Chimeric tomato plants show that aphid resistance and triacylglucose production are epidermal autonomous characters.

Abstract

Graft chimeras were generated using Lycopersicon pennellii and L. esculentum to determine the contribution of the three meristem layers (L1, L2, and L3) to trichome density, sugar ester production, and aphid resistance. Sugar esters, in the form of triacylglucoses, have been implicated in the aphid resistance of pennellii. One chimera possessed the epidermal layer (L1) of pennellii and the internal tissues (L2 and L3) of the aphid-susceptible esculentum. The second chimera had both the L1 and L2 of pennellii and the L3 of esculentum. Type IV trichome densities did not differ significantly among the chimeras and pennellii. Both chimeras accumulated sugar esters with similar sugar and fatty acid composition as pennellii. The concentration of epicuticular sugar ester on the chimeras was also comparable with that of pennellii. Leaf cage and feeding studies demonstrated that both chimeras are as resistant to aphids as is pennellii. The resistance could be reduced similarly on all three types of plants by removal of the type IV trichome exudate. These results indicate that the presence and density of the type IV trichomes and the amount and type of sugar esters produced are features determined by the genotype of the epidermis. These epidermal features are sufficient to account for the aphid resistance observed in pennellii.