There are numerous plant-parasitic nematodes in the world, but only a
handful are responsible for the largest part of an estimated $157 billion in
agricultural damage globally every year.
Nematodes are small worms that burrow into plant roots and feed off living
cells.

Now, Iowa State University researchers have contributed to the release of
the annotated genome of one of the most destructive nematodes: Meloidogyne
incognita - the southern root-knot nematode, as reported recently in the
journal Nature Biotechnology.

Sequencing the genome is a critical step toward comprehensively
understanding how the organism works and may pave the way for research on
ways to fight the pest.

"This is considered to be one of, if not the most important plant-parasitic
nematode species across the world," said Thomas Baum, professor and chair of
plant pathology and head of Iowa State University's contribution to the
genome sequence project.

Root-knot nematodes are so important because they can be found almost
anywhere in the world on almost any plant, he said. Nematodes are the most
abundant animals on earth.

"Many of the nematodes that are really bad pathogens are very specialized on
which plant they attack," said Baum. "This nematode has a huge host range.
For us nematologists, it is very interesting and challenging to study."

Because the pest is so widespread, many nematologists around the world were
eager to help with the project. The lead investigator was Pierre Abad of the
Insitut National de Recherche Agronomiquea, a French research group, with
help from researchers in Belgium, Holland, Great Britain, Switzerland, and
Iowa State University and North Carolina State University in the US.

"Because it is such a worldwide problem, people are eager to contribute,"
Baum said. "Also, because it is the first plant-parasitic nematode to have
its sequence released, people are very excited about it."

Chemical treatments for killing nematodes, called nematicides, are dangerous
to humans and other animals so they've been restricted in use for decades.
Technology for controlling nematodes has advanced little in the past three
decades.

Besides being a devastating crop pathogen, Meloidogyne incognita has some
remarkable biological adaptations that make it a fascinating organism to
study.

Baum said that the sex of the tiny worms, or better the lack thereof is very
intriguing. Only females reproduce and they do so without having sex, so it
remains a puzzle why males of the species even exist. And since the females
don't mate to reproduce, the offspring should be genetically identical to
the mother - like a clone - but they aren't. And as the offspring matures
into males or females, some start as females and then change into males.

Baum's group included postdoctoral researcher Tarek Hewezi and assistant
scientist Tom Maier from Iowa State. The three worked on a specific part of
the genome and performed manual annotations of genes. Professor Davis and
postdoctoral research associate, Noureddine Hamamouch, used the current
known parasitism genes to identify the full suite or predicted parasitism
genes in the root-knot nematode genome.

With this sequencing done, Baum thinks researchers can now try to understand
this nematode. He also cautions that finding ways to control this pest will
be a long process.

"For any effort in which you want to control the nematode, this is a great
resource," Baum said. "But having the genome is only one of many steps in
the right direction. Albeit, a very big one!"

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