Lina Wong

To gain insight into the factors driving the structure of bacterial communities in soil, we applied real-time PCR, PCR-denaturing gradient gel electrophoreses, and phylogenetic microarray approaches targeting the 16S rRNA gene across a range of different land usages in the Netherlands. We observed that the main differences in the bacterial communities were not related to land-use type, but rather to soil factors. An exception was the bacterial community of pine forest soils (PFS), which was clearly different from all other sites. PFS had lowest bacterial abundance, lowest numbers of operational taxonomic units (OTUs), lowest soil pH, and highest C : N ratios. C : N ratio strongly influenced bacterial community structure and was the main factor separating PFS from other fields. For the sites other than PFS, phosphate was the most important factor explaining the differences in bacterial communities across fields. Firmicutes were the most dominant group in almost all fields, except in PFS and deciduous forest soils (DFS). In PFS, Alphaproteobacteria was most represented, while in DFS, Firmicutes and Gammaproteobacteria were both highly represented. Interestingly, Bacillii and Clostridium OTUs correlated with pH and phosphate, which might explain their high abundance across many of the Dutch soils. Numerous bacterial groups were highly correlated with specific soil factors, suggesting that they might be useful as indicators of soil status.

Soil solarization associated with organic matters provides an effective control of several soil-borne fungi, which are difficult to eliminate using other methods; in addition, this association shortens the treatment time. The aim of this study was to assess the control of Fusarium oxysporum f. sp. lycopersici Race 2 by combining the amendment of "bitter" cassava (Manihot utilisima) and "sweet" cassava (Manihot dulcis) leaves with soil solarization. A field experimental was carried out, 3Kg/m² of the two types of cassava leaves were separately amended. Six treatments were tested, (solarizated+ "bitter" cassava, solarizated+"sweet" cassava, soil solarizated, soil, "bitter"cassava and "sweet"cassava). Fungus control was assessed based on the survival resistance structures on semi-seletive Komada medium at 7, 14, 21 and 28 days after the beginning of the experiment. Soil temperature values were monitored by a DataLogger Type CR23X (Campbell Scientific), and quantity of CO2 and O2 was monitored by a gas analyzer equipment (Testo 325-1). In solarizated treatments, soil temperature and trapping of CO2 were higher than the control (soil) and treatments with organic material incorporated without solarization. The association of both "bitter" and "sweet" cassava amendment with soil solarization inatived the pathogen whereas the other treatments had no effect, allowing the survival of the fungus.