Background: Besides fibers, cotton plants also produce a large amount of seeds with a high oil and protein content.
The use of these seeds is restricted by their high contents of the terpenoid gossypol, which is harmful to humans and
livestock. Using a genetic engineering approach, “Ultra-low gossypol cottonseed” (ULGCS) plants were produced by
knocking down an enzyme that catalyzes the formation of a precursor of gossypol. This was accomplished via RNAimediated
silencing of the target gene using a seed-specific α-globulin promotor. Since gossypol is also a crucial
defense mechanism against leaf-feeding herbivores, ULGCS plants might possess lower herbivore resistance than nonengineered
plants. Therefore, we tested the constitutive and inducible direct insect resistance of two ULGCS cotton
lines against the African cotton leafworm, Spodoptera littoralis.
Result: The herbivore was equally affected by both ULGCS lines and the control (Coker 312) line when feeding on fully
expanded true leaves from undamaged plants and plants induced by jasmonic acid. When plants were induced by
caterpillar-damage, however, S. littoralis larvae performed better on the ULGCS plants. Terpenoid analyses revealed that
the ULGCS lines were equally inducible as the control plants. Levels of terpenoids were always lower in one of the two
lines. In the case of cotyledons, caterpillars performed better on ULGCS cotton than on conventional cotton. This was
likely caused by reduced levels of gossypol in ULGCS cotyledons.
Conclusion: Despite those effects, the insect resistance of ULGSC cotton can be considered as largely intact and the
plants may, therefore, be an interesting alternative to conventional cotton varieties.