Filtrates of mixed Bacillus spp inhibit second-stage juvenile motility of root-knot nematodes

Abstract

The global expansion of soybean (Glycine max (L.) Merr.) exposes it to more diseases and pests such as nematodes. In South Africa particularly, Meloidogyne incognita and M. javanica are considered the predominant genera infecting soybean, but a more pathogenic root-knot species, M. enterolobii, was recently reported in the Mpumalanga Highveld of South Africa. The use of chemicals to manage these pests is usually preferred although various concerns exist regarding their potential impact on the environment. An increasing need for the development of less toxic alternatives for nematode management thus exists. This study determined the nematicidal activity of Bacillus spp. mixtures isolated from soybean rhizospheres on the motility of second-stage juveniles (J2) of mixed Meloidogyne communities co-occurring in these rhizospheres. Roots and soil from 10 soybean fields in the Mpumalanga Highveld were collected and Bacillus spp. isolated, while the population density and molecular identification of the co-existing Meloidogyne spp. were also done. The filtrates of the Bacillus spp. were then used in in vitro assays to determine their potential nematicidal activity. Results confirmed the presence of M. enterolobii (100%) M. incognita (50%) and M. javanica (40%) in the sampled fields, with single populations found in 20% and mixed communities in 80% of the fields. The filtrate mixture of B. cereus, B. megaterium, B. subtilis and B. thuringiensis caused approximately 85–90% immobility of Meloidogyne spp. J2 after 96 h. The results show that the use of Bacillus spp. mixtures can aid in the development of biocontrol products to combat root-knot nematodes and might be more effective than products from a single species in limiting J2 motility.