Potato glandular trichomes

Potato Glandular Trichomes A Physicochemical Defense Mechanism Against Insects... 

Behavioral and sensory disturbance. Potato glandular trichomes, in addition to acting as a physical barrier to pests, manufacture and/or store a profusion of plant metabolic products, some of which profoundly influence insect behavior and metabolism (19,20). The sesquiterpene components of potato trichome glands (21,22,23) are potentially powerful semiochemicals and one of these, E-6-farnesene, is well known for its ability to initiate evasive behavior in aphids (24). The dramatic alteration of aphid feeding behavior on S. berthaultii reported by Lapointe and Tingey (25) may be due to allomonal sesquiterpenes in trichome exudate and will be discussed later. 

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. 

Hybrid potatoes bearing glandular trichomes from the wile Bolivian potato, Solanum berthaultii, are well defended against infestation and colonization by aphids, leafhoppers, and flea beetles (12). Populations of these damaging pests on elite hybrids are often reduced more than 85%, compared to those on susceptible commercial cultivars (13). Furthermore, many hybrids severely disrupt aphid feeding behavior and host acceptance in a manner comparable to that of their wild parent, an important attribute considering the worldwide importance of aphids as vectors of potato virus pathogens. 

Potatoes bearing glandular trichomes also defend against the Colorado potato beetle, a devastating pest capable of total crop destruction (4). Although resistance will not eliminate the need for other control tactics in management of this pest, our field experience indicates that present levels of resistance in hybrids can substitute for as much as 40% of the current insecticide usage on susceptible cultivars (14). 

Table IV. Effect of removing type A (wipe) and type B (methanol dip) glandular trichomes of S. berthaultii (PI 310927) on feeding, growth, and mortality of neonate Colorado potato beetle. Adapted from (29)...

Table V. Activity of neonate Colorado potato beetle larvae on excised leaflets of either S. tuberosum, S. berthaultii PI 310927, or PI 310927 from which most of the glandular trichome exudate had been removed by wiping between tissue papers. Adapted from (24)...

Although glandular trichomes can interfere with predators and parasitoids of aphids and the Colorado potato beetle, the inhibitory effect is largely associated with entrapment by type B exudate and is minimized on plants bearing moderate densities of these trichomes (42.43). 

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. 

Tridecanone also conditions resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say), causing mortality of young larvae which disrupt the glandular trichomes (47-51), PI 134417 also possesses factors associated with leaf lamellae that kill decemlineata larvae during the late instars. These factors are mechanistically distinct from 2-tridecanone-mediated resistance (51-52),... 

Kennedy, G. G. and C. E. Sorenson. 1985, Role of glandular trichomes in the resistance of Lycopersicon hirsutum f, glabratum to Colorado potato beetle (Coleoptera Chrysomelidae). J. Econ. Entomol. 78 547-551. 

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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