Estudo de dois morfotipos de galhas foliares em Persea willdenovii kosterm: aspectos anatômicos, histoquímicos e fenológicos

Abstract

Galls are characterized by tissues with typical functions and patterns and are formed by cellular hypertrophy, tissue hyperplasia, cytological changes, and changes in the chemical profile, leading to a galler-plant interaction. The galler-plant synchrony is essential for the success of galls. Persea willdenovii is semideciduous tree that presents two morphotypes of leaf galls. This study aimed to evaluate the anatomical, histochemical profiles, and phenology of the two morphotypes of galls induced in P. willdenovii. The hypothesis of the study is that the two morphotypes induced in P. willdenovii, despite being leaf, will be divergent in their anatomical, histochemical and phenological characteristics due to the probable difference of the inducing taxa. Samples of ungalled leaves, leaves with young, mature and senescent galls, were collected in a forest and pasture area on the main campus of the Federal University of Lavras. Samples were fixed in 70% FAA and stored in 70% ethanol. Sections of the leaves and galls were made freehand, stained with safranin and Astra blue and mounted in 50% glycerin for anatomical studies. For the histochemical test, fresh material was collected, in which sections were made, and then we followed the protocol for each substance tested (reducing sugars, protein, starch, lipids, alkaloids, flavonoids, phenolic compounds and lignins). To evaluate the phenology of the host plant, we followed the model suggested by Fournier and Charpentier, and the gall phenology was performed by counting young, mature and senescent galls to obtain the proportions. One intralaminar globoid morphotype with a small projection towards the adaxial face and a large projection towards the abaxial face, the other spherical globoid induced on the adaxial face from leaf folding. The intralaminar globoid gall is closed, glabrous, with coloration ranging from green to red, the parenchymatous mesophyll has lignified outer cortex and non-lignified and vascularized inner cortex. The spherical globoid gall is open, green, and glabrous with a larval chamber formed by the folding of the limbus from a vascular bundle. Cortex has lignified peripheral layers and homogeneous parenchyma of compacted cells. Chemical composition of the galls showed little variation in the leaf histochemical profile. The development cycle of the two morphotypes was different, but with induction in both young and mature leaves. An unidentified Hemiptera was collected in the intralaminar globoid gall. The intralaminar globoid morphotype was not observed in the pasture area. This absence may be influenced by the nutritional conditions of the plant, the chemical characteristics of the soil, and may also indicate the inability of the galler to survive in open environments. Both morphotypes presented lignification of the outer layers contributing to gall protection and inner parenchymal layers without nutritive tissue, typical of galls induced by sucking insects. Chemical composition highlights the presence of phenolic compounds that did not prevent gall formation and may attenuate the oxidative stress caused by the feeding activity of the galler. In both morphotypes, gall induction occurs in both young and mature leaves, associated with the semideciduous characteristic of the host, allowing the galls to be multivoltine.