Viabilidade e parasitas de escleródios de Sclerotinia sclerotiorum sob diferentes condições de aeração

Abstract

The soybean crop begins to be present in the region of the western border of RS, as a crop rotation alternative to irrigated rice. Among the main diseases of soybean crops the white mold is one that may ultimately reach this region, however there are no studies that demonstrate the behavior of these survival structures in irrigated rice areas. Sclerotia are survival structures of the fungus Sclerotinia sclerotiorum, from which the pathogen can be perpetuated in a certain area even when there are no ideal conditions for its development. The objective of this study was to identify the parasites microorganisms and assess the viability of sclerotia of S. sclerotiorum submitted to different depths and soil moisture, under different aeration conditions. For that, sclerotia of S. sclerotiorum were produced and then buried in nylon bags in soil collected from the experimental area of Itaqui campus at depths of 2 and 10 cm, with soil irrigation kept under field capacity and saturated with water depth of 2cm. The containers with the sclerotia remained in plant growth chamber at 25 ° C for 60 days. Evaluations consisted in the removal of four bags of each treatment (each of them representing a repetition) at 15, 30, 45 and 60 days after implementation of the experiment. The sclerotia were placed in culture medium and the microorganisms were identified through stereoscopic and optical microscope, together with specialized bibliography. The viability of sclerotia was evaluated according to the number of sclerotia removed from the bags and after 60 days, by Neon-S culture medium. The microorganisms found paratizing the sclerotia were: actinomycetes; bacteria; chromista: Pythium; genera of fungi: Aspergillus, Cladosporium, Fusarium, Lichtheimia (Absidia), Mucor, Penicillium and Trichoderm. In treatments where the sclerotia were submitted to field capacity, parasites managed to derail up to 70% of the sclerotia at the end of 60 days. Regarding sclerotia submitted to saturated soil condition, after 60 days all were already non-viable by the existing soil parasites and humidity. It can be concluded that, among all parasites found in this experiment, the Trichoderma fungus, the chromista Pythium and the bacterias differ from the others, resulting in greater frequency of appearance during evaluations. The water saturated soil provides the total loss of the viability of sclerotia of S. sclerotiorum in both depths, while the soil in field capacity has a viability value of 25-30% after 60 days.