Infection of Winter Wheat by a beta-Glucuronidase-Transformed Isolate of Cephalosporium gramineum

ABSTRACT Field-grown winter wheat was inoculated with a beta-glucuronidase-transformed isolate of Cephalosporium gramineum in two field seasons to elucidate the mode of infection in resistant and susceptible cultivars. Colonization of viable root epidermis and cortical cells occurred as soon as 15 days postinoculation and the pathogen was found in the vascular tissues by 20 days postinoculation, well before freezing soil temperatures occurred. Penetration occurred directly through the root epidermis and through wounds adjacent to emerging secondary roots. The pathogen also penetrated through root cap cells and colonized meristematic tissues near root tips to gain access to the vascular system. Lower stem base colonization was observed where the pathogen penetrated directly through the epidermis, wounds, or senescent tissues. Appressorium-like structures, which appeared to aid penetration of cell walls, were often found within cells of both roots and stems after initial colonization. The mechanisms of resistance were not apparent, but less colonization occurred in resistant than in susceptible cultivars.     

Histology of Sclerotium cepivorum infection of onion roots and the spatial relationships of pectinases in the infection process

Sclerotium cepivorum (isolate Sc4) hyphae penetrated the epidermis and hypodermis of onion roots and grew into the cortex. Immediately following penetration only the cells through which S. cepivorum grew were lysed, but subsequently cells were killed and cell walls disintegrated ahead of the infection hyphae. Sclerotium cepivorum produced two polygalacturonases (PG) and two pectinesterases (PE) in culture. These isozymes were also found in infected onion root tissues and another PG and a PE were occasionally detected. Two isozymes of PG and three isozymes of PE diffused ahead of the infection hyphae. The spatial distribution of these enzymes was associated with cell death and cell wall degradation. The epidermis, hypodermis, endodermis and vascular tissues were more resistant to hydrolysis than the cortex, but only the endodermis and cells within it retained nuclei following hydrolysis of the surrounding cortical tissues. The cavity within the root cortex became filled with swollen, vacuolate S. cepivorum hyphae.     

Ultrastructural study on interaction between a sterile,white endophytic fungus and eggplant roots

Eggplant roots colonized by a sterile, white mycelial endophyte (SWM) were previously found to become highly resistant to Verticillium wilt. SWM alone, however, caused no visible, disease symptoms, such as wilting or necrosis. The mechanism of the symptomless infection by SWM was investigated in this study. Electron microscopy revealed that hyphae of SWM were abundant on and inside the root epidermal cells 2 weeks after inoculation. Many terminal appressoria formed from apical tips of hyphae, and heavy degradation of the host cell walls was evident where hyphae accumulated. By 4 weeks following inoculation, penetration pegs easily breached epidermal cells, and the infection hyphae penetrated outer cortical cells. In response to the hyphal ingress, numerous tubule-like vesicles and membrane-bound, multivesicular bodies accumulated in cortical cytoplasm near the infection sites of the outer cortical cells, but no visible signs of the host reactions were seen in the epidermal cells. Papillae developed at the spaces between cell walls and plasma membranes at the infection sites. The penetration hyphae often grew out of the papillae, but further hyphal ingress was halted in the middle cortical cell layer. By 8 weeks following inoculation, papillae that developed in these cells contained larger amounts of highly electron-dense material and were reinforced by multilamellate, fibrous elements. Hyphae that entered such papillae were confined to them, and the hyphal cytoplasm degenerated. As the result of the activated resistance reactions, root vascular cylinders remained intact, and the host plants did not wilt.     

Histological Comparison of Fibrous Root Infection of Disease-Tolerant and Susceptible Citrus Hosts by Phytophthora nicotianae and P. palmivora

ABSTRACT Phytophthora nicotianae and P. palmivora infect and cause rot of fibrous roots of susceptible and tolerant citrus rootstocks in Florida orchards. The infection and colonization by the two Phytophthora spp. of a susceptible citrus host, sour orange (Citrus aurantium), and a tolerant host, trifoliate orange (Poncirus trifoliata), were compared using light and electron microscopy. Penetration by both Phytophthora spp. occurred within 1 h after inoculation, regardless of the host species. No differences were observed in mode of penetration of the hypodermis or the hosts' response to infection. After 24 h, P. palmivora had a significantly higher colonization of cortical cells in susceptible sour orange than in tolerant trifoliate orange. Intracellular hyphae of both Phytophthora spp. were observed in the cortex of sour orange, and cortical cells adjacent to intercellular hyphae of P. palmivora were disrupted. In contrast, the cortical cells of sour orange and trifoliate orange adjacent to P. nicotianae hyphae and the cortical cells of trifoliate orange adjacent to P. palmivora were still intact. After 48 h, the cortical cells of both hosts adjacent to either Phytophthora spp. were disrupted. After 48 and 72 h, P. palmivora hyphae colonized the cortex of sour orange more extensively than the cortex of trifoliate orange; P. palmivora also colonized both hosts more extensively than P. nicotianae. A higher rate of electrolyte leakage among host-pathogen combinations reflected the combined effects of greater cell disruption by P. palmivora than by P. nicotianae, and the higher concentration of electrolytes in healthy roots of trifoliate orange than of sour orange. Although cellular responses unique to the tolerant host were not observed, reduced hyphal colonization by both pathogens in the cortex of trifoliate orange compared with sour orange is evidence for a putative resistance factor(s) in the trifoliate orange roots that inhibits the growth of Phytophthora spp.     

Ultrastructure of the Penetration and Infection of Pansy Roots by Thielaviopsis basicola

ABSTRACT Transmission electron microscopy was used to study the penetration and infection of pansy roots by Thielaviopsis basicola. Events observed in 7- to 10-day-old roots produced on moist filter paper differed slightly from those in roots from 4-week-old plants washed free of potting media prior to inoculation. By 3 h postinoculation (PI), epidermal cells of roots produced on filter paper exhibited aggregated cytoplasm and papilla formation in response to germ tube tips. The presence of callose in papillae was demonstrated using immunogold labeling. Papilla formation was not effective in preventing host cell penetration. A slender infection hypha emerged from a germ tube tip and grew through a papilla. Its tip then expanded to form a globose infection vesicle. By 6 h PI, infection hyphae emerged from infection vesicles, and invaded host cells showed signs of necrosis. By 8 h PI, infection hyphae had grown into cortical cells in spite of papilla formation in these cells. By 24 h PI, distinctive intracellular hyphae were present in necrotic cortical cells. In washed roots, most epidermal cells failed to respond to invasion. Hyphae simply grew through these cells and contacted cortical cells that exhibited aggregated cytoplasm and papillae formation. Infection structures similar to those produced in epidermal cells from roots grown on filter paper then formed in cortical cells of washed roots. The fact that T. basicola formed infection structures only in cells that responded to invasion suggests that T. basicola has a more complex relationship with its host than would be expected in a nectrotrophic pathogen. We believe that T. basicola is best described as a necrotrophic hemibiotroph.     

Colonization of resistant and susceptible lettuce cultivars by a green fluorescent protein-tagged isolate of Verticillium dahliae

Interactions between lettuce and a green fluorescent protein (GFP)-expressing, race 1 isolate of Verticillium dahliae, were studied to determine infection and colonization of lettuce cultivars resistant and susceptible to Verticillium wilt. The roots of lettuce seedlings were inoculated with a conidial suspension of the GFP-expressing isolate. Colonization was studied with the aid of laser scanning confocal and epi-fluorescence microscopes. Few differences in the initial infection and colonization of lateral roots were observed between resistant and susceptible cultivars. Hyphal colonies formed on root tips and within the root elongation zones by 5 days, leading to the colonization of cortical tissues and penetration of vascular elements regardless of the lettuce cultivar by 2 weeks. By 8 to 10 weeks after inoculation, vascular discoloration developed within the taproot and crown regions of susceptible cultivars well in advance of V. dahliae colonization. Actual foliar wilt coincided with the colonization of the taproot and crown areas and the eruption of mycelia into surrounding cortical tissues. Advance colonization of stems, pedicels, and inflorescence, including developing capitula and mature achenes was observed. Seedborne infection was limited to the maternal tissues of the achene, including the pappus, pericarp, integument, and endosperm; but the embryo was never compromised. Resistant lettuce cultivars remained free of disease symptoms. Furthermore, V. dahliae colonization never progressed beyond infected lateral roots of resistant cultivars. Results indicated that resistance in lettuce may lie with the plant's ability to shed infected lateral roots or to inhibit the systemic progress of the fungus through vascular tissues into the taproot.     

The process of antagonism of Sclerotium cepivorum in white rot affected onion roots by Trichoderma koningii

Trichoderma koningii (strain Tr5) grew in the epidermal mucilage of onion roots without entering healthy epidermal tissue. When placed on the epidermis of Sclerotium cepivorum -infected roots, T. koningii colonized epidermal passage cells, with little colonization of other epidermal tissues, then branched and spread throughout the root cortical tissues damaged by enzymes and toxins which diffused ahead of S. cepivorum hyphae, and impeded the path of the infection. When T. koningii colonized infected tissue, many S. cepivorum hyphae became detached at septa, cell walls dissolved and many hyphal apices burst. Contact between hyphae was not necessary for lysis to occur. T. koningii produced two endochitinases ( R _f 0·15 and 0·24) and two exo-acting chitinolytic enzymes ( R _f 0·46 and 0·62) during degradation of crabshell chitin and S. cepivorum cell walls. The R f 0·24 and 0·46 proteins were detected when T. koningii colonized S. cepivorum -infected roots and are likely to be a component of the antagonism process.     

Basal stem rot of oil palm (Elaeis guineensis); mode of root infection and lower stem invasion by Ganoderma boninense

Reproducible infection of intact roots of oil palm ( Elaeis guineensis ) with Ganoderma boninense , the cause of basal stem rot, showed penetration followed by rapid longitudinal progression of hyphae and colonization of the lower stem (bole). Light and transmission electron microscopy showed invasion of the root cortex, with no evidence of selective progression through the vascular system or lacunae. In newly colonized tissue the fungus behaved as a hemibiotroph, with numerous, wide, intracellular hyphae occupying entire host cells that possessed intact cell walls and contained discernible cytoplasm and organelles. In the bole this phase coincided with a complete depletion of previously abundant starch grains in advance of invasion. Subsequently, in the roots and colonized stem base, widespread necrotrophic, enzymatic attack of all layers of the host cell walls occurred. Hyphae were intra- and intercellular and intramural and associated host cell wall degradation was often at a distance from hyphae, resulting in cavities within cell walls. A third developmental stage was the formation of an extensive, melanized, tough mycelium or pseudo-sclerotium which surrounded roots and comprised many very thick-walled cells encasing more typical thin-walled hyphae. Macroscopic observation of and isolation from the bole of randomly felled, commercial palms provided confirmatory evidence that multiple infections originated in the roots before spreading into the base of long-established palms.     

Infection of resistant and susceptible cultivars of wheat by Pyrenophora tritici-repentis

Conidial germination, appressorial formation. penetration of epidermal walls, formation of intracellular vesicles and growth of intracellular hyphae in epidermal cells occurred within 12 h of inoculation. Hyphae then grew slowly between mesophyll cells for the next 12 h. Some papillae formed beneath appressoria and most infected epidermal cells retained stain by 24 h after inoculation, indicating major changes in cellular physiology. Slight differences between cultivars in some of these events were not related to resistance.
On the second day. intercellular hyphae emerged more extensively from the infection sites into the mesophyll of the susceptible cultivar Banks, and formed significantly larger mycelia than in the resistant cultivar BH1146 by 3-5 days from inoculation. Rapid intercellular growth then continued in the susceptible cultivar but not in the resistant cultivar. Necrotic lesions expanded faster in the susceptible cultivar from day 3. By day 10. most lesions in this cultivar were large and light brown with a conspicuous chlorotic margin but those in the resistant cultivar were small and dark brown with inconspicuous chlorosis.     

Ultrastructure of the Infection of Sorghum bicolor by Colletotrichum sublineolum

ABSTRACT Ultrastructural studies of the infection of susceptible and resistant cultivars of Sorghum bicolor by Colletotrichum sublineolum were conducted. Initial penetration events were the same on both susceptible and resistant cultivars. Germ tubes originating from germinated conidia formed globose, melanized appressoria, that penetrated host epidermal cells directly. Appressoria did not produce appressorial cones, but each penetration pore was surrounded by an annular wall thickening. Inward deformation of the cuticle and localized changes in staining properties of the host cell wall around the infection peg suggests that penetration involves both mechanical force and enzymic dissolution. In compatible interactions, penetration was followed by formation of biotrophic globular infection vesicles in epidermal cells. Filamentous primary hyphae developed from the vesicles and went on to colonize many other host cells as an intracellular mycelium. Host cells initially survived penetration. The host plasma membrane invaginated around infection vesicles and primary hyphae and was appressed tightly to the fungal cell wall, with no detectable matrix layer at the interface. Necrotrophic secondary hyphae appeared after 66 h and ramified through host tissue both intercellularly and intracellularly, forming hypostromatic acervuli by 114 h. Production of secondary hyphae was accompanied by the appearance of electron-opaque material within infected cells. This was thought to represent the host phytoalexin response. In incompatible interactions, infection vesicles and primary hyphae were formed in epidermal cells by 42 h. However, they were encrusted with electron-opaque material and appeared dead. These observations are discussed in relation to the infection processes of other Colletotrichum spp. and the host phytoalexin response.     

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.     

大豆疫霉菌对大豆下胚轴侵染过程的细胞学研究

 接种后1.5~24h,用光镜和电镜研究了2个大豆品种与大豆疫霉菌Ps411的亲和性和非亲和性互作。观察结果表明,大豆疫霉菌对大豆下胚轴的侵染过程可分为侵入前、侵入、皮层组织中的扩展和进入维管束组织4个连续阶段。大豆下胚轴接种后在25℃保湿培养,1.5h后游动孢子即形成休止孢并萌发产生附着孢,3h后侵入表皮细胞,6h后进入皮层组织,24h后进入维管束组织。病原菌主要以侵染菌丝直接侵入表皮,表皮细胞间隙是主要侵入部位。皮层细胞是病原菌定殖和发展的主要场所,胞间菌丝侵入皮层细胞并形成吸器。在菌丝与寄主细胞接触部位的寄主细胞壁与质膜之间常有胞壁沉积物的形成。在抗病品种上病菌的侵染事件与感病品种基本一致,但不能形成正常的吸器,胞壁沉积物明显多于感病品种,菌丝在寄主组织内的扩展明显受到抑制。利用β-1,3-葡聚糖免疫金标记单克隆抗体进行的免疫细胞化学的研究表明,胞壁沉积物内含有大量的β-1,3-葡聚糖,在大豆疫霉菌菌丝壁中也存在β-1,3-葡聚糖。以上结果表明,病原菌的侵染可诱导抗病寄主细胞内β-1,3-葡聚糖迅速的合成与积累、并形成胞壁沉积物,以抵御病菌的侵染与扩展。     

An Efficient Inoculation Method for Colonization of Chinese Cabbage Seedlings by the Root Endophytic Fungus Heteroconium chaetospira

To develop an efficient method to inoculate Chinese cabbage seedlings with the root endophytic fungus Heteroconium chaetospira, an appropriate nursery soil and glucose concentration for the nutrient medium for fungal colonization were determined. A grid-sheet method was established for estimating the degree of colonization of entire roots by the fungus. The fungus colonized at high frequencies when peat moss was used as the rooting medium. Colonization was highest (75%) when peat moss was amended with 0.1% glucose. Under these conditions, fungal hyphae developed intracellularly in root cortical cells. In contrast, under high glucose conditions, fungal colonization was restricted mostly to intercellular regions of epidermal or cortical root tissues. Here, hyphae formed inter- or intracellular microsclerotia. Received 19 August 2002/ Accepted in revised form 5 December 2002     

Interactions between Globodera pallida juveniles, Verticillium dahliae and three potato cultivars, with descriptions of associated histopathologies

Experiments carried out in agar culture showed that the potato cultivar Pentland Javelin is relatively resistant to infection by Verticillium dahliae because it has a multilayered cortex of thick-walled cells, each producing lignituber appositions to invading hyphae. Its thick-walled xylem vessels are difficult to penetrate, its large vessel lumens difficult to obstruct, and its ability to produce tyloses limits the spread of the fungus, By comparison. Maris Anchor roots have fewer cortical layers and very small xylem vessels which are more easily blocked by hyphae. Maris Peer is intermediate in both the number of cortical cell layers and the size of xylem vessels. Globodera pallida juveniles assist V. dahliae to evade the natural defences of the root by opening an invasion channel for the fungus. In Maris Anchor and Maris Peer, but not in Pentland Javelin, the nematode provokes a widespread hypersensitive response; the resulting cell wall lignification impedes the growth of those hyphae which invade several days after the nematode. Hyphae grow well in syncytia and this enhances the probability of their penetrating xylem vessels. Although V. dahliae is generally held to induce symptoms through xylem blockage, the phloem colonization which was noted may affect the growth of both plant and nematode through its effect on assimilate movement towards root lips and into syncytia.     

Fine Structure of the Early Interaction of Lily Roots with Fusarium oxysporum f.sp. lilii

The early interaction of lily roots with the cortical rot pathogen Fusarium oxysporum f.sp. lilii was studied using roots of lily bulblets grown in Hoagland's solution, inoculated with the pathogen, and sampled up to 48h later. Conidia produced germ tubes within 6h, which extended towards and into the mucilage covering the root elongation zone, and along and into the anticlinal grooves and middle lamellae of epidermal cells. By 24–48h, infecting hyphae had reached the periclinal walls and intercellular spaces between the epidermis and the outermost cells of the cortex. Penetration of intercellularly growing hyphae directly across host cell walls was not observed; invasion of the cell lumen only occurred by gradual infringing of hyphae upon successive primary wall layers. Non-cellulosic wall appositions rich in vesicles and covered by a cellulosic protective-like layer were formed in response to approaching hyphae in resistant cv.Connecticut King, but rarely in susceptible cv. Esther which seemed more susceptible to plasmolysis and rot. Finger-like projections of the appositions into the host cell cytoplasm likely represent early stages of transfer cell formation.     

Coffee resistance to Colletotrichum kahawae is associated with lignification, accumulation of phenols and cell death at infection sites

Histological and ultrastructural studies were undertaken to compare Colletotrichum kahawae growth and the sequence of responses it induced in resistant and susceptible coffee genotypes. Coffee resistance was characterized by a restricted fungal growth associated with hypersensitive-like cell death and early accumulation of phenolic compounds, such as flavonoids (cytoplasmic contents) and hydroxycinnamic acid derivatives (cell walls). This accumulation of phenols in the cell walls preceded their lignification and thickening. In the susceptible genotype, a late accumulation of hydroxycinnamic acid derivatives in a number of cell walls and the encasement of some intracellular hyphae were also observed, but these delayed host responses did not prevent fungal growth and sporulation.     

禾顶囊壳小麦变种对小麦种子根的侵染过程

 光镜和电镜观察表明,禾顶囊壳小麦变种(Gaeumannomyces graminis var.tritici,小麦全蚀病菌)对小麦种子根的侵染过程可分为侵入前、侵入表皮层、进入皮层和进入中柱等4个连续阶段。麦根接菌后在15℃下培养,48 h后侵入表皮层细胞,60 h后进入皮层,120 h后进入中柱。病原菌主要以侵染菌丝直接侵入表皮层,表皮细胞间隙和根毛基细胞是主要侵入部位,少数由附着枝侵入。菌丝穿透细胞壁有明显的酶解作用特征,菌丝先端前方胞壁上还产生电子密物质。皮层细胞是病原菌定殖和发展的主要场所,病原菌还能离解胞间层,形成胞外空间,特别有利于菌丝和菌丝束的扩展。在侵入位点的寄主细胞壁和质膜之间,形成多种形状的木质管,其数量与侵入菌丝的数目相对应,但木质管不能阻止菌丝进入细胞。菌丝进入中柱后,可阻塞导管和筛管。小麦细胞发生退行性病变,尤以细胞壁膨大崩坏和早期质壁分离最明显,细胞间隙还产生性质不明的黄色物质。     

Ultrastructural and cytochemical investigations of pathogen development and host reactions in susceptible and partially-resistant carrot roots infected by Pythium violae, the major causal agent for cavity spot

Two carrot genotypes, cultivar Nanco and line 24, susceptible and partially- resistant respectively to cavity spot, were compared ultrastructurally and cytochemically 24 h, 48 h and 72 h after root inoculation with a virulent Pythium violae isolate. The extent of pathogen ingress and the response of the host differed markedly with the two genotypes. In cv Nanco, growth of fungal hyphae was predominantly intracellular and was accompanied by pronounced damage; by 48 h after inoculation, pericycle and the first cell layers of the phloem parenchyma were invaded, resulting in host wall dissolution and cytoplasm aggregation. The growth of P. violae in line 24 was limited to the pericycle, even up to 72 h after inoculation; fungal colonization was accompanied by retraction of cytoplasm and in the appearance of granular or fibrillar material in the host cell lumen. Some affected host cells were filled with structureless osmophilic material. In cultivar Nanco, invading fungal hyphae were unaffected; by contrast in line 24, the cytoplasm of invading hyphae, particularly those inside the cell host, was disorganised and structureless. Infection and host response in the two cultivars were studied with two specific labels: Aplysia gonad lectin (AGL), a polygalacturonic acid-binding lectin, and an exoglucanase complexed to colloidal gold were used to locate pectin and cellulosic -(1,4)-glucans respectively in infected tissues. The decrease of cytochemical labeling beyong fungal penetration showed clearly hydrolysis of pectin and cellulose in cell walls of the cv Nanco. By contrast, the cell wall of line 24 remained largely intact, although, unlabeled amorphous and electron-dense material was observed inside the wall. Fibrillar or electron dense material commonly observed in infected tissue of line 24 apparently did not contain pectic or cellulosic substances. Moreover, material observed in host cells or fungal hyphae was also free of labeling. The origin and the chemical composition of these compounds as well as their possible role in the defence mechanisms of carrot against P. violae are discussed.     

Histochemical and Cytochemical Investigations of Phenols in Roots of Banana Infected by the Burrowing Nematode Radopholus similis

ABSTRACT The burrowing nematode Radopholus similis is one of the most damaging pathogens on banana plantations. The role of phenolics in plant defense responses to the nematode was histochemically and ultrastructurally investigated in susceptible and partially resistant cultivars. Histochemical observations of healthy roots revealed that high levels of lignin, flavonoids, dopamine, cafeic esters, and ferulic acids were associated with a very low rate of nematode root penetration in the resistant cultivar. The presence of lignified and suberized layers in endodermal cells contributed to limit invasion of the vascular bundle by the pathogen. After infection, flavonoids were seen to accumulate early in walls of cells close to the nematode-migrating channel in both cultivars and in all tissues of the infected resistant roots including the vascular tissues. The labeling pattern obtained with the gold-complexed laccase and with anti-pectin monoclonal antibodies showed that phenolics were distributed in a loosened pectin-rich material surrounding the nematode. This study provides indications that constitutive phenolics in banana roots are associated with the limitation of host penetration and colonization by R. similis. Accumulation of flavonoids in response to infection was detected in the vascular tissues of susceptible plants and in all root tissues in the partially resistant plants.     

多堆柄锈菌侵染玉米的细胞学及超微结构特征

为明确玉米对多堆柄锈菌Puccinia polysora侵染后病理反应的细胞学特征,利用扫描和透射电镜技术分析了玉米自交系与多堆柄锈菌互作中二者的细胞变化过程。多堆柄锈菌对玉米的侵染主要以直接穿透叶片表皮侵入为主,少量可从气孔和细胞间隙侵入。接种后,病菌夏孢子在感病自交系叶片上快速并大量萌发,在叶表生长蔓延并侵入表皮组织细胞,7 d后形成夏孢子堆;在抗病自交系上,病菌萌发、菌丝生长均受到明显抑制,少量入侵的病菌也由于寄主细胞死亡而导致菌丝和夏孢子干瘪死亡。侵染早期在感病寄主细胞间隙出现菌丝并穿透细胞壁,在胞内产生分枝菌丝,此时寄主细胞结构正常;随着菌丝进一步扩展,叶绿体等结构发生紊乱,被侵染细胞逐渐死亡。在抗病自交系上,接菌24 h后寄主即出现过敏性坏死反应,侵入位点与周围细胞快速坏死,抑制菌丝生长蔓延;叶绿体中清晰可见深色颗粒状物质;72 h后细胞壁外侧产生大量致密的深色结晶体,应为与抗病反应相关的酚类物质。表明抗多堆柄锈菌的玉米材料可能存在2种抗病途径,即寄主与病菌互作中由分子识别引起的免疫反应和病菌侵入后的系统防卫反应。