BIOFERTILIZERS AS COMPLEMENTS TO SYNTHETIC AND ORGANIC FERTILIZATION - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 160

Phytophthora palmivora, Pythium aphanidermatum, Micrococcus spp. , Aspergillus versicolor
and Phytophthora capsici, and against different parasitic nematodes of plants, including the
root-knot nematode Meloidogyne incognita (Benítez-Noyola, 2013).
On the other hand, certain species of the biocontrol fungus Trichoderma sp. are efficient
producers of many extracellular enzymes used in the food and textile industry. In addition,
they also have a great potential for the production of lignocellulosic biofuels due to their
ability to degrade complex polysaccharides (Kovacs et al. , 2009).
Finally, another advantage of using microorganisms as a means to control plant diseases
is that, unlike what happens with chemical pesticides, biofertilizers are less prone to induce
resistance because they possess multiple mechanisms to control the pathogens.
A CTION M ECHANISMS OF B IOFERTILIZERS
The mechanisms explaining the developmental and productivity responses of plants to
the inoculation with beneficial microorganisms can be direct or indirect.
D IRECT M ECHANISMS
Through these mechanisms, biofertilizers improve plant growth favoring the nutrition of
crops, either by increasing the availability and uptake of nutrients and water via hormonal
action or by altering the structure and the absorptive surface of roots.
Biological Nitrogen Fixation
This activity involves the enzymatic reduction of atmospheric nitrogen (N 2 ) to
ammonium (NH 4 ). In some plants this reductive process is performed in specialized structures
(such as the root nodules of legumes) and is catalyzed by the enzymatic complex of the
nitrogenase, which consists of two different proteins: dinitrogenase, the molybdenum-iron
protein, and dinitrogenase reductase, the iron protein (Seefeldt et al., 2009; Moure et al.,
2013).
Synthesis of Hormones
Hormones are natural compounds that in low concentrations are able to affect
fundamental morphological and physiological processes of plants. The production of
hormones (auxins, gibberellins and cytokinins) has been one of the preferred mechanisms
used by different researchers to explain the direct stimulation of growth by microorganisms
(Brown, 1974; Patten & Glick, 1996, García de Salamone et al. , 2005). In bacteria,
particularly Gram-negative, production of indole acetic acid (IAA) is one of the most
widespread mechanisms of growth promotion. The precursor of this hormone, the amino acid
tryptophan, is one of the compounds mostly abundant in root exudates (Kamilova et al. , 2006)