叶霉菌非亲和小种对番茄系统抗性的诱导及植株内水杨酸动态

 番茄叶霉菌小种4是番茄Cf5品系的非亲和小种,接种Cf5植株第3叶后,经不同诱导间隔期以亲和小种5接种第3叶和第4叶,15 d后检查叶霉病发病情况。试验表明,在诱导间隔期为3 d和5 d时,小种4诱导接种的第3叶和未经诱导接种的上位第4叶发病面积比不接种或接种小种5的对照显著降低,以5 d间隔期处理效果最好。上述2个叶位的发病分别比对照降低90%和85%。小种4接种第3叶后该叶位和上部未接种第4叶内水杨酸含量迅速增加,以接种后3 d含量最高,分别达4.02 μg/g鲜重和3.21μg/g鲜重,比对照分别高2倍和1.8倍。接种后5 d内始终保持较高水平。接种8 d后逐渐下降,但仍高于对照。水杨酸含量的增加早于抗性表现,因而可能在该系统的抗性诱导中起作用。     

Histological Aspects of a Hypersensitive Response in Poplar to Melampsora larici-populina

ABSTRACT The course of the infection and development of the biotrophic fungus Melampsora larici-populina on leaf tissue from the hybrid poplar Populus deltoides x P. nigra 'Ogy' was monitored at the histological level. Leaf disks were inoculated with one of two rust physiological races (E1 and E2), resulting in interactions that were either incompatible (race E1) or compatible (race E2). In the compatible interaction, the fungus rapidly colonized the leaf without inducing any apparent host response. Symptoms appeared on the leaf several days after inoculation just prior to spore dissemination. The incompatible interaction was characterized by the early collapse and disorganization of cytoplasm of infected cells 17 h after inoculation and within 2 h after the appearance of the first haustoria. Resistance to M. larici-populina was mediated through a hypersensitive response, since it was extremely localized and involved only the few cells that were in the immediate vicinity of each infected cell.     

Plant defence reactions against fusarium wilt in chickpea induced by incompatible race 0 of Fusarium oxysporum f.sp. ciceris and nonhost isolates of F. oxysporum

Germinated seeds of 'kabuli' chickpea cv. ICCV 4 were inoculated with a conidial suspension of the incompatible race 0 of Fusarium oxysporum f.sp. ciceris (Foc) or of nonhost F. oxysporum resistance 'inducers', and 3 days later were challenged by root dip with a conidial suspension of highly virulent Foc race 5. Prior inoculation with inducers delayed the onset of symptoms and/or significantly reduced the final amount of fusarium wilt caused by race 5. However, the extent of disease suppression varied with the nature of the inducing agent; the nonhost isolates of F. oxysporum were more effective at disease suppression than the incompatible Foc race 0. Inoculation with the inducers gave rise to synthesis of maackiain and medicarpin phytoalexins in inoculated seedlings; these did not accumulate in plant tissues but were released into the inoculum suspension. Inoculation with inducers also resulted in accumulation of chitinase, β-1,3-glucanase and peroxidase activities in plant roots. These defence-related responses were induced more consistently and intensely by nonhost isolates of F. oxysporum than by incompatible Foc race 0. The phytoalexins and, to a lesser extent, the antifungal hydrolases, were also induced after challenge inoculation with Foc race 5. However, in this case the defence responses were induced in both preinduced and noninduced plants infected by the pathogen. It is concluded that the suppression of fusarium wilt in this study possibly involved an inhibitory effect on the pathogen of preinduced plant defences, rather than an increase in the expression of defence mechanisms of preinduced plants following a subsequent challenge inoculation.     

Involvement of lipoxygenase,lipoxygenase pathway volatiles,and lipid peroxidation during the hypersensitive reaction of pepper leaves to Xanthomonas campestris pv. vesicatoria

Lipoxygenase activity and protein, production of lipid-derived volatiles, and lipid peroxidation levels were determined in pepper (Capsicum annuum L., cv. Early Calwonder-10R) leaves during the hypersensitive reaction induced by avirulent race 2 of Xanthomonas campestris pv. vesicatoria. Lipoxygenase activity increased during the collapse phase of the hypersensitive reaction (8 to 12 h after inoculation), and an increase in electrolyte leakage occurred. However, Western blot analysis revealed that lipoxygenase proteins decreased during the same period. When only one longitudinal half of a pepper leaf was inoculated with the avirulent bacterium race, a significant increase in lipoxygenase activity was observed in both inoculated and noninoculated leaf halves, 10 h after inoculation. In addition, lipoxygenase protein decreased in inoculated leaf halves, but remained unchanged in noninoculated ones. The evolution of some volatile compounds derived from the lipoxygenase pathway [(E,E)-2,4-hexadienal, 1-hexanol, 3-hexen-1-ol, 2,4-hexadienal and 2,4-eptadienal] and carotenoid degradation (α- and β-ionone) increased in the incompatible interaction during the collapse phase of the hypersensitive reaction. The level of the oxidative index (A₂₃₅/A₂₀₅) of leaf lipid extracts, determined to estimate lipid peroxidation, significantly increased in the advanced stage of the hypersensitive reaction. Furthermore, determination of the oxidative index in neutral lipid, glycolipid and phospholipid fractions showed that the oxidative index was significantly increased only in the glycolipid fraction. Lipoxygenase activity and protein, electrolyte leakage, volatiles and lipid peroxidation were not changed in pepper leaves inoculated with the virulent race 1 of X. campestris pv.vesicatoria during the time interval considered (2–12 h after inoculations). The hypothesis that a lipoxygenase with chloroplastic location is induced in the incompatible interaction, and which is responsible for the increase in lipid peroxidation is advanced.     

Influence of Abscisic Acid and the Abscisic Acid Biosynthesis Inhibitor, Norflurazon, on Interactions Between Phytophthora sojae and Soybean (Glycine max)

A comparison was made of the effects of abscisic acid (ABA) and the ABA biosynthesis inhibitor, norflurazon on the interaction between soybean leaves and Phytophthora sojae. Inoculation of leaves of cv. Harosoy resulted in a compatible interaction typified by the presence of spreading, water soaked lesions with ill-defined margins while inoculation of cv. Haro 1272 resulted in an incompatible interaction with lesions restricted to the inoculation site. Activity of phenylalanine ammonia lyase (PAL) slowly increased in the compatible interaction but in the incompatible interaction there was a rapid rise in activity within 8h after inoculation. When Haro 1272 plants were treated with ABA the normally incompatible interaction with race 1 was changed to what resembled a compatible interaction and activity of PAL was reduced to control levels. There was no visible effect on the compatible combination. In contrast when plants of cv. Harosoy were treated with norflurazon the normally compatible interaction with race 1 was changed to that which resembled an incompatible interaction and PAL activity increased to high levels rapidly. There was no effect of norflurazon on the incompatible interaction of cv. Haro 1272 with race 1. Stomata on leaves of cv. Harosoy treated with norflurazon closed within 2h of inoculation resembling the response of stomata in normal incompatible interactions but not compatible interactions where stomata remained open. On leaves of cv. Harosoy treated with norflurazon at sites 3 and 20mm from the inoculation point stomata also closed. These results extend and confirm the idea that ABA is a molecule that may regulate the outcome of the interaction between soybeans and P. sojae.     

Analysis of Defense-related Proteins in Stem Tissue of Carnation Inoculated with a Virulent and Avirulent Race of Fusarium oxysporum F.sp. Dianthi

The aim of this study was to learn more about the accumulation of defense-related proteins in stem tissue from carnation cultivar Pallas inoculated with 2 near-isogenic races, the avirulent race 1 and the virulent race 8 of Fusarium oxysporum f.sp. dianthi. Stem tissue was used, from which the epidermis, cortex and medulla were peeled off from the vascular cylinder. It appeared that chitinase activity was constitutively expressed in the intercellular fluids (IFs) of untreated leaves, stems and roots of carnation. The total chitinase activity in the IFs of stem tissue increased with time after inoculation. This increase was similar after inoculation with the virulent, the avirulent race and water. At least four chitinase isoenzymes, three acidic and one basic isoform, were detected in the IFs of inoculated plants. In contrast, total 1,3--glucanase activity was not detected in the IFs of untreated leaves, stems and roots. Furthermore, the increases in 1,3--glucanase activity in IFs of stem tissue were markedly higher in the compatible and incompatible interactions than in the water control, indicating that this activity is specially induced by elicitors common to both races 1 and 8 of Fusarium oxysporum f.sp. dianthi. Using an antiserum against 1,3--glucanase P3 of tomato, 2 bands were detected on immunoblots in the IFs of stem tissue inoculated with races 1 and 8. No bands were visible after inoculation with water. Total peroxidase activity increased with time in all combinations. One basic and one acidic peroxidase isoform were present in these IFs. Peroxidase activity in a cell wall fraction prepared from stem tissue was clearly higher, and its increase faster, than the activity in the soluble stem fraction. These increases were similar in the virulent, the avirulent race and the water control. The growth of the fungus Trichoderma viride was inhibited by the IFs obtained from stem tissue inoculated with the virulent and the avirulent race of Fusarium oxysporum f.sp. dianthi. However, the growth of Fusarium oxysporum f.sp. dianthi itself was not affected by these IFs.     

Ultrastructural study on scab resistance expressed in epidermal pectin layers of pear leaves

Proliferation and collapse of subcuticular hyphae of Venturia nashicola race 1 were studied ultrastructurally, after inoculation of susceptible Japanese pear cv. Kousui, resistant Japanese pear cv. Kinchaku, resistant Asian pear strain Mamenashi 12 and nonhost European pear cv. Flemish Beauty leaves, to understand the nature of the resistance mechanism. After cuticle penetration by the pathogen, the hyphae were observed at lower frequency in epidermal pectin layers and middle lamellae of leaves of the three resistant plants than in those of susceptible ones. This result suggested that fungal growth was suppressed in the incompatible interaction between pear and V. nashicola race 1. In the pectin layers of all inoculated plants, some hyphae had modifications such as breaks in the plasmalemma with plasmolysis, necrotic cytoplasm and degraded cell walls. More hyphae had collapsed in the leaves of the three resistant plants than in those of the susceptible cv. Kousui. In collapsed hyphae, the polymerized cell walls broke into numerous fibrous and amorphous pieces, showing that the scab resistance might be associated with cell wall-degrading enzymes from pear plants.     

Microtubule dynamics in compatible and incompatible interactions of soybean hypocotyl cells with Phytophthora sojae

The arrangement of microtubules in soybean ( Glycine max ) cells was examined during compatible and incompatible interactions of hypocotyls of soybean cv. Harosoy (susceptible) and cv. Haro 1272 (resistant) with race 1 of the soybean-specific pathogen Phytophthora sojae . Both reaction types were similar during the first 3 h after zoospore inoculation in terms of the number of cells penetrated, and depth penetrated into the cortex. By 3 h postinoculation, clear differences had developed between the two interaction types: incompatible interactions were characterized by a hypersensitive response that was confined to single penetrated cells; while compatibly responding cells appeared unchanged. Both types of response were characterized by autofluorescence of cell walls or cytoplasm and, at 6 h after inoculation, complete disorganization of cell cytoplasm. Reorientation and loss of microtubules was seen in the early stages of the incompatible interaction in association with cellular hypersensitivity, but not in compatible responses. In cells adjacent to those that reacted hypersensitively, there was little evidence of change in microtubule orientation. Treatment of hypocotyls with the microtubule depolymerizer oryzalin prior to inoculation did not alter the compatible response, but led to breakdown of the incompatible response. Changes in microtubule orientation and state are thus among the first structural changes that are visible within cells during incompatibility in this system.     

Accumulation of phytoalexins in susceptible and resistant near-isogenic lines of tomato infected with Verticillium albo-atrum or Fusarium oxysporum f.sp. lycopersici

The time course of accumulation of two phytoalexins, the terpenoid rishitin and the polyacetylene cis-tetradeca-6-ene-1,3-diyne-5,8-diol, was determined in near-isogenic susceptible and resistant tomato lines inoculated with either Verticillium albo-atrum or Fusarium oxysporum f.sp. lycopersici.Cultivars containing the Ve gene for verticillium wilt resistance accumulated phytoalexins at a rate similar to that in susceptible plants following stem inoculation with V. albo-atrum. Higher amounts of phytoalexins were isolated from susceptible than from resistant plants at 11 days after inoculation. Inoculum concentrations of 10⁵, 10⁶, 10⁷ and 10⁸ conidia ml⁻¹ had no differential effect on phytoalexin accumulation at 3 days after inoculation. Also, no differences were observed between fungal growth in susceptible and resistant cultivars during that period.A cultivar containing the I-1 gene for fusarium wilt resistance contained more rishitin than did susceptible plants at 2 and 3 days after inoculation with 10⁷ conidia of F. oxysporum f.sp. lycopersici ml⁻¹, but at 7 and 11 days after inoculation more rishitin had accumulated in the susceptible plants.No difference was observed between the rate of accumulation of phytoalexin in stem segments from resistant and susceptible plants inoculated by vacuum-infiltration.To estimate the concentration of phytoalexins in the xylem fluid, sap was expressed from vascular tissue and amounts of phytoalexins were determined in the sap and in the expressed tissue. Less than 5% of the phytoalexins present in stem segments was recovered from the sap, indicating that their concentration in the xylem fluid may be relatively low.The role of phytoalexins in resistance to verticillium and fusarium wilt is discussed.     

水稻与稻瘟病菌非亲和性互作中重要防御酶活性变化规律研究

 选以CO39为背景的水稻抗稻瘟病近等基因系,与稻瘟菌生理小种ZC₁₃(菌株97-151a)组成的3类典型非亲和性互作,以亲和性互作为对照,对各互作中过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)、几丁质酶及β-1,3-葡聚糖酶的活性变化规律进行了系统研究。完全非亲和性互作C101A51/97-151a、高度非亲和性互作C101L AC/97-151a及中度非亲和性互作C104 PKT/97-151a,POD比活性接种后即开始明显升高,48h前达到高峰,升高趋势一直持续到7d完全显症时,幅度基本与各互作非亲和程度呈正相关;亲和性互作CO39/97-151a接种后40 h POD比活性才开始升高,4~6 d达到高峰,峰值也较大。3类非亲和性互作PAL比活性在接种后0 h或16 h开始较明显升高,整个互作中形成3~4个较明显的峰;亲和性互作中PAL比活性一直明显下降。3类非亲和性互作外切几丁质酶比活性接种后即开始升高,基本一直保持升高趋势,在40 h前幅度较大,并形成1~3个较高的峰;亲和性互作外切几丁质酶比活性接种后即开始大幅度升高直至完全显症,48h后幅度远高于非亲和性互作。3类非亲和性互作β-1,3-葡聚糖酶比活性在24 h内开始较明显升高,在48h前形成2~3个较明显的峰;亲和性互作在接种后β-1,3-葡聚糖酶比活性即开始升高,在48h后显著高于非亲和性互作。讨论了POD、PAL、几丁质酶及β-1,3-葡聚糖酶参与水稻抗稻瘟病的可能性。     

Effects of leaf wetness duration, relative humidity, light and dark on infection and sporulation by Didymella rabiei on chickpea

No infection occurred at less than 95% relative humidity (r.h.) when chickpea plants were dried after inoculation with conidia of Didymella rabiei. Infection was significant when the dry leaves were exposed to 98% r.h. for 48 h. When inoculated plants were subjected to different leaf wetness periods, some infection occurred with 4 h wetness, and disease severity increased with wetness duration according to an exponential asymptote, with a maximum value after about 18 h. Germination of conidia and germ tube penetration increased linearly with increasing wetness periods when recorded 42 h after inoculation. With a 24-h wetness period, germination of conidia was first observed 12 h after inoculation and increased linearly with time up to 52 h (end of the experiment). Dry periods immediately after inoculation, followed by 24-h leaf wetness, reduced disease severity; as the dry period increased the severity decreased. Disease severity increased with increasing periods of darkness after inoculation. The number of pycnidia and the production of conidia on infected leaves increased only slightly with high r.h. (either in the light or in the dark), but large increases occurred over an 8-day period when the leaves were kept wet.     

Antioxidant,ethylene and membrane leakage responses to powdery mildew infection of near-isogenic barley lines with various types of resistance

Leaves of powdery mildew-susceptible barley (Hordeum vulgare cv. Ingrid) and related near-isogenic lines bearing various resistance genes (Mla12, Mlg or mlo5) were inoculated with Blumeria graminis f. sp. hordei race A6. Fungal attack induced several-fold increases in ethylene emission and electrolyte leakage in leaves of susceptible Ingrid beginning 3 days after inoculation. Activities of peroxidase, superoxide dismutase, glutathione S-transferase, ascorbate peroxidase and glutathione reductase enzymes were induced markedly in susceptible leaves 5–7 days after inoculation. Similar, but less pronounced pathogen-induced changes were detected in inoculated leaves of Mla-type resistant plants that show hypersensitive cell death upon inoculation, and, to an even lesser extent, in the Mlg and mlo lines, where no visible symptoms accompanied the incompatible interaction. Glutathione content increased only in susceptible barley 7 days after inoculation. Catalase activity, total ascorbate content and redox state were not influenced by inoculation in any of the genotypes. The activity of dehydroascorbate reductase was significantly reduced 3–5 days after inoculation in the susceptible parental plants and after 5 days in Mla and Mlg lines, while it was stable in the mlo barley. Slightly elevated levels of H₂O₂ were observed in the inoculated resistant plants. In contrast, H₂O₂ content decreased in the susceptible line 7 days after pathogen attack. These data indicate that high levels of antioxidants are involved in the compatible interaction of susceptible barley and powdery mildew by protecting the pathogen from oxidative damage.     

Saccharin-induced protection against powdery mildew in barley: effects on growth and phenylpropanoid metabolism

Treatment of barley ( Hordeum vulgare ) with 3 m m saccharin, applied as a foliar treatment to the first leaf or as a soil drench, provided significant control of powdery mildew ( Blumeria graminis f.sp. hordei ) on first and second leaves. This was unlikely to be the result of a direct effect of saccharin on the fungus, as application of the chemical to first leaves 2 h before inoculation did not affect conidial germination or formation of appressoria. Saccharin treatment had no significant effect on plant growth, except for a reduction in total leaf area in plants treated with a saccharin drench 14 days before inoculation with mildew. Phenylalanine ammonia-lyase activity was reduced significantly in second leaves 18 and 48 h after inoculation in plants treated with saccharin 14 days earlier. Peroxidase activity increased significantly in plants challenged with mildew within 6 days of saccharin application, although changes were not apparent until 48 h after pathogen challenge. On these occasions, treatment with saccharin resulted in a 33% increase in peroxidase activity compared with controls. In plants inoculated 10 or 14 days after saccharin application, cinnamyl alcohol dehydrogenase (CAD) activity increased prior to, and 18, 24 and 48 h after, inoculation of the barley plants with mildew. CAD activity increased approximately twofold compared with controls. However, in contrast to peroxidase, CAD activity was significantly higher in saccharin-treated plants prior to and after inoculation with powdery mildew, suggesting that saccharin primes CAD activity prior to pathogen challenge.     

Histopathology of compatibility and incompatibility between oilseed rape and Albugo Candida

Cotyledons of one resistant and three susceptible rape lines/cultivars were inoculated with zoospores of Albugo Candida race 7. Samples of whole cotyledons were examined by differential interference contrast microscopy. The time course of the infection process was followed histologically. Germination of zoospore cysts occurred 2-3 h after inoculation. Infection was initiated with germ-tubes penetrating through stomata. Haustorium formation was first observed in the palisade mesophyll cells adjacent to the substomatal chambers 8 h after inoculation.
Only after the establishment of the first haustorium did compatible and incompatible interactions begin to differentiate. In the resistant cultivar, most primary hyphae produced single haustoria. Necrosis of the invaded host cell was first observed 12 h after inoculation followed by cessation of fungal growth. The death of host cells was largely restricted to the penetration site; the adjacent non-penetrated cells remained apparently unaffected. In the susceptible hosts, necrosis of infected cells occurred only infrequently, and hyphal growth continued unabated, resulting in mycelial ramification into the mesophyll. Numerous haustoria were produced.
Histological studies showed that the earliest event distinguishing a compatible from an incompatible interaction occurred after formation of the first haustorium and that resistance was not manifested until the host mesophyll cell had come into contact with the first haustorium. The distinction between compatibility and incompatibility was substantiated by quantitative analysis of white rust development on both resistant and susceptible lines/cultivars.     

谷胱苷肽及其类似物诱导大豆活性氧和植保素的积累

 谷胱苷肽(Glutathione, GSH)是一种重要的抗氧化剂, 但它能诱导一些豆科等植物的防卫反应。本文采用大豆悬浮细胞体系分析了GSH及其衍生物诱导大豆活性氧和大豆植保素大豆素(glyceollin)的积累。GSH诱导大豆素和黄苷元的积累, 并有一定的剂量关系。N-乙酰半胱氨酸、巯基乙醇、二硫苏糖醇没有激发子活性, 但氧化型谷胱苷肽能激发大豆的防卫反应。在巯基被修饰的化合物中, S-对叠氮苯甲基谷胱苷肽和S-对氯苯甲基谷胱苷肽能够诱导大豆素和H₂O₂的产生, S-己基谷胱苷肽也能诱导一定量的H₂O₂积累。水杨酸和蛋白酶抑制剂DFP能增强芫菁素或者酵母细胞壁激发子诱导的大豆素积累, 但对GSH没有相似的增强效果。这些结果表明GSH中的巯基并不是激发所必需的, 大疏水基团能弥补巯基的作用。另外, GSH诱导大豆素积累信号传导途径可能与芫菁素的不同。     

Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on leaves of oilseed rape

Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae . Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20°C, but not at 24°C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12–20°C, 10 h at 8°C, 16 h at 6°C or 24 h at 4°C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16°C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16°C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20°C and to 26 days as temperature decreased to 4°C. At 8°C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6°C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12–16°C, and decreased as temperature decreased to 8°C or increased to 20°C. At temperatures from 8 to 20°C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by 'lesions' (both log₁₀-transformed) at different temperatures.     

In vitro Effect of the Phytoalexin Glyceollin I on Polygalacturonase and Oxalic Acid Production ofSclerotinia sclerotiorum

The polygalacturonase (PG) activity in culture filtrates fromSclerotinia sclerotiorum is reduced when glyceollin I, the major soybean phytoalexin, is present in the culture medium. When the enzyme activities in the culture filtrates are expressed per unit of fungal growth, PG activity decreases with increasing concentration of glyceollin I in the culture medium. The phytoalexin does not influence the isoenzyme pattern. This suggests that glyceollin I may inhibit quantitative but not qualitative enzyme production. Only the highest glyceollin I concentration tested inhibits oxalic acid production. The inhibitory effect on mycelial growth is confirmed. The data suggest a further hypothesis about the role of phytoalexin during pathogenesis.     

白叶枯病菌与非亲和水稻IRBB4悬浮细胞互作中蛋白类激发子的纯化和鉴定

 本研究对水稻白叶枯病菌与水稻悬浮细胞非亲和互作中蛋白类激发子进行了分离纯化和鉴定.白叶枯病菌JXOV与水稻IRBB4和IR24悬浮细胞互作36 h后的上清液,经Q-Sepharose阴离子交换层析柱分离,对分离的各组分进行抗病性诱导测定,结果表明JXOV与IRBB4非亲和互作的上清液中存在蛋白类激发子.有活性的蛋白组分经阴离子交换层析柱Mono-Q进一步纯化后,SDS-PAGE分析鉴定出2个具激发活性的蛋白,其分子量分别为17.2 kD和49.2 kD,等电点分别为5.8和6.2.利用上述激发子处理水稻能减少病斑长度并诱导水稻防卫酶活性的增加.     

A light and scanning-electron microscopic study of infection of tomato plants by virulent and avirulent races of Cladosporium fulvum

Infection of tomato plants byCladosporium fulvum Cooke was studied using light and scanning-electron microscopy. Races 1.2.3 and 4 ofCladosporium fulvum were used, whereas tomato cultivars, carrying the Cf2 gene (susceptible to race 1.2.3 and immune to race 4) and the Cf4 gene (immune to race 1.2.3 and susceptible to race 4) served as differentials. No differences were observed in growth between compatible and incompatible combinations during germination, subsequent formation of runner hyphae and stomatal penetration. Runner hyphae did not show directional growth towards stomata. Penetration usually occurred on the third or fourth day after inoculation. In compatible combinations the fungus grew intercellularly, often in close contact with spongy mesophyll cells. Under optimal conditions it did not cause visible damage to plant cells during early stages of infection. Under suboptimal conditions in winter, the host cells often reacted with callose deposition, but growth of the fungus did not appear to be inhibited. Ten to twelve days after inoculation conidiophores emerged through the stomata and produced conidia. In incompatible combinations fungal growth was arrested one to two days after penetration and confined to stomata and surrounding cells. Very soon the host cells, in contact with the fungus, deposited extensive amounts of callose. Later these cells turned brown and collapsed. At the surface of the host cells, contacted by fungal hyphae, abundant extracellular material could be observed by scanning-electron microscopy. Removing the epidermis of leaves before inoculation delayed the resistant response. On stripped leaves the rate of fungal growth was equal for both interactions up to ten days after inoculation, but the incompatible combination lacked sporulation.