Leaf characterization of Spermacoce verticillata at three stages of development

Abstract

Weed control is an essential practice in crop management. However, the use of herbicides may not be effective in certain situations, such as when problems are encountered in the application technology and when tolerant individuals and resistant biotypes are observed. In the cotton producing areas of the state of Bahia, Brazil, Spermacoce verticillata (shrubby false buttonweed) is not effectively controlled during burndown applications. During different developmental stages, plants can modify their leaves’ anatomical structures, which may influence herbicide control by modifying the retention, absorption, translocation and final effect of the chemical. This study assessed the morphological and histological differences in Spermacoce verticillata leaves at different stages of development. Leaves were collected from plants at different phenological stages (2-4 leaves, 4-6 leaves and flowering) and subjected to histological and scanning electron microscopy analyses. In the histological analysis, four leaves were collected from the upper nodes. The evaluated characteristics were the total leaf blade thickness, palisade and spongy parenchymal thicknesses, cuticle and epidermal cell thicknesses on the abaxial and adaxial surfaces and midrib height and width. Surface analyses were performed by observing the leaves under a scanning electron microscope. As the developmental stages of Spermacoce verticillata advanced, the plants began to show reduced leaf thickness due to the decreased abaxial epidermal thickness, transport vessel size and parenchymal thickness. At more advanced stages of development (4-6 leaves and flowering), the adaxial leaf surfaces showed fewer stomata and more trichomes.