Chemical composition of Crotalaria spectabilis seeds extracts and their action on different soybean nematodes

The quality of soybean production can be affected by plant-parasitic nematodes, such as Heterodera glycines and Meloidogine javanica, the main nematodes that are harmful to soybean [1]. Crotalarias spectabilis is used in agriculture as crop rotation system due to its antagonist effect on entomopathogenic nematodes [2]. Thus, the purpose of this study was to investigate the chemical composition of C. spectabilis seed extracts and their action on two different soybean nematodes. After alkaline extraction of the seeds (NaHCO₃ 5% m/v), the pH of the extract was adjusted to 7.1 ± 0.2. The suppression nematode assay consisted in exposing H. glycines and M. Javanica (J2) to the crude extract of C. spectabilis seeds, at five different concentrations (5.0 – 40.0 mg mL^-1). The control group was treated with distilled water. The samples were evaluated at two moments: 24h-exposure and after 24h-recovery. C. spectabilis seeds extract showed higher immobility rates for H. glycines (96%) after 24h-exposure when compared to M. javanica (38% of inactive nematodes), at 5.0 mg mL^-1. After 24h-recovery the LC₉₀ (lethal concentration) were 20 mg mL^-1 for H. glycines and 30 mg mL^-1 for M. javanica, however the LC₁₀₀ was at 40.0 mg mL^-1 for both nematode species. The chromatographic profile of the C. spectabilis extracts obtained by HPLC-UV/DAD showed the presence of saponins, such as, steroids glycosides and polycyclic terpenes, which may be responsible for the nematicide effect of C. spectabilis seeds on H. glycines and M. javanica nematodes. Such type of studies may lead to the development of a new nematicide for the control of soybean nematodes, necessary to obtain a competitive agricultural system.

CNPq and FA (Fundação Araucaria-PR, Brazil) and Embrapa soybean.

[1] Weaver, D. B. et al. J Nematol. 1995; 27: 585 – 591.

[2] Chitwood, D. J. Rev. Phytopathol. 2002; 40: 221 – 249.