Anatomy of different forage cacti with contrasting insect resistance

Anatomical aspects of four cacti with contrasting insect resistance using morpho-anatomical analysis and morphometry were evaluated. The following cacti were studied: F-21 [Nopalea cochenillifera (L.) Salm Dyck; IPA-200021]; Giant [Opuntia ficus-indica (L.) Mill.; IPA-100001]; IPA-20 [O. ficus-indica (L.) Mill.; IPA-100003] and Opuntia undulata Griffiths (IPA-200174). Previous research has indicated O. undulata and F-21 is resistant to Dactylopius opuntiae (Cockerell). Cladode measurements included cuticle thickness, epidermis and xylem cell wall as well as the area and perimeter of mesophyll cells. Morphometric analysis revealed that O. undulata has the largest proportion of epidermis and cuticle (39.24 and 220.41 μm, respectively). Regarding the thickness of the vascular bundles, O. undulata differed only from the IPA-20 variety (12.13 and 16.61 μm, respectively). In the mesophyll cells, F-21 had the greatest perimeter/area ratio. Morpho-anatomical analysis revealed a thick cuticle and epidermis with the presence of crystals, xylem vessels with ligneous fibers and a thick wall, and a large, thin-walled mesophyll. Epidermis was the main anatomical barrier, providing greater resistance and integrity of the cladode and varied among the studied cultivars. Cultivars with thicker epidermis also presented insect resistance in other studies. Further investigation is needed to prove that this particular trait has a causal influence on insect resistance.