Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 5, 2011
Publication Date: April 1, 2012
Citation: Wood, B.W., Reilly, C.C., Bock, C.H., Hotchkiss, M.W. 2012. Suppression of pecan scab by nickel. HortScience. 47(4):503-508. Interpretive Summary: Crop and economic loss to pecan scab disease, a fungus, is great in much of the U.S. pecan-belt during the typical growing seasons, and is especially great in abnormally wet seasons. Protection of orchards from excessive loss of nutmeat yield and quality requires both new and more economical approaches to scab control. We found that spraying canopies with nickel, an essential nutrient element, could improve natural tree resistance to the fungus while providing additional protection by being simultaneous toxic to the scab fungus. Timely foliar application of nickel alone, or as an additive to fungicides, offers a means of improving scab disease control in commercial orchards.
Technical Abstract: The economic cost of scab, caused by Fusicladium effusum, can substantially limit the profitability of pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivation in humid environments. Field and greenhouse experiments assessed the influence of nickel (Ni) on scab severity on fruit and foliage of Ni sufficient orchard trees, and laboratory experiments examined the in-vitro toxicity of Ni to F. effusum. Treatment of tree canopies with Ni sprays for increasing tree Ni nutrition slightly lowered disease severity. Host genotype influences efficacy, with cultivars of intermediate resistance (e.g., ‘Desirable’) being most responsive to Ni treatment, and those most susceptible to scab (i.e., ‘Wichita’ and ‘Apache’) being least responsive. Addition of Ni as a nutritional supplement co-applied with fungicides applied as air-blast sprays to commercial orchards and experimental plots generally reduced the severity of scab on both leaves and fruit, depending on cultivar and date of disease assessment (e.g., scab severity on fruit was reduced by 6-52% on ‘Desirable’ in orchard setting). Nickel supplemented fungicide sprays to ‘Desirable’ also increased fruit weight and kernel filling. In greenhouse experiments, Ni sprays reduced scab severity, and Ni was toxic to the fungus in vitro at concentrations applied to orchard trees. However, Ni was not nearly as efficacious as triphenyltin hydroxide, a standard fungicide used in commercial orchards. These studies establish that usage of Ni in an orchard nutrition management program can have a side effect of reducing severity of scab on foliage and fruit. It is likely that protection is both indirect via enhancement of plant health and resistance processes, and direct via toxicity to the scab fungus on the plant surface. We report that when fungicide-based disease management strategies for pecan scab include Ni for improving tree nutritional physiology there can be a further reduction in severity of pecan scab, especially with cultivars possessing at least moderate scab resistance. Similar benefit might also exist in host-fungi interactions involving other horticultural or agronomic crops.