Suppression of damping-off caused by Pythium spp in soil from the indigenous mexican chinampa agricultural system

Abstract

Soil from the traditional chinampa agroecosystem in the Valley of Mexico was compared to soil from a nearby modem agroecosystem in Chapingo. Several soil physical, chemical and biological features were monitored during an 8-month study. Damping-off caused by natural populations of Pythium spp was less in soils from the chinampa system than in soils under the modern system of cultivation. Disease caused by introduced inoculum of P. aphanidermatum was also suppressed in the chinampa agriculture soil. Biological factors associated with disease suppression in the traditional system were an increased amount of biological activity (measured by soil dehydrogenase activity), reduced rate of germination of P. aphanidermatum oospores, and elevated populations of Pseudomonas spp and saprophytic Fusarium spp. Physicochemical factors associated with suppression included lower pH values, and higher organic matter, Ca, K and Mg contents. Dynamic biological processes in the traditional agroecosystem may be responsible for the suppression of the pathogen, P. aphanidermatum, through increased biological activity brought about by the high content of organic matter and elevated mineral nutrient status of the soils.