Solarization to control Fusarium oxysporum f. sp. radicis-lycopersici on different substrates

Several works have shown the total or partial efficacy of solarization in reducing soil-borne diseases, by means of decreasing inoculum density, due to the thermal inactivation of pathogens. However, there is little information about the effects of solarization of cropping substrates with regard to the inoculum density that could be increased in the re-use of substrate. In this work, the effectiveness of solarization to control Fusarium oxysporum f. sp. radicis-lycopersici (Forl) was evaluated in three different tomato crop substrates: coconut fiber, perlite and rockwool. Substrate bags were previously inoculated and the presence of disease checked by the observation of symptoms. Population density was measured and then the bags were solarized for 3 months. After this time, tomato seedlings susceptible to Forl were transplanted. Every 2 weeks, bags were analyzed for the presence of F. oxysporum. Samples of the drainage were analyzed using Fusarium semi-selective medium. Percentages of isolates belonging to Forl were obtained for each sample by inoculating the isolates on tomato seedlings. The results show that solarization was able to drastically reduce the presence of F. oxysporum on substrate bags, including Forl. However, F. oxysporum colonies able to affect tomato seedlings were isolated from the three substrates and from the first sampling. Despite this, there was a 4-month delay in the appearance of disease for the three substrates, that suggesting solarization as an effective technique to control fungal populations, but not to eradicate them completely.