Morphological and anatomical characters of apple leaves associated with cultivar susceptibility to spider mite infestation

Abstract

Morphological and anatomical chaIacters of apple leaves associated with cultivar susceptibility to two-spotted spider mite (Tetranychus urticae (Koch.)) infestation were investigated. The following six apple cultivars were selected for the research: Close, Lobo ( suceptible) and Katja, Piros, Jester, Maivit (more resistant to mites infestation). The cultivars of a relatively lower susceptibility, (except Marvit) were provided with a poorer pubescence on abaxial epidermis of foliage leaf than those susceptible. There was no strict correlation between stomata number per unit of the leaf surface and the susceptibility to T.urticae infestation. A tight cell arrangement in the spongy mesophyll was particularly characteristic for cv Marvit, whereas in the leaves of cvs Close and Lobo this tissue was definitely loose. It seems that loose spongy mesophyll structure may facilitate feeding of mites.The results regarding the analysis of the lower (abaxial) epidermis of the leaves seem to suggest that the layout and thickness of cuticle, rather than the epidermal thickness itself could be a factor determining the susceptibility of apple cultivars to T.urcitae.