Suppression of Pecan Scab by Nickel Management Programs, Although It Is Integral Bruce W
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DISEASE AND PEST MANAGEMENT HORTSCIENCE 47(4):503–508. 2012. cells, tissues, and organs may reduce scab incidence and severity. Nickel is an essential nutrient element often disregarded by nutrient Suppression of Pecan Scab by Nickel management programs, although it is integral Bruce W. Wood1, Charles C. Reilly, Clive H. Bock, to certain essential metabolic processes (Bai et al., 2006, 2007, 2008). Pecan appears to and Michael W. Hotchkiss possess a relatively high Ni requirement with U.S. Department of Agriculture, Agricultural Research Service, Southeastern factors such as soil environment, weather, and Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA certain orchard management factors poten- 31008-0087 tially triggering transitory early-season Ni de- ficiency in orchard trees (Nyczepir et al., 2006; Additional index words. production, management, fungicides, triphenyltin hydroxide, nutrient Wood, 2010; Wood et al., 2004a, 2004b, elements, cultivars, resistance, fungi, Fusicladium effusum, fruit, pest management, nutrition, 2004c, 2006) when tissues of foliage, shoots, micronutrient, Carya illinoinensis and fruit are most susceptible to scab infection. As a transition metal physiochemically Abstract. The economic cost of pecan scab, caused by Fusicladium effusum G. Winter, can similar to copper (Cu)—an effective scab fun- substantially limit profitability of pecan [Carya illinoinensis (Wangenh.) K. Koch] gicide (Demaree and Cole, 1927)—Ni might cultivation in humid environments. Laboratory, greenhouse, and field studies found also possess direct toxicity to F. effusum.In- nickel (Ni) to inhibit growth of F. effusum and reduce disease severity on fruit and foliage deed, the fungicidal efficacies of Ni com- of orchard trees. Nickel was toxic to the fungus in vitro at concentrations applied to pounds were apparent by 1908, and by 1963, orchard trees, and Ni sprays reduced scab severity on foliage of pecan seedlings in there were 149 or more scientific references greenhouse experiments. Host genotype appears to influence Ni efficacy with fruit tissue noting Ni activity against certain fungal spe- of cultivars of intermediate resistance (i.e., ‘Desirable’) being most responsive to cies (Anonymous, 1964). Nickel salts are es- treatment and those most susceptible to scab (i.e., ‘Wichita’ and ‘Apache’) being least pecially efficacious with a U.S. patent (No. responsive. Addition of Ni as a nutritional supplement applied in combination with 2,971,880) issued to Rohm and Haas Co. (Keil fungicides applied as air-blast sprays to commercial orchards reduced severity of scab on and Frohlich, 1961) for use of Ni as a fungi- both leaves and fruit depending on cultivar and date of disease assessment (e.g., scab cide. Thus, timely foliar Ni application during severity on fruit was reduced by 6% to 52% on ‘Desirable’ in an orchard setting). Nickel- canopy expansion for improving tree nutri- supplemented fungicide sprays to ‘Desirable’ trees in commercial orchards also in- tional physiology, a growth phase when sus- creased fruit weight and kernel filling, apparently from improved disease control. ceptible hosts are most likely to be infected, Although the efficacy of Ni was typically much less than that of triphenyltin hydroxide might confer benefits indirectly by increasing (TPTH), a standard fungicide used in commercial orchards, Ni treatment of tree host resistance and directly by fungicidal canopies for increasing tree Ni nutrition slightly lowered disease severity. These studies activity against F. effusum. This study assesses establish that foliar Ni use in orchards potentially reduces severity of scab on foliage and efficacy of foliar Ni application in pecan fruit in scab-prone environments. The inclusion of Ni with fungicides for management of orchards for managing pecan scab and its pecan scab might reduce disease severity over that conferred by fungicide alone, potential as an integrated pest management tool. 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. Materials and Methods In vitro toxicity of nickel to F. effusum. Two experiments assessed the effect of Ni in Pecan scab (Seyran et al., 2010), caused and Wood, 1985), yet it is the physical damage vitro. In the first experiment, potato dextrose by Fusicladium effusum G. Winter, is the to developing fruit that makes the disease agar (PDA) was amended with different most important disease of pecan cultivated in especially problematic. Infection can result concentrations of Ni (0, 0.014, 0.028, 0.28, humid environments (Wood and Reilly, 1999). in fruit abortion, poor kernel filling, smaller 0.56, 2.80, 5.60, and 28.0 gÁL–1), and using a Almost all cultivated genotypes exhibit a de- nuts/kernels, and altered nutmeat composition. petri plate-based assay (15 mL PDA/plate), gree of scab susceptibility under conditions Scab control in commercial orchards typically the effect of Ni concentration on growth of F. favoring infection (Goff et al., 2003). With requires 3–18 fungicide cover sprays (Gottwald, effusum was measured; a well was created in more susceptible cultivars, wet conditions can 1985; Sparks, 1996; Turechek and Stevenson, the center of each agar plate using a transfer result in severe epidemics (Sparks et al., 2009). 1998). Although appropriate fungicide use tube, and 0.1 mL of a conidia suspension of Other environmental factors (e.g., soil mois- typically provides satisfactory scab control, F. effusum was added (1.0 · 106 conidia/mL). ture and temperature) affect timely availabil- protection is expensive, and disease control The conidia suspension was prepared from ity of nutrient elements, which may also affect is often disappointing. In addition, fungicides 3-week-old colonies of F. effusum (isolated susceptibility to pecan scab, as occurs in other might reduce carbon photoassimilation from ‘Desirable’ at Byron, GA) cultured on crops with either visual or physiological nu- (Gottwald and Wood, 1985; Wood et al., oatmeal agar. Each treatment was replicated trient deficiencies (Huber and Graham, 1999). 1985), which potentially influences flowering three times and the experiment repeated once. The susceptibility of pecan leaves to in- and crop load (Wood, 1989, 1995, 2011; Plates were incubated in the light (12-h day/ fection by F. effusum is greatest when foliage Wood et al., 2003; Worley, 1979a, 1979b). 12-h night) for 3 weeks before measuring the is young (18–28 d old or less) (Gottwald, Thus, there is need for improved scab disease diameter of the culture of F. effusum around 1985; Turechek and Stevenson, 1998; Wood management tools that increase efficacy and/ the well. In the second experiment, 250-mL et al., 1988). Scabbed foliage, shoots, and fruit or reduce control costs without adversely Erlenmeyer flasks containing 50 mL potato can exhibit lower photoassimilation (Gottwald affecting tree health and production potential. dextrose broth were amended with Ni (0, Toxicity, deficiency, or imbalances in ei- 0.014, 0.028, 0.28, and 2.80 gÁL–1) and in- ther essential or beneficial nutrient elements oculated with 0.1 mL of a conidia suspension can theoretically influence host susceptibility of F. effusum (1.0 · 106 conidia/mL) prepared Received for publication 22 Sept. 2011. Accepted to fungal diseases through disruption of met- as described for the plate assay. Each treat- for publication 10 Feb. 2012. The assistance of James Stuckey and Kirby abolic or physiological processes conferring ment was replicated three times. The flasks Moncrief is gratefully acknowledged for data disease resistance (Graham, 1983; Huber and were incubated for 3 weeks in an orbital collection. Graham, 1999). Because timely availability of shaker at 27 °C. The fungal mass was mea- 1To whom reprint requests should be addressed; nutrient elements can influence disease sever- sured by filtering the culture through No. 1 e-mail [email protected]. ity, ensuring optimal nutritional physiology of Whatman filter paper (Whatman International, HORTSCIENCE VOL. 47(4) APRIL 2012 503 Maidstone, U.K.) and dried in an oven at 80 °C for percent fruit surface diseased in early at 0.548 mLÁL–1) fungicide; and TPTH + Ni for 24 h to measure mycelium dry weight. August. Because the three cultivars were not treatments] structured as a randomized com- Data from both experiments were analyzed by randomly dispersed within the orchard, data plete block with single trees as blocks (i.e., analysis of variance (ANOVA) with Tukey’s were analyzed separately for each cultivar. 15 blocks) and a single fruit-bearing branch means separation (P = 0.05) using SAS Version Analysis was by ANOVA using Tukey’s HSD being the experimental unit for each treat- 9.2 (SAS Systems, Cary, NC). for means separation at P = 0.050 (analyses ment (n = 60). Branches sampled were from The effect of nickel spray concentration were performed in SAS Version 9.2). the sun-exposed midcanopy and situated to on severity of leaf and fruit scab. The effect In the second study, a factorial experiment protect against spray contamination from other of Ni on foliar scab was tested using 1-year-old assessed impact of Ni on pecan scab. A mixed treatments and had at least three fruiting seedlings of ‘Desirable’ grown in a potting cultivar 13-year-old orchard of ‘Desirable’, clusters. Treatments were applied using a soil mix (Metromix 330; SunGro, Bellevue, ‘Wichita’, and ‘Apache’ trees spaced 10 · 10 m pressurized hand sprayer and applied until WA) in 20-cm square containers. The ex- was commercially managed for water, pests, leaf drip. Sprays were applied at 2-week panding foliage of seedlings were sprayed to and nutrition (Hudson et al., 2002) with the intervals from soon after budbreak in early runoff with Ni at a concentration of 0 (non- first factor (fungicide treatment) at four levels: April to the end of July during early morning treated control), 0.025, 0.050, 0.100, 0.150, 1) non-treated control; 2) TPTH (SuperTin; to facilitate treatment efficacy.