Suppression of pecan scab by nickel

Abstract

The economic cost of pecan scab, caused by Fusicladium effusum G. Winter, can substantially limit profitability of pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivation in humid environments. Laboratory, greenhouse, and field studies found nickel (Ni) to inhibit growth of F. effusum and reduce disease severity on fruit and foliage of orchard trees. Nickel was toxic to the fungus in vitro at concentrations applied to orchard trees, and Ni sprays reduced scab severity on foliage of pecan seedlings in greenhouse experiments. Host genotype appears to influence Ni efficacy with fruit tissue of cultivars of intermediate resistance (i.e., 'Desirable') being most responsive to treatment and those most susceptible to scab (i.e., 'Wichita' and 'Apache') being least responsive. Addition of Ni as a nutritional supplement applied in combination with fungicides applied as air-blast sprays to commercial orchards reduced 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% to 52% on 'Desirable' in an orchard setting). Nickel supplemented fungicide sprays to 'Desirable' trees in commercial orchards also increased fruit weight and kernel filling, apparently from improved disease control. Although the efficacy of Ni was typically much less than that of triphenyltin hydroxide (TPTH), a standard fungicide used in commercial orchards, Ni treatment of tree canopies for increasing tree Ni nutrition slightly lowered disease severity. These studies establish that foliar Ni use in orchards potentially reduces severity of scab on foliage and fruit in scab-prone environments. The inclusion of Ni with fungicides for management of pecan scab might reduce disease severity over that conferred by fungicide alone, especially if targeted cultivars possess at least a moderate degree of scab resistance. Similar benefit from Ni sprays might also occur in host-fungi interactions involving other crops.