Field deficiency of nickel in trees: symptoms and causes

This communication reports that the mouse-ear or little-leaf disorder and the associated replant disease of pecan [Carya illinoinensis (Wangenh.) K. Koch] is a Ni deficiency and is cured by timely foliar application of Ni (at 100 mg L-1); thus documenting the first known example of Ni deficiency in orchard crops. Deficiency is inducible on soils with adequate Ni content by a) excessively high soil Zn, Cu, Mn, Fe, Ca, or Mg; b) root damage by root-knot nematodes; or c) dry and or cool soils at time of bud break. Symptoms associated with Ni deficiency, but varying with severity of deficiency, include early-season leaf chlorosis, dwarfing of foliage, blunting of leaf/leaflet tips, necrosis of leaf or leaflet tips, curled leaf/leaflet margins, dwarfed internodes, distorted bud shape, brittle shoots, cold-injury-like death of over-wintering shoots, diminished root system with dead fibrous roots, failure of foliar lamina to develop, rosetting and loss of apical dominance, dwarfed trees, and tree death. In addition to pecan, Ni deficiency is exhibited by river birch; and based on symptoms and soil characteristics; it also appears to occur in other woody perennial crops (e.g. plum, peach and Pyracantha sp., and citrus). Its occurrence in two prominent ureide transporting hydrophiles, raises the possibility that such species are most likely to experience Ni associated disorders than are other species. Observations implicate excessive soil accumulation of light metals from long-term fertilizer usage as a primary cause of Ni deficiency. These results raise the possibility that Ni is a contributing factor in certain recalcitrant maladies and replant disorders of certain woody perennial crops and support the role of Ni as an essential nutrient element for higher plants. Ni deficiency in field situations appears to be far more common than generally recognized; thus, meriting greater attention in horticultural production strategies and greater awareness by horticulturalists.