By Sharon Durham
Cowpea plants can indirectly perceive attack from fall armyworms by
detecting and responding to degradation products of their own tissues - the
first time this ability has been observed in plants, according to
Agricultural Research Service (ARS) scientists in Gainesville, Fla.
The scientists hope to capitalize on this discovery by finding a way
to intensify this defense response, thus boosting a plant's ability to
protect itself.

Previous studies have shown that plants have the ability to indirectly
perceive pathogen attacks and protect themselves against these microbes. But
this is the first time such a plant defense mechanism has been seen in
response to insect attacks. The findings are reported in the June issue of
Plant Physiology.

The indirect perception of insects means the plant doesn't recognize
the pests directly. Instead, the plant perceives abnormal digestive protein
fragments of itself - produced by insect digestion - as an insect attack.
This begins a series of biochemical responses geared to preventing further
injury.

Armyworms are a group of related caterpillars that defoliate a wide
range of crop plants. Plant physiologist Eric Schmelz and colleagues at the
ARS Center for Medical, Agricultural and Veterinary Entomology's Chemical
Research Unit isolated and identified a small peptide, called inceptin, from
the oral secretions of fall armyworm (Spodoptera frugiperda) larvae.

In cowpea plants (Vigna unguiculata) - also known as blackeyed peas -
this peptide triggers the production of ethylene and a series of other
defense-related phytohormones. In lab studies, only fall armyworm larvae
that produced inceptins significantly induced cowpea defenses.

Plants can perceive and defensively respond to attack either directly,
by impeding pest growth, or indirectly, by promoting advantageous
interactions with beneficial organisms.

In 2005, the United States produced almost 23,000 tons of cowpeas.
Worldwide, cowpeas rank among the top five food fiber crops because they can
tolerate poor, dry soils.

ARS is the U.S. Department of Agriculture's chief scientific research
agency.


[www.ars.usda.gov]