Use of reverse genetic approach to study the role of tobacco trichome-produced cembratrien-diols in pest/insect interaction
Diterpenes cembratiene-diols (CBT-diols), sucrose esters, labdanoids and hydrocarbons are prominent tobacco trichome exudate constituents. They are considered to be the first line of defense barriers against pests/insects through chemical toxicity, alteration of ovipositional behavior, allergic and irritant responses to herbivores. The particular role of CBT-diols in tobacco pest defense has not been clearly elucidated. Some data indicate their role in budworm oviposition stimulation and larvae toxicity, resistance to aphid colonization, aphid attraction, susceptibility to Japanese and flea beetles, and fungitoxic properties. The goal of this study was to test the impact of the absence of cembratriene-diols (CBT-diols absent due to cyclase knockdown) on the resistance/susceptibility of field-grown plants to infestation by aphids, budworms, and hornworms. Field experiments involved Nicotiana tabacum lines TKF 2002LC and DHK 960 and their RNAi knock down counterparts that had no or low levels of CBT-diols. The composition of trichome exudate was verified by GC-MS. The field design was a randomized complete block with 12 replications. No treatment with pesticides, insecticides or fungicides was made in the experimental field. Plants were evaluated for infestation and level of damage during the season, and the data was analyzed statistically. In line TKF 2002, removal of CBT-diols caused significant (P<0.001) prevention of aphid infestation in the entire knockdown population. This result is direct evidence that CBT-diols play an important role in aphid attraction and colonization.
In line DHK 960 the role of CBT-diols in aphid infestation was inconclusive due to a different response during the two-year experiment. Under low hornworm pressure there was a significant reduction (p<0.01) of percent damaged and infested DHK 960 knockdown plants. Results suggest that CBT-diols are favored by hornworms.