Glandular trichomes of Solatium berthaultii and resistance to the Colorado potato beetle

The defensive mechanisms of the wild potato, Solanum berthaultii Hawkes, to larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), were studied by selective removal of glandular trichomes and trichome exudates from leaflets, and by comparing performance on S. berthaultii and on the cultivated potato, S. tuberosum L., which lacks defensively active type A and B glandular trichomes. Removal of type A trichomes increased the proportion of larvae that fed on S. berthaultii. Removal of the exudate from type B trichomes increased the proportion of larvae that fed and led to a decrease in mortality. The predominant active compounds in type B exudate, i.e. fatty acid esters of sucrose, were only effective in the presence of type A trichomes. Sucrose esters did not affect larval feeding on S. tuberosum leaflets or on S. berthaultii leaf discs from which the type A trichomes had been removed. Growth of surviving larvae was not significantly affected by removing type A trichomes or type B exudate. Growth of larvae was significantly increased when S. berthaultii leaflets were presented in artificial diet which eliminated the physical barrier of the type B stalks. Growth was no different on artificial diet containing either S. berthaultii or S. tuberosum leaf material (fresh or lyophilized powder) but was poorer on these diets than on S. tuberosum leaflets. The presence of type A trichomes is a fundamental requirement for expression of S. berthaultii resistance to L1 L. decemlineata. Type B droplets containing sucrose esters increase the expression of resistance in the presence of defensively-active type A trichomes. Resume Trichomes glandulaires et resistance de Solanum berthaultii au doryphore Les mecanismes de defense de la pomme de terre sauvage, S. berthaultii Hawkes, aux larves de Leptinotarsa decemlineata Say, ont ete etudies par ablation selective des trichomes glandulaires et par l'elimination de leur exsudat des folioles, et par comparaison avec S. tuberosum L. qui a perdu les trichomes glandulaires defensifs A et B. L'ablation des trichomes A a augmente la proportion de larves ayant consomme S. berthaultii. L'elimination de l'exsudat des trichomes B a augmente la proportion de consommatrices et reduit la mortalite. Les principaux composes actifs de l'exsudat B, c'est-a-dire des esters d'acides gras de sucrose, n'etaient actifs qu'en presence de trichomes A. Les esters de sucrose n'ont pas modifie la consommation larvaire sur folioles de S. tuberosum, ou sur disques de feuilles de S. berthaultii dont les trichomes A avaient ete enleves. La croissance des larves survivantes n'a pas ete modifiee significativement par l'ablation des trichomes A ou l'elimination de l'exsudat de B. La croissance des larves a ete significativement augmentee quand les folioles de S. berthaultii ont ete incorpores dans l'aliment artificiel apres elimination de la barriere physique due aux pedoncules B. La croissance a ete de meme importance sur aliments artificiels contenant des feuilles (fraiches ou en poudre lyophylisee) de S. berthaultii ou de S. tuberosum, mais plus faible que sur folioles de S. tuberosum. La presence de trichomes A est indispensable a la resistance de S. berthaultii aux L, de L. decemlineata. Les gouttelettes de type B contenant des esters de sucrose augmentent l'expression de la resistance en presence d'une defense active par trichomes A.