An Alternative to Methyl Bromide: “Pasteuria” for Nematode Control

Plant parasitic nematodes are one of agriculture’s largest challenges. These microscopic worms burrow into the soil and attack plant roots causing damage to crops, causing an estimated $100 billion in worldwide crop damage annually. They have traditionally been controlled by fumigants, notably the problematic chemical methyl bromide. As fumigants are being phased due to negative human and environmental health effects, alternatives such as biological controls are being investigated.

Microbial pesticides have specific advantages over fumigants in the control of nematodes. Nematodes can burrow deep into the soil during fumigant applications to avoid contact. They can then ascend to the level of the plant roots after crops have emerged, at which point fumigants cannot be reapplied due to their toxicity and potential to damage crops. In contrast, many microbial pesticides can be applied to the post-emergent crops for protection throughout the plant life cycle. However, many microbial pesticides depend on the nematode consuming the microbe. This can present a challenge because plant pathogenic nematodes are generally herbivores.

More than 50 years ago, academic and USDA researchers discovered a genus of bacteria called Pasteuria to be a promising alternative for the control of nematodes. A particular advantage of Pasteuria over other biological controls is that it does not need to be eaten by the nematode to be effective. The Pasteuria spores are applied to the soil, and as a nematode passes, they attach to the nematode’s outer cuticle. The spores germinate and enter the nematode’s body causing death, spreading new spores into the soil. Each strain of the bacteria is specific to a particular species of nematode.

The primary technical challenge for commercialization of Pasteuria was development of an economically viable large-scale manufacturing process. The initial process developed in the laboratory involved growing live nematodes as hosts, growing the bacteria inside the hosts (in vivo), and extracting the spores to formulate the product. This process was too costly to scale up and a technological breakthrough was needed. The technical challenge was recently overcome by finding a way to grow the bacteria outside of a living host (in vitro). A new-patented process allows rapid and effective growth of multiple strains of Pasteuria penetrans in traditional commercial fermentation tanks using easily available growth media (Pasteuria, 2008). This technological advance significantly decreased the cost of production, making the product economically viable.

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