Effect of biofumigation with manure amendments and repeated biosolarization on Fusarium densities in pepper crops

In the region of Murcia (southeast Spain), sweet pepper has been grown as a monoculture in greenhouses for many years. Until 2005, when it was banned, soils were disinfested with methyl bromide (MB) to control pathogens and to prevent soil fatigue effects. The genus Fusarium plays an important role in the microbiological component associated with yield decline in pepper monocultures. In the present study, soils were treated with manure amendments, alone (biofumigation, B) or in combination with solarization (biosolarization, BS), with or without the addition of pepper plant residues. The B and BS treatments were compared with a treatment using MB. The extent of disinfestation was measured from the density of Fusarium spp. isolated from the soil before and after the respective treatments. Three different species were systematically isolated: Fusarium oxysporum, Fusarium solani and Fusarium equiseti. The repeated use of manure amendments with pepper crop residues, without solarization, was unable to decrease the Fusarium spp. density (which increased from 2,047.17 CFU g⁻¹ to 3,157.24 CFU g⁻¹ before and after soil disinfestation, respectively), unlike MB-treated soil (in which the fungi decreased from 481.39 CFU g⁻¹ to 23.98 CFU g⁻¹). However, the effectiveness of the repeated application of BS in diminishing doses (with or without adding plant residues) on Fusarium populations (reductions greater than 72%) was similar to or even greater than the effect of MB.