Sir

The reduced-caffeine transgenic coffee plant (S. Ogita et al. Nature 423, 823; 200310.1038/423823a) must be one of the first transgenic plants where a natural plant compound is suppressed. Caffeine has been proposed to form part of the plant's defence mechanisms, specifically against insects (J. A. Nathanson Science 226, 184–187; 1984) and slugs (R. Hollingsworth, J. Armstrong and E. Campbell Nature 417, 915–916; 2002). These transgenic plants may thus be more successful in testing this hypothesis than as an agricultural crop.

It is interesting that the transformation was carried out on Coffea canephora, the lower-grade robusta coffee, which has about twice as much caffeine as arabica has. As its name suggests, robusta is more resistant to attack by insects and diseases and it is likely that caffeine plays a role in that.

The coffee industry may be especially keen to reduce caffeine in robusta, as over the years it has gradually been slipping more of it into standard arabica blends. In the opinion of Ernesto Illy, chairman of the Institute for Scientific Information on Coffee and espresso maestro di tutti i maestri, this has contributed to the present sluggish demand for coffee world-wide as consumers drink less to maintain a constant caffeine intake (Coffee and Cocoa International 28, no. 6, 20–22; 2001).

Because coffee is a perennial plant that takes about three years to come into production and may stay in the ground for 20 or more years, changing to a new variety is a major investment. Farmers would need assurance that the new plant is as resistant to attack as other varieties. Unfortunately, it could take many years for an agent to adapt to the new plant, so short-term tests might be insufficient. Further, coffee is grown in many regions and habitats, so very widespread field trials would be needed.

Hence, although a low-caffeine plant would be a useful research tool, there could be unintended long-term consequences most acutely felt by the poor farmer.