Effect of mulching on the Phytophthora spp. inoculum density in the citrus root zone

In Morocco, Phytophthora root rot is one of the most harmful diseases affecting citrus crops. Phytophthora species persist in citrus orchards in the form of propagules that colonize the root zone of the rootstocks. For one year, a plastic mulching technique was applied to the new citrus varieties platform at the El-Menzeh experimental field of INRA Kénitra (Morocco). This study aimed to assess whether this practice reduces the density of Phytophthora inoculum in the root zone of citrus rootstocks. Composite soil samples were collected around the base of the trees at a depth of 15-20 cm, and the inoculum density of Phytophthora spp. was estimated using the dilution plating technique on selective BARPHY72 medium. The results showed that the density of Phytophthora spp. inoculum in the soil varied significantly depending on both the mulching technique and the rootstock. Mulching significantly reduced inoculum density in the root zone, and this reduction was more pronounced in Citrange carrizo rootstock compared to Citrus volkameriana. These findings support the recommendation of plastic mulching as an effective strategy for reducing Phytophthora spp. infection in citrus orchards.