Anomalies in Structure, Growth Characteristics, and Nutritional Composition as Induced by 2,4-Dichlorophenoxy Acetic Acid Drift Phytotoxicity in Grapevine Leaves and Clusters

Abstract

Drift hazards and the effects of 2,4-dichlorophenoxy acetic acid (2,4-D) spray drift on woody perennials have been commonly observed since its discovery in the 1940s; however, 2,4-D-induced phytotoxicity, morphogenesis, and structural and compositional anomalies of their vegetative and reproductive structures are not well understood. Healthy and 2,4-D-injured shoots of grapevine (Vitis vinifera L.) from a commercial vineyard experiencing persistent drift were compared. The morphoanatomy of healthy and 2,4-D-injured leaves and berries were examined using light and scanning electron microscopy (SEM). Along with the microscopic examinations, stomatal conductance (gS), leaf growth characteristics, and mineral composition were also determined. The morphoanatomy of healthy leaves resembled that of a typical angiospermic leaf. By contrast, shoots exposed to 2,4-D phytotoxicity displayed epinastic behavior and developed grotesquely malformed leaves that were thick, fan-shaped, enated, and interveinally puckered as a result of fasciation of veins. The cellular architecture, including the vascular bundles, was altered as a result of the formation of parenchymatous replacement tissues. The gS, leaf index, leaf area, and petiole dimensions were significantly reduced in the 2,4-D-injured leaves. 2,4-D-injured leaves; however, accumulated high levels of nitrogen, potassium, and iron compared with healthy leaves. The clusters (fertilized inflorescences) of the injured shoots developed epinastic curvature and predominantly bore live green ovaries (seedless unripened pseudofruit) instead of true berries (fertilized fully ripened fleshy fruit). These abnormalities are expected to severely perturb the vital functions of photosynthesis and transpiration as evidenced by low gS and poor fruit set leading to senescence and localized necrosis ultimately causing death of current-season shoots.