Submitted to: Journal of Applied Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 26, 2013
Publication Date: N/A
Interpretive Summary: A comparative study of six citrus rootstock seedlings to increasing levels of rhizosphere Cu [CuEDTA (0.05 to 2.00 ppm)] in sand culture at pH 5.86 was conducted for a period of 108 days. The study supports work by others that citrus rootstocks disproportionally accumulate more Cu in roots than in leaves, and that they differ in translocation of Cu from roots to leaves. Other nutrients analyzed (Ca, K, P, Fe, Mn, and Zn) also accumulated in roots more than in leaves. The exception was Mg which accumulated nearly equally in roots and leaves (as a mean of rootstocks). In addition to plant nutrition, rootstocks were also subjectively assessed for nutrient disorder in relation to Cu treatment. Based on visual leaf symptoms on youngest leaves in the highest Cu treatment (2.00 ppm), ‘Volkamer’ lemon was the least, and ‘Swingle’ citrumelo the most susceptible to Cu with the other rootstocks falling in between these extremes as follows: (most visual symptoms) ‘Swingle’ citrumelo > ‘Cleopatra’ mandarin / ‘Flying Dragon’ trifoliate > US-812 / US-897 > ‘Volkamer’ lemon (least visual symptoms).
Technical Abstract: Florida citrus groves that have been under continuous production for many years often have high levels of soil-fraction copper (Cu) from the use of Cu-containing fertilizers and pesticides. On such groves, citrus trees may develop Cu toxicity which negatively impacts growth and nutrition. The objectives of this study were to investigate the growth and nutritional response of six citrus rootstock seedling varieties grown in sand in 3.8 L containers to increasing concentrations of Cu-ethylenediaminetetraacetic acid (CuEDTA). Citrus rootstocks included in the study were: ‘Swingle’ citrumelo [SC (Citrus paradisi × Poncirus trifoliata)], ‘Volkamer’ lemon [VL (C. volkameriana)], ‘Cleopatra’ mandarin [CM (Citrus reticulata)], ‘Flying Dragon’ trifoliate [FD (P. trifoliata)], ‘US-812’ [US812 (‘Sunki’ mandarin × ‘Benecke’ trifoliate)], and ‘US-897’ [US897 (CM× FD)]. Incorporated into a complete nutrient solution, Cu was supplied at 0.05, 0.25, 1.00, and 2.00 mg/L. Citrus rootstock but not Cu treatment was significant for root and leaf dry mass with FD and VL having the least and greatest total plant dry mass, respectively. Rootstock and Cu treatment was significant for root and leaf Cu. As a mean of Cu treatments, foliar Cu ranged from 4.05 µg/g (CM) to 7.74 µg/g (US812); and root Cu ranged from 30.18 µg/g (FD) to 61.08 µg/g (VL). Rootstock but not Cu treatment was significant for calcium (Ca), potassium (K), magnesium (Mg), phosphorous (P), iron (Fe), manganese (Mn), and zinc (Zn). 'Volkamer' lemon had significantly higher levels of foliar Ca, K, and Mg than the other rootstocks; and along with US812, the highest level of foliar Fe. For all nutrients analyzed except for Mg, accumulation was greater in roots than leaves. Magnesium, as a mean of rootstocks, accumulated equally in roots and leaves. Subjective analysis of plants at harvest for nutrient disorder revealed that young terminal-growth leaves of VL and SC in the highest Cu treatment (2.00 mg/L) showed few to pronounced symptoms of micronutrient disorder, respectively, that correlated with increasing Cu treatment. Based on visual symptoms in the highest Cu treatment that included interveinal chlorosis and leaf/leaflet deformation/cupping, plants segregated as follows from greatest to least expression of the observed micronutrient-like disorder: SC > CM/FD > US812/US897 > VL. The study supports work by others that citrus rootstocks disproportionally accumulate more Cu in roots than in leaves, and that they differ in translocation of Cu from roots to leaves.