Fusarium oxysporum f. sp. radicis-lycopersici can Induce Systemic Resistance in Barley Against Powdery Mildew

Drench inoculation of the undisturbed roots of barley seedlings with Fusarium oxysporum f. sp. radicis‐lycopersici (FORL) significantly reduced the primary infection frequency of Blumeria graminis f. sp. hordei (BGH) on the first leaves. The length of secondary hyphae and subsequent conidial production of BGH were also found to be significantly reduced by preinoculation with FORL. The reduction in infection frequency was observed as early as 48 h after inducer treatment, namely when plants were challenge‐inoculated immediately following inoculation with FORL. The induced resistance continued up to 16 days after treatment as indicated by the reduction in infection frequency, up to 22 days after treatment when evaluated as a reduction in the length of secondary hyphae, and up to 35 days after treatment when evaluated as a reduction in conidial production. Characteristics of FORL that may explain its success as an inducer of resistance against barley powdery mildew are discussed.     

Host-Pathogen Interactions : XX. BIOLOGICAL VARIATION IN THE PROTECTION OF SOYBEANS FROM INFECTION BY PHYTOPHTHORA MEGASPERMA F. SP. GLYCINEA

Phytophthora megasperma f.sp. glycinea, which causes soybean (Glycine max) root and stem rot, exists as several races which differ in their ability to infect a range of soybean cultivars. A glycoprotein-rich fraction (Fraction I) isolated from fungal culture fluid protects soybean seedlings from infection with compatible races. In an early study (13), seedlings were protected only by Fraction I purified from incompatible races. In 1979, seedlings were better protected by Fraction I isolated from incompatible races than by Fraction I isolated from compatible races. In 1980, seedlings were protected equally well by Fraction I from incompatible and compatible races. Materials similar in composition to Fraction I did not protect seedlings from infection. No cause could be identified for the apparent change, during the 3-year period, in the race specificity of the protection assay. Variability in the bioassay prohibited further purification or characterization of Fraction I components that protect seedlings from infection.     

Induction of Resistance or Susceptibility in Pea to Races of Pseudomonas syringae pv. pisi

The phenomena of induced resistance and induced susceptibility were investigated in the pea-Pseudomonas syringae pv. pisi system, using two pea cultivars, Early Onward and Hurst Green Shaft, and races 1 and 2 of the pathogen. Preliminary treatment with heat-killed bacteria induced resistance in peas to infection by P. s. pv. pisi; the resistance induced was dependent on the time interval between the preliminary and challenge inoculations. The mechanism of induced resistance appears to vary between the cultivars. Similarly, both races of the pathogen appear to have different resistance-inducing efficiencies. Resistance in cvs Early Onward and Hurst Green Shaft to the compatible bacterium could not be induced by preliminary inoculation with live cells of an incompatible race. Heat-killed cells of the races failed to induce the hypersensitive reaction in cultivars that normally show this response when challenged with live avirulent bacteria. Preliminary inoculation with live race 1 cells failed to induce susceptibility in cv. Early Onward to live race 2 cells, irrespective of the challenge inoculation interval. On cv. Hurst Green Shaft, however, preliminary inoculation with live race 2 cells induced limited susceptibility to live race 1 cells. Preliminary treatment with sterile distilled water followed by challenge of the same leaves 24 h later with a compatible race induced a moderate resistance response in both cultivars.     

Induction of Resistance or Susceptibility in Pea to Races of Pseudomonas syringae pv. pisi

The phenomena of induced resistance and induced susceptibility were investigated in the pea-Pseudomonas syringae pv. pisi system, using two pea cultivgars, Early Onward and Hurst Green Shaft, and races 1 and 2 of the pathogen. Preliminary treatment with heat-killed bacteria induced resistance in peas to infection by P. s. pv. pisi; the resistance induced was dependent on the time interval between the preliminary and challenge inoculations. The mechanism of induced resistance appears to vary between the cultivars. Similarly, both races of the pathogen appear to have different resistance-inducing efficiencies. Resistance in cvs Early Onward and Hurst Green Shaft to the compatible bacterium could not be induced by preliminary inoculation with live cells of an incompatible race. Heat-killed cells of the races failed to induce the hypersensitive reaction in cultivars that normally show this response when challenged with live avirulent bacteria. Preliminary inoculation with live race 1 cells failed to induce susceptibility in cv. Early Onward to live race 2 cells, irrespective of the challenge inoculation interval. On cv. Hurst Green Shaft, however, preliminary inoculation with live race 2 cells induced limited susceptibility to live race 1 cells. Preliminary treatment with sterile distilled water followed by challenge of the same leaves 24 h later with a compatible race induced a moderate resistance response in both cultivars.     

The Relationship between Systemic Resistance Induced by Pruning and Accumulation of Antifungal Substances in Barley Seedlings

Infection by a compatible race of Erysiphe graminis f. sp. hordei on barley secondary leaves was significantly suppressed upon pruning of the primary leaves when E. graminis hordei was inoculated 3–12 h after the pruning, but it, was rather enhanced during 15–21 h. The accumulation of antifungal substances was detected in hot ethanol extracts of barley seedlings from 15–27 h after pruning the primary leaves. Taking the time of the infection process of a challenger (E. graminis, hordei) into consideration, timing of systemic resistance induced upon pruning coincided with the accumulation of antifungal substances.     

Evaluation of Rice Cultivars under Greenhouse Conditions for Adult-Plant Resistance to Pyricularia oryzae

Six rice cultivars showing various types of resistance or susceptibility to Pyricularia oryzae in the field were compared under controlled environmental conditions. The resistance of the cultivars with adult-plant resistance was race-specificat early growth stage. On all cultivars tested, blast infection became increasingly reduced on either leaves of adult plants or older leaves, as observed in rice plants of different leaf stages infected with different individual races. Their increase inhost resistance was marked by an apparent transition in infection type and reduced blast severity depending on leaf age and developmental stage of plants. The ranking of disease severity of the adult-plantresistant cultivars to different races was constant during plant development, whereas that of the susceptible cultivars was differential. It is suggested that different degrees of resistance in rice cultivars may exist in seedlings and be consistently maintained during plant development, probably becoming more distinct as rice plants mature.     

虉草营养器官解剖结构与抗旱耐涝性及利用之间的关系

为了从显微结构上进一步探讨虉草(Phalaris arundinacea L.)的抗旱耐涝性及与利用的关系,于2011年采用常规石蜡切片技术,对其根、茎叶3种营养器官进行解剖观察。结果表明,虉草根的结构自外而内依次为表皮、皮层、维管束鞘、初生韧皮部和初生木质部;茎由表皮、基本组织和维管束构成;叶片内部结构可分为表皮、叶肉和叶脉3部分。根皮层大的细胞间隙和气腔,初生木质部的后生大导管和茎基本组织解体形成的髓腔都是虉草良好的通气组织,是其耐水淹的主要显微特征。茎、叶片角质化的表皮和叶表皮所含的丰富泡状细胞组是虉草具有抗旱性的主要解剖结构特征。叶肉细胞排列紧密且只有少量气孔分布于叶片下表皮,这样的结构可减少蒸腾;叶肉细胞富含叶绿体,增强光合作用,获得更多的同化产物,确保了植株在干旱条件下也有足够的光合产物来维持正常的生理活动。茎、叶维管束部分大量的木纤维起到支撑作用。虉草根的皮层和维管柱部分、茎的基本组织和维管束部分、叶的叶脉部分都含有大面积的厚壁细胞,厚壁细胞中含有丰富的粗纤维和木质素。丰富的粗纤维、木质素等成分则是虉草能成为新能源燃料植物的必备条件。     

A Histological Evaluation of Induced Resistance to Phytophthora infestans (Mont.) de Bary in Potato Leaves

Systemically induced resistance against Phytophthora infestans in the potato cultivar ‘Bintje’ was studied histologically at the light microscopy level on the leaf surface, in the epidermis and in the mesophyll of challenged potato leaves. Systemic disease resistance was induced by a local pre-infection with the same fungus. On the leaf surface of induced plants, the germination of cysts was enhanced. In the epidermis of induced plants, papilla deposition increased and penetration decreased, whereas in the mesophyll of induced plants the spread of hyphae was reduced. It is suggested that the reduction of disease severity in induced plants is the result of the combined action of several successive defence reactions.     

Dynamic reorganization of microtubules and microfilaments in flax cells during the resistance response to flax rust infection

The cytoskeleton in plant cells is a dynamic structure that can rapidly respond to extracellular stimuli. Alteration of the organization of microtubules and actin microfilaments was examined in mesophyll cells of flax, Linum usitatissimum L., during attempted infection by the flax rust fungus, Melampsora lini (Ehrenb.) Lev. Flax leaves that had been inoculated with either a compatible (yielding a susceptible reaction) or an incompatible (yielding a resistant reaction) strain of M. lini were embedded in butyl-methylmethacrylate resin; sections of this material were immunofluorescently labelled with anti-tubulin or anti-actin and examined using confocal laser scanning microscopy. In uninfected leaves, microtubules in the mesophyll cells formed a transverse array in the cell cortex. Microfilaments radiated through the cytoplasm from the nucleus. In an incompatible interaction, microtubules and microfilaments were extensively reorganized in mesophyll cells that were in contact with fungal infection hyphae or haustorial mother cells before penetration of the cell by the infection peg. After the initiation of haustorium development, microtubules disappeared from the infected cells, and growth of the haustoria ceased. In an incompatible interaction, hypersensitive cell death occurred in more than 70% of infected cells but occurred in less than 20% of cells in compatible interactions. After the infected cell had undergone hypersensitive cell death, the cytoskeleton in neighbouring cells became focused on the walls shared with the necrotic cell. In compatible interactions, reorganization of the cytoskeleton was either not observed at all or was observed much less frequently up to 48 h after inoculation.Abbreviations FITC fluorescein isothiocyanate - WGA wheatgerm agglutinin We thank Dr. G.J. Lawrence for providing valuable discussions and materials.     

Resistance of cocoa to vascular-streak dieback disease

Water-soluble exudates from young cocoa leaves markedly inhibited germination of spores of Oncobasidium theobromae in vitro, but there was no correlation between the inhibitory activity of a clone and its field resistance to vascular-streak dieback. Germinating spores penetrated young leaves and the path of penetration was marked by the browning of adjacent epidermal and mesophyll cells. At the appearance of the earliest leaf symptoms the infections in the stem were confined to the vascular traces of that leaf, but spread subsequently into the secondary xylem. Clones varied in their ability to produce tyloses in response to wounding or infection and a ranking of 10 clones on tylose frequency correlated significantly with the ranking based on field resistance, but the variability was too great for this to be useful in resistance prediction. There was no significant difference in vessel size between resistant and susceptible clones. A highly significant correlation existed between vessel and branch cross-sectional areas in six clones.     

芭蕉芋叶片结构特征及其与抗旱性的关系

运用石蜡切片法和指甲油印迹法,对3个芭蕉芋品种的叶片解剖结构——叶片厚度、叶肉厚度、上表皮厚度、下表皮厚度、气孔密度、气孔长度及宽度、长细胞长度及宽度、短细胞长度及宽度等10项相关指标进行测定,分析芭蕉芋抗旱性与叶片结构之间的关系。结果表明:(1)芭蕉芋的表皮结构与抗旱性有一定的关系,表现为抗旱性强的品种气孔密度大,且长、短细胞体积小、排列紧密。(2)芭蕉芋叶片、叶肉、上下表皮厚度与抗旱性关系在不同品种间差异不显著。(3)芭蕉芋叶肉及上、下表皮占叶片横切面的比例与抗旱性存在显著相关关系。(4)芭蕉芋叶片保水能力与叶肉比例呈极显著负相关关系,与上表皮比例呈极显著正相关关系。     

Histopathological Studies of Resistance of Sunflower (Helianthus annuus L.) to Downy Mildew (Plasmopara halstedii)

Histopathological studies of the infection of sunflower seedlings by downy mildew ( Plasmopara halstedii ) have shown that penetration of roots and the lower part of the hypocotyl occurs for both compatible combinations (suseptibility) and incompatible combinations (resistance). After penetrating susceptible genotypes, the parasite develops intercellular hyphae and intracellular haustoria, leading to systemic invasion. In contrast, in resistant plants, as soon as colonization develops, hypersensitive-like reactions occur in the parenchyma, with the appearance of necrotic zones surrounded by dividing cells. Growth of the parasite is strongly inhibited and most hyphae are blocked before they reach the cotyledonary node.     

Changes in proteins and isoenzymes in leaves of wheat when infected by stem rust

Summary Biuret assay, gel electrophoresis and immunochemistry were used to study concentrations, forms and activities of proteins of uredospores of Puccinia graminis Pers. f. sp. tritici, in healthy wheat leaves, wheat leaves that had been inoculated with incompatible races of stem rust and leaves which had become rusted.The soluble proteins of primary leaves increased by 25–117% following infection by compatible races of stem rust. There was a corresponding decrease of proteins in uninfected younger leaves. Infection by an incompatible strain of rust led to a temporary 29% increase in soluble proteins.Immunoelectrophoresis and gel electrophoresis of infected leaves showed the presence in them of the forms of malate dehydrogenase, glucose-6-phosphate dehydrogenase, catalase and -amylase characteristic of the rust fungus. In the infected leaves, the activity of certain bands of host glucose-6-phosphate dehydrogenase and catalase changed with the development of the pathogen; the malate dehydrogenase and -amylase of the host were unaffected. In leaves inoculated with an incompatible race there were no obvious changes of any of these enzymes.     

Race cultivar-specific differences in callose deposition in soybean roots following infection with Phytophthora megasperma f.sp. glycinea

Primary roots of soybean (Glycine max (L.), Merrill, cv. Harosoy 63) seedlings were inoculated with zoospores from either race 1 (incompatible, host resistant) or race 3 (compatible, host susceptible) of Phytophthora megasperma f.sp. glycinea and total callose was determined at various times after inoculation. From 4 h onward, total callose was significantly higher in roots showing the resistant rather than the susceptible response. Local callose deposition in relation to location of fungal hyphae was determined in microtome sections by its specific fluorescence with sirofluor and was quantified on paper prints with an image-analysis system. Callose deposition, which occurs adjacent to hyphae, was found soon after inoculation (2, 3 and 4 h post inoculation) only in roots displaying the resistant response, and was also higher at 5 and 6 h after inoculation in these resistant roots than in susceptible roots. Early callose deposition in the incompatible root-fungus reaction could be a factor in resistance of soybean against P. megasperma.Abbreviation pi post inoculation     

Effects of R-(1-amino-2-phenylethyl)phosphonic acid on glyceollin accumulation and expression of resistance to Phytophthora megasperma f.sp. glycinea in soybean

(R)-(1-Amino-2-phenylethyl)phosphonic acid (R-APEP), an inhibitor of phenylalanine ammonia-lyase (PAL), was applied to the tap root of 42-h-old soybean (Glycine max. (L.) Merrill cv. Harosoy 63) seedlings during inoculation with zoospores of the incompatible race 1 of Phytophthora megasperma f.sp. glycinea (Pmg1) for 2 h and during a subsequent incubation period. In contrast to L-2-aminooxy-3-phenylpropionic acid, R-APEP was not toxic to the zoospores which remained virulent in presence of the inhibitor. A 50% inhibition of PAL activity in vitro was observed with 4.2 M R-APEP and with 36 M of the S-enantiomer. When R-APEP at 330 M was applied for a total of 36 h to the seedlings, resistance against Pmg 1 was abolished. Such seedlings were indistinguishable in appearance from those seedlings which had been inoculated with the compatible race 3 of Pmg. Roots treated with R-APEP at 330 M showed a reduction of about 47% in glyceollin content when measured 12 h after inoculation, and with 1 mM a 67% reduction. In contrast, treatment with S-APEP (1 mM) caused only a 20% reduction in glyceollin content. As determined by indirect immunofluorescence of fungal hyphae in cryotome cross-sections of roots, the growth pattern of the incompatible race 1 of Pmg changed to that of the compatible race 3 under conditions where R-APEP caused loss of resistance against Pmg 1. The results support the concept of an important role of glyceollin in resistance of soybean against incompatible races of the fungus.Abbreviations R-APEP, S-APEP R.S enantiomers of (1-amino-2-phenylethyl)phosphonic acid - L-AOPP L-2-aminooxy-3-phenylpropionic acid - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - Pmg 1 Phytophthora megasperma f.sp. glycinea race 1 - Pmg 3 Phytophthora megasperma f.sp. glycinea race 3     

在条锈菌侵染早期小麦初生叶内多聚核糖体水平与蛋白质合成能力的变化

小麦初生叶接种条锈菌毒性生理小种（ＣＹ２９）及其弱毒突变菌系（ＣＹ２９－ｍｕｔ３）后,呈不亲和反应的寄主叶片可溶性蛋白质合成能力在接种后２４ｈ显著高于未接种对照,但其后逐渐降低,直至接近对照;而呈亲和性反应的寄主叶片可溶性蛋白质合成在侵染早期与对照相近,但与膜结合蛋白质在９６ｈ时大大高于对照。对接种叶中核糖体的密度梯度分析证实：呈不亲和反应寄主叶片游离多聚核糖体及亲和反应的寄主内与膜结合多聚核糖体均有特异性增加。上述结果表明寄主的抗病和感病反应均与蛋白质合成能力的变化有关。     

Induced Systemic Resistance in Tomato Plants against Phytophthora infestans

Infection of lower leaves of tomato plants with Phytophthora infestans followed by a period unfavourable to disease development increased the general resistance of the plants against the pathogen. Induced resistance to a second infection of upper leaves was expressed in the development of necrotic lesions that were sharply defined and reduced in size. Sporulation of the pathogen was suppressed. Lesions on unprotected plants expanded with a sporulating zone passing gradually to the healthy tissue under the same conditions. Induced resistance delayed and reduced penetration of the pathogen into the epidermis and subsequent colonisation of the mesophyll by formation of papillae in epidermal cells and hypersensitive-like reactions of penetrated, mesophyll cells.     

Interaction between Pseudomonas syringae pv. Pisi and Isolated Pea Mesophyll Protoplasts

The interaction between five races of Pseudomonas syringae pv. pisi (PSP) and isolated mesophyll protoplasts obtained from five pea cultivars was studied. There was no trend in the attachment of bacterial cells to surfaces of compatible and incompatible host protoplasts. The viability of protoplasts from compatible and incompatible host-pathogen interactions did not differ significantly; however, changes in the viability of cultivar Kelvedon Wonder protoplasts, compatible with all five races, was relatively more stable following inoculation with bacteria than those of cultivar Fortune, incompatible with all of the five races. Protoplast cell wall regeneration did not take place until 24–48 h after isolation. It is concluded that the use of pea protoplasts as a model system for studying the pea-PSP interaction appears to have considerable potential for the future, but more basic research is required.     

Light and Electron Microscopy Studies on the Infection of a Wild‐type and Metalaxyl‐resistant Isolate of Phytophthora sojae in Soybean Hypocotyls

Resistance of soybean cultivars, depending on single dominant genes to Phytophthora sojae, may easily be overcome by emerging new virulent races. Light microscopy (LM) and electron microscopy (EM) were used to study the infection process of the wild‐type isolate Ps411 and metalaxyl‐resistant mutant Ps411‐M of P. sojae in hypocotyls of soybean seedlings grown from untreated and metalaxyl‐treated seeds. The isolate Ps411‐M of P. sojae exhibited a high degree of resistance to metalaxyl compared to Ps411. The pathogenic fitness of Ps411‐M in hypocotyls of soybean seedlings was lower compared to Ps411. LM observations showed distinct differences in the infection process of both isolates in hypocotyls of treated soybean seedlings. EM studies revealed differences in the prepenetration stage between Ps411 and Ps411‐M on hypocotyls grown from seeds treated with 0.02% metalaxyl until the whole seed surface coated. The number of infection sites was markedly reduced and few hyphae continued to spread. Numerous ultrastructural alterations in hyphae were observed in treated hypocotyls infected with Ps411, including pronounced thickening of hyphal cell walls and encasement of haustorium‐like bodies; electron‐dense material was deposited in host cell walls in contact with hyphal cells. Neither the prepenetration process nor penetration or spread of hyphae in the hypocotyls of the resistant isolate was affected in treated compared to non‐treated tissue. While in treated hypocotyls infected with the wild‐type isolate, host defence reactions were induced, no such reactions were detected in treated hypocotyls infected with the resistant isolate. Hypocotyls from metalaxyl‐treated seeds infected with the wild‐type isolate resembled an incompatible interaction, whereas during infection with the metalaxyl‐resistant mutant, the compatible interaction was not changed.