1. IntroductionFrom spring 2010 onw

1. IntroductionFrom spring 2010 onward, a disease of increasing virulence, wasobserved in numerous apple (Malus domestica Borkh.) orchardslocated in several Italian alpine valleys. The incidence and sever-ity of the disease increased during last years and it is becominga serious economic threat for the area, strongly devoted to applecultivation.Symptoms of the disease include: alteration of the bark colourthat turns to red rusty, occurrence of blisters and flaking off of theepidermis. Underneath, necrosis appear in the external and woodytissues, starting from the grafting point up to the first branch. Theextension of necrosis varies from a few centimetres to the wholelength of the trunk, but it remains superficial and localized to theouter secondary xylem layer. Symptoms on flower, leaf or fruit are not recorded, although the disease is frequently related to an overalldecline of the plant. The reported symptomatology is ascribable tothe “apple blister bark” syndrome.Some experiences of a similar syndrome have already beendescribed over the past decades. Similar symptoms had beenreported in South Africa in the 1960’s (Mansvelt and Hattingh,1968), and in Piedmont (North-West of Italy) in 1997 (Scortichiniand Morone, 1997). In both cases the researchers indicated Pseu-domonas syringae pv. syringae van Hall as the responsible pathogen.P. syringae pv. syringae survives, as an epiphyte, during spring onleaves of several spontaneous plants without causing any symp-toms. During autumn bacterial cells can reach the apple tree bypassive transport (i.e. rain, wind) and start to multiply on the bark.The bacteria penetrate through natural openings (i.e. lenticels) aswell as lesions and start the colonization of the plant (Scortichiniand Morone, 1997).In Trentino-Alto Adige (North-East of Italy), Prodorutti et al.(2012) reported that, in apple orchards affected by blisterbark and dieback, P. syringae pv. syringae has been isolatedtogether with fungi such as Phomopsis spp., Neonectria spp., and Botryosphaeriaceae, the latter generally considered as endophytesand saprophytes (Udayanga et al., 2011) and requiring serious pre-disposing factors to cause visible damages. The study conducted inPiedmont also indicated the presence of Phomopsis mali, Sphaerop-sis malorum and Nectria galligena isolated in decreasing order(Scortichini and Morone, 1997). Their presence was attributed tothe weakening of the plant induced by P. syringae pv. syringae .In the apple blister bark syndrome, physiological stresses,adverse agronomic or climatic conditions, biotic agents can allbe considered as predisposing factors potentially involved on theoccurrence of the symptoms (Prodorutti et al., 2012). Previous stud-ies conducted on host–pathogen interactions have recognised aplant-vigour mediated aetiology, stressing the physiological statusas a discriminant on plant vulnerability (Kogel et al., 2006; Bostocket al., 2014).Several biotic and abiotic components and their combination(Atkinson and Urwin, 2012), are potential causes of variability in themanifestation of disease and the severity of symptoms. Among theenvironmental factors, the proximity and magnitude of inoculumto the host (Lovell et al., 2004; Horsfall and Dimond, 1962), abioticfactors, such water stress (Pandey et al., 2015; Ramegowda andSenthil-Kumar, 2015), general status of soil fertility (Braun et al.,2010) and poor plant-soil interactions in replant conditions, medi-ated by the root system (Polverigiani et al., 2014), have all beenindicated as predisposing components.Soil physical (Bengough and Mullins, 1990), chemical and bio-logical fertility strongly affect root activity. Water stress, hypoxia,and mechanical impedance are among the major physical causes ofpoor root growth and development (Bengough et al., 2010). Totalroot biomass, as well as biomass allocation pattern are influencedby soil characteristics. Under stress conditions, the productionof fibrous roots is particularly compromised, roots show smallerdiameters, a lower ramification index and a lower integrity of theroot’s cell membrane (Polverigiani et al., 2014). Besides some firstattempts to identify the predisposing conditions, the full set of fac-tors inducing the apple blister bark disease is still undefined. Thepresent study aims to verify the influence of substrate character-istics on root development, plant physiological status and growth,and the consequent risk of blister bark disease occurrence linkedto the presence of P. syringae pv. syringae in apple orchards locatedin Valtellina (Sondrio province).

ผลลัพธ์ (อังกฤษ) 3:

1. IntroductionFrom spring 2010 onward a disease, of increasing virulence wasobserved in, numerous apple (Malus domestica. Borkh.) orchardslocated in several Italian alpine valleys. The incidence and sever-ity of the disease increased during last. Years and it is becominga serious economic threat for, the area strongly devoted to applecultivation.Symptoms of the disease. Include: alteration of the bark colourthat turns to, red rusty occurrence of blisters and flaking off of theepidermis, Underneath,. Necrosis appear in the external and woodytissues starting from, the grafting point up to the first branch. Theextension. Of necrosis varies from a few centimetres to the wholelength of the trunk but it, remains superficial and localized to theouter. Secondary xylem layer. Symptoms on flower leaf or, fruit are, not recorded although the disease is frequently related to. An overalldecline of the plant. The reported symptomatology is ascribable tothe "Apple blister bark syndrome.Some experiences." Of a similar syndrome have already beendescribed over the past decades. Similar symptoms had beenreported in South Africa. In the 1960 "s (Mansvelt, and Hattingh 1968), and in Piedmont (North-West of Italy) in 1997 (Scortichiniand Morone 1997,,). In both cases the researchers indicated Pseu-domonas syringae pv. Syringae van Hall as the responsible pathogen.P. Syringae. PV. Syringae survives as an, epiphyte during spring, onLeaves of several spontaneous plants without causing any, symp-toms. During autumn bacterial cells can reach the apple tree bypassive transport (i.e. Rain wind), and start to multiply on the. Bark.The bacteria penetrate through natural openings (i.e. Lenticels) aswell as lesions and start the colonization of the. Plant (Scortichiniand, Morone 1997). In Trentino-Alto Adige (North-East of Italy), Prodorutti et al. (2012), reported that. In apple orchards affected by blisterbark, and dieback P. Syringae pv. Syringae has been isolatedtogether with fungi such. As Phomopsis spp, Neonectria spp, and Botryosphaeriaceae the latter, generally considered as endophytesand saprophytes. (Udayanga et al, 2011) and requiring serious pre-disposing factors to cause visible damages. The study conducted inPiedmont. Also indicated the presence of, Phomopsis Mali Sphaerop-sis malorum and Nectria galligena isolated in decreasing order (Scortichini. And, Morone 1997). Their presence was attributed tothe weakening of the plant induced by P. Syringae pv. Syringae. In the. Apple blister bark, stresses syndrome physiological, agronomic adverse or climatic conditions biotic agents, can allbe considered. As predisposing factors potentially involved on theoccurrence of the symptoms (Prodorutti et al, 2012). Previous stud-ies. Conducted on Host - pathogen interactions have recognised aplant-vigour, mediated aetiology stressing the physiological statusas. A discriminant on plant vulnerability (Kogel et al, 2006; Bostocket Al, 2014). Several biotic and abiotic components and. Their combination (Atkinson, and Urwin 2012), are potential causes of variability in themanifestation of disease and the. Severity of symptoms. Among theenvironmental factors the proximity, and magnitude of inoculumto the host (Lovell et al.,. 2004; Horsfall, and Dimond 1962), abioticfactors such water, stress (Pandey et al, 2015; Ramegowda andSenthil-Kumar 2015),,, General status of soil fertility (Braun et al, 2010) and poor plant-soil interactions in replant conditions medi-ated by,, The root system (Polverigiani et al, 2014), have all beenindicated as predisposing components.Soil physical (Bengough and. Mullins, the 1990), chemical and bio-logical fertility strongly affect root activity. Water stress hypoxia and mechanical impedance,,, Are among the major physical causes ofpoor root growth and development (Bengough et al, 2010). Totalroot biomass as well,, As biomass allocation pattern are influencedby soil characteristics. Under stress conditions the productionof, fibrous roots. Is particularly compromised roots smallerdiameters, show, lower a ramification index and a lower integrity of theroot s. " Cell membrane (Polverigiani et al, 2014). Besides some firstattempts to identify the predisposing conditions the full,, Set of fac-tors inducing the apple blister bark disease is still undefined. Thepresent study aims to verify the influence. Of substrate character-istics on root development plant physiological, status and growth and the, consequent risk of blister. Bark disease occurrence linkedto the presence of P. Syringae pv. Syringae in apple orchards locatedin Valtellina (Sondrio. Province).