Phytotoxic substances

SAMPIETRO, D. A.; ARISTIMUÑO FICOSECO, M. E.; JUAREZ, J. H.; VATTUONE, M. A.

Soil Sickness

Studium Press LLC

Lugar: Houston; Año: 2011; p. 81 - 101

Phytotoxins are natural or synthetic compounds poisonous for the plant growth and/or development. In soil sickness, there are 3 kinds of compounds: (i). Plant phytotoxins: These can function as allelopathic compounds and sometimes donor and receptor plants are of the same plant specie. In this situation, these compounds are named autotoxins. Crop autotoxicity is due to the autotoxins released from the crop residues or old roots into the soil. These substances accumulate in soils that have lost their original physico-chemical and biological properties (Sampietro, 2006). Autotoxicity has been reported in rice, wheat, maize, sugarcane, alfalfa and vegetable crops like cucumber, carrot, watermelon, eggplant, tomato and pea (Singh et al., 1999). (ii). Microbial phytotoxins: The monoculture often favours the proliferation of phytopathogenic fungi. Several of them produce mycotoxins which are secondary metabolites toxic to several organisms including humans, animals and crop plants. Penicillum, Aspergillus and Fusarium are genera of mycotoxigenic fungi often associated with soil sickness (Politycka, 2005). (iii). Pesticides: They are intensively used in monoculture, specially herbicides. Large amounts of these compounds reach the soil and their fate depends on their chemical nature, the type of soil, the climate and the agricultural practices. They can cause soil microbial imbalance and can accumulate in soil with harmful effects on crop plants (Singh et al., 1999). Analysis of phytotoxic substances is most important in soil sickness. First, phytotoxins should be extracted from the substrate (i.e. soil, roots or plant residues). Then, a preliminary qualitative and quantitative analysis of the extracted compounds is possible using colorimetric methods as well as simple separation techniques such as planar chromatography together with appropriate reagents and internal standards. Nevertheless, accurate separation and identification needs more sophisticated apparatus and expensive chromatographic systems [Gas or high performance liquid chromatography coupled to appropriate detectors (i.e. Mass spectrometers, fluorometric or ultraviolet-visible absorbance detectors)]. Selection of these chromatographic and detection systems will depend on the chemical nature of phytotoxic substances to be analysed. In this chapter, we provide examples of general methods for qualitative and quantitative analysis of phytotoxic substances associated with soil sickness.