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Control of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) with resistance elicitors
Crop Protection 40 (2012) 59e62
Contents lists available at SciVerse ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Short communication
Control of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) with resistance elicitors Simon J.P. Oxley, Dale R. Walters* Crop & Soil Systems Research Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 August 2011 Received in revised form 10 April 2012 Accepted 22 April 2012
Field trials were conducted over two years (2008/2009 and 2009/2010) to examine the effect of a combination of resistance elicitors on light leaf spot (Pyrenopeziza brassicae) on oilseed rape (Brassica napus). The elicitor combination comprised acibenzolar-S-methyl (ASM), b-aminobutyric acid (BABA) and cis-jasmone (CJ), and its effects were compared to those of the following fungicide treatments: [1] prothioconazole (used in 2009), and [2] prothioconazole/tebuconazole, and metconazole (used in 2010). In both years, the elicitor combination applied on its own, provided significant control of light leaf spot. In 2009, the elicitor combination was more effective than the fungicide in reducing light leaf spot severity at GS1.9, while levels of disease control at GS3.1 and 4.5 were similar for both elicitor and fungicide treatments. In 2010, the elicitor combination was less effective than the fungicide programmes in reducing light leaf spot severity at GS1.9, but produced similar levels of disease control at GS3.1 and was more effective than the fungicide at GS4.5. Probably because of the relatively low light leaf spot severity observed in the 2009 and 2010 field experiments, none of the treatments produced a significant effect on yield. Based on these data, and in view of the poor performance of fungicides in regions at high risk from light leaf spot, resistance elicitors might offer the potential for a new approach to controlling light leaf spot on oilseed rape. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Disease control Induced resistance Oilseed rape Systemic acquired resistance Pyrenopeziza brassicae
1. Introduction Resistance can be induced both locally and systemically by application of various agents to plants (Walters et al., 2007; Reglinski and Walters, 2009). One form of induced resistance, known as systemic acquired resistance (SAR), involves a restriction of pathogen growth and a suppression of disease symptom development, and its onset is associated with salicylic acid (SA) accumulation at sites of infection and systemically, and with the coordinated activation of a specific set of genes encoding pathogenesis-related (PR) proteins. Application to plants of SA or one of its functional analogues e.g. acibenzolar-S-methyl (ASM; also known as benzothiadiazole [BTH]; marketed in Europe as BionÒ and in North America as ActigardÒ), induces SAR and activates the same set of PR genes. Induced resistance offers the prospect of broad spectrum disease control using the plant’s own resistance mechanisms. As a result, there has been considerable interest in the development of agents (known as resistance elicitors or plant activators) which can mimic natural inducers of resistance (Lyon,
* Corresponding author. Tel.: þ44 131 535 4020; fax: þ44 131 535 4144. E-mail address: [email protected] (D.R. Walters). 0261-2194/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2012.04.028
2007). Examples of elicitors include ASM, which has been shown to elicit SAR in a wide range of plantepathogen interactions (Leadbeater and Staub, 2007), the non-protein amino acid baminobutyric acid (BABA; Cohen et al., 2010), and the oxylipin, cisjasmone (CJ) (Walters et al., 2007). A major obstacle to the use of induced resistance in practical crop protection is its variable efficacy under field conditions. Insufficient attention has been paid to investigating the mechanisms underlying variable efficacy and approaches that might be adopted to incorporate elicitors into crop protection practice, such as use of elicitors and fungicides together in the same disease control programme, and use of combinations of elicitors. In this paper, we report the results of field experiments over two years, undertaken to determine the potential for use of an elicitor combination to control light leaf spot (Pyrenopeziza brassicae Sutton & Rawlinson) on winter oilseed rape (Brassica napus L.). Winter oilseed rape is an important crop worldwide and the third most important crop in the United Kingdom, after wheat and barley. Light leaf spot is a major disease of oilseed rape (Boys et al., 2007), and can result in yield losses of 1.4 t/ha per annum (Oxley and Evans, 2009). Triazole fungicides applied in the autumn can provide effective control, although control can be considerably less effective in areas at high risk from P. brassicae. The elicitor
60
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combination used in the present work was ASM, BABA and CJ. In previous work, the efficacy of these elicitors in controlling foliar pathogens of barley was examined individually and in combination, with greatest disease control achieved using the combination of ASM, BABA and CJ (Walters et al., 2010, 2011). 2. Materials and methods Field experiments were conducted in 2008/2009 and 2009/2010 at Boghall Farm, Edinburgh, Scotland, UK, on a site which was cropped with spring barley in the 2006/2007 and 2007/2008 seasons. The winter oilseed rape cultivar Castille was used, which has a resistance rating to light leaf spot of 5 (www.hgca.com). Seeds were sown in a randomised block design at a seed rate of 100 seeds m2 and an individual plot size of 22 m 2 m. Three replicate plots were planted per treatment, including untreated controls. Plots received standard fertiliser and herbicide regimes. The field experiments compared the effects of the elicitor combination with standard fungicide treatments used to control foliar pathogens of winter oilseed rape in Scotland. Treatments were applied in the autumn/winter (GS1.6) and spring (GS3.3) with a knapsack sprayer using an equivalent spray volume of 200 L ha1. The elicitor and fungicide treatments used in the field trials were: 2009 Elicitor 1: ASM (0.175 g l1) þ BABA (0.1 g l1) þ CJ (0.625 g l1), plus adjuvant (Warrior, Intracrop, Lechlade, UK; 0.25 ml/l); applied in the autumn/winter and spring. Fungicide: ProlineÒ (Bayer; prothioconazole, 250 g/l); applied in the autumn/winter and spring. In 2008/2009, autumn/winter treatments were applied on 12 December 2008, and spring treatments on 1 April 2009.
values are shown in graphs. Comparison of treatment means was performed using Fisher’s protected least significant difference (LSD) test. 3. Results In 2009, most effective control of light leaf spot on oilseed rape at GS1.9 was achieved using the elicitor combination, which provided complete protection against infection (Fig. 1A). In contrast, the fungicide, prothioconazole, reduced light leaf spot severity from 11% in the untreated control to 5.4%, a reduction of 49% (Fig. 1A). The mixture of the elicitor combination and prothioconozole also provided excellent control, reducing light leaf spot severity to less than 1% compared to untreated plants (a 98%
A
B
2010 Elicitor 1: ASM þ BABA þ CJ (as for 2009, above). Fungicide 1: CarambaÒ (BASF; metconazole, 60 g/l); applied in the autumn and spring. Fungicide 2: ProlineÒ (Bayer; prothioconazole, 250 g/l; applied in (Bayer; prothioconazole the autumn) plus ProsaroÒ þ tebuconazole, 125:125 g/l; applied in the spring). In 2009/2010, autumn/winter treatments were applied on 2 December 2009 and spring treatments on 22 April 2010. ASM was a gift from Syngenta (BionÒ, 50 WG), BABA was purchased from Sigma Chemical Company, Poole, Dorset, UK, and CJ was purchased from Sigma Aldrich, Dorset, UK. Control plots received no elicitor or fungicide treatment and experimental plots were not artificially inoculated, but relied on natural inoculum. Symptoms of light leaf spot were assessed visually in each plot at GS1.9 (2 March 2009 and 9 March 2010), GS3.1 (30 March 2009 and 13 April 2010) and GS4.5 (14 May 2009 and 21 May 2010). There was a 14-day interval between application of the second treatments and disease assessment at GS1.9. Ten plants from each plot, chosen at random, were used to estimate the percentage leaf area affected. Disease assessments were carried out in the field using the UK recommended list protocol (www.hgca.com): visual examination of the crop canopy in three areas of each plot; ignore all naturally senescent tissue; include all necrosis and chlorosis attributable to light leaf spot; estimate percentage area affected and record the average percentage area of crop affected with light leaf spot in the three areas. Plots were harvested at normal harvest time and yields expressed as tonnes/ha. All data were subjected to analysis of variance (ANOVA) using the GenStat Release 11.1 statistical program. Percent leaf area diseased values from field experiments were log-transformed prior to analysis and back-transformed
C
Fig. 1. Effects of elicitor and fungicide treatments on light leaf spot severity on winter oilseed rape in a field experiment in 2008/2009. Treatments were applied in the autumn (12 December 2008) and spring (1 April 2009), and light leaf spot severity assessed at GS1.9 (2 March 2009) [A], GS3.1 (30 March 2009) [B], and GS4.5 (14 May 2009) [C]. UT ¼ untreated; Elic ¼ elicitor combination (ASM þ BABA þ CJ); Fung ¼ fungicide (ProlineÒ, Bayer; prothioconazole, 250 g/l). Bars with different letters are significantly different at P < 0.05 (LSD).
S.J.P. Oxley, D.R. Walters / Crop Protection 40 (2012) 59e62
reduction) (Fig. 1A). At GS3.1, light leaf spot severity was reduced from 13% in untreated plants, to 1.3% in elicitor-treated plots, and to 1.67% in plots treated with prothioconazole. A similar level of control was achieved with the elicitor and fungicide mixture (Fig. 1B). The situation was largely unchanged at GS4.5, with both the elicitor combination and prothioconazole reducing light leaf spot severity from 8.5% in untreated plants to less than 1%, a reduction of 93% (Fig. 1C). The mixture of elicitor and prothioconazole reduced light leaf spot severity to 1.2% (Fig. 1C). In 2010, the elicitor combination again provided substantial control of light leaf spot (Fig. 2). However, in contrast to 2009, the two fungicide treatments (prothioconazole/tebuconazole and metconazole) reduced light leaf spot severity more substantially at GS1.9 than the elicitor combination (Fig. 2A). In contrast, at GS3.1, the elicitor combination reduced light leaf spot severity from 10% in untreated plants to 2%, with metconazole reducing disease severity to 5.3%, and prothioconazole/tebuconazole producing no significant effect on light leaf spot (Fig. 2B). This trend was maintained at GS4.5, with the elicitor combination reducing light leaf spot severity from 9.3% in untreated plants to 0.7% and prothioconazole/tebuconazole and metconazole reducing disease severity to 2.2% and 6.0%, respectively (Fig. 2C). At this stage, best control of light leaf spot was obtained with the mixture of elicitor and metconazole (Fig. 2C). In both 2009 and 2010, there was no significant effect of treatment on yield (data not shown).
61
Elicitors can divert host assimilates away from plant growth and yield towards defence, and as a result, can lead to reduced growth and yield in some crops (Walters and Heil, 2007). However, no such growth and yield reductions were observed in plants treated with elicitors which prime the plant for enhanced defence (Van Hulten et al., 2006; Walters et al., 2009). The data presented here suggest that use of the elicitor combination is not associated with yield reductions. The absence of significant increases in yield following elicitor and fungicide treatments might reflect the relatively low light leaf spot severity observed in the field experiments in 2009 and 2010.
A
4. Discussion The data presented here represent the first report of control of light leaf spot on oilseed rape using resistance elicitors. The data show that a combination of resistance elicitors, applied in both the autumn and the spring, provided control of light leaf spot on oilseed rape that was, in some cases, superior to that provided by two commercial fungicides. In order to control light leaf spot effectively, fungicides need to be applied in the autumn (Coules et al., 2002). Triazole fungicides can provide good levels of disease control, although under high-risk conditions, levels of control can be considerably lower than expected (Oxley and Evans, 2009). Indeed, the results presented in this paper showed levels of light leaf spot control of 70% or less with fungicide treatments applied in the autumn and again in the spring. The elicitor combination used in the present work, ASM þ BABA þ CJ, has been shown recently to control Rhynchosporium secalis on spring barley, especially if used with reduced rate fungicide (Walters et al., 2010). However, while the levels of control of R. secalis achieved on barley were moderate when the elicitor combination was applied on its own, on oilseed rape, control of light leaf spot ranged from 80 to 100%. In spring barley, high levels of disease control were provided when the elicitor combination was applied first, followed by a later application of fungicide (Walters et al., 2010). In contrast, in oilseed rape, combined application of elicitor and fungicide was, in most cases, less effective than elicitor applied on its own. P. brassicae has a long symptomless phase until the first visible necrotic lesions appear in January/February (Gilles et al., 2000). In the present work, light leaf spot severity was assessed visually and future work in this area should determine not just visual symptoms, but also the extent of symptomless infection. Elicitors have been shown previously to control foliar pathogens on oilseed rape under controlled and field conditions. Thus, menadione sodium bisulphite (MSB) was shown to enhance local and systemic resistance to infection by Leptosphaeria maculans (phoma stem canker) on oilseed rape seedlings (Borges et al., 2003), while ASM applied in the autumn, was shown to reduce both the incidence and severity of Phoma stem canker on oilseed rape in field experiments (Liu et al., 2006).
B
C
Fig. 2. Effects of elicitor and fungicide treatments on light leaf spot severity on winter oilseed rape in a field experiment in 2009/2010. Treatments were applied in the autumn (2 December 2009) and spring (22 April 2010), and light leaf spot severity assessed at GS1.9 (9 March 2010) [A], GS3.1 (13 April 2010) [B], and GS4.5 (21 May 2010) [C]. UT ¼ untreated; Elic ¼ elicitor combination (ASM þ BABA þ CJ); Fung 1 ¼ fungicide (CarambaÒ, BASF; metconazole, 60 g/l); Fung 2 ¼ fungicide (ProlineÒ [Bayer; prothioconazole, 250 g/l] plus ProsaroÒ [Bayer; prothioconazole þ tebuconazole, 125:125 g/l]). Bars with different letters are significantly different at P < 0.05 (LSD).
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On barley, the combination of ASM þ BABA þ CJ was demonstrated to provide better control of R. secalis than any of the elicitors used singly (Walters et al., 2010). Interestingly, recent work has suggested that this elicitor combination activates SAR in barley (Walters et al., 2011), although whether it does so in oilseed rape awaits investigation. Irrespective of the defence signalling involved in oilseed rape, the levels of disease control obtained in this study suggest that induced resistance is worthy of investigation as an approach to disease control in this important crop. References Borges, A.A., Cools, H.J., Lucas, J.A., 2003. Menadione sodium bisulphite: a novel plant defence activator which enhances local and systemic resistance to infection by Leptosphaeria maculans. Plant Pathol. 52, 429e436. Boys, E.F., Roques, S.E., Ashby, A.M., Evans, N., Latunde-Dada, A.O., Thomas, J.E., West, J.S., Fitt, B.D.L., 2007. Resistance to infection by stealth: Brassica napus (winter oilseed rape) and Pyrenopeziza brassicae (light leaf spot). Eur. J. Plant Pathol. 118, 307e321. Cohen, Y., Rubin, A.E., Kilfin, G., 2010. Mechanisms of induced resistance in lettuce against Bremia lactucae by DL-b-aminobutyric acid (BABA). Eur. J. Plant Pathol. 126, 553e573. Coules, A.E., Lunn, G.D., Rossall, S., 2002. Disease and Canopy Control in Oilseed Rape Using Triazole Fungicides. In: BCPC Conference e Pests and Diseases, vols. 1 & 2, pp. 617e622. Gilles, T., Evans, N., Fitt, B.D.L., Jeger, M.J., 2000. Epidemiology in relation to methods for forecasting light leaf spot (Pyrenopeziza brassicae) severity on winter oilseed rape (Brassica napus) in the UK. Eur. J. Plant Pathol. 106, 593e600.
Leadbeater, A., Staub, T., 2007. Exploitation of induced resistance: a commercial perspective. In: Walters, D., Newton, A., Lyon, G. (Eds.), Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK, pp. 229e242. Liu, S.Y., Liu, Z., Fitt, B.D.L., Evans, N., Foster, S.J., Huang, Y.J., Latunde-Dada, A.O., Lucas, J.A., 2006. Resistance to Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape) induced by L. biglobosa and chemical defence activators in field and controlled environments. Plant Pathol. 55, 401e412. Lyon, G., 2007. Agents that can elicit induced resistance. In: Walters, D., Newton, A., Lyon, G. (Eds.), Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK, pp. 9e29. Oxley, S.J.P., Evans, A.E., 2009. Winter Oilseed Rape Pests and Diseases. SAC Technical Note TN620, ISSN 0142 7695. Reglinski, T., Walters, D., 2009. Induced resistance for plant disease control. In: Walters, D. (Ed.), Disease Control in Crops: Biological and Environmentally Friendly Approaches. Wiley-Blackwell, Oxford, UK, pp. 62e92. Van Hulten, M., Pelser, M., Van Loon, L.C., Pieterse, C.M.J., Ton, J., 2006. Costs and benefits of priming for plant defense in Arabidopsis. Proc. Natl. Acad. Sci. USA 103, 5602e5607. Walters, D., Heil, M., 2007. Costs and trade-offs associated with induced resistance. Physiol. Mol. Plant Pathol. 71, 3e17. Walters, D., Newton, A., Lyon, G., 2007. Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK. Walters, D.R., Paterson, L., Havis, N.D., 2010. Control of foliar diseases of spring barley using resistance elicitors. In: Proc. Crop Prot. Northern Britain, pp. 91e96. Walters, D.R., Paterson, L., Sablou, C., Walsh, D.J., 2011. Existing infection with Rhynchosporium secalis compromises the ability of barley to express induced resistance. Eur. J. Plant Pathol. 130, 73e82. Walters, D.R., Paterson, L., Walsh, D.J., Havis, N.D., 2009. Priming for plant defense in barley provides benefits only under high disease pressure. Physiol. Mol. Plant Pathol. 73, 95e100.
Contents lists available at SciVerse ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Short communication
Control of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) with resistance elicitors Simon J.P. Oxley, Dale R. Walters* Crop & Soil Systems Research Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 August 2011 Received in revised form 10 April 2012 Accepted 22 April 2012
Field trials were conducted over two years (2008/2009 and 2009/2010) to examine the effect of a combination of resistance elicitors on light leaf spot (Pyrenopeziza brassicae) on oilseed rape (Brassica napus). The elicitor combination comprised acibenzolar-S-methyl (ASM), b-aminobutyric acid (BABA) and cis-jasmone (CJ), and its effects were compared to those of the following fungicide treatments: [1] prothioconazole (used in 2009), and [2] prothioconazole/tebuconazole, and metconazole (used in 2010). In both years, the elicitor combination applied on its own, provided significant control of light leaf spot. In 2009, the elicitor combination was more effective than the fungicide in reducing light leaf spot severity at GS1.9, while levels of disease control at GS3.1 and 4.5 were similar for both elicitor and fungicide treatments. In 2010, the elicitor combination was less effective than the fungicide programmes in reducing light leaf spot severity at GS1.9, but produced similar levels of disease control at GS3.1 and was more effective than the fungicide at GS4.5. Probably because of the relatively low light leaf spot severity observed in the 2009 and 2010 field experiments, none of the treatments produced a significant effect on yield. Based on these data, and in view of the poor performance of fungicides in regions at high risk from light leaf spot, resistance elicitors might offer the potential for a new approach to controlling light leaf spot on oilseed rape. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Disease control Induced resistance Oilseed rape Systemic acquired resistance Pyrenopeziza brassicae
1. Introduction Resistance can be induced both locally and systemically by application of various agents to plants (Walters et al., 2007; Reglinski and Walters, 2009). One form of induced resistance, known as systemic acquired resistance (SAR), involves a restriction of pathogen growth and a suppression of disease symptom development, and its onset is associated with salicylic acid (SA) accumulation at sites of infection and systemically, and with the coordinated activation of a specific set of genes encoding pathogenesis-related (PR) proteins. Application to plants of SA or one of its functional analogues e.g. acibenzolar-S-methyl (ASM; also known as benzothiadiazole [BTH]; marketed in Europe as BionÒ and in North America as ActigardÒ), induces SAR and activates the same set of PR genes. Induced resistance offers the prospect of broad spectrum disease control using the plant’s own resistance mechanisms. As a result, there has been considerable interest in the development of agents (known as resistance elicitors or plant activators) which can mimic natural inducers of resistance (Lyon,
* Corresponding author. Tel.: þ44 131 535 4020; fax: þ44 131 535 4144. E-mail address: [email protected] (D.R. Walters). 0261-2194/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2012.04.028
2007). Examples of elicitors include ASM, which has been shown to elicit SAR in a wide range of plantepathogen interactions (Leadbeater and Staub, 2007), the non-protein amino acid baminobutyric acid (BABA; Cohen et al., 2010), and the oxylipin, cisjasmone (CJ) (Walters et al., 2007). A major obstacle to the use of induced resistance in practical crop protection is its variable efficacy under field conditions. Insufficient attention has been paid to investigating the mechanisms underlying variable efficacy and approaches that might be adopted to incorporate elicitors into crop protection practice, such as use of elicitors and fungicides together in the same disease control programme, and use of combinations of elicitors. In this paper, we report the results of field experiments over two years, undertaken to determine the potential for use of an elicitor combination to control light leaf spot (Pyrenopeziza brassicae Sutton & Rawlinson) on winter oilseed rape (Brassica napus L.). Winter oilseed rape is an important crop worldwide and the third most important crop in the United Kingdom, after wheat and barley. Light leaf spot is a major disease of oilseed rape (Boys et al., 2007), and can result in yield losses of 1.4 t/ha per annum (Oxley and Evans, 2009). Triazole fungicides applied in the autumn can provide effective control, although control can be considerably less effective in areas at high risk from P. brassicae. The elicitor
60
S.J.P. Oxley, D.R. Walters / Crop Protection 40 (2012) 59e62
combination used in the present work was ASM, BABA and CJ. In previous work, the efficacy of these elicitors in controlling foliar pathogens of barley was examined individually and in combination, with greatest disease control achieved using the combination of ASM, BABA and CJ (Walters et al., 2010, 2011). 2. Materials and methods Field experiments were conducted in 2008/2009 and 2009/2010 at Boghall Farm, Edinburgh, Scotland, UK, on a site which was cropped with spring barley in the 2006/2007 and 2007/2008 seasons. The winter oilseed rape cultivar Castille was used, which has a resistance rating to light leaf spot of 5 (www.hgca.com). Seeds were sown in a randomised block design at a seed rate of 100 seeds m2 and an individual plot size of 22 m 2 m. Three replicate plots were planted per treatment, including untreated controls. Plots received standard fertiliser and herbicide regimes. The field experiments compared the effects of the elicitor combination with standard fungicide treatments used to control foliar pathogens of winter oilseed rape in Scotland. Treatments were applied in the autumn/winter (GS1.6) and spring (GS3.3) with a knapsack sprayer using an equivalent spray volume of 200 L ha1. The elicitor and fungicide treatments used in the field trials were: 2009 Elicitor 1: ASM (0.175 g l1) þ BABA (0.1 g l1) þ CJ (0.625 g l1), plus adjuvant (Warrior, Intracrop, Lechlade, UK; 0.25 ml/l); applied in the autumn/winter and spring. Fungicide: ProlineÒ (Bayer; prothioconazole, 250 g/l); applied in the autumn/winter and spring. In 2008/2009, autumn/winter treatments were applied on 12 December 2008, and spring treatments on 1 April 2009.
values are shown in graphs. Comparison of treatment means was performed using Fisher’s protected least significant difference (LSD) test. 3. Results In 2009, most effective control of light leaf spot on oilseed rape at GS1.9 was achieved using the elicitor combination, which provided complete protection against infection (Fig. 1A). In contrast, the fungicide, prothioconazole, reduced light leaf spot severity from 11% in the untreated control to 5.4%, a reduction of 49% (Fig. 1A). The mixture of the elicitor combination and prothioconozole also provided excellent control, reducing light leaf spot severity to less than 1% compared to untreated plants (a 98%
A
B
2010 Elicitor 1: ASM þ BABA þ CJ (as for 2009, above). Fungicide 1: CarambaÒ (BASF; metconazole, 60 g/l); applied in the autumn and spring. Fungicide 2: ProlineÒ (Bayer; prothioconazole, 250 g/l; applied in (Bayer; prothioconazole the autumn) plus ProsaroÒ þ tebuconazole, 125:125 g/l; applied in the spring). In 2009/2010, autumn/winter treatments were applied on 2 December 2009 and spring treatments on 22 April 2010. ASM was a gift from Syngenta (BionÒ, 50 WG), BABA was purchased from Sigma Chemical Company, Poole, Dorset, UK, and CJ was purchased from Sigma Aldrich, Dorset, UK. Control plots received no elicitor or fungicide treatment and experimental plots were not artificially inoculated, but relied on natural inoculum. Symptoms of light leaf spot were assessed visually in each plot at GS1.9 (2 March 2009 and 9 March 2010), GS3.1 (30 March 2009 and 13 April 2010) and GS4.5 (14 May 2009 and 21 May 2010). There was a 14-day interval between application of the second treatments and disease assessment at GS1.9. Ten plants from each plot, chosen at random, were used to estimate the percentage leaf area affected. Disease assessments were carried out in the field using the UK recommended list protocol (www.hgca.com): visual examination of the crop canopy in three areas of each plot; ignore all naturally senescent tissue; include all necrosis and chlorosis attributable to light leaf spot; estimate percentage area affected and record the average percentage area of crop affected with light leaf spot in the three areas. Plots were harvested at normal harvest time and yields expressed as tonnes/ha. All data were subjected to analysis of variance (ANOVA) using the GenStat Release 11.1 statistical program. Percent leaf area diseased values from field experiments were log-transformed prior to analysis and back-transformed
C
Fig. 1. Effects of elicitor and fungicide treatments on light leaf spot severity on winter oilseed rape in a field experiment in 2008/2009. Treatments were applied in the autumn (12 December 2008) and spring (1 April 2009), and light leaf spot severity assessed at GS1.9 (2 March 2009) [A], GS3.1 (30 March 2009) [B], and GS4.5 (14 May 2009) [C]. UT ¼ untreated; Elic ¼ elicitor combination (ASM þ BABA þ CJ); Fung ¼ fungicide (ProlineÒ, Bayer; prothioconazole, 250 g/l). Bars with different letters are significantly different at P < 0.05 (LSD).
S.J.P. Oxley, D.R. Walters / Crop Protection 40 (2012) 59e62
reduction) (Fig. 1A). At GS3.1, light leaf spot severity was reduced from 13% in untreated plants, to 1.3% in elicitor-treated plots, and to 1.67% in plots treated with prothioconazole. A similar level of control was achieved with the elicitor and fungicide mixture (Fig. 1B). The situation was largely unchanged at GS4.5, with both the elicitor combination and prothioconazole reducing light leaf spot severity from 8.5% in untreated plants to less than 1%, a reduction of 93% (Fig. 1C). The mixture of elicitor and prothioconazole reduced light leaf spot severity to 1.2% (Fig. 1C). In 2010, the elicitor combination again provided substantial control of light leaf spot (Fig. 2). However, in contrast to 2009, the two fungicide treatments (prothioconazole/tebuconazole and metconazole) reduced light leaf spot severity more substantially at GS1.9 than the elicitor combination (Fig. 2A). In contrast, at GS3.1, the elicitor combination reduced light leaf spot severity from 10% in untreated plants to 2%, with metconazole reducing disease severity to 5.3%, and prothioconazole/tebuconazole producing no significant effect on light leaf spot (Fig. 2B). This trend was maintained at GS4.5, with the elicitor combination reducing light leaf spot severity from 9.3% in untreated plants to 0.7% and prothioconazole/tebuconazole and metconazole reducing disease severity to 2.2% and 6.0%, respectively (Fig. 2C). At this stage, best control of light leaf spot was obtained with the mixture of elicitor and metconazole (Fig. 2C). In both 2009 and 2010, there was no significant effect of treatment on yield (data not shown).
61
Elicitors can divert host assimilates away from plant growth and yield towards defence, and as a result, can lead to reduced growth and yield in some crops (Walters and Heil, 2007). However, no such growth and yield reductions were observed in plants treated with elicitors which prime the plant for enhanced defence (Van Hulten et al., 2006; Walters et al., 2009). The data presented here suggest that use of the elicitor combination is not associated with yield reductions. The absence of significant increases in yield following elicitor and fungicide treatments might reflect the relatively low light leaf spot severity observed in the field experiments in 2009 and 2010.
A
4. Discussion The data presented here represent the first report of control of light leaf spot on oilseed rape using resistance elicitors. The data show that a combination of resistance elicitors, applied in both the autumn and the spring, provided control of light leaf spot on oilseed rape that was, in some cases, superior to that provided by two commercial fungicides. In order to control light leaf spot effectively, fungicides need to be applied in the autumn (Coules et al., 2002). Triazole fungicides can provide good levels of disease control, although under high-risk conditions, levels of control can be considerably lower than expected (Oxley and Evans, 2009). Indeed, the results presented in this paper showed levels of light leaf spot control of 70% or less with fungicide treatments applied in the autumn and again in the spring. The elicitor combination used in the present work, ASM þ BABA þ CJ, has been shown recently to control Rhynchosporium secalis on spring barley, especially if used with reduced rate fungicide (Walters et al., 2010). However, while the levels of control of R. secalis achieved on barley were moderate when the elicitor combination was applied on its own, on oilseed rape, control of light leaf spot ranged from 80 to 100%. In spring barley, high levels of disease control were provided when the elicitor combination was applied first, followed by a later application of fungicide (Walters et al., 2010). In contrast, in oilseed rape, combined application of elicitor and fungicide was, in most cases, less effective than elicitor applied on its own. P. brassicae has a long symptomless phase until the first visible necrotic lesions appear in January/February (Gilles et al., 2000). In the present work, light leaf spot severity was assessed visually and future work in this area should determine not just visual symptoms, but also the extent of symptomless infection. Elicitors have been shown previously to control foliar pathogens on oilseed rape under controlled and field conditions. Thus, menadione sodium bisulphite (MSB) was shown to enhance local and systemic resistance to infection by Leptosphaeria maculans (phoma stem canker) on oilseed rape seedlings (Borges et al., 2003), while ASM applied in the autumn, was shown to reduce both the incidence and severity of Phoma stem canker on oilseed rape in field experiments (Liu et al., 2006).
B
C
Fig. 2. Effects of elicitor and fungicide treatments on light leaf spot severity on winter oilseed rape in a field experiment in 2009/2010. Treatments were applied in the autumn (2 December 2009) and spring (22 April 2010), and light leaf spot severity assessed at GS1.9 (9 March 2010) [A], GS3.1 (13 April 2010) [B], and GS4.5 (21 May 2010) [C]. UT ¼ untreated; Elic ¼ elicitor combination (ASM þ BABA þ CJ); Fung 1 ¼ fungicide (CarambaÒ, BASF; metconazole, 60 g/l); Fung 2 ¼ fungicide (ProlineÒ [Bayer; prothioconazole, 250 g/l] plus ProsaroÒ [Bayer; prothioconazole þ tebuconazole, 125:125 g/l]). Bars with different letters are significantly different at P < 0.05 (LSD).
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On barley, the combination of ASM þ BABA þ CJ was demonstrated to provide better control of R. secalis than any of the elicitors used singly (Walters et al., 2010). Interestingly, recent work has suggested that this elicitor combination activates SAR in barley (Walters et al., 2011), although whether it does so in oilseed rape awaits investigation. Irrespective of the defence signalling involved in oilseed rape, the levels of disease control obtained in this study suggest that induced resistance is worthy of investigation as an approach to disease control in this important crop. References Borges, A.A., Cools, H.J., Lucas, J.A., 2003. Menadione sodium bisulphite: a novel plant defence activator which enhances local and systemic resistance to infection by Leptosphaeria maculans. Plant Pathol. 52, 429e436. Boys, E.F., Roques, S.E., Ashby, A.M., Evans, N., Latunde-Dada, A.O., Thomas, J.E., West, J.S., Fitt, B.D.L., 2007. Resistance to infection by stealth: Brassica napus (winter oilseed rape) and Pyrenopeziza brassicae (light leaf spot). Eur. J. Plant Pathol. 118, 307e321. Cohen, Y., Rubin, A.E., Kilfin, G., 2010. Mechanisms of induced resistance in lettuce against Bremia lactucae by DL-b-aminobutyric acid (BABA). Eur. J. Plant Pathol. 126, 553e573. Coules, A.E., Lunn, G.D., Rossall, S., 2002. Disease and Canopy Control in Oilseed Rape Using Triazole Fungicides. In: BCPC Conference e Pests and Diseases, vols. 1 & 2, pp. 617e622. Gilles, T., Evans, N., Fitt, B.D.L., Jeger, M.J., 2000. Epidemiology in relation to methods for forecasting light leaf spot (Pyrenopeziza brassicae) severity on winter oilseed rape (Brassica napus) in the UK. Eur. J. Plant Pathol. 106, 593e600.
Leadbeater, A., Staub, T., 2007. Exploitation of induced resistance: a commercial perspective. In: Walters, D., Newton, A., Lyon, G. (Eds.), Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK, pp. 229e242. Liu, S.Y., Liu, Z., Fitt, B.D.L., Evans, N., Foster, S.J., Huang, Y.J., Latunde-Dada, A.O., Lucas, J.A., 2006. Resistance to Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape) induced by L. biglobosa and chemical defence activators in field and controlled environments. Plant Pathol. 55, 401e412. Lyon, G., 2007. Agents that can elicit induced resistance. In: Walters, D., Newton, A., Lyon, G. (Eds.), Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK, pp. 9e29. Oxley, S.J.P., Evans, A.E., 2009. Winter Oilseed Rape Pests and Diseases. SAC Technical Note TN620, ISSN 0142 7695. Reglinski, T., Walters, D., 2009. Induced resistance for plant disease control. In: Walters, D. (Ed.), Disease Control in Crops: Biological and Environmentally Friendly Approaches. Wiley-Blackwell, Oxford, UK, pp. 62e92. Van Hulten, M., Pelser, M., Van Loon, L.C., Pieterse, C.M.J., Ton, J., 2006. Costs and benefits of priming for plant defense in Arabidopsis. Proc. Natl. Acad. Sci. USA 103, 5602e5607. Walters, D., Heil, M., 2007. Costs and trade-offs associated with induced resistance. Physiol. Mol. Plant Pathol. 71, 3e17. Walters, D., Newton, A., Lyon, G., 2007. Induced Resistance for Plant Defence: a Sustainable Approach to Crop Protection. Blackwell Publishing, Oxford, UK. Walters, D.R., Paterson, L., Havis, N.D., 2010. Control of foliar diseases of spring barley using resistance elicitors. In: Proc. Crop Prot. Northern Britain, pp. 91e96. Walters, D.R., Paterson, L., Sablou, C., Walsh, D.J., 2011. Existing infection with Rhynchosporium secalis compromises the ability of barley to express induced resistance. Eur. J. Plant Pathol. 130, 73e82. Walters, D.R., Paterson, L., Walsh, D.J., Havis, N.D., 2009. Priming for plant defense in barley provides benefits only under high disease pressure. Physiol. Mol. Plant Pathol. 73, 95e100.