Eremanthus erythropappus hosts globoid stem galls induced by Neolasioptera sp. (Diptera: Cecidomyiidae) close to the stem apex, which do not compromise the shoot apical meristem (SAM). We hypothesize that maintenance of the SAM, as well as the increasing number of leaves per branch and of galled stem lengths and diameters, are a consequence of alterations in vascular cells and, consequently, in the priority for water flow from non‐galled stems to the stem galls. Our study focuses on the globoid stem galls to evaluate if gall induction and development promote changes in structure and function of secondary xylem cells.
Anatomical, cytological, histometric and physiological methods were used to analyse non‐galled stem branches (NGS), mature globoid stem galls and stem portions below and above the galls.
These analyses revealed that vessel elements are larger in stem galls and in stem portions above the galls. Under Neolasioptera sp. induction activity, the vascular cambium of E. erythropappus produces less numerous but larger vessel elements and overproduces parenchyma cells.
Contrary to the vascular constriction hypothesis proposed for bacterial galls, the vascular traits of the Neolasioptera sp. stem galls on E. erythropappus result in priority for water flow to galls and the non‐galled portions above the galls, allowing the maintenance of galled stem growth and development.
Context Galls are products of an intrinsic relationship between specific parasites and their host plants. Gall formation involves alterations in the developmental pattern of the host organs in which environmental conditions may also impose constraints. Aims We hypothesised that the adaptive features of the host plants reflect the stressors of the xeric and mesic environments and influence the establishment and success of the associated galls. Methods We analysed anatomical, histometric, and histochemical alterations induced by two species of Eriophyidae, on Miconia ibaguensis adapted to the Brazilian Cerrado (xeric environment) and on Miconia notabilis adapted to the forests of the equatorial region (mesic environment). Key results The adaptive leaf characteristics of M. ibaguensis and M. notabilis to both xeric and mesic environments, such as the trichomes, cuticle and mesophyll thickness, number of mesophyll layers, the proportion of intercellular spaces, differences in the intensity detection of phenolic and starch are kept in the galls. The higher density of emergences in M. notabilis may increase the protection against the natural enemies of the eriophyids, which are commonly more abundant in mesic than in xeric environments. Conclusions These traits are important not only for the survival of the two host plants but also for the success of the two species of galling Eriophyidae in distinct environments. Implications These findings indicate the success of the gall inducers of the same taxa in distinct environments, which can be explored in different systems.
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