Phoma macrostoma: The infection process

Karen L. Bailey, Wayne Pitt, Frances Leggett, Christine Sheedy, Joanne Derby

Research output: Book chapter/Published conference paperConference paperpeer-review


Phoma macrostoma boasts potential as a bioherbicide to control susceptible broadleaved weeds but not harm resistant nontarget hosts. Isolate 94-44B causes intense chlorosis and mortality of broadleaved weeds such as Canada thistle (Cirsium arvense) and dandelion (Taraxacum officinale) when applied to the soil. The symptoms are caused by the production of a novel group of phytotoxic metabolites called macrocidins. The objective of this study was to determine the pathway of infection that leads to the plant damage. This was accomplished by first determining which infective unit (i.e. conidia and/or mycelium) resulted in plant damage. Then the infection process was microscopically observed from infested granules placed in the soil through the various stages of colonization and penetration in resistant (barley) and susceptible (dandelion) hosts. Conidia caused no plant damage to targeted weeds when inoculated using either a foliar spray of a conidial suspension or granules containing conidia placed in the soil. Only mycelium of the fungus applied either pre-emergently to soil ahead of weed seed emergence or post-emergently to soil containing established weeds resulted in significant plant damage. Microscopic observations showed P. macrostoma mycelium germinated from formulated granules in soil colonizing roots of both dandelion and barley within seven days of application. The fungus entered the hosts at sites proximal to root hairs growing intercellularly without penetrating cells, In dandelion, mycelium deeply pentrated towards the root core, proliferating around the vascular trachea disrupting the competence of neighboring cells. In barley, mycelial growth was restricted to epidermal layers and there was no disruption of any root cell structures. There appears to be two modes of action affecting resistance and susceptibility, namely the effect of macrocidins on the plants and the ability to control mycelial growth within the host.
Original languageEnglish
Title of host publicationInternational Symposium on Biological Control of Weeds
Number of pages1
Publication statusPublished - 2011
EventXth International Bioherbicide Group Workshop - Kohala Coast of the Big Island in Hawaii, New Zealand
Duration: 10 Sep 2011 → …


WorkshopXth International Bioherbicide Group Workshop
CountryNew Zealand
Period10/09/11 → …

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