOA, DIBOA-glycoside, and BOA) levels were directly determined using gas chromatography. Results showed that rye tissue harvested in March was the most toxic to indicator species, with toxicity decreasing thereafter. Likewise the BX concentration in rye shoot tissue increased early in the season and then decreased over time. Thus, phytotoxicity measured by bioassay and BX levels measured by GC have a similar but not identical temporal profile. The observed decrease in phytotoxic potential and plant BX levels in rye later in the season appears to correlate with the transition from vegetative to reproductive growth.

Herbicidal Activity of Curvulinic Acid Isolated from Nimbya alternantherae

A phytotoxic compound, identified as 2-(2-acetyl-3,5-dihydroxyphenyl) acetic acid (curvulinic acid), was isolated from liquid cultures of the phytopathogenic fungus Nimbya alternantherae. The activity of curvulinic acid on seed germination and seedling growth of Capsella bursa-pastoris was evaluated. Percentage seed germination of C. bursa-pastoris was decreased with increasing concentrations of curvulinic acid. The compound had stronger inhibitory effects on root length than shoot length. At a concentration of 600 μg·mL−1, curvulinic acid caused 73.5% and 66.7% growth inhibition on roots and shoots with IC50 values of 204.7 and 281.1 μg·mL−1, respectively. The finding of curvulinic acid in N. alternantherae and its herbicidal activity are reported here for the first time.