Biocontrol of the root-knot nematode, Meloidogyne incognita, using an eco-friendly formulation from Bacillus subtilis, lab. and greenhouse studies

Aymen Ghnaam Basyony,Gaber Attia Abo-Zaid

doi:10.1186/s41938-018-0094-4

Abstract

Culture broth, cell pellet suspension and cell free supernatant of 14 Bacillus subtilis isolates obtained from different Egyptian locations were checked for their ability to repress egg hatching and juvenile (J2) activity of root-knot nematode, Meloidogyne incognita under laboratory environment. Treatments using culture broth of B. subtilis isolates B10 and B8, at a concentration of 50%, recorded lowest percentages of hatched eggs reaching 44.7 and 46.3%, respectively. Culture broth of B. subtilis isolate B10 at the same concentration showed a higher percentage of juvenile mortality reached 99.7%. Batch fermentation was completed, using B. subtilis isolate B10 (Accession No. EF583055), which gave the lowest percentage of hatched eggs and the highest percentage of juvenile mortality of M. incognita, for maximizing biomass production and suppression effects of culture broth. Batch fermentation no. 2, which started in a bioreactor with optical density of 0.5, was the best process that achieved a higher cell biomass and percentage of juvenile mortality of 4.52 g/l and 74.3%, respectively, using culture broth of 5%. Under greenhouse conditions, culture broth, cell pellet suspension, and cell-free supernatant of B. subtilis isolate B10 were used to test their potential for reducing number of galls and egg masses in the roots of tomato plants. The treatment of using culture broth at a concentration 10 ml/pot, 2 × 109 cfu/ml in a soil infested with M. incognita, was highly significant in decreasing number of galls and egg masses reaching the average of 9.3 and 6.7, with reduction percentage of 81.1 and 89.5%, respectively, compared with the control treatment of M. incognita only. In addition, B. subtilis isolate B10 was formulated and applied as bionematicide to test its efficiency in reducing number of galls and egg masses. Treatment with bioformulation at a concentration of 0.1 g/pot was more significant than the other concentrations in reducing number of galls and egg masses, reaching the average of 12 and 7 with a reduction percentage of 69.7 and 71.2%, correspondingly.

Highlights

The root-knot nematodes, Meloidogyne spp., are one of the highly important soil-borne pathogens that cause great economic damages to horticultural and field crops, and considered one of the most dangerous plant-parasitic nematodes, which can infect approximately all of the world’s main crop plants (Oka et al 2000)
Culture broth and supernatant of B. subtilis isolates B10 and B8 had a maximum activity against egg hatching of M. incognita; the percentages of hatched eggs were 44.7 and 46.3%, using a culture broth, while it reached 53.3 and 54.7%, respectively, by using the supernatant
Cell pellet suspension of B. subtilis isolate B3 recorded the lowest percentage of hatched eggs, reaching 67% compared with the treatments with cell pellet suspension of B. subtilis isolates B10 and B8, Fig. 7 Dissolved oxygen, agitation, and aeration as a function of time during batch fermentation no. 1 of Bacillus subtilis isolate B10 where the percentage of hatched eggs recorded 78.3 and 81.7%, respectively (Fig. 1)

Summary

Introduction

The root-knot nematodes, Meloidogyne spp., are one of the highly important soil-borne pathogens that cause great economic damages to horticultural and field crops, and considered one of the most dangerous plant-parasitic nematodes, which can infect approximately all of the world’s main crop plants (Oka et al 2000). Huang et al (2016) reported that the highest ovicidal activity against M. incognita documented, using a combination of Syncephalastrum racemosum and Paecilomyces lilacinus at a concentration of 50%, reduced 70% of egg hatching than the control. Bacillus spp. can produce lytic enzymes, cyclic lipopeptides (Gray et al 2006), and many secondary metabolites that play an essential role in biocontrol of Meloidogyne spp. Many lytic enzymes are produced by B. cereus, including chitinase and glucanse (Csuzi 1978). Cyclic lipopeptides of surfactin and iturin produced by B. subtilis were more able to inhibit egg hatching of M. incognita and play an imperative role in increasing the percentage of juvenile mortality (Kavitha et al 2012). Population densities and galls of root-knot nematodes, Meloidogyne spp. decreased by using the treatments with Pseudomonas aeruginosa, B. subtilis, and antagonistic fungus P. lilacinus (Prakob et al 2009).

Objectives

Methods

Results