Screening of potential biofumigant plants against the root pathogen Phytophthora cinnamomi
Abstract: The in vitro effectiveness of 15 potential biofumigant species belonging to the genera Sinapis, Diplotaxis, Cardaria, Brassica, Eruca, Lepidium, Armoracia and Erucastrum, has been tested to inhibit mycelial growth of Phytophthora cinnamomi, which represents the main causal agent of Quercus root rot in oak-rangeland ecosystems in southern Spain. The above-ground part of the selected plants was harvested, frozen and lyophilized. Cultures of the pathogen were exposed to volatile compounds released by the rehydrated plant material at different doses. Plants belonging to Diplotaxis, Armoracia and Brassica genera reached a total inhibition of the mycelial growth, showing a fungicidal action against P. cinnamomi. A high degree of inhibition (> 80%) was also obtained by Lepidium, Eruca, Erucastrum and Sinapis, but these plants exhibited only a fungistatic action. Two species with different glucosinolate profiles, Diplotaxis erucoides (rich in Sinigrin) and Lepidium sativum (rich in aromatic GSLs), were tested for their ability to reduce the viability of the pathogen in the soil. Natural soil from a rangeland was artificially infested with resistant spores of P. cinnamomi (650 chlamydospores per gram of dry soil) and transferred to plastic containers containing the biofumigant materials and incubated at 25 °C in the dark. After 1 day, 4 days or 8 days of incubation, soils were analysed by plating soil-water suspensions in selective NARPH medium and resulting P. cinnamomi colonies counted. Diplotaxis erucoides was the most effective biofumigant, significantly decreasing the viability of resistant spores in the soil. Plants containing high levels of the aliphatic GSL Sinigrin should be considered as potential biofumigants to be used in soils infested by P. cinnamomi.