Potatoes, insects resisted glandular trichomes

Glandular trichome constituents have been associated with insect resistance in a number of other crops, including cotton, tomato, potato, tobacco and alfalfa (73). However, this is the first time that glandular trichomes or any plant natural product has been implicated in the defense of pollen against predation. 

We have been involved in mechanistic studies aimed at understanding the basis of glandular trichome-based insect resistance in wild Solarium (potato) and Lycopersicon (tomato) species. Much effort has focused on identification of wild members of the Solanaceae with potentially useful resistance traits for introgression into Solarium tuberosum and Lycopersicon esculentum. In many cases resistance has been shown to be conferred by glandular trichomes, modified epidermal cells (i) which function as physical and/or chemical barriers against insect attack (2-10 > Tingey, this volume). 

The wild tomato, Lycopersicon pennellii, and the wild potato, Solanum berthaultiif are two species which exhibit insect resistance conferred by glandular trichomes. S, berthaultii and L. pennellii have been the focus of efforts at Cornell University to transfer trichome-based insect resistance traits. This chapter reviews our knowledge of the biochemistry of glandular trichome-based insect resistance in these species. 

The exudate of the glandular trichomes of Solanum ber-thaultii are effective against aphids and similar insect pests. One part of the defense involves the immobilization of the insects in the exudate which hardens (Harbome, 1989). This exudate proved to be a mixture of sucrose esters, of which 3,4-di-0-isobutyryl-6-C>-caprylsucrose is a major component. These compounds also appear to provide resistance to potato blight (Harbome, 1989). A similar series of compounds is found in the trichomes of other solanaceous plants of the genera Datura, Lycopersicon, Nicotiana, and Petunia. A series of esters of sucrose with -p-coumaric acid (such as 104) and acetate from Prunus maximowiczii proved to be responsible for the very bitter taste of the fruits (Shimazaki et al., 1991) (Fig. 15.18). 

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