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Dr Yong-Ju HuangPost-Doctoral Scientist |
 |
Many important fungal plant diseases have a symptomless (latent) phase between infection and appearance of symptoms or production of new inoculum, which may last for several months. QTL-mediated quantitative host resistance often operates during the symptomless phase of pathogen growth to slow development of epidemics, for example through increasing the length of the symptomless phase or decreasing inoculum for secondary infection. For effective control of plant pathogens with a long symptomless phase, fungicides may need to be applied before development of symptoms. To improve control of many fungal plant diseases with a symptomless phase, whether by breeding disease resistant cultivars or by use of fungicides, there is a need to understand the symptomless phase.
The L. maculans–B. napus pathosystem is a good model system to investigate generic questions about symptomless pathogen growth because there are available tools and suitable materials. Firstly, L. maculans, cause of phoma stem canker on B. napus (Fig. 1), represents a range of pathogens which are hemibiotrophic. L. maculans has two periods of symptomless growth. The first period (5-10 days) of symptomless growth occurs after the penetration of stomata in leaf tissues before the appearance of necrotic leaf lesions (phoma leaf spot) (Fig. 1 & 2). The second symptomless period (4-5 months) occurs after appearance of leaf lesions before the appearance of cankers on stems (Fig. 1 & 2). Since stem canker is the main cause of damage, this project focuses on the second symptomless period, which can be considered in two stages: (a) symptomless growth from the leaf lesion down the leaf petiole to the stem; (b) symptomless growth through stem tissues before appearance of stem canker. Secondly, new molecular tools and new host materials are available for this pathosystems (Fig.3 & 4). The newly developed GFP-expressing L. maculans isolates and TaqMan L. maculans-specific probe now make it possible to investigate mechanism of resistance to symptomless growth of L. maculans in B. napus tissues. Further to the development of two mapping populations, near isogenic lines (NILs) for the target regions have recently been developed in INRA (Rennes).
Figure 1 Symptoms on leaf (phoma leaf spots in autumn/winter) and stem (stem canker in summer at harvest)
Figure 2. Seasonal cycle of phoma stem canker epidemics in Europe in relation to components of oilseed rape (B. napus) resistance to L. maculans (Fitt et al., 2006, European Journal of Plant Pathology 114: 3-15)
Phoma stem canker is a disease of world-wide importance on oilseed rape. In the UK, phoma stem canker is the most serious disease on winter oilseed rape, which caused €56M per season in harvest years 2000-2002 (www.cropmonitor.co.uk). Effective control of severe stem canker epidemics depends on the use of fungicides and the timing of fungicide applications is crucial for effective control of the disease. It is hypothesised that current triazole fungicides operate against L. maculans during symptomless growth down the leaf petiole to the stem. Since the systemic growth of L. maculans from leaves to stems is symptomless and several months elapse between appearance of phoma leaf spots (in autumn) and appearance of stem cankers (in spring) (Fig. 1 & 2), it has been difficult to assess the effects of fungicides on stem canker development. With availability of new tools (GFP and quantitative PCR) and near isogenic lines (NILs) of B. napus with different levels of resistance, it is now possible to assess not only effects of fungicide on symptomless development of L. maculans but also interactions between host resistance and effectiveness of fungicide application.
Figure 3. Symtomless growth of L. maculans from leaf lesion down the leaf petiole to plant stem to form stem canker. Use of GFP and qPCR to visualise and quantify the symptomless growth of L. maculans before the formation of stem canker
Figure 4. Symptomless growth of L. maculans in oilseed rape leaf petiole (a) and stem (b) visualised by GFP reporter. Samples viewed with white light (a-1, b-1) or a GFP filter (a-2, b-2)
This project is using L. maculans–B. napus pathosystem as a model system, using new tools (GFP and quantitative PCR) and new materials (NILs) of B. napus to understand operation of resistance to pathogen symptomless growth phase.
It is a BBSRC Industry Partnership Award (IPA) project with collaboration between Rothamsted Research, INRA (Rennes) and DuPont. It aims to answer two questions:
1. Is oilseed rape resistance restricting symptomless growth of the phoma stem canker pathogen down the leaf petiole and into the plant stem the key component of quantitative resistance (field resistance) to the disease?
2. Are current fungicides effective against the pathogen (L. maculans) only if applied before the pathogen causes stem symptoms?
This involves four objectives:
1. To determine whether the main component of quantitative resistance operates during L. maculans symptomless growth down oilseed rape leaf petiole.
2. To determine whether the main component of quantitative resistance operates during L. maculans symptomless colonisation of plant stem.
3. To investigate the genetic control of quantitative resistance to symptomless growth of L. maculans in leaf petiole and plant stem, exploiting results of field and controlled environment experiments in relation to existing and new genetic mapping information to further resolve the QTL regions.
4. To investigate interactions between effects of fungicides and effects of genetic resistance on symptomless growth of L. maculans in B. napus leaf petiole and plant stem.
Huang YJ, Balesdent MH, Li ZQ, Evans N, Rouxel T and Fitt BDL (2010). Fitness cost of virulence differs between the AvrLm1 and AvrLm4 loci in Leptosphaeria maculans (phoma stem canker of oilseed rape). European Journal of Plant Pathology 126: 279–291.
Stonard JF, Latunde-Dada AO, Huang YJ, West JS, Evans N, Fitt BDL (2010). Geographic variation in severity of phoma stem canker and Leptosphaeria maculans/ L. biglobosa populations on UK winter oilseed rape (Brassica napus). European Journal of Plant Pathology 126: 97–3109.
Huang YJ, Pirie EJ, Evans N, Delourme R, King GJ, Fitt BDL (2009). Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape). Plant Pathology 58: 314–323.
Huang YJ, Liu Z, West JS, Todd AD, Hall AM, Fitt BDL (2007). Effects of temperature and rainfall on date of release of ascospores of Leptosphaeria maculans (phoma stem canker) from winter oilseed rape (Brassica napus) debris in the UK. Annals of Applied Biology 151: 99-111.
Salam MU, Fitt BDL, Aubertot J-N, Diggle AJ, Huang YJ, Barbetti MJ, Gladders P, Jedryczka M, Khangura RK, Wratten N, Fernando WGD, Penaud A, Pinochet X, Sivasithamparam K (2007). Two weather-based models for predicting the onset of seasonal release of ascospores of Leptosphaeria maculans or L. biglobosa. Plant Pathology 56: 412-423.
Liu SY, Liu R, Latunde-Dada A O, Cools HJ, Foster SJ, Huang YJ, Fitt BDL (2007). Comparison of Leptosphaeria biglobosa-induced and chemically induced systemic resistance to L. maculans in Brassica napus. Chinese Science Bulletin 52: 660-667.
Huang YJ, Evans N, Li ZQ, Eckert M, Chevre AM, Renard M, Fitt BDL (2006). Temperature and leaf wetness duration affect phenotypic expression of Rlm6-mediated resistance to Leptosphaeria maculans in Brassica napus. New Phytologist 170 : 129-141.
Fitt BDL, Huang YJ, van den Bosch F, West JS (2006). Co-existence of related pathogen species on arable crops in space and time. Annual Review of Phytopathology 44: 163-182.
Huang YJ, Li ZQ, Evans N, Rouxel T, Fitt BDL and Balesdent MH. (2006) Fitness cost associated with loss of the AvrLm4 avirulence function in Leptosphaeria maculans (phoma stem canker of oilseed rape). European Journal of Plant Pathology 114: 77-89.Liu SY, Liu Z, Fitt BDL, Evans N, Foster SJ, Huang YJ, Latunde-Dada A O and Lucas JA (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 Pathology 55:401-412.
West JS, Latunde-Dada AO, Huang YJ, Evans N, Fitt BDL (2006) Avirulence management for durable control of stem canker of oilseed rape in Europe. Aspects of Applied Biology 80, Delivering sustainability within profitable farming systems – is it possible?. Pp171-176, The Association of Applied Biologists, Wellesbourne.
Huang YJ, Fitt BDL, Jedryczka M, Dakowska S, West JS, Gladders P, Steed JM and Li ZQ (2005). Patterns of ascospore release in relation to phoma stem canker epidemiology in England (Leptosphaeria maculans) and Poland (L. biglobosa). European Journal of Plant Pathology 111: 263-277.
Liu SY, Fitt BDL, Liu RH, Evans N, Dong CH and Huang YJ (2004). Amplification of plant defensin and oxalic acid oxidase genes and their expressions induced by pathogens and chemicals in Brassica napus. Chinese Journal of Oil Crop Sciences 26: 43-49.
Huang YJ, Toscano-Underwood C, Hu XJ. and Hall AM (2003). Effects of temperature on ascospore germination and penetration of oilseed rape (Brassica napus) leaves by A- or B-group Leptosphaeria maculans (phoma stem canker). Plant Pathology 52: 245-255.
Huang YJ, BDL Fitt and AM Hall (2003). Survival of A-group and B-group Leptosphaeria maculans (phoma stem canker) ascospores in air and mycelium on oilseed rape stem debris. Annals of Applied Biology 143: 359-369.
Toscano-Underwood C, Huang YJ, Fitt BDL and Hall AM (2003). Effects of temperature on maturation of pseudothecia of Leptosphaeria maculans and L. biglobosa on oilseed rape stem debris. Plant Pathology 52: 726-736.
West JS, Balesdent M-H, Rouxel T, Narcy JP, Huang YJ, Roux J, Steed JM, Fitt BDL, Schmit J (2002). Colonisation of winter oilseed rape tissues by A/Tox+ and B/Tox0 Leptosphaeria maculans (phoma stem canker) in France and England. Plant Pathology, 51: 311-321.
West JS, Fitt BDL, Leech PK, Biddulph JE, Huang YJ, Balesdent M-H (2002). Effects of timing of Leptosphaeria maculans ascospore release and fungicide regime on phoma leaf spot and phoma stem canker development on winter oilseed rape (Brassica napus). Plant Pathology 51: 454-463.
Huang YJ, Toscano-Underwood C, Fitt BDL, Todd AD, West JS, Koopmann B, Balesdent MH (2001). Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape). Annals of Applied Biology 139: 193-207.
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