Soil biofumigant treatments for control of the alien pathogen Phytophthora cinnamomi

摘要

Phytophthora cinnamomi is one of the most serious plant pathogens worldwide, considered among the 100 of the World's Invasive Alien Species. A high number of woody hosts have been described'for this pathogen, but it is especially virulent causing root rot on holm oak (Quercus ilex), cork oak (Quercus suber), chestnut (Castanea sativa) and avocado (Persea americana) in southern Europe. Disease control is difficult due to the longevity of P. cinnamomi resistant spores in the soil, the ability of the pathogen to invade the soil at high depths, and its mobility in waterlogged soils, favouring dispersal. A suitable strategy for disease control in seminatural forest ecosystems is the use of biofumigant crops able to prevent P. cinnamomi infections. Biofumigation is based on the release of toxic volatil compounds (mainly isothiocyanates) from the enzimatical lysis of glucosinolates present in the plant material in the soil. Effects of different genotypes of three potential biofumigant species (Brassica carinata, Brassica juncea, Brassica napus) collected at different phenological stages, were tested on vegetative and reproductive stages of the pathogen. Firstly, the inhibition of mycelial growth was tested by exposing cultures of the pathogen to different doses of plant material. The minimum effective dose for inhibition of the mycelial growth was tested against sporangial production and infective zoospores release. The most' effective genotypes against mycelial growth and sporangial production were tested on the viability of resistant spores (chlamydospores) in natural soil artificially infested (650 chlamydospores per gram of soil) and transferred to plastic containers with the biofumigant material at different doses. The experiments were carried out in two different ways: (1) with soil incubated in hermetically closed containers; and (2) in open containers. HPLC analysis of glucosinolate content of plant material correlated the high biofumigant ability against P. cinnamomi found in two species (B. juncea and B. carinata) with the high content in Sinigrin present in the most effective plant tissues.