- Email: [email protected]
Postharvest salicylic acid treatment reduces storage rots in water-stressed but not unstressed sugarbeet roots
Postharvest Biology and Technology 85 (2013) 162–166
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Research note
Postharvest salicylic acid treatment reduces storage rots in water-stressed but not unstressed sugarbeet roots Karen Klotz Fugate a,∗ , Jocleita Peruzzo Ferrareze b,1 , Melvin D. Bolton a , Edward L. Deckard c , Larry G. Campbell a , Fernando L. Finger d a
USDA-ARS, Northern Crop Science Laboratory, 1605 Albrecht Blvd. N., Fargo, ND 58102-2765, USA Departamento de Biologia Vegetal, Universidade Federal de Vic¸osa, 36571-000 Vic¸osa, MG, Brazil c Department of Plant Sciences, North Dakota State University, P.O. Box 6050, Fargo, ND 58108-6050, USA d Departamento de Fitotecnia, Universidade Federal de Vic¸osa, 36571-000 Vic¸osa, MG, Brazil b
a r t i c l e
i n f o
Article history: Received 15 January 2013 Accepted 3 June 2013 Keywords: Beta vulgaris Botrytis cinerea Pers. ex Fr. Clamp rot Drought Penicillium claviforme Bainier Phoma betae Frank
a b s t r a c t Exogenous application of salicylic acid (SA) reduces storage rots in a number of postharvest crops. SA’s ability to protect sugarbeet (Beta vulgaris L.) taproots from common storage rot pathogens, however, is unknown. To determine the potential of SA to reduce storage losses caused by three common causal organisms of sugarbeet storage rot, freshly harvested roots were treated with 0.01, 0.1, 1.0 or 10 mM SA, inoculated with Botrytis cinerea, Penicillium claviforme, or Phoma betae, and evaluated for the severity of rot symptoms after incubation at 20 ◦ C and 90% relative humidity. Roots were obtained from plants that received sufficient water or were water-stressed prior to harvest. Roots from water-stressed plants were included since water-stress increases sugarbeet root susceptibility to storage rot and SA mitigates drought effects in other plant species. SA at concentrations of 0.01–10 mM had no effect on the severity of storage rot caused by B. cinerea, P. claviforme, or P. betae in roots from plants that received sufficient water prior to harvest. However, SA at these same concentrations reduced the severity of rot symptoms for all three pathogens in roots from plants that were water stressed before harvest. For water-stressed roots, all concentrations of SA produced statistically equivalent reductions in the weight of rotted tissue for each pathogen, and on average, SA reduced rot severity due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively. SA reduced rot from all three pathogens by reducing lesion size, but did not affect the incidence of infection. The ability of SA to reduce rot severity in water-stressed roots, but not in roots that received sufficient water before harvest suggests that SA alleviated the negative impact of water stress but did not directly protect sugarbeet roots against storage rots. © 2013 Published by Elsevier B.V.
1. Introduction Salicylic acid (SA) is an endogenous plant hormone involved in a wide range of plant growth and developmental processes including the activation and priming of plant defense responses (Conrath et al., 2002; Loake and Grant, 2007). A diverse array of pathogens induce SA biosynthesis, and SA accumulation is involved in elicitation of both local and systemic plant defense responses, including the hypersensitive response, synthesis of pathogenesis-related (PR) proteins, and systemic acquired resistance (Loake and Grant, 2007; Bolton, 2009). Applied exogenously, SA induces resistance against a number of fungal, bacterial, and viral plant pathogens (Murphy
∗ Corresponding author. Tel.: +1 701 239 1356; fax: +1 701 239 1349. E-mail address: [email protected] (K.K. Fugate). 1 Present address: Universidade Federal de Santa Catarina, Campus de Curitibanos, 89520-000 Curitibanos, SC, Brazil. 0925-5214/$ – see front matter. © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.postharvbio.2013.06.005
et al., 1999; Achuo et al., 2004), and the compound has received considerable attention as a nontoxic alternative to synthetic fungicides for reducing storage rot losses in postharvest plant products (reviewed in Asghari and Aghdam, 2010). SA also has been found to mitigate the effects of abiotic stresses including stress due to drought and high and low temperatures (Senaratna et al., 2000; Nazar et al., 2011). In sugarbeet (Beta vulgaris L.), treatments with SA or analogs of SA reduced the severity of several production diseases. These include the seedling disease caused by Aphanomyces cochliodes Drechs (Metzger and Weiland, 2008), Cercospora leaf spot caused by Cercospora beticola Sacc. (Bargabus et al., 2002), and beet rust caused by Uromyces betae Tul. ex Kick (Ata et al., 2008). The ability of SA to protect against storage rots, however, is unknown. Storage rots of sugarbeet are caused by a number of pathogens, including Botrytis cinerea Pers. ex Fr., Penicillium claviforme Bainier, and Phoma betae Frank (Bugbee, 1982; Campbell and Klotz, 2006). B. cinerea is found in sugarbeet growing regions throughout the
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
world, is an aggressive pathogen, and is active over a wide range of temperatures (Gaskill and Seliskar, 1952; Campbell and Klotz, 2006). P. claviforme is prevalent in U.S. storage piles and is one of the more aggressive of the Penicillium species that are pathogenic to stored sugarbeet (Bugbee, 1975; Bugbee and Cole, 1976). P. betae is responsible for a crown rot that typically develops after prolonged storage. Rot due to this organism, however, can occur at any time after harvest (Bugbee, 1982). The sugarbeet industry, currently, has few methods available to limit storage rot losses. Fungicides capable of reducing the incidence and severity of storage rot have been identified (Mumford and Wyse, 1976; Miles et al., 1977). However, these fungicides often have negative effects on root storage properties in the absence of disease (Akeson et al., 1979) and are not used by the industry. Germplasm with improved resistance to rotcausing pathogens has been identified (Gaskill, 1950b; Bugbee and Cole, 1979). However, this germplasm is not utilized in current commercial hybrids since introduction of additional traits slows progress toward other breeding goals and increases the time and expense for hybrid development (Campbell and Klotz, 2006). Alternative methods to control sugarbeet storage rots, therefore, are desirable. In research described here, we investigate the ability of SA to limit sugarbeet storage rot using varying concentrations of SA applied as postharvest treatments. Sugarbeet roots were freshly harvested, treated with SA at concentrations of 0.01–10 mM, inoculated with B. cinerea, P. claviforme, or P. betae, and subsequently evaluated for the severity of rot symptoms after incubation at storage conditions favorable for disease development. Since SA has been implicated as a protectant against drought stress (Kadioglu et al., 2011) and drought stress is reported to increase sugarbeet root susceptibility to storage rot-causing organisms (Cormack and Moffatt, 1961), the potential of postharvest SA treatments to protect water-stressed roots against B. cinerea, P. claviforme, and P. betae also was determined.
2. Materials and methods 2.1. Plant material, growing conditions, and SA treatments Sugarbeet hybrid VDH66156 (SESVanderhave, Tienen, Belgium) was greenhouse grown in Sunshine Mix #1 (Sun Gro Horticulture, Seba Beach, Alberta, Canada) in 15-L pots with supplemental light under a 16 h/8 h light/dark regime. Plants were fertilized with a controlled-release fertilizer (Multicote 4, Sun Gro Horticulture). For experiments in which no water stress was administered, plants were watered as needed and taproots were harvested 16–17 weeks after planting. For experiments in which water stress was applied, plants were watered as needed for 16 weeks after planting, after which water was withheld until harvest. Roots were harvested 2 d after all plants were severely wilted. Plants were considered severely wilted when all leaves were flaccid and were incapable of recovering turgidity overnight. Roots were harvested by hand, all leaf and petiole material was removed with a knife, and roots were gently washed to remove adhering potting media. SA treatments were administered by submerging roots in aqueous solutions of 0.01, 0.1, 1.0, or 10 mM SA (Sigma–Aldrich, St. Louis, MO, USA) for 1 h at room temperature, using at least 7 roots per treatment. Controls were roots that were treated similarly with water. SA treatments were applied on the day of harvest. Roots were subsequently incubated at 20 ◦ C and 90% relative humidity for 3 d to allow for induction of defense responses (Fugate et al., 2012). Roots were then inoculated as described below with a single storage rotcausing pathogen per experiment. All experiments were repeated at least once.
163
2.2. Storage rot resistance assays Roots were inoculated with B. cinerea, P. claviforme, or P. betae as previously described (Fugate et al., 2012). Briefly, two holes (12 mm × 10 mm; diameter × depth) were drilled into each root with a hand-held drill on opposite sides of the root in the region where root girth was greatest. Roots were inoculated by inserting a 10 mm diameter plug, obtained from fungal-covered potato dextrose agar (PDA; Difco, Sparks, MD, USA) plates, into each hole, with the mycelial-covered side of the agar plug in contact with the root tissue. Roots were incubated at 20 ◦ C and 90% relative humidity until severe disease symptoms were visually evident on control roots, approximately 20, 30, and 50 d for B. cinerea, P. claviforme, and P. betae, respectively. To evaluate root rot severity, rotted, discolored tissue from each root was removed using a knife, taking care to include all discolored tissue but no healthy-appearing tissue, and the weight of this tissue was determined. 2.3. Statistical analysis Data were normalized to express the weight of rotted tissue for each treatment as a fraction of the rotted tissue of the control by dividing each data point in an experiment by the average weight for the control. SA concentration and experimental repetition were used as main effects for analyses of variance using a general linear model (Minitab, ver. 16, State College, PA, USA) with ˛ = 0.05. Since repetitions of experiments were not significantly different for each disease-causing organism, data from the two experimental repetitions were combined. Where an ANOVA indicated significant SA treatment differences, Tukey’s range test was used to identify treatment differences (˛ = 0.05). 3. Results and discussion Postharvest SA treatments of 0.01 to 10 mM had no effect on the severity of rot caused by B. cinerea, P. claviforme, or P. betae in roots harvested from plants that received sufficient water prior to harvest (Fig. 1A–C, left panels). Variations in the relative weight of rotted tissue were observed between SA treatments and the water-treated controls for roots inoculated with each of the three pathogens and incubated at storage conditions that promote disease development. However, these variations in weight were generally small, and no differences in weight due to SA treatment were statistically significant (˛ = 0.05). In contrast, when roots were obtained from plants that were water stressed prior to harvest, postharvest SA treatments effectively reduced rot due to B. cinerea, P. claviforme, and P. betae (Fig. 1A–C, right panels). SA applied at concentrations of 0.01–10 mM reduced the weight of rotted tissue by 49–58% in roots inoculated with B. cinerea. In roots inoculated with P. claviforme, SA treatments reduced the weight of rotted tissue by 30–53%. In roots inoculated with P. betae, SA treatments reduced the weight of rotted tissue by 47–74%. All concentrations of SA provided statistically similar reductions in the weight of rotted tissue for each of the three pathogens. On average, postharvest SA treatment reduced the weight of rotted tissue due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively. Visual inspection indicated that SA reduced the weight of rotted tissue in roots from water-stressed plants by reducing the size of the lesion formed by the pathogen (Fig. 2). Reductions in rot severity due to SA treatment were evidenced by reductions in the depth and breadth of necrotized tissue extending from the infection site. SA, however, did not reduce the incidence of disease since symptoms of infection were evident at all inoculation sites of SA-treated and water-treated roots.
164
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
Penicillium claviforme
C
Phoma betae
rotted tissue (relative weight)
B
rotted tissue (relative weight)
Botrytis cinerea
rotted tissue (relative weight)
unstressed
A
water-stressed
1.5
a 1.16
1.0 1.00
1.02
0.97
0.96
1.00
b
b
0.46
0.51
b
b
0.44
0.42
b
b
0.51
0.47
0.5
0.0 1.5
1.21
a
1.0 1.00
0.92
0.89
1.00
0.97
b b
0.70
0.5 0.49
0.0 1.5
a 1.26 1.0 1.00
1.02
0.98
0.95
1.00
b
b 0.5
0.53 0.42
b 0.46
b 0.26
0.0 0
0.01
0.1
1
10
salicylic acid concentration (mM)
0
0.01
0.1
1
10
salicylic acid concentration (mM)
Fig. 1. Relative weight of rotted tissue in sugarbeet roots after postharvest salicylic acid (SA) treatment, inoculation with Botrytis cinerea (A), Penicillium claviforme (B), or Phoma betae (C), and incubation at 20 ◦ C and 90% relative humidity until severe disease symptoms were evident on control roots (0 mM SA) using roots from plants that received sufficient water (unstressed) or were water-stressed prior to harvest. Roots for water-stress experiments were obtained from plants that were severely wilted for 2 d prior to harvest (right panels); unstressed roots were obtained from plants that did not experience water stress prior to harvest (left panels). Harvested roots were treated for 1 h at room temperature with SA solutions and incubated for 3 d at 20 ◦ C and 90% relative humidity prior to inoculation. Weight of rotted tissue is expressed as a fraction of the weight of rotted tissue of the control. Each graph presents data for a single replicated experiment. Experimental repetitions were not statistically different by ANOVA, and data within a graph are the combined results of two experimental repetitions, with at least 7 replicates per repetition. For experiments with roots from unstressed plants, treatment differences were not statistically significant by ANOVA. For experiments with roots from water-stressed plants, treatments with different letters within a graph are statistically different based on Tukey’s range test. For all statistical analyses, ˛ = 0.05.
For a number of postharvest crops, application of SA has been found to reduce storage rots, including those caused by B. cinerea and Penicillium species. SA-related reductions in fungal storage diseases have been documented for cherry, kiwi, melon, pepper, and strawberry fruits, and reductions in storage rot caused by B. cinerea in tomato fruit and P. expansum in peach and pear fruits have been reported (Yao and Tian, 2005; Cao et al., 2006; Asghari and Aghdam, 2010; Choi and Hwang, 2011; Wang et al., 2011; Yang et al., 2011). However, for sugarbeet roots harvested from healthy, unstressed plants, SA was ineffective in reducing disease symptoms caused by B. cinerea, P. claviforme, or P. betae. Similarly, exogenous SA was found to be ineffective against B. cinerea on Arabidopsis and tobacco leaves (Govrin and Levine, 2002; Achuo et al., 2004). The ability of exogenous SA to protect against storage rots or a particular rot-causing pathogen, therefore, differs between plant species or organs.
In plants, SA is thought to trigger defense mechanisms against biotrophic and hemibiotrophic pathogens, but is uninvolved in defense against necrotrophic pathogens (Glazebrook, 2005; Robert-Seilaniantz et al., 2011). Defenses against necrotrophic pathogens are generally thought to be initiated by jasmonic acid (JA), which is antagonistic to SA and uninvolved in biotrophic defenses. However, exceptions to this generalized model of plant defense are common and reports of SA-induced protection against necrotrophic pathogens (Murphy et al., 2000; Yao and Tian, 2005; Babalar et al., 2007) and JA-induced protection against biotrophs (Mitchell and Walters, 1995; Thaler et al., 2004) are found. The ability of SA to protect against a pathogen, therefore, cannot be predicted by the pathogen’s lifestyle and must be determined experimentally for each pathogen-plant species interaction, necessitating studies such as this. In stored sugarbeet roots, SA provided no protection against the necrotrophic pathogens, B. cinerea, P.
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
165
Fig. 2. External (A) and internal symptoms (B) of storage rot for roots obtained from water-stressed plants after treatment with 0 or 10 mM salicylic acid (SA), inoculation with Botrytis cinerea, Penicillium claviforme, or Phoma betae, and incubation at 20 ◦ C and 90% relative humidity until severe disease symptoms were evident on control roots (0 mM SA). Roots were obtained from plants that were severely wilted for 2 d prior to harvest. Roots were treated for 1 h at room temperature with water (control) or 10 mM SA, then incubated for 3 d at 20 ◦ C and 90% relative humidity prior to inoculation. Rot symptoms for a single SA concentration are shown since all SA treatments provided statistically equivalent control. (A) Composite picture from a single experimental repetition showing all roots for a treatment. Since a single pathogen was used for each experiment, pictures are from three separate experiments. (B) Longitudinal sections of representative roots from each treatment using a root that contained near average weights of rot for the treatment.
claviforme, and P. betae. Rot due to these pathogens, however, has been shown to be reduced by JA treatment (Fugate et al., 2012). Defense mechanisms in postharvest sugarbeet root, therefore, are consistent with most plant species and the current model of plant defense mechanisms (Glazebrook, 2005; Robert-Seilaniantz et al., 2011). Although exogenous SA increases necrotrophic disease susceptibility for some plant/pathogen interactions due to antagonism between SA and JA signaling pathways (El Oirdi et al., 2011), SA did not increase disease susceptibility to the necrotrophic pathogens used in this research. Despite the inability of SA to affect storage rot severity for sugarbeet roots obtained from unstressed plants, SA significantly reduced storage rot severity on roots harvested from water-stressed plants. The reduction in storage rot in SA-treated, water-stressed sugarbeet roots was likely due to an alleviation of the effects of water stress by SA rather than a direct decrease in disease susceptibility of the roots. In other plant species, SA has been demonstrated to alleviate drought stress and minimize the detrimental physiological effects of water stress (Loutfy et al., 2012; Saruhan et al., 2012). For sugarbeet root, an increase in storage rot susceptibility is one such detrimental effect of preharvest water stress (Gaskill, 1950a). The reduction in storage rot in SA-treated,
water-stressed sugarbeet roots was unlikely to be the result of a direct decrease in disease susceptibility since SA did not reduce storage rot severity in roots from unstressed plants.
4. Conclusions Postharvest SA treatments of 0.01–10 mM did not affect the severity of storage rot caused by B. cinerea, P. claviforme, or P. betae for sugarbeet roots harvested from plants that received sufficient water prior to harvest. However, for roots obtained from plants that were water stressed before harvest, postharvest SA treatments significantly reduced rot due to B. cinerea, P. claviforme, or P. betae. In these roots, SA reduced the severity of rot symptoms, but did not affect the incidence of infection. SA treatments of 0.01–10 mM provided statistically equivalent reductions in the weight of rotted tissue for each of the three pathogens, and on average, SA reduced the severity of storage rot due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively, in roots from plants that were water stressed before harvest. The ability of SA to reduce rot severity in water-stressed roots, but not in roots that received sufficient water before harvest, suggests that SA alleviated the negative
166
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
impacts of water stress but did not directly protect sugarbeet roots from storage rot-causing pathogens. Acknowledgements The authors thank John Eide for technical assistance, CNPq (Brazil) for J.P.F.’s scholarship, and the Beet Sugar Development Foundation and the Sugarbeet Research and Education Board of Minnesota and North Dakota for partial financial support of this research. Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. References Achuo, E.A., Audenaert, K., Meziane, H., Höfte, M., 2004. The salicylic acid-dependent defence pathway is effective against different pathogens in tomato and tobacco. Plant Pathol. 53, 65–72. Akeson, W.R., Yun, Y.M., Sullivan, E.F., 1979. Effect of chemicals on sucrose loss in sugarbeets during storage. J. Am. Soc. Sugar Beet Technol. 20, 255–268. Asghari, M., Aghdam, M.S., 2010. Impact of salicylic acid on post-harvest physiology of horticultural crops. Trends Food Sci. Technol. 21, 502–509. Ata, A.A., El-Samman, M.G., Moursy, M.A., Mostafa, M.H., 2008. Inducing resistance against rust disease of sugar beet by certain chemical compounds. Egypt. J. Phytopathol. 36, 113–132. Babalar, M., Asghari, M., Talaei, A., Khosroshahi, A., 2007. Effect of pre- and postharvest salicylic acid treatment on ethylene production, fungal decay and overall quality of Selva strawberry fruit. Food Chem. 105, 449–453. Bargabus, R.L., Zidack, N.K., Sherwood, J.E., Jacobsen, B.J., 2002. Characterisation of systemic resistance in sugar beet elicited by a non-pathogenic, phyllospherecolonizing Bacillus mycoides, biological control agent. Physiol. Mol. Plant Pathol. 61, 289–298. Bolton, M.D., 2009. Primary metabolism and plant defense – fuel for the fire. Mol. Plant Microbe Interact 22, 487–497. Bugbee, W.M., 1975. Penicillium claviforme and Penicillium variabile: pathogens of stored sugar beets. Phytopathology 65, 926–927. Bugbee, W.M., 1982. Storage rot of sugar beet. Plant Dis. 66, 871–873. Bugbee, W.M., Cole, D.F., 1976. Sugarbeet storage rot in the Red River Valley, 1974–1975. J. Am. Soc. Sugar Beet Technol. 19, 19–24. Bugbee, W.M., Cole, D.F., 1979. Comparison of thiabendazole and genetic resistance for control of sugar beet storage rot. Phytopathology 69, 1230–1232. Campbell, L.G., Klotz, K.L., 2006. Storage. In: Draycott, A.P. (Ed.), Sugar Beet. Blackwell Publishing Ltd., Oxford, UK, pp. 387–408. Cao, J., Zeng, K., Jiang, W., 2006. Enhancement of postharvest disease resistance in Ya Li pear (Pyrus bretschneideri) fruit by salicylic acid sprays on the trees during fruit growth. Eur. J. Plant Pathol. 114, 363–370. Choi, H.W., Hwang, B.K., 2011. Systemic acquired resistance of pepper to microbial pathogens. J. Phytopathol. 159, 393–400. Conrath, U., Pieterse, C.M.J., Mauch-Mani, B., 2002. Priming in plant–pathogen interactions. Trends Plant Sci. 7, 210–216. Cormack, M.W., Moffatt, J.E., 1961. Factors influencing storage decay of sugar beets by Phoma betae and other fungi. Phytopathology 51, 3–5. El Oirdi, M., El Rahman, T.A., Rigano, L., El Hadrami, A., Rodriguez, M.C., Daayf, F., Vojnov, A., Bouarab, K., 2011. Botrytis cinerea manipulates the antagonistic effects between immune pathways to promote disease development in tomato. Plant Cell 23, 2405–2421. Fugate, K.K., Ferrareze, J.P., Bolton, M.D., Deckard, E.L., Campbell, L.G., 2012. Postharvest jasmonic acid treatment of sugarbeet roots reduces rot due to Botrytis
cinerea, Penicillium claviforme, and Phoma betae. Postharvest Biol. Technol. 65, 1–4. Gaskill, J.O., 1950a. Effects of wilting, drought, and temperature upon rotting of sugar beets during storage. Proc. Am. Soc. Sugar Beet Technol. 6, 653–659. Gaskill, J.O., 1950b. Possibilities for improving storage-rot resistance of sugar-beets through breeding. Proc. Am. Soc. Sugar Beet Technol. 6, 664–669. Gaskill, J.O., Seliskar, C.E., 1952. Effect of temperature on rate of rotting of sugarbeet tissue by two storage pathogens. Proc. Am. Soc. Sugar Beet Technol. 7, 571–574. Glazebrook, J., 2005. Contrasting mechanisms of defense against biotrophic and necrotrophic pathogens. Annu. Rev. Phytopathol. 43, 205–227. Govrin, E.M., Levine, A., 2002. Infection of Arabidopsis with a necrotrophic pathogen, Botrytis cinerea, elicits various defense responses but does not induce systemic acquired resistance (SAR). Plant Mol. Biol. 48, 267–276. Kadioglu, A., Saruhan, N., Sa˘glam, A., Terzi, R., Acet, T., 2011. Exogenous salicylic acid alleviates effects of long term drought stress and delays leaf rolling by inducing antioxidant system. Plant Growth Regul. 64, 27–37. Loake, G., Grant, M., 2007. Salicylic acid in plant defence – the players and protagonists. Curr. Opin. Plant Biol. 10, 466–472. Loutfy, N., El-Tayeb, M.A., Hassanen, A.M., Moustafa, M.F.M., Sakuma, Y., Inouhe, M., 2012. Changes in the water status and osmotic solute contents in response to drought and salicylic acid treatments in four different cultivars of wheat (Triticum aestivum). J. Plant Res. 125, 173–184. Metzger, M.S., Weiland, J.J., 2008. Growth promotion may compensate for losses due to moderate Aphanomyces root rot. J. Sugar Beet Res. 45, 1–17. Miles, W.G., Shaker, F.M., Nielson, A.K., Ames, R.R., 1977. A laboratory study of the ability of fungicides to control beet rotting fungi. J. Am. Soc. Sugar Beet Technol. 19, 288–293. Mitchell, A.F., Walters, D.R., 1995. Systemic protection in barley against powdery mildew infection using methyl jasmonate. Asp. Appl. Biol. 42, 323–326. Mumford, D.L., Wyse, R.E., 1976. Effect of fungus infection on respiration and reducing sugar accumulation of sugarbeet roots and use of fungicides to reduce infection. J. Am. Soc. Sugar Beet Technol. 19, 157–162. Murphy, A.M., Chivasa, S., Singh, D.P., Carr, J.P., 1999. Salicylic acid-induced resistance to viruses and other pathogens: a parting of the ways? Trends Plant Sci. 4, 155–160. Murphy, A.M., Holcombe, L.J., Carr, J.P., 2000. Characteristics of salicylic acid-induced delay in disease caused by a necrotrophic fungal pathogen in tobacco. Physiol. Mol. Plant Pathol. 57, 47–54. Nazar, R., Iqbal, N., Syeed, S., Khan, N.A., 2011. Salicylic acid alleviates decreases in photosynthesis under salt stress by enhancing nitrogen and sulfur assimilation and antioxidant metabolism differentially in two mungbean cultivars. J. Plant Physiol. 168, 807–815. Robert-Seilaniantz, A., Grant, M., Jones, J.D.G., 2011. Hormone crosstalk in plant disease and defense: more than just jasmonate-salicylate antagonism. Annu. Rev. Phytopathol. 49, 317–343. Saruhan, N., Saglam, A., Kadioglu, A., 2012. Salicylic acid pretreatment induces drought tolerance and delays leaf rolling by inducing antioxidant systems in maize genotypes. Acta Physiol. Plant. 34, 97–106. Senaratna, T., Touchell, D., Bunn, E., Dixon, K., 2000. Acetyl salicylic acid (Aspirin) and salicylic acid induce multiple stress tolerance in bean and tomato plants. Plant Growth Regul. 30, 157–161. Thaler, J.S., Owen, B., Higgins, V.J., 2004. The role of the jasmonate response in plant susceptibility to diverse pathogens with a range of lifestyles. Plant Physiol. 135, 530–538. Wang, Y.Y., Li, B.Q., Qin, G.-Z., Li, L., Tian, S.P., 2011. Defense response of tomato fruit at different maturity stages to salicylic acid and ethephon. Sci. Hortic. 129, 183–188. Yang, Z., Cao, S., Cai, Y., Zheng, Y., 2011. Combination of salicylic acid and ultrasound to control postharvest blue mold caused by Penicillium expansum in peach fruit. Innovat. Food Sci. Emerg. Technol. 12, 310–314. Yao, H., Tian, S., 2005. Effects of pre- and post-harvest application of salicylic acid or methyl jasmonate on inducing disease resistance of sweet cherry fruit in storage. Postharvest Biol. Technol. 35, 253–262.
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Research note
Postharvest salicylic acid treatment reduces storage rots in water-stressed but not unstressed sugarbeet roots Karen Klotz Fugate a,∗ , Jocleita Peruzzo Ferrareze b,1 , Melvin D. Bolton a , Edward L. Deckard c , Larry G. Campbell a , Fernando L. Finger d a
USDA-ARS, Northern Crop Science Laboratory, 1605 Albrecht Blvd. N., Fargo, ND 58102-2765, USA Departamento de Biologia Vegetal, Universidade Federal de Vic¸osa, 36571-000 Vic¸osa, MG, Brazil c Department of Plant Sciences, North Dakota State University, P.O. Box 6050, Fargo, ND 58108-6050, USA d Departamento de Fitotecnia, Universidade Federal de Vic¸osa, 36571-000 Vic¸osa, MG, Brazil b
a r t i c l e
i n f o
Article history: Received 15 January 2013 Accepted 3 June 2013 Keywords: Beta vulgaris Botrytis cinerea Pers. ex Fr. Clamp rot Drought Penicillium claviforme Bainier Phoma betae Frank
a b s t r a c t Exogenous application of salicylic acid (SA) reduces storage rots in a number of postharvest crops. SA’s ability to protect sugarbeet (Beta vulgaris L.) taproots from common storage rot pathogens, however, is unknown. To determine the potential of SA to reduce storage losses caused by three common causal organisms of sugarbeet storage rot, freshly harvested roots were treated with 0.01, 0.1, 1.0 or 10 mM SA, inoculated with Botrytis cinerea, Penicillium claviforme, or Phoma betae, and evaluated for the severity of rot symptoms after incubation at 20 ◦ C and 90% relative humidity. Roots were obtained from plants that received sufficient water or were water-stressed prior to harvest. Roots from water-stressed plants were included since water-stress increases sugarbeet root susceptibility to storage rot and SA mitigates drought effects in other plant species. SA at concentrations of 0.01–10 mM had no effect on the severity of storage rot caused by B. cinerea, P. claviforme, or P. betae in roots from plants that received sufficient water prior to harvest. However, SA at these same concentrations reduced the severity of rot symptoms for all three pathogens in roots from plants that were water stressed before harvest. For water-stressed roots, all concentrations of SA produced statistically equivalent reductions in the weight of rotted tissue for each pathogen, and on average, SA reduced rot severity due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively. SA reduced rot from all three pathogens by reducing lesion size, but did not affect the incidence of infection. The ability of SA to reduce rot severity in water-stressed roots, but not in roots that received sufficient water before harvest suggests that SA alleviated the negative impact of water stress but did not directly protect sugarbeet roots against storage rots. © 2013 Published by Elsevier B.V.
1. Introduction Salicylic acid (SA) is an endogenous plant hormone involved in a wide range of plant growth and developmental processes including the activation and priming of plant defense responses (Conrath et al., 2002; Loake and Grant, 2007). A diverse array of pathogens induce SA biosynthesis, and SA accumulation is involved in elicitation of both local and systemic plant defense responses, including the hypersensitive response, synthesis of pathogenesis-related (PR) proteins, and systemic acquired resistance (Loake and Grant, 2007; Bolton, 2009). Applied exogenously, SA induces resistance against a number of fungal, bacterial, and viral plant pathogens (Murphy
∗ Corresponding author. Tel.: +1 701 239 1356; fax: +1 701 239 1349. E-mail address: [email protected] (K.K. Fugate). 1 Present address: Universidade Federal de Santa Catarina, Campus de Curitibanos, 89520-000 Curitibanos, SC, Brazil. 0925-5214/$ – see front matter. © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.postharvbio.2013.06.005
et al., 1999; Achuo et al., 2004), and the compound has received considerable attention as a nontoxic alternative to synthetic fungicides for reducing storage rot losses in postharvest plant products (reviewed in Asghari and Aghdam, 2010). SA also has been found to mitigate the effects of abiotic stresses including stress due to drought and high and low temperatures (Senaratna et al., 2000; Nazar et al., 2011). In sugarbeet (Beta vulgaris L.), treatments with SA or analogs of SA reduced the severity of several production diseases. These include the seedling disease caused by Aphanomyces cochliodes Drechs (Metzger and Weiland, 2008), Cercospora leaf spot caused by Cercospora beticola Sacc. (Bargabus et al., 2002), and beet rust caused by Uromyces betae Tul. ex Kick (Ata et al., 2008). The ability of SA to protect against storage rots, however, is unknown. Storage rots of sugarbeet are caused by a number of pathogens, including Botrytis cinerea Pers. ex Fr., Penicillium claviforme Bainier, and Phoma betae Frank (Bugbee, 1982; Campbell and Klotz, 2006). B. cinerea is found in sugarbeet growing regions throughout the
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
world, is an aggressive pathogen, and is active over a wide range of temperatures (Gaskill and Seliskar, 1952; Campbell and Klotz, 2006). P. claviforme is prevalent in U.S. storage piles and is one of the more aggressive of the Penicillium species that are pathogenic to stored sugarbeet (Bugbee, 1975; Bugbee and Cole, 1976). P. betae is responsible for a crown rot that typically develops after prolonged storage. Rot due to this organism, however, can occur at any time after harvest (Bugbee, 1982). The sugarbeet industry, currently, has few methods available to limit storage rot losses. Fungicides capable of reducing the incidence and severity of storage rot have been identified (Mumford and Wyse, 1976; Miles et al., 1977). However, these fungicides often have negative effects on root storage properties in the absence of disease (Akeson et al., 1979) and are not used by the industry. Germplasm with improved resistance to rotcausing pathogens has been identified (Gaskill, 1950b; Bugbee and Cole, 1979). However, this germplasm is not utilized in current commercial hybrids since introduction of additional traits slows progress toward other breeding goals and increases the time and expense for hybrid development (Campbell and Klotz, 2006). Alternative methods to control sugarbeet storage rots, therefore, are desirable. In research described here, we investigate the ability of SA to limit sugarbeet storage rot using varying concentrations of SA applied as postharvest treatments. Sugarbeet roots were freshly harvested, treated with SA at concentrations of 0.01–10 mM, inoculated with B. cinerea, P. claviforme, or P. betae, and subsequently evaluated for the severity of rot symptoms after incubation at storage conditions favorable for disease development. Since SA has been implicated as a protectant against drought stress (Kadioglu et al., 2011) and drought stress is reported to increase sugarbeet root susceptibility to storage rot-causing organisms (Cormack and Moffatt, 1961), the potential of postharvest SA treatments to protect water-stressed roots against B. cinerea, P. claviforme, and P. betae also was determined.
2. Materials and methods 2.1. Plant material, growing conditions, and SA treatments Sugarbeet hybrid VDH66156 (SESVanderhave, Tienen, Belgium) was greenhouse grown in Sunshine Mix #1 (Sun Gro Horticulture, Seba Beach, Alberta, Canada) in 15-L pots with supplemental light under a 16 h/8 h light/dark regime. Plants were fertilized with a controlled-release fertilizer (Multicote 4, Sun Gro Horticulture). For experiments in which no water stress was administered, plants were watered as needed and taproots were harvested 16–17 weeks after planting. For experiments in which water stress was applied, plants were watered as needed for 16 weeks after planting, after which water was withheld until harvest. Roots were harvested 2 d after all plants were severely wilted. Plants were considered severely wilted when all leaves were flaccid and were incapable of recovering turgidity overnight. Roots were harvested by hand, all leaf and petiole material was removed with a knife, and roots were gently washed to remove adhering potting media. SA treatments were administered by submerging roots in aqueous solutions of 0.01, 0.1, 1.0, or 10 mM SA (Sigma–Aldrich, St. Louis, MO, USA) for 1 h at room temperature, using at least 7 roots per treatment. Controls were roots that were treated similarly with water. SA treatments were applied on the day of harvest. Roots were subsequently incubated at 20 ◦ C and 90% relative humidity for 3 d to allow for induction of defense responses (Fugate et al., 2012). Roots were then inoculated as described below with a single storage rotcausing pathogen per experiment. All experiments were repeated at least once.
163
2.2. Storage rot resistance assays Roots were inoculated with B. cinerea, P. claviforme, or P. betae as previously described (Fugate et al., 2012). Briefly, two holes (12 mm × 10 mm; diameter × depth) were drilled into each root with a hand-held drill on opposite sides of the root in the region where root girth was greatest. Roots were inoculated by inserting a 10 mm diameter plug, obtained from fungal-covered potato dextrose agar (PDA; Difco, Sparks, MD, USA) plates, into each hole, with the mycelial-covered side of the agar plug in contact with the root tissue. Roots were incubated at 20 ◦ C and 90% relative humidity until severe disease symptoms were visually evident on control roots, approximately 20, 30, and 50 d for B. cinerea, P. claviforme, and P. betae, respectively. To evaluate root rot severity, rotted, discolored tissue from each root was removed using a knife, taking care to include all discolored tissue but no healthy-appearing tissue, and the weight of this tissue was determined. 2.3. Statistical analysis Data were normalized to express the weight of rotted tissue for each treatment as a fraction of the rotted tissue of the control by dividing each data point in an experiment by the average weight for the control. SA concentration and experimental repetition were used as main effects for analyses of variance using a general linear model (Minitab, ver. 16, State College, PA, USA) with ˛ = 0.05. Since repetitions of experiments were not significantly different for each disease-causing organism, data from the two experimental repetitions were combined. Where an ANOVA indicated significant SA treatment differences, Tukey’s range test was used to identify treatment differences (˛ = 0.05). 3. Results and discussion Postharvest SA treatments of 0.01 to 10 mM had no effect on the severity of rot caused by B. cinerea, P. claviforme, or P. betae in roots harvested from plants that received sufficient water prior to harvest (Fig. 1A–C, left panels). Variations in the relative weight of rotted tissue were observed between SA treatments and the water-treated controls for roots inoculated with each of the three pathogens and incubated at storage conditions that promote disease development. However, these variations in weight were generally small, and no differences in weight due to SA treatment were statistically significant (˛ = 0.05). In contrast, when roots were obtained from plants that were water stressed prior to harvest, postharvest SA treatments effectively reduced rot due to B. cinerea, P. claviforme, and P. betae (Fig. 1A–C, right panels). SA applied at concentrations of 0.01–10 mM reduced the weight of rotted tissue by 49–58% in roots inoculated with B. cinerea. In roots inoculated with P. claviforme, SA treatments reduced the weight of rotted tissue by 30–53%. In roots inoculated with P. betae, SA treatments reduced the weight of rotted tissue by 47–74%. All concentrations of SA provided statistically similar reductions in the weight of rotted tissue for each of the three pathogens. On average, postharvest SA treatment reduced the weight of rotted tissue due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively. Visual inspection indicated that SA reduced the weight of rotted tissue in roots from water-stressed plants by reducing the size of the lesion formed by the pathogen (Fig. 2). Reductions in rot severity due to SA treatment were evidenced by reductions in the depth and breadth of necrotized tissue extending from the infection site. SA, however, did not reduce the incidence of disease since symptoms of infection were evident at all inoculation sites of SA-treated and water-treated roots.
164
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
Penicillium claviforme
C
Phoma betae
rotted tissue (relative weight)
B
rotted tissue (relative weight)
Botrytis cinerea
rotted tissue (relative weight)
unstressed
A
water-stressed
1.5
a 1.16
1.0 1.00
1.02
0.97
0.96
1.00
b
b
0.46
0.51
b
b
0.44
0.42
b
b
0.51
0.47
0.5
0.0 1.5
1.21
a
1.0 1.00
0.92
0.89
1.00
0.97
b b
0.70
0.5 0.49
0.0 1.5
a 1.26 1.0 1.00
1.02
0.98
0.95
1.00
b
b 0.5
0.53 0.42
b 0.46
b 0.26
0.0 0
0.01
0.1
1
10
salicylic acid concentration (mM)
0
0.01
0.1
1
10
salicylic acid concentration (mM)
Fig. 1. Relative weight of rotted tissue in sugarbeet roots after postharvest salicylic acid (SA) treatment, inoculation with Botrytis cinerea (A), Penicillium claviforme (B), or Phoma betae (C), and incubation at 20 ◦ C and 90% relative humidity until severe disease symptoms were evident on control roots (0 mM SA) using roots from plants that received sufficient water (unstressed) or were water-stressed prior to harvest. Roots for water-stress experiments were obtained from plants that were severely wilted for 2 d prior to harvest (right panels); unstressed roots were obtained from plants that did not experience water stress prior to harvest (left panels). Harvested roots were treated for 1 h at room temperature with SA solutions and incubated for 3 d at 20 ◦ C and 90% relative humidity prior to inoculation. Weight of rotted tissue is expressed as a fraction of the weight of rotted tissue of the control. Each graph presents data for a single replicated experiment. Experimental repetitions were not statistically different by ANOVA, and data within a graph are the combined results of two experimental repetitions, with at least 7 replicates per repetition. For experiments with roots from unstressed plants, treatment differences were not statistically significant by ANOVA. For experiments with roots from water-stressed plants, treatments with different letters within a graph are statistically different based on Tukey’s range test. For all statistical analyses, ˛ = 0.05.
For a number of postharvest crops, application of SA has been found to reduce storage rots, including those caused by B. cinerea and Penicillium species. SA-related reductions in fungal storage diseases have been documented for cherry, kiwi, melon, pepper, and strawberry fruits, and reductions in storage rot caused by B. cinerea in tomato fruit and P. expansum in peach and pear fruits have been reported (Yao and Tian, 2005; Cao et al., 2006; Asghari and Aghdam, 2010; Choi and Hwang, 2011; Wang et al., 2011; Yang et al., 2011). However, for sugarbeet roots harvested from healthy, unstressed plants, SA was ineffective in reducing disease symptoms caused by B. cinerea, P. claviforme, or P. betae. Similarly, exogenous SA was found to be ineffective against B. cinerea on Arabidopsis and tobacco leaves (Govrin and Levine, 2002; Achuo et al., 2004). The ability of exogenous SA to protect against storage rots or a particular rot-causing pathogen, therefore, differs between plant species or organs.
In plants, SA is thought to trigger defense mechanisms against biotrophic and hemibiotrophic pathogens, but is uninvolved in defense against necrotrophic pathogens (Glazebrook, 2005; Robert-Seilaniantz et al., 2011). Defenses against necrotrophic pathogens are generally thought to be initiated by jasmonic acid (JA), which is antagonistic to SA and uninvolved in biotrophic defenses. However, exceptions to this generalized model of plant defense are common and reports of SA-induced protection against necrotrophic pathogens (Murphy et al., 2000; Yao and Tian, 2005; Babalar et al., 2007) and JA-induced protection against biotrophs (Mitchell and Walters, 1995; Thaler et al., 2004) are found. The ability of SA to protect against a pathogen, therefore, cannot be predicted by the pathogen’s lifestyle and must be determined experimentally for each pathogen-plant species interaction, necessitating studies such as this. In stored sugarbeet roots, SA provided no protection against the necrotrophic pathogens, B. cinerea, P.
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
165
Fig. 2. External (A) and internal symptoms (B) of storage rot for roots obtained from water-stressed plants after treatment with 0 or 10 mM salicylic acid (SA), inoculation with Botrytis cinerea, Penicillium claviforme, or Phoma betae, and incubation at 20 ◦ C and 90% relative humidity until severe disease symptoms were evident on control roots (0 mM SA). Roots were obtained from plants that were severely wilted for 2 d prior to harvest. Roots were treated for 1 h at room temperature with water (control) or 10 mM SA, then incubated for 3 d at 20 ◦ C and 90% relative humidity prior to inoculation. Rot symptoms for a single SA concentration are shown since all SA treatments provided statistically equivalent control. (A) Composite picture from a single experimental repetition showing all roots for a treatment. Since a single pathogen was used for each experiment, pictures are from three separate experiments. (B) Longitudinal sections of representative roots from each treatment using a root that contained near average weights of rot for the treatment.
claviforme, and P. betae. Rot due to these pathogens, however, has been shown to be reduced by JA treatment (Fugate et al., 2012). Defense mechanisms in postharvest sugarbeet root, therefore, are consistent with most plant species and the current model of plant defense mechanisms (Glazebrook, 2005; Robert-Seilaniantz et al., 2011). Although exogenous SA increases necrotrophic disease susceptibility for some plant/pathogen interactions due to antagonism between SA and JA signaling pathways (El Oirdi et al., 2011), SA did not increase disease susceptibility to the necrotrophic pathogens used in this research. Despite the inability of SA to affect storage rot severity for sugarbeet roots obtained from unstressed plants, SA significantly reduced storage rot severity on roots harvested from water-stressed plants. The reduction in storage rot in SA-treated, water-stressed sugarbeet roots was likely due to an alleviation of the effects of water stress by SA rather than a direct decrease in disease susceptibility of the roots. In other plant species, SA has been demonstrated to alleviate drought stress and minimize the detrimental physiological effects of water stress (Loutfy et al., 2012; Saruhan et al., 2012). For sugarbeet root, an increase in storage rot susceptibility is one such detrimental effect of preharvest water stress (Gaskill, 1950a). The reduction in storage rot in SA-treated,
water-stressed sugarbeet roots was unlikely to be the result of a direct decrease in disease susceptibility since SA did not reduce storage rot severity in roots from unstressed plants.
4. Conclusions Postharvest SA treatments of 0.01–10 mM did not affect the severity of storage rot caused by B. cinerea, P. claviforme, or P. betae for sugarbeet roots harvested from plants that received sufficient water prior to harvest. However, for roots obtained from plants that were water stressed before harvest, postharvest SA treatments significantly reduced rot due to B. cinerea, P. claviforme, or P. betae. In these roots, SA reduced the severity of rot symptoms, but did not affect the incidence of infection. SA treatments of 0.01–10 mM provided statistically equivalent reductions in the weight of rotted tissue for each of the three pathogens, and on average, SA reduced the severity of storage rot due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively, in roots from plants that were water stressed before harvest. The ability of SA to reduce rot severity in water-stressed roots, but not in roots that received sufficient water before harvest, suggests that SA alleviated the negative
166
K.K. Fugate et al. / Postharvest Biology and Technology 85 (2013) 162–166
impacts of water stress but did not directly protect sugarbeet roots from storage rot-causing pathogens. Acknowledgements The authors thank John Eide for technical assistance, CNPq (Brazil) for J.P.F.’s scholarship, and the Beet Sugar Development Foundation and the Sugarbeet Research and Education Board of Minnesota and North Dakota for partial financial support of this research. Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. References Achuo, E.A., Audenaert, K., Meziane, H., Höfte, M., 2004. The salicylic acid-dependent defence pathway is effective against different pathogens in tomato and tobacco. Plant Pathol. 53, 65–72. Akeson, W.R., Yun, Y.M., Sullivan, E.F., 1979. Effect of chemicals on sucrose loss in sugarbeets during storage. J. Am. Soc. Sugar Beet Technol. 20, 255–268. Asghari, M., Aghdam, M.S., 2010. Impact of salicylic acid on post-harvest physiology of horticultural crops. Trends Food Sci. Technol. 21, 502–509. Ata, A.A., El-Samman, M.G., Moursy, M.A., Mostafa, M.H., 2008. Inducing resistance against rust disease of sugar beet by certain chemical compounds. Egypt. J. Phytopathol. 36, 113–132. Babalar, M., Asghari, M., Talaei, A., Khosroshahi, A., 2007. Effect of pre- and postharvest salicylic acid treatment on ethylene production, fungal decay and overall quality of Selva strawberry fruit. Food Chem. 105, 449–453. Bargabus, R.L., Zidack, N.K., Sherwood, J.E., Jacobsen, B.J., 2002. Characterisation of systemic resistance in sugar beet elicited by a non-pathogenic, phyllospherecolonizing Bacillus mycoides, biological control agent. Physiol. Mol. Plant Pathol. 61, 289–298. Bolton, M.D., 2009. Primary metabolism and plant defense – fuel for the fire. Mol. Plant Microbe Interact 22, 487–497. Bugbee, W.M., 1975. Penicillium claviforme and Penicillium variabile: pathogens of stored sugar beets. Phytopathology 65, 926–927. Bugbee, W.M., 1982. Storage rot of sugar beet. Plant Dis. 66, 871–873. Bugbee, W.M., Cole, D.F., 1976. Sugarbeet storage rot in the Red River Valley, 1974–1975. J. Am. Soc. Sugar Beet Technol. 19, 19–24. Bugbee, W.M., Cole, D.F., 1979. Comparison of thiabendazole and genetic resistance for control of sugar beet storage rot. Phytopathology 69, 1230–1232. Campbell, L.G., Klotz, K.L., 2006. Storage. In: Draycott, A.P. (Ed.), Sugar Beet. Blackwell Publishing Ltd., Oxford, UK, pp. 387–408. Cao, J., Zeng, K., Jiang, W., 2006. Enhancement of postharvest disease resistance in Ya Li pear (Pyrus bretschneideri) fruit by salicylic acid sprays on the trees during fruit growth. Eur. J. Plant Pathol. 114, 363–370. Choi, H.W., Hwang, B.K., 2011. Systemic acquired resistance of pepper to microbial pathogens. J. Phytopathol. 159, 393–400. Conrath, U., Pieterse, C.M.J., Mauch-Mani, B., 2002. Priming in plant–pathogen interactions. Trends Plant Sci. 7, 210–216. Cormack, M.W., Moffatt, J.E., 1961. Factors influencing storage decay of sugar beets by Phoma betae and other fungi. Phytopathology 51, 3–5. El Oirdi, M., El Rahman, T.A., Rigano, L., El Hadrami, A., Rodriguez, M.C., Daayf, F., Vojnov, A., Bouarab, K., 2011. Botrytis cinerea manipulates the antagonistic effects between immune pathways to promote disease development in tomato. Plant Cell 23, 2405–2421. Fugate, K.K., Ferrareze, J.P., Bolton, M.D., Deckard, E.L., Campbell, L.G., 2012. Postharvest jasmonic acid treatment of sugarbeet roots reduces rot due to Botrytis
cinerea, Penicillium claviforme, and Phoma betae. Postharvest Biol. Technol. 65, 1–4. Gaskill, J.O., 1950a. Effects of wilting, drought, and temperature upon rotting of sugar beets during storage. Proc. Am. Soc. Sugar Beet Technol. 6, 653–659. Gaskill, J.O., 1950b. Possibilities for improving storage-rot resistance of sugar-beets through breeding. Proc. Am. Soc. Sugar Beet Technol. 6, 664–669. Gaskill, J.O., Seliskar, C.E., 1952. Effect of temperature on rate of rotting of sugarbeet tissue by two storage pathogens. Proc. Am. Soc. Sugar Beet Technol. 7, 571–574. Glazebrook, J., 2005. Contrasting mechanisms of defense against biotrophic and necrotrophic pathogens. Annu. Rev. Phytopathol. 43, 205–227. Govrin, E.M., Levine, A., 2002. Infection of Arabidopsis with a necrotrophic pathogen, Botrytis cinerea, elicits various defense responses but does not induce systemic acquired resistance (SAR). Plant Mol. Biol. 48, 267–276. Kadioglu, A., Saruhan, N., Sa˘glam, A., Terzi, R., Acet, T., 2011. Exogenous salicylic acid alleviates effects of long term drought stress and delays leaf rolling by inducing antioxidant system. Plant Growth Regul. 64, 27–37. Loake, G., Grant, M., 2007. Salicylic acid in plant defence – the players and protagonists. Curr. Opin. Plant Biol. 10, 466–472. Loutfy, N., El-Tayeb, M.A., Hassanen, A.M., Moustafa, M.F.M., Sakuma, Y., Inouhe, M., 2012. Changes in the water status and osmotic solute contents in response to drought and salicylic acid treatments in four different cultivars of wheat (Triticum aestivum). J. Plant Res. 125, 173–184. Metzger, M.S., Weiland, J.J., 2008. Growth promotion may compensate for losses due to moderate Aphanomyces root rot. J. Sugar Beet Res. 45, 1–17. Miles, W.G., Shaker, F.M., Nielson, A.K., Ames, R.R., 1977. A laboratory study of the ability of fungicides to control beet rotting fungi. J. Am. Soc. Sugar Beet Technol. 19, 288–293. Mitchell, A.F., Walters, D.R., 1995. Systemic protection in barley against powdery mildew infection using methyl jasmonate. Asp. Appl. Biol. 42, 323–326. Mumford, D.L., Wyse, R.E., 1976. Effect of fungus infection on respiration and reducing sugar accumulation of sugarbeet roots and use of fungicides to reduce infection. J. Am. Soc. Sugar Beet Technol. 19, 157–162. Murphy, A.M., Chivasa, S., Singh, D.P., Carr, J.P., 1999. Salicylic acid-induced resistance to viruses and other pathogens: a parting of the ways? Trends Plant Sci. 4, 155–160. Murphy, A.M., Holcombe, L.J., Carr, J.P., 2000. Characteristics of salicylic acid-induced delay in disease caused by a necrotrophic fungal pathogen in tobacco. Physiol. Mol. Plant Pathol. 57, 47–54. Nazar, R., Iqbal, N., Syeed, S., Khan, N.A., 2011. Salicylic acid alleviates decreases in photosynthesis under salt stress by enhancing nitrogen and sulfur assimilation and antioxidant metabolism differentially in two mungbean cultivars. J. Plant Physiol. 168, 807–815. Robert-Seilaniantz, A., Grant, M., Jones, J.D.G., 2011. Hormone crosstalk in plant disease and defense: more than just jasmonate-salicylate antagonism. Annu. Rev. Phytopathol. 49, 317–343. Saruhan, N., Saglam, A., Kadioglu, A., 2012. Salicylic acid pretreatment induces drought tolerance and delays leaf rolling by inducing antioxidant systems in maize genotypes. Acta Physiol. Plant. 34, 97–106. Senaratna, T., Touchell, D., Bunn, E., Dixon, K., 2000. Acetyl salicylic acid (Aspirin) and salicylic acid induce multiple stress tolerance in bean and tomato plants. Plant Growth Regul. 30, 157–161. Thaler, J.S., Owen, B., Higgins, V.J., 2004. The role of the jasmonate response in plant susceptibility to diverse pathogens with a range of lifestyles. Plant Physiol. 135, 530–538. Wang, Y.Y., Li, B.Q., Qin, G.-Z., Li, L., Tian, S.P., 2011. Defense response of tomato fruit at different maturity stages to salicylic acid and ethephon. Sci. Hortic. 129, 183–188. Yang, Z., Cao, S., Cai, Y., Zheng, Y., 2011. Combination of salicylic acid and ultrasound to control postharvest blue mold caused by Penicillium expansum in peach fruit. Innovat. Food Sci. Emerg. Technol. 12, 310–314. Yao, H., Tian, S., 2005. Effects of pre- and post-harvest application of salicylic acid or methyl jasmonate on inducing disease resistance of sweet cherry fruit in storage. Postharvest Biol. Technol. 35, 253–262.