Researchers at Plant Research International have achieved a breakthrough in the development of chrysanthemums with resistance to thrips, bringing the ecological cultivation of chrysanthemums a step closer. This is the conclusion of the thesis with which Seetharam Annadana, a Plant Research International guest member of staff from India, obtained his doctorate at the University of Wageningen on 7 December 2001. Annadana developed new techniques which make possible the genetic modification of two thirds of the available varieties of chrysanthemum. In addition, he identified better so-called promoters: genetic switches to ensure that the genes incorporated into the chrysanthemums will be sufficiently active.

With his thesis, Annadana has laid the grounds for effective genetic modification of the chrysanthemum. Researchers hope to develop chrysanthemums resistant to insects with the help of this technology. Being a major pest, thrips is generally regarded to be the main factor impeding the ecological production of chrysanthemums.

At present, the damage caused by thrips can only be adequately prevented using chemical pesticides. Consequently, various ecological practices cannot be applied, such as the use of certain biological control systems. The development of thrips-resistant chrysanthemums would entail using far less chemical pesticide, or even none at all.

As no chrysanthemum or wild relative has been found that is sufficiently resistant, hopes are rested on the use of genetic modification. Annadana improved the protocol for the genetic modification of chrysanthemums on a number of important points, and many existing varieties can now be effectively genetically modified.

Furthermore, he investigated what type of genes could be used to make chrysanthemums resistant to thrips. He discovered that genes encoding so-called protease inhibitors might be suitable. These substances inhibit the activity of certain enzymes in the digestive tract of the thrips. Many plants create protease inhibitors naturally when attacked by insects. Annadana tested the effectiveness of various inhibitors and found that egg production was reduced by as much as 50%.

Plant Research International has now started research on whether the incorporation of protease inhibiting genes can in fact lead to resistance to thrips.