Influence of mustard biofumigation on growth, conidial germination and propagule recovery of Ilyonectria macrodidyma-complex species

Black foot caused by Ilyonectria spp. is a significant economic problem resulting in the decline and death of vines. Biofumigation using mustard has recently shown potential to reduce this disease. In vitro sandwich plate assays and a soil box assay were used to compare the effect of biofumigation using standard brown mustard and a recently released cultivar Caliente 199 to suppress Ilyonectria macrodidyma, I. novozelandica and I. torresensis isolates associated with black foot disease in New Zealand. Both mustards reduced mycelial growth and conidial germination of all isolates, but overall efficacy of the two mustards varied between experiments and is probably related to plant physiology at harvest. In combination with soil, however, mustard efficacy was reduced. Isolates within a species differed in susceptibility to biofumigation. In addition, the relative effect of biofumigation on mycelial growth versus conidial germination varied for isolates, with I. macrodidyma Ack1a the most susceptible isolate with regards to conidial germination but least with regards to mycelial growth. Recovery of mesh bags containing mycelial or conidial inoculum of each species after burial in mustard amended or unamended soil in the box bioassay indicated the rapid conversion of inocula into chlamydospores. Amending soil with either mustard cultivar did not change the overall dynamics of propagule conversion over time, however, it significantly affected the numbers of conidia and chlamydospores recovered from conidial inoculum after different incubation times. Mustard biofumigant crops have potential to be incorporated into an integrated strategy for management of black foot in vineyards and nurseries