Effects of mesophilic and thermophilic composts on suppression of Fusarium root and stem rot of greenhouse cucumber

Three composts were tested for their ability to suppress root and stem rot caused by the soil borne fungal pathogen Fusarium oxysporum f. sp. radicis-cucumerinum (FORC) on cucumber. Two of the composts were prepared from separated dairy solids either by windrow (WDS) or vermicomposting (VMC) while the third, obtained from International Bio-Recovery (IBR), was prepared from vegetable refuse using aerobic digestion. Three sets of potting mixes were prepared by mixing the composts with sawdust at varying ratios, and seeded with cucumber cv. Corona. After 14 days of growth in the greenhouse, inoculum of FORC (20 mL of 5 x 10(6) micro-conidia per mL) was applied to each pot at three different times (14, 21, and 35 days). In unamended inoculated pots, the pathogen caused stunted growth and reduced flowers. Amendment of WDS in the potting mix suppressed these symptoms, while VMC and IBR had no effect. All three composts reduced the FORC colony forming units (cfu) at the end of the experiment (10 weeks). There was a large increase of fluorescent bacteria near the vicinity of roots particularly in WDS amended potting mixes. When water extracts of the composts were plated onto acidified potato dextrose agar (APDA), only IBR contained a potent thermostable inhibitor to FORC. This inhibitor was removed by activated charcoal but was not partitioned into petroleum ether at acid, basic, or neutral pH. Inhibition of FORC by IBR was not due to electrical conductivity or trace elements in the compost. Contrasting effectiveness of the WDS and VMC made from the same waste suggests that composting method can influence the disease suppression properties of the finished compost.     

Suppression of fusarium wilts by fluorescent pseudomonads: Mechanisms and applications

Fluorescent pseudomonads are involved in the natural suppressiveness of some soils to fusarium wilts. These bacteria have been applied successfully to suppress fusarium wilts of various plant species grown in conducive soils and growing substrates. Suppression of fusarium wilts by fluorescent pseudomonads can be ascribed to direct and indirect effects against pathogenic Fusarium oxysporum. Direct effects are expressed by a reduction of the saprophytic growth of the pathogen leading to delay and reduction of root infections. This antagonism was demonstrated to be related to siderophore‐mediated iron competition. Iron competition was also shown to enhance the antagonistic effect of non‐pathogenic F. oxysporum by making the pathogen more susceptible to fungal competition for carbon. Indirect effects of fluorescent pseudomonads against pathogenic F. oxysporum are mainly related to the induction of host plant resistance which can be associated with the bacterial lipopolysaccharides. Suppression of fusarium wilts by some fluorescent pseudomonads could also be related to their ability to detoxify fungal metabolites such as fusaric acid. Association of different mechanisms of suppression increases the efficacy and consistency of the biological control under various experimental conditions. Increased knowledge of mechanisms of suppression now enables management of the environment, to some extent, to favour expression of the beneficial activities. These activities are only expressed if the bacterial density is sufficiently high.     

枯萎病不同抗性黄瓜(Cucumis sativus L.)根系分泌物氨基酸组分与抗病的相关性

以5种对枯萎病不同抗性黄瓜品种为试材,对其根系分泌物氨基酸组分进行测定,并对氨基酸组分与黄瓜品种枯萎病抗病性之间的相关性进行了分析。结果表明：在中抗品种根系分泌中检测到的16种氨基酸：半胱氨酸Cys、苏氨酸Thr、丙氨酸Ala、缬氨酸Val、异亮氨酸Lle、天冬氨酸Asp、亮氨酸Leu、苯丙氨酸Phe、甘氨酸Gly、甲硫氨酸Met、组氨酸His、谷氨酸Glu、酪氨酸Tyr、赖氨酸Lys、丝氨酸Ser和精氨酸Arg。其中的精氨酸在感病品种中没有被检出,组氨酸和精氨酸组分在抗病品种中没有被检出。根系分泌物中总氨基酸含量随品种抗性的增加而降低;精氨酸、丝氨酸和赖氨酸的含量与品种对枯萎病的病情指数呈负相关,其他13种氨基酸组分含量与品种对枯萎病的病情指数呈正相关,其中苯丙氨酸含量与病情指数呈显著正相关。丝氨酸与苯丙氨酸、天冬氨酸、丙氨酸、甘氨酸的比值均与品种对枯萎病的病情指数呈显著负相关,其中Ser／Phe与品种对枯萎病的病情指数呈极显著负相关。     

日光温室黄瓜生长发育模拟模型

实现日光温室黄瓜生长发育动态模拟预测,可为日光温室黄瓜智慧生产管理提供技术支撑.本研究依据黄瓜生长发育的光温反应特性,以‘津优35’为试验品种,利用2年4茬分期播种试验观测数据建立基于钟模型的温室黄瓜发育模拟模型.依据温室黄瓜叶片生长与关键气象因子(温度和辐射)的关系,以辐热积(TEP)为自变量构建了黄瓜叶面积指数(LAI)模拟模型;依据单位叶面积光合作用对叶面积指数和日长的二重积分,结合黄瓜不同器官的呼吸消耗,构建了黄瓜干重生产分配模拟模型,结合器官含水量,构建了黄瓜器官鲜重模拟模块.基于各子模块构建了温室黄瓜生长发育模拟模型,确定了模型品种参数并进行检验.结果表明: 日光温室黄瓜移栽期-伸蔓期、移栽期-初花期、移栽期-采收初期和移栽期-拉秧期的模拟值与观测值的均方根误差(RMSE)在3.9～10.5 d,归一化均方根标准误差(nRMSE)在6.5%～28.6%,符合度指数(D)在0.79～0.97.LAI与TEP呈S型曲线变化关系,LAI模拟值与实际观测值的RMSE为0.19,nRMSE为17.2%,D值为0.90.根、茎、叶、花和果干重模拟值与实际观测值的RMSE在0.39～8.94 g·m^-2,nRMSE在10.9%～17.7%,D值均为0.98以上.表明模型能够较准确地模拟黄瓜关键发育期、叶面积和各器官干鲜重,定量化日光温室黄瓜生长发育过程.     

不同供水吸力对温室黄瓜光合特性及根系活力的影响

采用一种负水头供水控水盆栽装置,通过设定不同供水吸力（1、3、5、7、9、11、1 3 kPa）来控制不同土壤含水量,研究土壤水分对黄瓜光合、荧光参数的变化及根系生长的 影响.结果表明：供水吸力与土壤含水量呈反比对应关系,各处理控制的土壤含水量范围为 14.3%～42.2%;随供水吸力的增强,不同生育时期黄瓜叶片净光合速率都呈抛物线变化 趋势,初花期7～11 kPa处理和采收期3～5 kPa处理叶片的净光合速率较强,采收期9～13 k Pa的高供水吸力处理叶片净光合速率较低是由气孔限制因素导致的,而1～5 kPa低供水处理 下叶片PSⅡ光量子转化成化学能的效率较高,实际光化学效率较高,光抑制发生的可能性较 低;不同生育时期叶片叶绿素含量和蒸腾速率与净光合速率呈明显的正相关关系;随供水吸 力的增强,黄瓜根系生长及活力呈抛物线变化趋势,5 kPa处理的根系活力最高,7 kPa处理 的根系干物质量最大.说明3～7 kPa的供水吸力处理更有利于温室黄瓜根系生长与叶片净 光合速率的提高.     

太阳能消毒对温室土壤环境效应及防治黄瓜根结线虫病效果

采用室内测定与大田试验相结合的方法,研究了太阳能不同消毒方式对温室土壤环境的效应及对温室黄瓜根结线虫病的控制效果.结果表明,垄沟式覆盖地膜处理对温室土壤温度、土壤酶的活性、微生物数量的影响最明显,处理16d,棚室10、20、30、40、50cm深土壤的最高温度依次是59.1、57.7、56.6、48.9、47.6℃,平均每天超过55、50、45℃持续时间分别为7.5、8.5h和16h;土壤温度的升高,有利于提高对根结线虫的杀灭效果.0～20cm土壤脲酶、蔗糖酶、碱性磷酸酶、过氧化氢酶分别降低43.3%、18.7%、20.1%和13.1%;土壤真菌、细菌、放线菌数量分别降低96.0%、84.8%、53.9%.垄沟式未覆膜处理对土壤环境的影响次之,平面式未覆膜的影响最小,酶活性降低及土壤微生物数量下降对土壤的活性有一定的负效应.垄沟式覆膜太阳能消毒对温室黄瓜根结线虫控制效果最显著,持效期最长,能有效杀灭温室0～50cm土壤内根结线虫;处理后第1年和第2年对温室黄瓜根结线虫控制效果均达到100%,第3年防效96.7%,第5年仍达72.8%.垄沟式未覆膜控制效果次之;平面式未覆膜控制效果最差,持效期最短.     

Genetic diversity and biocontrol potential of fluorescent pseudomonads producing phloroglucinols and hydrogen cyanide from Swiss soils naturally suppressive or conducive to Thielaviopsis basicola-mediated black root rot of tobacco

Pseudomonas populations producing the biocontrol compounds 2,4-diacetylphloroglucinol (Phl) and hydrogen cyanide (HCN) were found in the rhizosphere of tobacco both in Swiss soils suppressive to Thielaviopsis basicola and in their conducive counterparts. In this study, a collection of Phl+ HCN+Pseudomonas isolates from two suppressive and two conducive soils were used to assess whether suppressiveness could be linked to soil-specific properties of individual pseudomonads. The isolates were compared based on restriction analysis of the biocontrol genes phlD and hcnBC, enterobacterial repetitive intergenic consensus (ERIC)-PCR profiling and their biocontrol ability. Restriction analyses of phlD and hcnBC yielded very concordant relationships between the strains, and suggested significant population differentiation occurring at the soil level, regardless of soil suppressiveness status. This was corroborated by high strain diversity (ERIC-PCR) within each of the four soils and among isolates harboring the same phlD or hcnBC alleles. No correlation was found between the origin of the isolates and their biocontrol activity in vitro and in planta. Significant differences in T. basicola inhibition were however evidenced between the isolates when they were grouped according to their biocontrol alleles. Moreover, two main Pseudomonas lineages differing by the capacity to produce pyoluteorin were evidenced in the collection. Thus, Phl+ HCN+ pseudomonads from suppressive soils were not markedly different from those from nearby conducive soils. Therefore, as far as biocontrol pseudomonads are concerned, this work yields the hypothesis that the suppressiveness of Swiss soils may rely on the differential effects of environmental factors on the expression of key biocontrol genes in pseudomonads rather than differences in population structure of biocontrol Pseudomonas subcommunities or the biocontrol potential of individual Phl+ HCN+ pseudomonad strains.     

Development of formulations of biological agents for management of root rot of lettuce and cucumber

The effect of various carrier formulations of Bacillus subtilis and Pseudomonas putida were tested on germination, growth, and yield of lettuce and cucumber crops in the presence of Pythium aphanidermatum and Fusarium oxysporum f.sp. cucurbitacearum, respectively. Survival of B. subtilis and P. putida in various carriers under refrigeration (about 0 degree C) and at room temperature (about 22 degrees C) was also studied. In all carrier formulations, B. subtilis strain BACT-0 survived up to 45 days. After 45 days of storage at room temperature (about 22 degrees C), populations B. subtilis strain BACT-0 were significantly higher in vermiculite, kaolin, and bacterial broth carriers compared with other carriers. Populations of P. putida were significantly higher in vermiculite, peat moss, wheat bran, and bacterial broth than in other carriers when stored either under refrigeration (about 0 degree C) or at room temperature (about 22 degrees C) for 15 or 45 days. Germination of lettuce seed was not affected in vermiculite, talc, kaolin, and peat moss carriers, but germination was significantly reduced in alginate and bacterial broth carriers of B. subtilis compared to the non-treated control. Germination of cucumber seed was not affected by any of the carriers. Significantly higher fresh lettuce and root weights were observed in vermiculite and kaolin carriers of B. subtilis compared with P. aphanidermatum-inoculated control plants. Lettuce treated with vermiculite, and kaolin carriers of B. subtilis, or non-inoculated control lettuce plants had significantly lower root rot ratings than talc, peat moss, bacterial broth, and P. aphanidermatum-inoculated control plants. Growth and yield of cucumber plants were significantly higher in vermiculite-based carrier of P. putida than the other carriers and Fusarium oxysporum f.sp. cucurbitacearum-inoculated plants.     

Impact of two fluorescent pseudomonads and an arbuscular mycorrhizal fungus on tomato plant growth,root architecture and P acquisition

The ability of fluorescent pseudomonads and arbuscular mycorrhizal fungi (AMF) to promote plant growth is well documented but knowledge of the impact of pseudomonad-mycorrhiza mixed inocula on root architecture is scanty. In the present work, growth and root architecture of tomato plants (Lycopersicon esculentum Mill. cv. Guadalete), inoculated or not with Pseudomonas fluorescens 92rk and P190r and/or the AMF Glomus mosseae BEG12, were evaluated by measuring shoot and root fresh weight and by analysing morphometric parameters of the root system. The influence of the microorganisms on phosphorus (P) acquisition was assayed as total P accumulated in leaves of plants inoculated or not with the three microorganisms. The two bacterial strains and the AMF, alone or in combination, promoted plant growth. P. fluorescens 92rk and G. mosseae BEG12 when co-inoculated had a synergistic effect on root fresh weight. Moreover, co-inoculation of the three microorganisms synergistically increased plant growth compared with singly inoculated plants. Both the fluorescent pseudomonads and the myco-symbiont, depending on the inoculum combination, strongly affected root architecture. P. fluorescens 92rk increased mycorrhizal colonization, suggesting that this strain is a mycorrhization helper bacterium. Finally, the bacterial strains and the AMF, alone or in combination, improved plant mineral nutrition by increasing leaf P content. These results support the potential use of fluorescent pseudomonads and AMF as mixed inoculants for tomato and suggest that improved tomato growth could be related to the increase in P acquisition.     

The influence of mineral and carbon sources on biological control of charcoal rot fungus,Macrophomina phaseolina by fluorescent pseudomonads in tomato

AIMS: To determine the influence of various trace minerals and carbon source on the biocontrol performance of Pseudomonas aeruginosa strain IE-6S+ and P. fluorescens strain CHA0 against Macrophomina phaseolina. METHODS AND RESULTS: In dual culture plate assay, P. aeruginosa IE-6S+ and P. fluorescens CHA0 inhibited radial growth of M. phaseolina producing zones of inhibition. Czapek's dox agar medium amended with both zinc and glucose remarkably improved antifungal activities of the bacterial inoculants. Under glasshouse conditions, soil amendment with zinc and/or glucose alone did not reduce M. phaseolina infection in tomato roots but did reduce significantly when used in combination with IE-6S+ or CHA0. Soil amendments with zinc and/or glucose increased fresh shoot weights but zinc amendment greatly reduced bacterial populations in the rhizosphere. CONCLUSIONS: Mineral and carbon amendments enhance the biocontrol performance of fluorescent pseudomonads against M. phaseolina. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of mineral and carbon amendments that favour biocontrol of certain bacterial strains may provide clues to soil factors or components of nutrient solutions in hydroponic culture that will improve the level and reliability of control.     

温室CO2施肥对黄瓜幼苗根系生长及分泌物和伤流液组成的影响

为探讨温室蔬菜CO2施肥的根际效应,以黄瓜幼苗为试材,研究了CO2施肥(上午施肥/上、下午施肥;施肥浓度/对照浓度(950±50)/(350±50)μmol/molCO2)对根系生长及分泌物和伤流液组成的影响。结果表明,CO2施肥明显促进黄瓜幼苗根系发育,根系生物量显著增加;单株根系分泌物中氨基酸、糖、有机酸和酚酸总量增加,但单位鲜重根系分泌量却呈现增幅减少、无变化甚至降低趋势,说明单株分泌量增加主要由根系生长量的增加所引起。CO2施肥促进幼苗对养分的吸收,伤流液中矿质元素、ZT浓度增加,但GA、ABA和IAA浓度降低;与上午CO2施肥相比,上、下午均CO2施肥的效果更明显。CO2施肥促进了黄瓜幼苗根系发育及其代谢活性,为地上部的旺盛生长创造了条件。     

Effect of osmolarity and dehydration on alginate production by fluorescent pseudomonads

Alginate is produced as an exopolysaccharide by many fluorescent pseudomonads. However, pseudomonads often have a nonmucoid phenotype in standard laboratory media. Growth in the presence of 0.3M sodium chloride or 3–5% ethanol reportedly can lead to the generation of mucoid variants of nonmucoid strains ofPseudomonas aeruginosa. We wished to determine whether alginate production by other fluorescent pseudomonads is affected by sodium chloride and ethanol. Eight alginate-producing strains of saprophytic and phytopathogenic pseudomonads were grown as broth cultures containing 0–0.7M sodium chloride or 0–5% ethanol for 24–30 h at 28° or 35°C. Culture supernatant fluids were subjected to ethanol precipitation, and the amount of alginate present was estimated by measuring the uronic acid content. The presence of sodium chloride and ethanol caused significant stimulation of alginate production by all strains tested exceptP. viridiflava ATCC 13223 andP. fluorescens W4F1080. The optimal concentration of sodium chloride ranged from 0.2 to 0.5M; that for ethanol ranged from 1 to 3%. Moreover, inclusion of the nonmetabolizable, nonionic solute sorbitol showed a similar stimulation of alginate production. The stimulation of alginate production by high medium osmolarity and dehydration appears to be a trait shared by fluorescent pseudomonads.Reference to brand or firm name does not constitute endorsement by the U.S. Department of Agriculture overothers of a similar nature not mentioned.     

Growth promotion and inhibition by antibiotic-producing fluorescent pseudomonads on citrus roots

Summary Forty-three strains of feeder root colonizing fluorescent pseudomonads from rough lemon (Citrus jambhiri Lush.) roots were examined for effects on rough lemon and sweet orange (Citrus sinensis Osbeck) seedlings. Plants inoculated with a single bacterial soil-drench had, after 10 months, a range of stimulatory (to 116%) and inhibitory effects (to 52%). Stimulatory bacteria particularly increased growth of root systems. Cultivar-specific inhibition and stimulation was evident in inoculations of rough lemon and sweet orange seedlings. Populations of fluorescent rhizobacteria on inoculated and noninoculated, as well as on stimulated and nonstimulated seedlings, did not differ significantly (10.8×10⁶ to 30.3×10⁶ CFU/g root). Population of fluorescent rhizobacteria on seedlings were higher than populations on feeder roots from grove trees (2.8 to 5.7×10⁶ CFU/g). Ninety-four and 81% of 251 fluorescent strains produced antibiotics against the fungusGeotrichum candidum and the bacteriumErwinia stewartii, respectively. Antibiotic activities of 90% of the antibiotic producing strains were repressed by Fe³⁺, indicating siderophore production. In comparison, only 9.6 and 15% of 94 randomly selected nonfluorescentPseudomonas strains were antibiotic producers. Differences between stimulatory and inhibitory or neutral bacteria were not apparent from antibiosis tests. On the basis of physiological tests,Pseudomonas putida was the most abundant (>62%) pseudomonad species on rough lemon roots. Growth stimulating strains appeared to be in bothP. putida andP. fluorescens groups. FewP. aeruginosa strains were identified on citrus roots.Florida Agricultural Experiment Stations Journal Series No.     

Disease development of Pythium root rot in bulbous Iris and Crocus

Iris bulbs and Crocus corms were planted at two planting dates in sandy soil infested with Pythium spp. At monthly intervals during the growing season root rot infection was assessed over 3 consecutive years and disease development curves were predicted for both crops. The disease development was remarkably different for Iris and Crocus and the curve shape was determined by the crop rather than by the Pythium species. Planting date had a significant effect on disease development in both crops. No correlation was found between disease development and soil temperature.     

Beneficial effects of fluorescent pseudomonads on seed germination, growth promotion, and suppression of charcoal rot in groundnut (Arachis hypogea L.)

Rhizobacteria are used as inoculants to enhance crop yield and for biological control of fungal pathogens. Fluorescent pseudomonads isolated from the rhizosphere of groundnut showed suppression of the phytopathogen Macrophomina phaseolina that causes charcoal rot of groundnut, an economically important agroproduct. Two strains of fluorescent pseudomonads, designated as PS1 and PS2, were selected as a result of in vitro antifungal activity. After 5 days of incubation at 28+/-1 degrees , both PS1 and PS2 caused clear inhibition zones in dual cultures, restricting the growth of M. phaseolina by 71% and 74%, respectively. Both the strains were capable of producing siderophores, indole acetic acid, and hydrocyanic acid, and causing phosphate solubilization under normal growth conditions. These strains, when used as inoculants in groundnut, enhanced germination up to 15% and 30% with subsequent increase in grain yield by 66% and 77%, respectively. Conversely, when the pathogen alone was testeds 57% decrease in yield was recorded. Thus the studies revealed the potential of the two pseudomonads not only as biocontrol agents against M. phaseolina, but also as a good growth promoter for groundnut.     

Effect of tissue wounding and time of soil inoculation on pepper root rot development

Five-week-old pepper plants with wounds created on stems and roots were transplanted to soils having inoculum of Phytophthora capsici incorporated for different lengths of time. Disease severity (39.99%) on root trimmed seedlings was not significantly different (P ≤ 0.05) from the severity (36.24%) obtained on stem lacerated seedlings. The wound treatments did not result in significantly different rates of lesion extension per day; stem lacerated seedling had the fastest, 1.99 mm/day lesion extension rate, followed by 1.90 and 1.89 mm/day extension rates obtained on root trimmed and unwounded treatments, respectively. However, time of soil inoculation had significant effect on severity; root trimmed and stem lacerated treatments had 46.3% and 39.8% severities, respectively. Tissue wounding × time of soil inoculation interaction did not have significant effect on disease severity; stem lacerated seedlings transplanted to 1-day and 3-day inoculated soils gave highest severity (49.9%), followed by seedlings inoculated at the time of transplantation. Root trimmed seedlings inoculated at the time of transplantation had highest severity (61.1%), while the lowest severity was obtained on seedlings transplanted to 5-day inoculated soil.     

Relations between grapevine replant disease and root colonization of grapevine (Vitis sp.) by fluorescent pseudomonads and endomycorrhizal fungi

In pot experiments cuttings of grapevine rootstock cultivar 5C were grown on a soil from a grapevine nursery affected with replant disease (replant soil) and on a similar soil that had not been planted with grapevines before (non-replant soil). Plants were also inoculated with the vesicular-arbuscular (VA) mycorrhizal fungus,Glomus mosseae, or left without mycorrhizal fungus inoculation. Shoot and root growth, mycorrhization of roots and numbers of total aerobic bacteria and fluorescent pseudomonads on the rhizoplane of grapevines were determined at several sampling dates. On replant soil, numbers of fluorescent pseudomonads on the rhizoplane were higher compared to non-replant soil, before differences in shoot and root weight between replant and non-replant soil occurred. Without inoculation withG. mosseae, the mycorrhization of roots was much lower on replant soil (13%) than on non-replant soil (51%). On replant soil, inoculation withG. mosseae increased mycorrhization to 39% and increased shoot length, leaf area and shoot weight. The beneficial effect of VA-fungus inoculation on replant soil was not due to increased nutrient concentrations in leaves. On replant soil, the inoculation withG. mosseae reduced the number of fluorescent pseudomonads on rhizoplane of grapevine, while the numbers of total aerobic bacteria were not influenced by inoculation withG. mosseae. These results suggest a direct or indirect role of fluorescent pseudomonads in replant disease of grapevine.     

Effect of formulated root endophytic fungus Piriformospora indica and plant growth promoting rhizobacteria fluorescent pseudomonads R62 and R81 on Vigna mungo

In the present investigation, the effect of three beneficial organisms (root endophytic fungus Piriformospora indica (Pi) and pseudomonads strains R62 and R81) and their four different consortia (Pi+R62, Pi+R81, R62+R81, Pi+R62+R81) was investigated on the plant Vigna mungo through their inorganic carrier-based (talcum powder and vermiculite) formulations. All the treatments resulted in significant increase in growth parameters under glasshouse as well as field conditions and showed a consistency in their performance on moving from glasshouse to field conditions. In glasshouse conditions, a maximum increase of 4.5-fold in dry root weight and 3.9-fold in dry shoot weight compared to control was obtained with vermiculite-based consortium formulation of Pi+R81. In field studies using vermiculite as carrier, a maximum enhancement of 3.2-fold in dry root weight, 3.0-fold in dry shoot weight, 8.4-fold in number of nodules and 4.0-fold in number of pods in comparison to control was obtained with the bio-inoculant formulation containing consortium of Pi+R81. The same treatment also caused the highest improvement of 1.9-fold in nitrogen content and 1.7-fold in phosphorus content, while the highest increase of 1.4-fold in potassium content was obtained with Pi alone.     

Histopathological and biochemical aspects of grafted and non-grafted cucumber infected with stem rot caused by Fusarium spp.

Cucumber grafting has been used in Egypt recently to induce soil diseases tolerance. The impact of various grafting techniques on the vulnerability of grafted cucumber seedlings to Fusarium which stimulates the stem rot was investigated. Consequently, the anatomical and physiological studies were carried out on the diseased and healthy grafted cucumber seedlings, comparing with the non-grafted ones. Fusarium equiseti (MW216971.1) caused a severe stem rot of the grafted seedling through affecting the connection area of the different grafting methods, leading to complete seedling death. The hole insertion grafting method significantly exhibited the highest diseases incidence (100%), and mean disease severity index (5) when inoculated with F. equiseti. The pathogen remarkably affected the graft union area causing tissue discoloration and decay. The levels of antioxidant enzymes and total phenols were significantly enhanced in the diseased grafted and self-rooted cucumber. However, the diseased grafted cucumber recorded significantly the highest values of the antioxidant enzymes activities and total phenolic content when compared with the self-rooted ones. The results of SDS-PAGE profile revealed variations in the leaves protein profile of the grafted and self- rooted seedlings in response to Fusarium infection. Taken together, grafting cucumber onto a resistant rootstock using the splice technique can alleviate the stem rot severity caused by Fusarium spp. by enhancing the histological, physiological and molecular defense response of the grafted seedling.