Physiological Response of Grapevines to Vascular Pathogens: a Review
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Plant defence against pathogens 7 Physiological response of grapevines to vascular pathogens: a review D.C. Mundy1 and M.A. Manning2 1he New Zealand Institute for Plant & Food Research Limited, Marlborough Wine Research Centre, P.O. Box 845, Blenheim 7240, New Zealand 2he New Zealand Institute for Plant & Food Research Limited, Mt Albert Research Centre, Private Bag 92169, Auckland, New Zealand Corresponding author: [email protected] Abstract The successful infection of a grapevine vascular system by a plant pathogen and expression of disease symptoms occur only when the pathogen has overcome the wound response and other defences of the vine. Even when pathogens do successfully infect the vascular system of grapevines, symptom expression is not often observed in the first season. Symptoms may be observed in one year but the same vine can have reduced or no symptoms the following season. Information is presented on physiological stress in association with trunk diseases as one factor that may contribute to symptom expression in vines. A hypothesis of grapevine wound response is proposed as part of the discussion of vine physiological response. Information on individual trunk diseases and physiological interactions is also provided. Keywords grape, wound response, symptoms, stress, trunk disease. INTRODUCTION A complex series of interactions between the function. During infection and establishment, causal agent and the grapevine has already the pathogen can colonise other tissue as well occurred before trunk disease symptoms are as/before the vessels (Pascoe & Cottral 2000). In observed on vines in the vineyard. Many of the order to induce vascular disease symptoms, the steps before the expression of trunk disease xylem cell’s function is oten reduced (Hopkins symptoms occur in the wood, where they are 1989; Edwards et al. 2007). A vine responding to not easily observed. he time delay between an infection will have a limited pool of resources infection and symptom expression with diseases to allocate to defence mechanisms. Abiotic stress like eutypa dead-arm makes understanding may limit the vine’s ability to allocate resources to the relationship between disease and symptom infection, resulting in subsequent colonisation of expression more diicult. tissues by the pathogen. A successful trunk pathogen has contended Oten disease symptoms are both spatially and with the vine’s wound response and other defences. temporally removed from the initial infection Toxins produced by the pathogen and other of the vine (Rudelle et al. 2005; Sosnowski et al. pathogenicity factors have had the opportunity 2007). When symptoms are observed in woody to interact with the vine’s normal physiological plants, the expression may not be the same from New Zealand Plant Protection 64: 7-16 (2011) www.nzpps.org © 2011 New Zealand Plant Protection Society (Inc.) www.nzpps.org Refer to http://www.nzpps.org/terms_of_use.html Plant defence against pathogens 8 season to season (Octave et al. 2006; Sosnowski et 1941). he wound response signalling pathway al. 2007), possibly because of changes in the vine shares common components (e.g. jasmonate reserves. Host response to vascular infection is a signals) with those activated following insect dynamic interaction between host and parasite in and pathogen attack. he rate of response has which resistance is the rule and susceptibility the implications for the disease resistance of the exception (Beckman 1964). plant (Bostock & Stermer 1989). Generalised cell response to wounding PRUNING WOUND RESPONSE includes signalling pathways that are triggered Using a model system for wound response in by elicitors, including ion luxes, oxidative lowering plants and investigations of grapevine burst and synthesis of signal compounds such pathogen interactions, a hypothesis of grapevine as ethylene, salicylic acid and jasmonic acid response for further investigation has been (Belhadj et al. 2006). he pathogen may act on generated (see below). General wound response the elicitor signal pathways, producing toxin- of lowering plants has received considerable induced symptoms remote from the site of study and review (Bloch 1941; Bostock & Stermer production (Valtaud et al. 2009). hese defence 1989). he structure and physiology of grapevines, pathways include reinforcement of plant which may be important to wound response, cell walls, accumulation of phytoalexins and have also been investigated and summarised other antimicrobial compounds, and proteins (Pratt 1974; Mullins et al. 1992). Understanding inhibitory or hydrolytically active towards grapevine wound response is important, as microbes may be induced (Belhadj et al. 2006). several grapevine vascular pathogens are believed Bostock & Stermer (1989) described three to enter the vine via mechanical injuries such as wound response types in plants, with the most pruning wounds (Eutypa lata, Botryosphaeria complex being observed in woody perennial stems species, Phaeoacremonium species) (Mundy as well as potato tubers, which have been used as a & Manning 2010; Rolshausen et al. 2010; model system for understanding the response. he Úrbez-Torres & Gubler 2010). Recent studies response process involves three key steps: (i) the of grapevine wounds (Pascoe & Cottral 2000; cells adjacent to the wound dying from autolysis, Harvey & Hunt 2006; Sun et al. 2006; Eskalen et (ii) existing parenchyma cells undergoing al. 2007; Sun et al. 2007; Weber et al. 2007; Sun rediferentiation and lignosuberization to form a et al. 2008; Rolshausen et al. 2010; Úrbez-Torres boundary zone with increased physical resistance & Gubler 2010) and the use of wound dressings and (iii) the formation of a suberized wound (Moller & Kasimatis 1980; Jaspers 2001; John et periderm below the boundary zone as a result al. 2005) in relation to grapevine trunk disease of meristematic activity (Bostock & Stermer pathogens have provided observations for the 1989). Biochemical changes in individual cells’ model proposed. induced responses to pathogen attack and/or Plants resist pathogen attack via multilayered mechanical wounding include the accumulation constitutive and inducible defences. For example, of phenols, phytoalexin production, synthesis of high lignin production in cell walls has been hydrolytic enzymes, and cell wall reinforcement reported to confer tolerance to E. lata (Rolshausen with the phenolic polymers suberin and/or lignin et al. 2008). When a plant is cut (or mechanically (Hawkins & Boudet 1996). damaged), resulting in disruption to the vascular Within the vascular tissue, the vine responds system, a multi-step wound response is activated to wounding of the vessels by the production (Bloch 1941; Bostock & Stermer 1989; Hawkins of tyloses. Tyloses form when the protoplasmic & Boudet 1996). Wound responses take place at membrane of the parenchyma cells next to the cellular and tissue levels, with the degeneration xylem cells extends into the vessel via the pit or necrosis of cells at the wound site providing to form a balloon-like structure that, in grapes, signals to surrounding healthy cells (Bloch eventually becomes ligniied (Pratt 1974). When © 2011 New Zealand Plant Protection Society (Inc.) www.nzpps.org Refer to http://www.nzpps.org/terms_of_use.html Plant defence against pathogens 9 a large number of tyloses form, they can block tissue and undiferentiated cells start to form the vessel. he formation of tyloses and other a periderm. Within the vessels, gels or tyloses responses occur over time in response to the form depending on the season. For a large cut initial wounding event. Hawkins & Boudet to the vine, up to 7 years of xylem may need to (1996) developed a model system for studying be sealed to prevent water loss and microbial the gene expression response to mechanical entry. Phenolic compounds are deposited at the wounding in lowering plants and used it to wound, and over time the wound becomes less investigate changes over time (1–7 days) in lignin susceptible to infection by trunk pathogens. and suberin deposition. Investigations have indicated that the timing of he formation of tissue impervious to water the wounding event can determine the length of and microorganism penetration is a common the wound susceptibility. feature of wound response of woody plants associated with resistance to pathogens (Bostock PHYSIOLOGICAL STRESS AND & Stermer 1989). When physical barriers are SYMPTOM EXPRESSION produced, this is oten in association with Interactions between disease symptom expression production of anti-microbial phenolics (Del Rio and grapevine stress have been suggested as et al. 2001; Treutter 2005) and a reduction in the one possible explanation for inconsistent visual availability of simple sugars (and other nutrients) symptoms for some vascular diseases. In seasons at the wound site (Bostock & Stermer 1989). when growth of the vine is not inhibited by abiotic factors, foliar symptoms of E. lata in Unique features of grapevines grapes are not oten observed or are reduced in Grapevine xylem has some distinct physiological severity (Sosnowski et al. 2007). In seasons when and structural features that distinguish it from vines experience abiotic stresses, individual vine other lowering plants. In grapevines, the reserves may inluence symptom expression. secondary xylem is described as difuse-porous If vine stress does have a role in symptom with ladder-like thickening surrounded by living expression, then the mechanism of this reaction xylem parenchyma (Mullins et al. 1992).