Complex meristematic activity induced by Eucecidoses minutanus on Schinus engleri turns shoots into galls.

PREMISE OF THE STUDY Gall-inducing organisms change the development of their host plant organs, showing ontogenetical patterns not observed in the non-galled plants. In current work, ontogenetic studies on galls induced by Eucecidoses minutanus on Schinus engleri revealed novelties in plant developmental responses to the galling stimuli. METHODS The ontogenesis, histochemistry, and histometry of Schinus engleri bud galls were investigated in parallel to the instars of E. minutanus, providing evidence for the morphogenetic changes that occur with each larval stage. KEY RESULTS Gall ontogenetic phases demonstrated an intricate relationship with the inducer's development. First and second-instar larvae induced pericycle and pith cells to dedifferentiate into the gall inner meristem, whose hyperplasia and cell hypertrophy characterized the gall growth and development phase. The innermost layers were lipid-rich nutritive cells lining the larval chamber. Additional vascular bundle rows were produced in young galls. Third and fourth instar-larvae related to the gall maturation phase, with centripetal lignification of the outer parenchyma cell layers, epidermis stratification, and activation of a cambium-like meristem (CLM). The CLM activity resulted in new layers of nutritive cells differentiated inwards, which replaced the first layers of nutritive cells, consumed by E. minutanus larvae, and, also, increased parenchyma cell layers outwards. Gall wall thickness increased until the end of gall maturation. CONCLUSIONS E. minutanus induces a structurally complex globoid stem gall, modifying all host plant tissues and stimulating a novel meristematic pattern in S. engleri. The gall developmental steps are related to the gall inducer instars. This article is protected by copyright. All rights reserved.