The Effects of Supplemental Nickel on Mouse Ear Disorder of Three Diospyros Species

American persimmon (Diospyros virginiana L.) is a multipurpose tree endemic to the eastern United States with potential for broader use in managed landscapes or for producing desirable fruits. Whereas most members of this genus originate from tropical and subtropical regions, the American persimmon could expand landscape diversity and fruit production applications in northern climates. Due to purported challenges with transplant success, American persimmon is likely best suited to production in containers. Recent observations of container-nursery crop production indicate that American persimmon is susceptible to mouse ear disorder (MED), a function of nickel deficiency. We hypothesized that American-and Asian-origin persimmon species are susceptible to MED and that supplementing nickel with a foliar spray will ameliorate the disorder, whereas urea supplementation will exacerbate symptoms. Our objectives were to characterize symptoms of MED in American persimmon (D. virginiana L.), Japanese persimmon (Diospyros kaki Thunb.), and dateplum persimmon (Diospyros lotus L.), as well as to determine whether MED could be corrected by foliar application of nickel or other compounds presumed to interact with the urease metabolic pathway, such as urea. In a randomized greenhouse study, symptomatic seedlings of each species were evaluated by comparing a nontreated control (H₂O spray), to foliar spray treatments of Nickel Plus^VR (169 mg/L Ni), NiCl₂ (169 mg/L Ni), urea (150 mg/L N), and combined NiCl₂ (169 mg/L Ni) and urea (150 mg/L N). Following treatment, the plants were evaluated using a MED severity rating scale including leaf characterization metrics (chlorophyll content index, count, surface area, dry mass, and specific area), as well as metrics characterizing stem traits (elongation and dry mass). The results suggest that the addition of supplemental nickel is effective at correcting MED for Diospyros species displaying symptoms; however, application should reflect species differences and grower conditions to optimize growth on a case-by-case basis. This study offers valuable insights for improving the cultivation of persimmons in container nursery production settings, contributing to the development and advancement of American persimmon as an emerging specialty crop.