Ação de Crotalaria juncea e C. spectabilis na eclosão, população residual e desenvolvimento de Meloidogyne incognita e M. enterolobii

Abstract

Root-knot nematodes of the genus Meloidogyne cause high yield losses in crops of agronomic interest, and cultural control using antagonistic plants, such as species of the genus Crotalaria, is a widely adopted strategy. These Fabaceae are recognized for their nematicidal potential, with emphasis on Crotalaria juncea and C. spectabilis. The present study aimed to evaluate the mode of action of these antagonistic plants on Meloidogyne enterolobii and M. incognita by assessing the effect of root exudates on the hatching of second-stage juveniles (J2), monitoring nematode development in crotalaria roots after 20 days and the infectivity of the residual population in the substrate, as well as following the development of M. enterolobii J2 in stained roots of the Fabaceae and tomato plants at different periods after inoculation (7, 20, and 30 days). For this purpose, eggs of the two root-knot nematode species were exposed to root exudates of C. juncea, C. spectabilis, jimsonweed (Datura stramonium), millet (Pennisetum glaucum), and tomato (Solanum lycopersicum), or to distilled water, with daily evaluations for 15 days. Seedlings of crotalarias and tomato plants were inoculated with 5,000 eggs of M. enterolobii and M. incognita to assess nematode development in roots and the residual population in the substrate after cultivation of the Fabaceae. Additionally, the development of M. enterolobii J2 was evaluated in stained roots of the species at different periods after inoculation. In general, root exudates did not suppress J2 hatching, except for exudates of C. juncea and jimsonweed, which reduced the hatching of M. enterolobii juveniles by 50%. Although J2 penetration into crotalaria roots occurred, no nematode development, gall formation, or egg mass production was observed after 20 days, whereas in tomato plants the nematodes formed numerous galls and showed high reproduction. The residual population in substrates previously cultivated with crotalarias remained infective. In stained roots, only J2 were observed at 7 days in all species; at 20 days, only J2 were found in crotalarias, while in tomato plants stages from J2 to females were present. At 30 days, the presence of some galls was observed in C. juncea and C. spectabilis, contrasting with the high reproduction observed in tomato plants. The results indicate that crotalaria root exudates do not suppress J2 hatching, that juveniles penetrate their roots but do not complete the life cycle, and that the residual nematode population in substrates previously cultivated with these antagonistic plants remains infective.