Effect of Soil Fumigants on Fungal Communities in Protected Pepper Crops in Southeast Spain

In Southeast Spain about 2,000 ha of pepper crops are grown as a monoculture under greenhouse conditions. Soils have been usually disinfested with methyl bromide (MB) for over 25 years until its banning in 2005. There were two main reasons that justified the use of MB in this area: the reduction of the incidence of soil-borne pathogens (Phytophthora capsici and Meloidogyne incognita) and the effect of "soil fatigue". There are signs of a strong microbiological component in the soil fatigue effect. Assays were performed in greenhouses where different alternatives to MB were studied: the combination of 1,3-dicholoropropene + chloropicrin (1,3-D+Pic) and propylene oxide. Both fumigants were compared with MB. Disinfestation effects were measured through the soil fungal density isolated before and after fumigation, only in one greenhouse, with two types of analyses to determine the total fungal density as well as the Fusarium spp. density. In addition, soil samplings were made during the growing season in two greenhouses to complete our knowledge of fumigant effects. Results showed that 1,3-D+Pic at 50 g.m(-2) was the only fumigant able to reduce significantly the total fungal density (from 8,470 CFU.g(-1) dry soil before soil fumigation to 2,500 CFU.g(-1) dry soil after soil fumigation) while both MB (from 9,000 CFU.g(-1) to 12,730 CFU.g(-1)) and propylene oxide at 600 L.ha(-1) (from 13,700 CFU.g(-1) to 14,770 CFU.g(-1)) were not able to do. In relation to the total Fusarium spp. density, MB did not reduce it either (from 394.30 CFU.g(-1) to 318.63 CFU.g(-1)) although 1,3-D+Pic (from 111.69 CFU.g(-1) to 1.80 CFU.g(-1)) and propylene oxide (from 983.61 CFU.g(-1) to 16.21 CFU.g(-1)) did.