Selected cultural and environmental parameters influence disease severity of dandelion caused by the potential bioherbicidal fungi,Phoma herbarumandPhoma exigua

Abstract

Selected cultural and environmental variables were investigated for their influence on the efficacy of Phoma herbarum and Phoma exigua to cause disease on dandelion (Taraxacum officinale) under growth room conditions. In both species, mycelial fragments caused significantly greater disease severity on dandelion than spore suspensions. Mycelial age was not an important factor in disease severity caused by P. herbarum, with all cultures causing high disease ratings. However, younger cultures of P. exigua caused the greatest disease severity on dandelion, but significantly less than that caused by P. herbarum. The initial pH of the growth medium (potato dextrose broth) did not affect disease severity caused by either Phoma species. Increasing concentrations of mycelia of P. herbarum were applied to dandelions that were then exposed to various leaf wetness durations. Disease severity increased with increasing leaf wetness duration. For dandelions exposed to no leaf wetness duration, the greater the mycelial concentration, the greater the disease rating. However, for dandelions exposed to all leaf wetness durations, all concentrations of mycelia caused similar disease ratings. As P. herbarum caused high disease ratings on dandelion, it therefore warrants further investigation as a potential bioherbicide for the control of this weed.

Occurrence ofPhoma argillaceaonRubus spectabilisin British Columbia and an evaluation of its potential as a forest weed biological control agent

“…Our results show that Phoma mycelia causes more disease than conidia and confirms reports that Phoma mycelia are more infective than conidia (Neumann and Boland 2002;Stewart-Wade and Boland 2004). Another important requirement for establishment of disease is inoculum concentration.…”

“…Another important requirement for establishment of disease is inoculum concentration. Increasing the inoculum concentration often confers greater initial disease severity as reported on other plant-pathogen systems, such as the dandelion-Phoma system (Neumann and Boland 2002;Stewart-Wade and Boland 2004). Our study showed that various dilutions of P. argillacea mycelia, when provided with sufficient leaf wetness period, causes high disease severity (>70%) and can be effectively used at low concentrations (0.5% (v/v) or 3.5 × 10 2 CFU/mL).…”

“…to control dandelion (Taraxacum officinale G.H. Weber ex Wiggers) (Neumann and Boland 2002;Stewart-Wade and Boland 2004) and salal (Gaultheria shallon Pursh.) (Zhao and Shamoun 2005), a Phoma species to control Canada thistle (Cirsium arvense (L.) Scop.)…”

Biological Control of Spreading Dayflower (Commelina diffusa) with the Fungal Pathogen Phoma commelinicola

“…For example, mycelial suspensions of P. herbarum incited significantly more disease severity than conidia on dandelion (Taraxacum officinale Weber) [48]. Similarly, mycelial fragments of P. exigua and P. herbarum incited significantly more disease severity of T. officinale than fungal conidia [49]. Zhao and Shamoun [36] found that culture growth media and age of mycelial cultures could affect the disease severity of P. exigua on the perennial evergreen weedy shrub, salal (Gaultheria shallon Pursh).…”

Oil emulsions increase efficacy ofPhoma herbarumto control dandelion but are phytotoxic

“…was isolated from leaf lesions on dandelion in southern Ontario (Neumann Brebaum & Boland 1999). The potential of P. herbarum as a bioherbicide for dandelion was studied in controlled environments and optimal leaf wetness duration for high disease severity was 16 Á/24 h continuous or 2)/12 h discontinuous (i.e., interrupted by 12 h) (Neumann Brebaum 1998;Stewart-Wade & Boland 2004). The addition of adjuvants increased disease severity of dandelion caused by P. herbarum in both controlled and field environments, but there was variation in disease severity between field seasons .…”