By: Martha Zarain

The development of diseases in agricultural crops and in general, of any other biological system, depends on the complex interrelation between the host, the pathogen and the environmental conditions. So, in the case of soil pathogens, it opens the opportunity of interactions with other microorganisms that occupy the same ecological niche. For example, in the case of nematodes, it has been seen in many crops the correspondence of the development of other diseases caused by other soil pathogens.

It is estimated that one gram of surface soil hosts a multitude of microorganisms, about 106-108 bacterial, 106-107 actinomycetes, 5 x 104-106 fungal colonies, 105-106 protozoa and 104-5X 105 algae, among others.

Many of these organisms are saprophytic, meaning they have little effect on agricultural crops, however, the humid soil environment is favorable for both, the activities of plant parasitic nematodes and the growth and multiplication of pathogenic fungi therefore it is not surprising that a variety of relationships have proven to exist between them.

So the development of the symptoms of a disease is often not only determined by the responsible pathogen, but depends on a complex interrelation between host, pathogen and prevailing environmental conditions, as previously mentioned. In addition to this, plants in the natural environment are rarely subjects to the influence of a single potential pathogen. This is especially true in soil pathogens, where there is an enormous interaction with other microorganisms that occupy the same ecological niche.

Plant parasitic nematodes cause serious crop losses worldwide and are among the most important agricultural pests. Nematode management is more difficult than other pests, because nematodes inhabit mostly on the soil and they usually attack the plant roots. Although nematicide chemicals are generally effective, easy to apply, and demonstrate rapid effects, they have been gradually withdrawn from the market in some developed countries due to health and environmental safety concerns. The search of innovative and sustainable alternatives to the environment for the management of plant parasitic nematode populations has become increasingly important.

A viable alternative arises from the fact that nematodes in the soil are subject to bacteria and fungi infections. Bacteria are numerically the most abundant organisms in the soil. In the last twenty years, extensive research has been carried out to evaluate its potential to control parasitic nematodes of the plant. Through the efforts of these investigations, it has been found that nematophagous bacteria are widely distributed, have different modes of action, and have wide ranges of action. A variety of nematophagous bacterial groups have been isolated from the soil, from the tissues of the host plants and from the nematodes and their eggs and cysts, and it has great potential since they affect nematodes in a variety of ways: for example, parasitizing; producing toxins, antibiotics or enzymes; interfering with the nematode - host-plant recognition; competing for nutrients; inducing systemic resistance of plants; and promoting the health of plants.

The group of rhizobacteria to which a broad range of bacteria from the LIVENTIA portfolio belong as: Bacillus sp, Lysinibacillus sp Microbacterium sp, Alcaligenes sp and Arthrobater sp. have also been studied for the control of plant parasitic nematodes, and are among the dominant populations in the rhizosphere that can fight nematodes. The rhizobacteria reduce the number of nematodes mainly by regulating the behavior of nematodes in the recognition of plants, competing for essential nutrients, promoting plant growth, inducing systemic resistance, or directly attacking them through the production of toxins, enzymes and other metabolic products, which is why the action potential of this group of bacteria is widened before the multifactorial attack of pathogens.

Gottlieb D, 1976. Production and role of antibiotics in soil. Journal of Antibiotics 29, 987–1000.
Wallace HR, 1978. The diagnosis of plant diseases of complex etiology. Annual Review of Phytopathology 16, 379–402.
Koenning SR, Overstreet C, Noling JW, Donald PA, Becker JO & Fortnum BA (1999) Survey of crop losses in response to phytoparasitic nematodes in the United States for 1994. J Nematol 31: 587–618.
Schneider SM, Rosskopf EN, Leesch JG, Chellemi DO, Bull CT & Mazzola M (2003) Research on alternatives to methyl bromide: pre-plant and post-harvest. Pest Manag Sci 59: 814–826.
Siddiqui ZA & Mahmood I (1999) Role of bacteria in the management of plant parasitic nematodes: a review. Bioresource Technol 69: 167–179.