Glandular trichomes aphid resistance

Glandular trichomes of j>. berthaultii provide the greatest levels of resistance against immature life stages of pest species. Encasement of feet and mouthparts of the green peach aphid by trichome exudate is greatest on nymphs and least on adult aphids, parallelling the trends in mortality (6). 

Figure. 1. Nature of glandular trichome-mediated aphid resistance in 5. berthaultiL Key (1) Carboxylic acid sucrose esters (CASE), (2) Viscous type B trichome exudate, (3) Increased aphid movement and attempts to escape, (4) Adhesive aphid tarsi, (5) Enhanced rupture of type A trichome membrane , (6) Polyphenoloxidase + 02 + substrate, (7) Aphid alarm pheromone, E-(B)=famesene, (8) Encasement of tarsi by trichome exudate, (9) Greater effective tarsal size, (10) Decreased aphid mobility, (11) Occlusion of mouthparts by trichome exudate, (12) Starvation and death. Adapted from (38).

There are primarily two classes of foliar glandular trichomes that contribute to the insect resistance of S. berthaultii and L. pennellii. Type A trichomes of S. berthaultii (referred to as Type VI in the genus Lycopersicon (H.) ) condition resistance to small-bodied insect pests such as aphids and leafhoppers by an... 

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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