Techniques and methods used in studies of resistance to Panonychus ulmi in apple varieties

Abstract

Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20-25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants.There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.Resume-En conditions d'infestation naturelle au champ, des variations ont ete observees au niveau des densites de population de P. ulmi selon les cultivars consideres. De nombreuses techniques de laboratoire permettent de determiner les ecarts de sensibilite ou de resistance a l'encontre de P. ulmi chez les differents cultivars. En termes de comportement et de fecondite de P. ulmi en fonction des repetitions, la variation minimale fut observee pour les insectes femelles eleves sur des disques foliaires de 20-25 cm de diametre, ou dans de petites cages en matiere plastique installees sur les feuilles de jeunes pommiers en pots. Les feuilles utilisees dans le cadre des essais bioecologiques doivent etre prelevees au meme endroit sur les arbres. En outre, il convient d'etudier la densite et la fecondite des populations de P. ulmi au niveau des feuilles portees par les bois de retour courts. Signalons egalement qu'un conditionnement preable aux divers cultivars n'eut aucun effet sur la fecondite de l'insecte femelle lorsque celle-ci fut mise en presence de nouvelles plantes. La resistance moyenne des pommiers vis-a-vis de P. ulmi n'est pas le resultat d'un mecanisme unique agissant independamment. Elle est le fruit d'un nombre considerable d'attributs morphologiques, anatomiques et chimiques des feuilles, lesquelles s'expriment differemment suivant les cultivars.

Influence of three irrigation levels on the reproduction of european red mite Panonychus ulmi Koch and on some biochemical characteristics of leaves of potted apple plants

“…For hoth rootstocks, fccundity in the high water regime was about eiglu cggs/feinale significanhly l()wer than that observcd with normal irrigation. Considering the ti -irce irrigation trealmeflis, there was a significam position of leaves (mineraIs, aminoacids and sugars) and eventually ou the concentration of phcnolic compounds which are mainly represented hy phloridzin in apple leaves (Bielak & Dabrowski 1985). We must also think oF the planes Lurgor.…”

Changes in biochemical composition of needles of ornamental dwarf spruce (Picea glauca ‘Conica’) induced by spruce spider mite (Oligonychus ununguis Jacobi, Acari: Tetranychidae) feeding

“…Phenolics and terpenoids are known to be in duced by mite-pests feed ing and they usu ally act as re pellents, de ter rents or tox ins against her biv o rous mites (Bielak and Dąbrowski 1985, Tomczyk 1996, 2001, Kiełkiewicz 2003. Our find ings showed the strong in crease of phenolics in slightly dam aged P. glauca 'Conica' nee dles but it did not re sult from the in crease in the polyphenolic level.…”