Effect of Brassica Biofumigant Amendments on Different Stages of the Life Cycle of Phytophthora cinnamomi

The oomycete plant pathogen Phytophthora cinnamomi causes a highly destructive root rot that affects numerous hosts. Integrated management strategies are needed to control P. cinnamomi in seminatural oak rangelands. We tested how biofumigation affects crucial stages of the pathogen's life cycle in vitro, in infested soils under laboratory conditions and in planta. Different genotypes of three potential biofumigant plant species (Brassica carinata, Brassica juncea, Brassica napus) were collected at different phenological stages, analysed for their glucosinolate contents, and subsequently tested. The most effective genotypes against mycelial growth and sporangial production were further tested on the viability of chlamydospores in artificially infested natural soils and in planta on Lupinus luteus, a host highly susceptible to P. cinnamomi. Brassica carinata and B. juncea genotypes inhibited mycelial growth, decreased sporangial production, and effectively inhibited the viability of chlamydospores in soil, but only B. carinata decreased disease symptoms in plants. Effective genotypes of Brassica had high levels of the glucosinolate sinigrin. Biofumigation with Brassica plants rich in sinigrin has potential to be a suitable tool for control of oak root disease caused by P. cinnamomi in Spanish oak rangeland ecosystems.