Biofumigation with Brassica seed-based products combined with calcium carbonate to control Phytophthora cinnamomi root rot in cork and holm oaks

Abstract

The root rot of holm and cork oaks caused by Phytophthora cinnamomi is one of the main phytosanitary problems in dehesas and montados, open woodlands of the Southern Iberian Peninsula. Biofumigation with seed meals rich in sinigrin is a promising technique to diminish the impact of this disease, but verification of its effectiveness is necessary before applying it in the field. The effectiveness to reduce sporangial production of P. cinnamomi and to control disease in holm and cork oak plants of biofumigation with non-defatted seed meal of Brassica juncea and pellets of defatted seed meal of Brassica carinata, combined or not with calcium carbonate, was tested in experimental conditions. The combinations of biofumigant materials and CaCO3 in vitro experiments were more effective in reducing the production of sporangia than the application separately, even with high doses of biofumigants. In plant experiments, none of the treatments significantly reduced disease symptoms in holm oak plants. In cork oak plants, the most effective treatment was seed meal of B. juncea (1.34 g L−1 of substrate) combined with CaCO3 (1.5 g L−1of substrate), although treatments with both doses of B. juncea seed meal (1.34 and 2.68 g L−1 of substrate) and with pellets of B. carinata (1.5 g L−1 of substrate) combined with CaCO3 (1.5 g L−1 of substrate) also significantly reduced root symptom severity in contrast with the inoculated control. Biofumigation with B. juncea seed meal or with B. carinata pellets, combined with the application of CaCO3 can be a tool to integrate control strategies into the disease in the dehesas.