Natural occurrence of Pasteuria nishizawae in soybean areas

Abstract

Soybean (Glycine max (L.) Merrill) is a widely grown crop of economic prominence. Brazil is considered as the second largest worldwide producer and exporter. Soybean cyst nematode, Heterodera glycines Ichinohe, in one of the most serious threats for this crop, considered as its most destructive parasite. The first report of this disease in Brazil was recorded during the 1991/1992 harvest. Control of nematodes is more challenging if compared with other plant diseases control. Thus, there is a growing demand to search for alternative control practices that will not harm the environment nor the human being. Therefore, the highly specific bacteria Pasteuria spp. Metchnikoff, represents an auspicious biological control agent against nematodes. The biological control of the soybean cyst nematode with the bacterium Pasteuria nishizawae Sayre has proven an excellent choice and has been studied by different scientists. The objective of this work was to determine the natural occurrence of Pasteuria nishizawae in Brazilian soils. The experiment was performed under greenhouse conditions at the Research unit from Syngenta® in Uberlandia-MG, Brazil, with soil samples originated from soybean planted areas from the Brazilian states of Bahia, Goiás, Mato Grosso and Paraná. Fractions of 150 cm³ of soil were withdrawn to be processed by the centrifugal flotation technique in sucrose solution. Aliquots of 1 mL from the obtained suspension were observed in Peters' chamber with the aid of an inverted light microscope, in order to verify the absence or presence of bacterial endospores attached to the cuticle of the nematodes extracted from the soil samples. The frequency of Pasteuria nishizawae incidence was of 100% within the samples analyzed.