Plants have developed sophisticated molecular mechanisms to detect pathogens and parasites and to activate immune response. Immune response in plants is regulated by phytohormones that are low molecular weight molecules which interact in a complex network to regulate also many aspects of plant growth, photosynthesis, flowering, reproduction, seed production and response to environmental abiotic challenges. Innate immune system in plants should be considered as within plant growth processes; thus, expressing constitutive defence systems occurs only at the cost of plant growth and encounters the risk of allocating resources to defence in the absence of natural pathogens and pests. An effective alternative is to fine-tune immune responses by modulating the "immunological memory" of plants, as it occurs in animals. An aspect of this modulation may be represented by the so-called "priming" by which previously attacked plants respond more quickly or more strongly to a subsequent attack. The priming may be realized by Systemic Acquired Resistance (SAR) that is typically induced following effector-triggered immunity (ETI) or, in other words, R gene-mediated resistance. Salicylic acid (SA) is the key regulator of either R gene-mediated resistance to biotrophic pathogens or SAR. Priming is a relatively low-cost mechanism of advancing plant defence, as resources are not used until the threat returns. Another distinct pathway that is associated with induced immune response in plants is based on the plant hormones jasmonic acid (JA) and ethylene (ET) functioning as signaling molecules. JA and ET are involved in an induced systemic resistance (ISR) mediated by beneficial soil organisms such as arbuscular mycorrhiza forming fungi (AMF) and plant growth promoting rhizobacteria (PGPR). Hormone network interactions are as important for plant immune system expression that pathogens and parasites have developed sophisticated molecular mechanisms to deregulate the biosynthesis of hormones and/or to interfere with hormonal signalling pathways thus impairing plant defence response. It should be clear that there will be no effective durable crop protection strategy if the health of the soil and the quality of the irrigation water of the monitored cropping systems will be not carefully taken into consideration in any integrated pest management. A natural stimulation of the immune system of plants should be pursued by enriching the soil of the fields, particularly those intensively cropped, with AMF and PGPR. Therefore, a holistic approach to durable crop protection strategies should be pursued in the consideration of the very complex relationship occurring between plants and changing natural environments, which may be characterized by a vast array of biotic attackers and abiotic challenges, also in view of new concerns as global warming.

Seven tomato cultivars and 9 hybrids coming from a breeding programme, susceptible or resistant to root-knot nematode by carrying the resistance gene Mi-1, were compared by determining free phenol content and catalase (CAT) activity in their leaves. A host suitability test based on the determination of the number of egg masses per root system (EM), after inoculation with an avirulent field population of Meloidogyne incognita, confirmed the response to root-knot nematodes of the positive and negative controls, and revealed that all the hybrids except one were highly resistant to the infection. Catalase activity and free phenols extracted from leaves were detected on 3 different groups of tomato plants: 1) known susceptible cultivars; 2) known resistant cultivars; 3) accessions from the breeding programme. The level of catalase activity of the groups 2 and 3 was similar and approximately 2-fold higher than that of the group 1. Conversely, no consistent difference was found in free phenol content among the 3 groups. Moreover, one pair of susceptible and resistant tomato cultivars was used to check changes of anti-oxidant activities due to nematode infection. Catalase and peroxidase activities were measured in roots 5 days after inoculation with 300 and 600 juveniles (J2) of a M. incognita population, and in uninoculated roots used as controls. Catalase was found to be inhibited and enhanced, respectively, in infected resistant and susceptible roots, with respect to controls. The degree of inhibition was higher in the resistant roots inoculated with 600 J2. Guaiacol peroxidase activity did not change after inoculation of susceptible plants, whereas it was enhanced in infected resistant roots compared with controls. The use of catalase activity as a biochemical marker of Mi-1-mediated resistance in tomato is proposed.

The expression pattern of pathogenesis-related genes PR-1, PR-2 and PR-5, considered as markers for salicylic acid (SA)-dependent systemic acquired resistance (SAR), was examined in the roots and shoots of tomato plants pre-treated with SA and subsequently infected with root-knot nematodes (RKNs) (Meloidogyne incognita). PR-1 was up-regulated in both roots and shoots of SA-treated plants, whereas the expression of PR-5 was enhanced only in roots. The over-expression of PR-1 in the whole plant occurred as soon as 1 day after SA treatment. Up-regulation of the PR-1 gene was considered to be the main marker of SAR elicitation. One day after treatment, plants were inoculated with active juveniles (J2s) of M.incognita. The number of J2s that entered the roots and started to develop was significantly lower in SA-treated than in untreated plants at 5 and 15 days after inoculation. The expression pattern of PR-1, PR-2 and PR-5 was also examined in the roots and shoots of susceptible and Mi-1-carrying resistant tomato plants infected by RKNs. Nematode infection produced a down-regulation of PR genes in both roots and shoots of SA-treated and untreated plants, and in roots of Mi-carrying resistant plants. Moreover, in resistant infected plants, PR gene expression, in particular PR-1 gene expression, was highly induced in shoots. Thus, nematode infection was demonstrated to elicit SAR in shoots of resistant plants. The data presented in this study show that the repression of host defence SA signalling is associated with the successful development of RKNs, and that SA exogenously added as a soil drench is able to trigger a SAR-like response to RKNs in tomato. © 2013 BSPP AND JOHN WILEY & SONS LTD.

All potato cultivars are susceptible to root-knot nematodes (Meloidogyne spp.) which infest the roots and inducegalls on the surface and necrotic spots in the flesh tuber of potato, Solanum tuberosum. Infested tubers areunacceptable for processing and fresh market. Tubers are also putative source of dissemination of the nematode. AFrench nematode- resistant tetraploid potato genotype gained from ex-S. sparsipilum material hybridized with S.tuberosum in F1 and in their back cross progenies and designated as 02T.155.6 was tested and compared in thepresent study in Egypt as a suitable different environment. Histopathological changes and chitinase activity inducedby M. incognita population, of common occurrence in Egypt, in four French tetraploid materials and two commoncultivars known as nematode- resistant and susceptible potato genotypes were investigated. Hypertrophied cellswere initiated in both cortical and steler regions of the roots which were then developed to abnormal xylemelements expanding into the cortex in French susceptible genotypes designated as 02T.149.6, 02T.150.54, and02T.157.16. Nematode within the vascular tissue (stele) could induce giant cell development close to nematodeheads. The largest number of such induced cells was shown by the cultivars Spunta and Diamant. The clone02T.155.6 with putative nematode resistance demonstrated none or very little nematode development. Recentlydead second stage juveniles could also indicate incompatible plant reaction to the invading nematodes in02T.155.6. M. incognita, Giza population, resistance was generally more coherent to 02T.155.6 as demonstrated byour histological investigations but less coherent as shown by another Egyptian M. incognita population. Chitinaseactivity was enhanced in M. incognita (Giza)-inoculated with respect to uninoculated roots in all plants. Afterinoculation, such an activity generally increased more in roots of a potato genotype previously known to haveresistance or relatively low numbers of both nematode galls and eggmasses than in the other tested cultivars.Peroxidase and catalase activities of nematode- inoculated with respect to uninoculated potato roots werepresented and discussed.

Management of plant parasitic nematodes with nematode predators, parasites or antagonists is an eco-friendly approach that may avoid the problems arisen by the use of toxic chemicals. Fungi belonging to Trichoderma spp. are well known in literature for their role in control of plant parasitic nematodes. Root-knot nematodes (RKNs), Meloidogyne spp., are obligate parasites that cause the formation of familiar galls on the roots of many cultivated plants. The interaction between the M. incognita motile second stage juveniles (J2s) and the isolate ITEM 908 of Tricoderma harzianum was examined in its effect on the nematode infestation level of susceptible tomato plants.To gain insight into the mechanisms by which ITEM 908 interacts with nematode-infected tomato plants, the expression patterns of the genes PR1 (marker of Salycilic Acid-depending resistance signalling pathway) and JERF3 (marker of the Jasmonic Acid/Ethylene-depending resistance signalling pathway) were detected over time in: i) untrreated roots; ii) roots pre-treated with the fungus;- iii) roots inoculated with the nematode; iv) pre-treated and inoculated roots.Infestation parameters were checked in untreated plants and plants treated with the fungus to test the effect of the fungus on nematode infestation level and to compare this effect with the expression of the genes PR1 and JERF3, involved in induced resistance.

Different concentrations of the systemic acquired resistance (SAR) elicitors, salicylic acid (SA), methylsalicylicacid (MetSA), acibenzolar-S-methyl (ASM) and 2,6-dicholoroisonicotinic acid (INA), wereprovided to tomato seedlings as root-dip or soil-drench one day before inoculation with the root-knotnematode, Meloidogyne incognita. Nematode infestation was evaluated by counting egg masses/plant(EM), eggs/plant (Pf), and sedentary forms/plant (SF) in treated and untreated plants seven weeks afterinoculation. An index of plant fitness (PF) was also calculated to assess the costs of chemically-inducedresistance and the possible phytotoxicity of the treatments. SA and ASM were found to be effectiveelicitors of resistance when applied at suitable concentrations and method of application. Soil-drenchwith SA and root-dip in ASM were the most effective treatments as they markedly reduced bothnematode reproduction (less than 50% that of untreated plants) and infestation (50e70% EM reduction).MetSA was less effective than SA in eliciting resistance because of its negative effects on plant fitnesswhen it was provided as soil-drench. INA did not reduce nematode infestation at any of the nonphytotoxicrates. The reduction of nematode infestation and reproduction by SA applied as soil-drenchwas potentiated when the soil was enriched with humic acids. Soil-drenching with SA and MetSA werethe only treatments that caused a long-lasting induction of plant defences as they inhibited the infestationby the second generation of the nematode.

Root knot nematodes (Meloidogyne spp.) are important pests of a wide range of crops, including tomato. Resistance of tomato to root-knot nematodes is conferred by the single dominant gene Mi-1, which currently is present in all commercially available resistant tomato cultivars. However, several resistance-breaking populations are being collected worldwide. Two isolates coming fromthe same standard population of Meloidogyne incognita, one selected for virulence against Mi-1 (SM1) and the other left avirulent (avr1), have been used in this study. qRT-PCR was used to detect transcript levels of the manganese superoxide dismutase (Mn-SOD) gene from (a)virulent pre-parasitic second-stage juveniles (J2). Over-expression of the Mn-SOD gene was found in the virulent isolate compared with the avirulent counterpart. The enzyme activity of membrane-bound mitochondrial Mn-SOD was assayed in J2 and adult females as the fraction of total SOD activity insensitive to hydrogen peroxide (H2O2). J2 from SM1 showed about a two-fold higher enzyme activity than J2 from avr1; conversely, no difference was found when adult females were tested. Proteins of J2 extracts were separated by n-PAGE on special mini-gels and stained for SOD. One slow migrating and three fast migrating bands were stained. SOD activity of the slow migrating band was H2O2-insensitive and enriched by treatment with the detergent Triton X-100. J2 survival was monitored in suspensions provided or not provided with the cell oxygen radical generator paraquat, at high concentration. Virulent J2responded to paraquat treatment by increasing life extension with respect to control conditions; by contrast, avirulent J2 suffered major mortality in the presence of paraquat. Mn-SOD gene expression is discussed in relation to nematode fitness in oxidative stresses and vir phenotype.

Plant-parasitic nematodes are pests of a wide range of economically important crops, causing severe losses to agriculture. Natural genetic resistance of plants is expected to be a valid solution of the many problems nematodes cause all over the world. Progress in resistance applications is particularly important for the less-developed countries of tropical and subtropical regions, since use of resistant cultivars may be the only possible and economically feasible control strategy in those farming systems. Resistance is being considered of particular importance also in modern high-input production systems of developed countries, as the customary reliance on chemical nematicides has been restricted or has come to an end. This review briefly describes the genetic bases of resistance to nematodes in plants and focuses on the chances and problems of its exploitation as a key element in an integrated management program. Much space is dedicated to the major problem of resistance durability, in that the intensive use of resistant cultivars is likely to increasinglyinduce the selection of virulent populations able to ‘‘break’’ the resistance. Protocols of pest-host suitability are described, as bioassays are being used to evaluate local nematode populations in their potential to be selected on resistant germplasm and endanger resistant crops. The recent progress in using robust and durable resistances against nematodes as an efficient method for growers in vegetable cropping systems is reported, as well as the possible use of chemicals that do not show any unfavourable impact on environment, to induce in plants resistance against plant-parasitic nematodes.

Suitability of susceptible and resistant tomato cultivars to infestation of (a)-virulent populations of root-knot nematodes has been assessed by considering the amount of sedentary stages into the roots as an additional infestation factor to the reproduction rates. Different tomato-nematode interactions have been studied in strictly standardized glasshouse conditions and infestation assessed by measuring egg masses, eggs, and sedentary stages present in single roots 7 weeks after inoculation with 300 active second stage juveniles (J2). Field nematode avirulent populations and populations selected for virulence were inoculated on susceptible tomato, on tomato carrying the resistance gene Mi.1 in the heterozygous state, and on tomato carrying Mi.1-gene in the homozygous state. Infestation degree of each combination was expressed by means of an index, the Infestation Potential (IP), which integrated all the measured infestation variables. IPs of field populations on susceptible tomato were found to be about 2-fold higher than those of populations selected for virulence. Moreover, IPs of virulent populations on homozygous resistant tomato were lower than those on heterozygous resistant tomato. This kind of approach in determining nematode-tomato suitability can help to predict the impact that virulent root-knot nematode populations may have on resistant tomato cropping.

Nematodes of the genus Meloidogyne are obligate parasites that infect a wide range of different crops in all agricultural regions worldwide and cause significant losses of both yield and quality of produce. Trichoderma spp. have long been known to be a feasible biological alternative to chemicals for control of several soil-borne plant pathogens. More recently, it has been shown that Trichoderma spp. may be effective also in control of plant parasitic nematodes. However, very little is known on the mechanism(s) by means of which these antagonistic fungi can limit nematode infestation. In order to assess the capability of the antagonistic strain T. harzianum ITEM 908 to elicit resistance to M. incognita in tomato plants, we investigated the expression of the genes PR-1 (marker of the salicylic acid-depending resistance signalling pathway, SAR) and JERF3 (marker of the jasmonic acid/ethylene-depending resistance signalling pathway, ISR) during the interaction between ITEM 908 and M. incognita on susceptible tomato plants. Our findings suggest that jasmonic acid/ethylene-mediated resistance to M. incognita, is induced in tomato roots by treatment with T. harzianum ITEM 908, whereas, salicylic acid-mediated resistance, seems not to be involved in the interaction between this strain and tomato plants, at least in the roots. We also investigated the effect of T. harzianum ITEM 908 on infestation parameters, such as egg mass production, female fecundity and reproduction potential of M. incognita on the infested tomato roots. The presence of a suitable amount of T. harzianum ITEM 908 in soil (106 CFU/g of rhizosphere soil) significantly reduced all of the infestation parameters investigated. It is still to be established whether nematode infestation is reduced by ISR induction in roots or by a putative nemato-static and/or nemato-toxic activity of ITEM 908 in the soil, or a combination of both.

Salicylic acid (SA) and its synthetic functional analogue acibenzolarS-methyl (BTH) are able to activate in plants the systemic acquired resistance (SAR) which is an effective natural defence against many parasites and pathogens. In this study, the quantitative aspects of the interaction between SA and BTH and four humic acids isolated from soil (S-HA), peat (P-HA), compost (C-HA) and a mixture of peat and compost (M-HA) were evaluated by constructing the adsorption kinetics and isotherms. The adsorption of SA and BTH at concentrations of 0.05 and 0.01 mM, respectively, onto S-HA resulted rapid and complete in few hours. SA adsorption onto S-HA, P-HA and M-HA followed a linear model with adsorption constants ranging between 150 e 200 ml g -1, whereas onto C-HA it followed the Freundlich model with a K f value of 44 ml g-1. BTH adsorption onto all HA followed the Freundlich model with Kf values ranging between 559 ml g -1for M-HA and 6460 ml g-1 for P-HA.

Isoelectric focusing was used to separate proteins from cyst extracts of potato cyst nematode (PCN) populations. In a first set of assays, cyst extracts from standard populations of Globodera rostochiensis pathotypes Ro1, Ro2, Ro3, Ro2/3, Ro4, and Ro5, and G. pallida pathotypes Pa2 and Pa3, were loaded on isoelectric focusing gels. Gels were stained for superoxide dismutase (SOD), esterase, and glucose-6-phosphate isomerase (GPI). Twelve bands of SOD activity were detected, six (B1-B6) migrating towardsthe basic zone and the other six (A1-A6) migrating towards the acidic zone, starting from the loading point. A cluster analysis was carried out based on a data matrix that reported the presence or absence of SOD bands on the isozyme electrophoresis patterns (IEPs). Globodera spp. were clearly distinguished and, within G. rostochiensis, Ro2 and Ro4 shared a high level of similarity, respectively, with Ro3 and Ro5; moreover, Ro1 could be clearly distinguished from Ro2/3 and Ro4/5. Globodera pallida Pa2 and Pa3 also shared a highlevel of similarity. In contrast, esterase and GPI IEPs did not discriminate among G. rostochiensis standard pathotypes. Subsequently, 14 field populations of G. rostochiensis, five from Italy and nine from Venezuela, and three field populations of G. pallida, two from Italy and one from Chile, were assayed to obtain SOD IEPs. Italian populations had previously been identified at pathotype level by bioassays according to the generally accepted international test using different resistant potato cultivars and clones. The cluster analysis carried out on the SOD IEPs of all the populations tested formed four distinct groups within G. rostochiensis and only one within G. pallida. Pathotype ident ification of Globodera populations by SOD IEPs was not able to discriminate between bioassay standard couples Ro2/Ro3, Ro4/Ro5 and Pa2/Pa3. Therefore, three groups were assigned to Ro1, Ro2/3 and Ro4/5, and a fourth group to Pa2/Pa3. Four Venezuelan populations, not identified at pathotype level by bioassays, formed a distinct fifth group. By means of the method described herein, four additional unknown Venezuelan populations could be assigned to Ro1 group and one to Ro2/Ro3 group;one G. pallida population from Chile was assigned to Pa2/Pa3 group.

Activators of systemic acquired resistance (SAR), such as salicylic acid (SA) and its synthetic functional analogs, benzo(1,2,3)thiadiazole-7-carbothionic acid-S-methyl ester (BTH) and 2,6-dichloroisonicotinic acid (INA), were tested on tomato, eggplant, and pepper for the control of the root-knot nematode Meloidogyne incognita. Effects on plant fitness, nematode reproduction, and root galling were screened in relation to different methods of application, to different applied dosages of chemicals, and to different plant growth stages. Dosages applied to plants were in relation to plant weights. These chemicals were also tested for their possible nematotoxic activity in vitro. RESULTS: Soil-drenches of SA and INA, and root dip application of SA and BTH, inhibited nematode reproduction, at specific dosage ranges, without affecting plant growth. SA and INA were able to reduce root galling, as well. Foliar sprays of both SA and BTH were ineffective against nematode attacks. Plants tolerated SA more than the other chemicals tested. BTH at elevated concentrations increased the mortality of nematode juveniles and reduced egg hatching in vitro. CONCLUSIONS: SAR activators at concentrations suitable for different plant growth stages and applied by the proper method can possibly be included in IPM programs for nematode management.

The emergence of virulent root-knot nematode populations, able to overcome the resistance conferred by some of the resistance genes (R-genes) in Solanaceous crops, i.e., Mi(s) in tomato, Me(s) in pepper, may constitute a severe limitation to their use in the field. Research has been conducted to evaluate the durability of these R-genes, by comparing the reproduction of several laboratory-selected and wild virulent Meloidogyne incognita isolates, on both susceptible and resistant tomatoes and peppers. We first show that the Me1 R-gene in pepper behaves as a robust R-gene controlling avirulent and virulent Me3, Me7 or Mi-1 isolates. Although the reproductive potential of the virulent isolates was highly variable on susceptible and resistant plants, we also confirm that virulence is highly specific to a determined Rgene on which selection has occurred. Another significant experimental result is the observation that a reproductive fitness cost is associated with nematode virulence against Mi-1 in tomato and Me3 and Me7 in pepper. The adaptative significance of trade-offs between selected characters and fitness-related traits, suggests that, although the resistance can be broken, it may be preserved in some conditions if the virulent nematodes are counter-selected in susceptible plants. All these results have important consequences for the management of plant resistance in the field.