Four pillars are required to support a successful biocontrol fungus

Abstract

Despite biocontrol conceptually being a useful way to control specific pests, there are very few products that are used beyond the glasshouse level, into the field. Only if organisms meet four criteria (four pillars) will they be widely used in the field to replace or augment conventional agrichemicals. (i) The virulence of the biocontrol agent must be enhanced to overcome evolutionary barriers either by mixing with synergistic chemicals or with one or more organisms, and/or by mutagenic or transgenic enhancing of virulence of the biocontrol fungus. (ii) Inoculum production must be cost‐effective; many inocula are produced by expensive, labour‐intensive solid‐phase fermentation. (iii) Inocula must be formulated both to have long shelf life of inocula as well as being formulated to establish on, and control the target pest. Usually spores are formulated, while chopped mycelia from liquid culture are cheaper to produce and are immediately active upon application. (iv) After fulfilling these three criteria, the product must be biosafe: not produce mammalian toxins that affect users and consumers, and have a host range that does not include crops and beneficial organisms, and in most cases that it will not spread from application sites or have environmental residues beyond those needed to control the target pest. © 2023 Society of Chemical Industry.

The Toothpick Project: commercialization of a virulence‐selected fungal bioherbicide for Striga hermonthica (witchweed) biocontrol in Kenya

“…They are host-specific, safe, non-toxic, effective if enhanced for virulence, specifically selected for multiple sites of inhibition of a certain weed, lowered chance of weed resistance, and with lower local development and manufacturing costs. 4,6,13 They appear to persist in the soil for many years, providing farmers with a long-term solution. The combined developments of virulence enhancement and the cost-cutting, secondary inoculum distribution systems were key to success of this project.…”

“…Bioherbicides are chosen for their host specificity, 2,5,6 as use of multi-host pathogens would lead to escapes from the area of application, and severe regulatory and agronomic sanctions would result. Unfortunately, host specificity is a two-edged sword, in that no pathogen could last for long if it seriously damages its only host.…”

The future of microbial bioherbicides

“…Sixteen of the articles in this issue are from conference participants 2–17 . Four related articles from non‐participants are also included 18–21 . The article by Duke gives the rationale for the meeting, discussing the many microbial bioherbicides that have failed and detailing the technical and economic reasons for lack of success 2 .…”

“…The four pillars of successful biocontrol of weeds with microbial plant pathogens are detailed by Gressel. 18 They are:…”

Why are there no widely successful microbial bioherbicides for weed management in crops?

“…As with chemical herbicides, this can be solved by training, although effective use of microbial bioherbicides is usually more complicated. However, most of the problem is due to a lack of adequate microbe virulence under a wide enough set of environmental conditions 34 . As discussed above, the problem can be improved with formulation and better application technology, but much of it is due to a microbe that is not sufficiently virulent or host‐specific.…”