EFFECT OF BIOSOLARISATION ON THE MICROBIAL POPULATIONS OF SUBSTRATES INFESTED WITH FUSARIUM OXYSPORUM BY PCR-DGGE.

Biosolarisation consists of combining solarisation and organic matter application for controlling soilborne pathogens. The effects of this control strategy on the microbial community is almost unknown and needs to be investigated with molecular tools. The aim of the research was to investigate how biosolarisation can affect the structure of the microbial populations evaluated by a culture independent method using DGGE of PCR-amplified 18S-ITS genes-coding fragments from DNA extracted directly from infested substrate. Substrate samples were artificially infested with Fusarium oxysporum f. sp. conglutinans (FOC) and F. oxysporum f.sp. basilici (FOB) in order to evaluate the shift in fungal population by using culture independent methods. Solarisation was carried out with transparent polyethylene film during the summer period in a greenhouse located in Northern Italy, in combination or not with Brassica carinata defatted seed meals and/or compost. Biosolarisation treatment was carried out in a growth chamber by heating the substrate for 7 and 14 days at optimal (55-52 degrees C for 6 h, 50-48 degrees C for 8 h and 47-45 degrees C for 10 h/day) and sub-optimal (50-48 degrees C for 20 h, 45-43 degrees C for 8 h and 40-38 degrees C for 10 h/day) temperatures. Plate counts and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analyses were performed to evaluate the effect of biosolarisation on the microbial population. The abundance of FOC and FOB was reduced as a consequence of biosolarisation, while bacterial populations were higher compared to control samples during the experiment. PCR-DGGE fingerprints of the ascomycete community obtained from DNA directly extracted from infested substrate samples showed that the use of organic amendments increased the similarity of the fungal populations.