Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

喷施外源GA对SMV侵染的野生大豆抗病性的影响

 大豆花叶病毒(SMV)是影响大豆生产的主要病害之一,在全球范围内对大豆生产造成影响。赤霉素(GA)是重要的植物激素之一,喷施外源GA对SMV侵染的野生大豆抗病反应的影响尚不清楚。通过测定喷施外源GA后接种SMV的野生大豆植株内源水杨酸(SA)含量,抗氧化酶活性及抗病基因表达,发现与对照相比,喷施外源GA的野生大豆植株的株高、根长、叶面积、植株干重、内源水杨酸含量、过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)活性及抗病相关基因GmPR-1、GmPR-10和GmNPR1的表达显著增加。说明在病毒侵染野生大豆之前喷施GA可以促进植株的生长,诱导植株抗病反应,降低病毒危害。     

Effect of plant elicitors on the reproduction of the root-knot nematode Meloidogyne chitwoodi on susceptible hosts

Sustainable strategies for plant-parasitic nematode control are required to reduce dependence on chemical nematicides. Foliar application of various compounds can induce a systemic defence response that reduces nematode infestation. The effects of benzothiadiazole (BTH), β-aminobutyric acid (BABA), jasmonates (cis-jasmone and methyl jasmonate) and salicylic acid (SA) in the development and reproduction of the root-knot nematode Meloidogyne chitwoodi in tomato plants were assessed. The effects of BTH and of the jasmonates were further tested on potato plants. Pot assays were conducted using tomato plants cv. Tiny Tim or potato cv. Désirée treated with foliar sprays and inoculated with 300 second stage juveniles. Nematode development and reproduction were assessed 21 and 45 days after inoculation. Treatment with SA had a negative effect on nematode development in tomato plants but did not affect reproduction and methyl jasmonate treatment was the most effective in reducing nematode penetration (58 %). Nematode development was significantly affected in potato plants sprayed with cis-jasmone. Nematode penetration was reduced by 90, 67 and 81 % in plants treated with BTH, cis-jasmone and methyl jasmonate respectively, although the reproduction factor (Rf) was only significantly lower in the BTH treatment (Rf?=?7.6) when compared to the control (Rf?=?18.1). Our results suggest that both the SA and JA pathways play an important role in plant defence mechanisms against root-knot nematode development and reproduction for both plants, and should be considered in the design of integrated pest management approaches.     

The effect of salicylic and jasmonic acids on tomato physiology and tolerance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> (CMV)

Cucumber mosaic virus (CMV) is one of the most important plant viruses responsible for sharp reductions in the production of many cultivated plants. Activities of antioxidant enzymes, photosynthetic capacity, proline and total soluble carbohydrates (TSC) content were measured in the leaves of tomato (Solanum lycopercicum cv. Falat) plants treated with phytohormones (salicylic and jasmonic acids and their combination) and inoculated with CMV at 0, 1, 2, 4, 6, 8, and 15 days after the treatments. Based on the results, catalase (CAT) activity decreased in the healthy and infected plants, but peroxidase (POD) activity increased in the CMV-infected plants signifying that POD is more active in H₂O₂ scavenging in tomato. Because the hormone treatments inhibited the reduction in the enzyme activity, it may be considered as a controlling method against CMV. Superoxide dismutase (SOD) activity was lower in the control until 6 days post inoculation (dpi), but increased after 8 dpi. The infected plants and the hormone-treated plants showed an increased SOD activity from 0 to 15 dpi. Phenylalanine ammonia lyase (PAL) activity also increased in all the treatments over the time period (0-15 dpi). Net photosynthesis (NP) rate and chlorophyll content decreased under the virus infection and hormone treatment, whereas control plants had the highest NP and chlorophyll content. Proline accumulation occurred in the infected and hormone- treated plants, but TSC content decreased in comparison to the control. Reduction of TSC content was not significant in the hormone and virus- treated plants. Expression of CMV coat protein gene (CMV-CP) was decreased by approximately 34% in SA+JA+CMV treatment in comparison to the CMV-infected plants. In conclusion, CMV had harmful effect on physiological traits of tomato plants, but hormone application induced resistance. This resistance may be accomplished through the combination of both hormone-related signaling pathways which likely established a strong resistance network together.     

The salicylic acid-dependent defence pathway is effective against different pathogens in tomato and tobacco

The role of salicylic acid (SA) was investigated in basal defence and induced resistance to powdery mildew ( Oidium neolycopersici ) and grey mould ( Botrytis cinerea ) in tomato ( Lycopersicon esculentum ) and tobacco ( Nicotiana tabacum ). A comparison of NahG transgenic tomato and tobacco (unable to accumulate SA) to their respective wild types revealed that in tomato, SA was not involved in basal defence against O. neolycopersici but NahG tobacco showed an enhanced susceptibility to O. neolycopersici infection, the effect becoming more obvious as the plants grew older. In contrast, SA played no role in the basal defence of tobacco against B. cinerea , but seemed to contribute to basal defence of tomato against B. cinerea. Activation of the SA-dependent defence pathway via benzothiadiazole (BTH) resulted in induced resistance against O. neolycopersici in tobacco but not in tomato. Microscopic analysis revealed that BTH treatment could prevent penetration of the Oidium germ tube through tobacco leaves, whereas penetration was successful on tomato leaves irrespective of BTH treatment. In contrast, soil or leaf treatment with BTH induced resistance against B. cinerea in tomato but not in tobacco. It is concluded that the SA-dependent defence pathway is effective against different pathogens in tomato and tobacco.     

Salicylic acid mediated multi-pronged strategy to combat bacterial blight disease (<Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis> pv. <Emphasis Type="Italic">punicae</Emphasis>) in pomegranate

Pomegranate bacterial blight disease caused by Xanthomonas axonopodis pv. punicae is one of the most serious threat to the pomegranate industry in India. So far, the chemicals used to control this pathogen alone are less effective. In this article, an attempt was made to supplement chemical control through improving the systemic acquired resistance of plant using nutrients such as nitrogen (N) and salicylic acid (SA) as elicitor. The study revealed that foliar application of SA at the rate of 300 ppm increased above-ground dry mass of plant by 64.97%, improved chlorophyll content of leaves and resulted higher concentration of macro-elements and micro-elements, particularly Mn and Zn, in leaves. It also significantly increased the activities of nitrate reductase (NR), superoxide dismutase (SOD), catalase and peroxidase. However, the maximum response of SA was recorded when it was sprayed after soil application of N at 100% of the recommended dose. As a consequence, this combination recorded the least bacterial blight infection with average severity of 11.58% followed by without-N application under challenge inoculation of the pathogen. However, sustainable production cannot be realized without N application. The integration of this strategy for activation of defence mechanism of plant with the bactericide streptocycline resulted in further reduction of bacterial blight disease incidence and severity under field condition to very low levels (3.84% and 18.57% respectively).     

外源硫化氢对加工番茄种子耐盐性及抗氧化酶的影响

为明确硫化氢对盐胁迫下加工番茄种子萌发的缓解作用,用Na Cl半致死浓度为85 mmol·L~(-1)的KT-63(耐盐性弱)和半致死浓度为120 mmol·L~(-1)的KT-18(耐盐性强)为材料,用各自的半致死浓度与不同浓度的NaHS(0.2,0.4,0.6,1.0 mmol·L~(-1))分别配成混合液处理种子。结果表明,随着NaHS浓度的增加,种子的发芽率、发芽势、发芽指数、活力指数、SOD、POD、CAT活性呈先上升后下降的趋势,其中与盐胁迫单独处理相比,用0.4mmol·L~(-1)NaHS处理,种子的发芽率、发芽势、发芽指数、活力指数、SOD、POD、CAT活性在KT-63中分别提升70%、250%、120%、130%、6.7%、150%和180%,在KT-18中分别提升50%、250%、60%、80%、4.3%、160%和200%,而MDA的含量显著降低,并且对KT-63的缓解效应强于KT-18。综上所述,H2S(0.4 mmol·L~(-1))有效缓解了加工番茄萌发过程中盐胁迫的抑制作用,促进了种子的萌发。     

喷施外源GA对SMV侵染的野生大豆抗病性的影响

 大豆花叶病毒(SMV)是影响大豆生产的主要病害之一,在全球范围内对大豆生产造成影响。赤霉素(GA)是重要的植物激素之一,喷施外源GA对SMV侵染的野生大豆抗病反应的影响尚不清楚。通过测定喷施外源GA后接种SMV的野生大豆植株内源水杨酸(SA)含量,抗氧化酶活性及抗病基因表达,发现与对照相比,喷施外源GA的野生大豆植株的株高、根长、叶面积、植株干重、内源水杨酸含量、过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)活性及抗病相关基因GmPR-1、GmPR-10和GmNPR1的表达显著增加。说明在病毒侵染野生大豆之前喷施GA可以促进植株的生长,诱导植株抗病反应,降低病毒危害。     

拮抗细菌诱导番茄植株抗灰霉病机理研究

 拮抗细菌多粘类芽孢杆菌(Paenibacillus polymyxa) W3菌株悬浮液及其滤液可以诱导番茄叶片对灰霉病(Botrytis cinerea)的系统抗性。W3及其滤液诱导处理后,植株叶内苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、多酚氧化酶(PPO)和超氧化物歧化酶(SOD)活性明显增强。诱导后1 d,PAL活性最大,是对照的3.8~3.9倍,6 d后仍为对照的2.5倍;POD和PPO诱导后3 d活性最高,分别比对照增加34.7%~54.1%和78.5%~78.7%,6 d后仍比对照高;SOD活性诱导后2d达高峰,6 d后稍高于对照。活性氧(O₂^-)产生速率诱导后1 d最大,比对照增加85.6%~88.6%,以后急剧下降,6 d后接近对照。此外,W3诱导后1 d或2 d,处理叶和上一叶位叶片水杨酸含量明显上升,分别是对照的2.6倍和1.6倍,这表明该拮抗细菌诱导的系统抗性可能与水杨酸介导有关。     

北方旱寒区冬油菜根系抗寒指标分析

为了研究北方旱寒区冬油菜根部生理特性与其抗寒性的相关性,对6个不同抗寒性冬油菜品种整个生育期根部的干物质积累、含水量、可溶性蛋白含量及相关保护性酶活性的变化进行了分析,并将各指标与越冬率进行了相关性分析,用与越冬率相关性显著、极显著的6个指标对冬油菜进行聚类分析。结果表明,降温前,各指标与越冬率的相关性均不显著;降温后,越冬率与可溶性蛋白含量、SOD活性极显著正相关,与POD、APX活性显著正相关,与根直径、根冠比、CAT活性正相关,与根含水量负相关;根据聚类分析结果,可将试验材料分为3类,第1类：07－G01,天油2号,天油4号,此类抗寒性弱,为耐寒性品种;第2类：上党,74－1,此类抗寒性一般,为中抗寒性品种;第3类：陇油6号,此类抗寒性强,为强抗寒性品种。由此推断,在北方旱寒区,冬油菜越冬前根直径大、根冠比高、根含水量低有利于冬油菜安全越冬;降温后,冬油菜可溶性蛋白、SOD、POD 、CAT和APX酶活性值越高,其抗寒性越强。     

36%噻虫啉水分散粒剂对番茄幼苗根系活力及生理生化指标的影响

为明确土壤中施用噻虫啉对番茄植株生长的影响,分别用36%噻虫啉水分散粒剂有效成分1.0、1.5、2.0、2.5、3.0和5.0 mg/株处理盆栽番茄植株,测定处理后30 d番茄幼苗的生长量、叶片保护酶活性及根系活力。结果表明:1.0~2.5 mg/株噻虫啉处理均可提高番茄幼苗展开叶片数、株高、主根长和鲜重等生理指标,3.0 mg/株处理与对照相比无显著差异,而5.0 mg/株处理则对番茄幼苗生长有显著的抑制作用。不同剂量的噻虫啉处理均可提高番茄幼苗叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)的活性及根系活力。PPO和SOD活性在2.0 mg/株噻虫啉处理时达到最大值,分别为47.9和14.2 U/(min·g FW),比对照高29.6%和49.5%;POD、CAT和PAL活性在2.5 mg/株剂量时达到最大值,分别为46.0、62.4和26.0 U/(min·g FW),比对照高47.0%、36.7%和35.3%。1.0~5.0 mg/株噻虫啉处理后番茄幼苗根系活力比对照提高2.7%~33.1%。研究表明,土壤施用适量的噻虫啉可显著促进番茄幼苗植株的生长。     

Salicylic acid induced alleviation of oxidative stress caused by clethodim in maize (Zea mays L.) leaves

Salicylic acid is used for regulation of oxidative stress in plants subjected to unfavorable environmental conditions. Application of herbicides for the purpose of weed killing can affect not only the weeds but also the main crop as well. Many herbicides have the ability to cause oxidative stress and further degradation of cell components. In this work, SA was used to alleviate the oxidative stress caused in response to clethodim herbicide in maize leaves. The results demonstrated that, spraying of clethodim caused yellowing of leaves and sometimes browning or drying of leaf tips with high clethodim doses. Contrary, leaves showed no injuries when treated with 1 mM SA 3 days prior clethodim application. Elevated amounts of H₂O₂ and MDA were detected in clethodim treated leaves compared with control indicating ROS formation and lipid peroxidation. Excessive ROS formation led to oxidative stress which followed by degradation of membranous structures. In SA treated leaves, the contents of H₂O₂ and MDA were more or less similar to the corresponding controls. A change in the antioxidant enzymes activities due to clethodim and SA treatment was noticed. For example, the activities of POD and APX were induced while SOD and CAT were more or less reduced in response to clethodim. SA treatment prior clethodim application could induce POD but inhibit CAT. Moreover, SOD and APX activities were adjusted to be similar to those of the control. Another mechanism of SA regulation of the oxidative stress occurred through the formation of antioxidants in the form of phenolic compounds. For that, spraying SA with or without clethodim could accumulate phenolic compounds greatly. The DPPH free radical scavenging assay for leaf extracts had confirmed a change in antioxidant status. Furthermore, SA could enhance accumulation of total proteins and free amino acids in clethodim and SA treated leaves compared with the control. This work was to provide evidence for the ability of SA to regulate clethodim herbicide detoxification through regulation of the antioxidant status of maize leaf cells.     

Attenuation of Negative Effects of Saline Stress in two Lettuce Cultivars by Salicylic Acid and Glycine Betaine

Reducing destructive effects of lettuce plants irrigated with saline water was investigated in two field experiments conducted at Ismailia Governorate in 2012–2013 and 2013–2014. Two lettuce (Lactuca sativa L.) cultivars, Great Lakes and Balady, irrigated with saline water (3.22 dS/m) were treated using two levels of salicylic acid (SA) and glycine betaine (GB) as a foliar application (200, 400 ppm and 15, 30 Mm, respectively). Generally, application of SA and GB enhanced growth parameters, i.?e. plant height; root length; number of leaves per plant; plant fresh and dry weight; leaf relative water content (LRWC); membrane permeability (MP); lipid peroxidation (MDA); chlorophyll a, b and carotenoid content in leaf; proline; total soluble sugars (TSS); superoxide dismutase (SOD) and peroxidase (POD) activity; and Na, K, Ca content. GB treatments significantly increased most recorded growth parameters, especially at 30 mM, while this treatment decreased values of MP, (MDA) and Na content in two lettuce cultivars.     

3种盐胁迫对玉米幼苗生长及叶片抗氧化酶和离子累积的影响

选取2个玉米品种(金玉819和金单999),探讨了3种盐胁迫(NaCl、Na_2SO_4和NaNO_3)对玉米幼苗生长、抗氧化酶活性以及叶片中K~+、Na~+、Ca~(2+)累积的影响。结果表明:3种不同类型的盐胁迫均会导致玉米幼苗鲜重下降,地上部鲜重金玉819下降超过28.6%,金单999下降超过18%;盐胁迫下金玉819叶片SOD酶活上升2.1倍以上, POD酶活性最高上升4.5倍,APX最高上升2.1倍,CAT最高上升2.2倍;金单999叶片SOD酶活最高上升2.1倍,APX最高上升1.6倍,CAT最高上升1.9倍。2个基因型玉米胁迫下叶片内Na~+含量上升4.5～6.3倍;NaCl和NaNO_3处理下,K~+/Na~+比对照降低90%～93%,而Na_2SO_4处理下K~+/Na~+下降78%～82%,金玉819和金单999的Ca~(2+)/Na~+比对照分别降低了85%～90%和92%～94%。综合分析表明NO~-_3引起的次生盐害对玉米生产危害较大。与金单999相比,金玉819对盐胁迫更加敏感,相同Na~+浓度处理下,金玉819的鲜重和SOD酶活性下降显著且拥有较低的K~+/Na~+和Ca~(2+)/Na~+值。     

Activation of tomato plant defence responses against bacterial wilt caused by Ralstonia solanacearum using DL-3-aminobutyric acid (BABA)

In this study, we investigated the ability of DL-3-aminobutyric acid (BABA) to protect tomato against bacterial wilt caused by Ralstonia solanacearum. This was combined with studies of accumulation of total phenolic compounds, free and total salicylic acid (SA), and activity of enzymes related to plant defence, i.e., polyphenol oxidase (PPO) and catalase (CAT). Under greenhouse conditions, tomato plants pre-treated by soil drenching with BABA profoundly reduced disease severity of bacterial wilt compared to plants receiving a soil drench with water. Thus, BABA reduced leaf wilting index by 75.3 % and vascular browning index by 69.9 %, without any in vitro inhibitory activity on the pathogen. BABA treatment significantly reduced the population of R. solanacearum in stems of tomato plants and additionally also significantly increased both fresh and dry weight of roots and shoots of tomato plants compared with the inoculated control. Application of BABA resulted in a high increase in PPO activity both in plants with and without inoculation. Compared to water-treated plants, treatment with BABA also induced a significant increase of total phenolic compounds as well as of free and total SA in leaves of both inoculated and non-inoculated tomato plants at all sampling times. CAT activity decreased in tomato plants treated with BABA in comparison with the water-treated control plants and the decrease in activity correlated with an increasing total SA accumulation. These findings suggest that BABA treatment resulted in induction of resistance to bacterial wilt in tomato.     

Up-regulation of antioxidants in tobacco by low concentrations of H₂O₂ suppresses necrotic disease symptoms

Pretreatment of tobacco leaves with low concentrations (5 to 10 mM) of H?O? suppressed hypersensitive-type necrosis associated with resistance to Tobacco mosaic virus (TMV) or Pseudomonas syringae pv. phaseolicola. The same pretreatment resulted in suppression of normosensitive necrosis associated with susceptibility to Botrytis cinerea. This type of H?O?-mediated, induced disease symptom resistance correlated with enhanced host antioxidant capacity, i.e., elevated enzymatic activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (POX) after viral and bacterial infections. Induction of genes that encode the antioxidants superoxide dismutase (SOD), CAT, and APX was also enhanced early after TMV infection. Artificial application of SOD and CAT suppressed necroses caused by viral, bacterial, or fungal pathogens similarly as H?O? pretreatment, implying that H?O?-mediated symptom resistance operates through enhancement of plant antioxidant capacity. Pathogen multiplication was not significantly affected in H?O?-pretreated plants. Salicylic acid (SA), a central component of plant defense, does not seem to function in this type of H?O?-mediated symptom resistance, indicated by unchanged levels of free and bound SA and a lack of early up-regulation of an SA glucosyltransferase gene in TMV-infected H?O?-pretreated tobacco. Taken together, H?O?-mediated, induced resistance to necrotic symptoms in tobacco seems to depend on enhanced antioxidant capacity.     

螺旋粉虱感染蜡蚧轮枝菌对其保护酶和解毒酶活性的影响

测定了螺旋粉虱3龄若虫在感染蜡蚧轮枝菌后几种保护酶和解毒酶的活性变化情况.结果表明,螺旋粉虱在感染蜡蚧轮枝菌后不同时间其体内保护酶和解毒酶的活性会产生一定程度的变化.螺旋粉虱的SOD、GST和EST比活力在感染36 h后达到最大值,显著高于同期对照组的比活力,分别为对照组的1.21、1.27倍和1.47倍;感染后36 h和48 h,CAT的比活力显著高于对照组的比活力;而感染后不同时间的POD及MFO比活力差异不显著,与对照组的比活力也无显著性差异.初步判断,螺旋粉虱感染蜡蚧轮枝菌后,其体内的防御机制与SOD、CAT、GST及EST活性有一定的相关性,与POD和MFO活性关联不大.     

Salicylic Acid Induces Resistance to Alternaria solani in Hydroponically Grown Tomato

ABSTRACT Alternaria solani is the causal agent of early blight disease in tomato and is responsible for significant economic losses sustained by tomato producers each year. Because salicylic acid (SA) is an important signal molecule that plays a critical role in plant defense against pathogen invasion, we investigated if the exogenous application of SA would activate systemic acquired resistance (SAR) against A. solani in tomato leaves. The addition of 200 muM SA to the root system significantly increased the endogenous SA content of leaves. Free SA levels increased 65-fold over basal levels to 5.85 mug g(-1) fresh weight (FW) after 48 h. This level of SA had no visible phytotoxic effects. Total SA content (free SA + SA-glucose conjugate) increased to 108 mug g(-1) FW after 48 h. Concomitant with elevated SA levels, expression of the tomato pathogenesis-related (PR)-1B gene was strongly induced within 24 h of the addition of 200 muM SA. PR-1B expression was still evident after 48 h; however, PR-1B induction was not observed in plants not receiving SA treatment. Challenge inoculation of SA-treated tomato plants using conidia of A. solani resulted in 83% fewer lesions per leaf and a 77% reduction in blighted leaf area as compared with control plants not receiving SA. Our data indicate that root feeding 200 muM SA to tomato plants can (i) significantly elevate foliar SA levels, (ii) induce PR-1B gene expression, and (iii) activate SAR that is effective against A. solani.     

Effect of salicylic acid treatment on tomato plant physiology and tolerance to potato virus X infection

Salicylic acid (SA) is an inducer of systemic acquired resistance (SAR) and could be a potential candidate in the control of plant virus diseases. In this study we assayed under controlled conditions the potential effect of three doses of exogenous SA treatment on tomato plants infected with Potato virus X (PVX) and measured their effects on: different physiological parameters (gas exchange, stable isotopes, chlorophyll content), the activation of secondary metabolism, viral accumulation and induction of the expression of pathogenesis-related proteins (PRs) such as ß-1, 3-glucanase (PR2) and chitinase (PR3). SA treatment increased the expression of PR2, the activity of phenylalanine ammonia lyase (PAL) and the concentration of antioxidant compounds at 7 days post-treatment. Earlier expression of PR3 compared to PR2 was observed. SA treatment delayed the detection of PVX by ELISA in uninoculated leaves of mechanically infected tomato plants. Although the effect of PVX infection on physiological parameters was weak, moderate SA treatments showed enhanced photosynthesis, particularly for infected plants. The results obtained confirm that SA promotes major changes in the induction of resistance in tomato plants and suggest that treatment with exogenous SA could be considered to reduce the infections caused by PVX.