The composition of wall alterations and appositions (reaction material) and their role in the resistance of onion bulb scale epidermis to colonization by Botrytis allii

Ultrastructural examination of deposits of reaction material (RM) showed them to be composed of paramural granules (osmiophilic to varying degrees) lying within amorphous electron–dense material. Epidermal cell walls per se became increasingly electron–dense around the short infection hyphae produced by Botrytis allii. Fluorescence microscopy, histochemical tests and microautoradiography showed the accumulation of phenolic compounds at infection sites. Use of phenylalanine and cinnamate for E.M. autoradiography demonstrated the accumulation of phenolics within paramural granules, amorphous aggregates and within the penetrated cell wall, Paramural deposits were soluble in organic solvents and probably represented reservoirs of low MW phenolics which were progressively incorporated into insoluble polymers within the cell wall. Initial synthesis or accumulation of phenolics appeared to take place in rough endoplasmic reticulum during the first 2 h after cuticle penetration. Suppression of RM deposition and wall alterations was achieved by treatment of bulb scales with cycloheximide. Tissues treated with the protein synthesis inhibitor became susceptible to colonization by B. allii. Accumulation of phenolics at infection sites rendered the onion cell walls resistant to attack by a mixture of cell wall–degrading enzymes, Methanolic extracts of epidermal strips containing RM deposits contained very weakly active inhibitors of B. allii germ–tube growth. The role of RM deposits and wall alterations in the resistance of onion epidermis to colonization by Botrytis is discussed.     

Light and Scanning Electron Microscopy Studies on the Infection of Oriental Lily Leaves By Botrytis Elliptica

Light, scanning electron and fluorescent microscopy were used to observe the infection process of Botrytis elliptica on leaves of oriental lily (cv. Star Gazer). At 20 °C and 100% relative humidity, conidia germinated on both adaxial and abaxial foliar surfaces, but germ tubes failed to invade epidermal cells on the adaxial surface. On abaxial surfaces, short (< 20 m) swollen germ tube appressoria penetrated through stomatal openings (19%), through the epidermis near guard cells (52%), or directly through epidermal cells (29%). Esterase activity was detected on germ tubes and conidia after 6 h of incubation, and deformation of the cuticle on abaxial surfaces of lily was observed surrounding infection sites. By 3 h after inoculation, almost 70% of the conidia had germinated, but no penetration was observed. At 6 h after inoculation, almost one-third of germinated conidia had penetrated epidermal cells, and water-soaked lesions were associated with 20% of the penetrations. By 9 h after inoculation, approximately 60% of the germinated conidia had penetrated plant tissues, and water-soaked lesions were associated with 60% of the infections. Fluorescent microscopy with a specific fungal stain allowed assessment of successful infection and visualization of sub-epidermal hyphae. We conclude that penetration of abaxial foliar surfaces of oriental lilies by B. elliptica occurs via short swollen germ tube appressoria mostly near stomata.     

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。     

Subcuticular-Intracellular Hemibiotrophic and Intercellular Necrotrophic Development of Colletotrichum acutatum on Almond

ABSTRACT The early infection and colonization processes of Colletotrichum acutatum on leaves and petals of two almond cultivars with different susceptibility to anthracnose (i.e., cvs. Carmel and Nonpareil) were examined using digital image analysis of light micrographs and histological techniques. Inoculated tissue surfaces were evaluated at selected times after inoculation and incubation at 20 degrees C. Depth maps and line profiles of the digital image analysis allowed rapid depth quantification of fungal colonization in numerous tissue samples. The results showed that the early development of C. acutatum on petals was different from that on leaf tissue. On petals, conidia germinated more rapidly, germ tubes were longer, and fewer appressoria developed than on leaves. On both tissues, penetration by the pathogen occurred from appressoria and host colonization was first subcuticular and then intracellular. On petals, colonizing hyphae were first observed 24 h after inoculation and incubation at 20 degrees C, whereas on leaves they were seen 48 to 72 h after inoculation. Intercellular hyphae were formed before host cells became necrotic and macroscopic lesions developed on petals >/=48 h and on leaves >/=96 h after inoculation. Histological studies complemented data obtained by digital image analysis and showed that the fungus produced infection vesicles and broad hyphae below the cuticle and in epidermal cells. In both tissues, during the first 24 to 48 h after penetration fungal colonization was biotrophic based on the presence of healthy host cells adjacent to fungal hyphae. Later, during intercellular growth, the host-pathogen interaction became necrotrophic with collapsed host cells. Quantitative differences in appressorium formation and host colonization were found between the two almond cultivars studied. Thus, on the less susceptible cv. Nonpareil fewer appressoria developed and host colonization was reduced compared with that on cv. Carmel.     

Virus-induced changes in the response of faba bean to infection by Botrytis

Prior infection of faba bean with the viruses bean yellow mosaic and bean leaf roll increased host susceptibility to subsequent infection by Botrytis fabae and B. cinerea. Cell necrosis beneath inoculum droplets, rate and extent of lesion spread and sporulation of B. fabae were all increased on detached leaves from virus-infected compared with healthy plants. Changes were most marked in young leaves showing conspicuous symptoms of systemic virus infection and in plants virus-infected for at least 2-4 weeks. Localized lesions produced by B. cinerea or a low concentration of B. fabae conidia (10³ spores/ ml) showed increased cell necrosis but were not transformed into aggressive, spreading lesions on virus-infected leaves.     

Microscopy of invasion of red clover roots by Trichocladium basicola, and effects of benomyl and prochloraz

Roots of red clover seedlings grown on plates of water agar, or water agar containing benomyl or prochloraz, were inoculated with conidia of Trichocladium basicola and examined by light and transmission electron microscopy. Penetration of host epidermal cells occurred from about 16 h after inoculation of untreated or fungicide-treated seedlings. Intracellular hyphae were constricted at septa and had a beaded appearance. They invaginated the host plasmalemma, but had no obvious deleterious effect on the cytoplasm until they had grown to fill much of the lumen, when host cells degenerated and died. As colonization of the cortex progressed, straight, unconstricted hyphae were formed and from these reproductive hyphae developed, which produced endoconidiophores and chlamydospores on the root surface. Penetration of host cell walls appeared to involve localized action of fungal enzymes. Papillae were often found at sites of penetration, but these rarely obstructed fungal development. Seedlings treated with prochloraz had fewer sites of fungal penetration, and fewer cells in the beaded hyphae than untreated seedlings or those treated with benomyl. Both fungicides caused abnormalities in fungal ultrastructure. Hyphae treated with benomyl were often found to contain lomasomes, while those treated with prochloraz had thickened, fragmented walls, and disorganized cell contents.     

Histological and ultrastructural characterization of the leaf infection events of Colletotrichum fructicola on Malus domestica ‘Gala’

Glomerella leaf spot (GLS), characterized by black necrotic spots and severe defoliation, is a destructive foliar disease of apple. Widely grown cultivars such as Gala and Golden Delicious are highly susceptible to GLS. Currently, the infection biology of the causal pathogen, Colletotrichum fructicola, on apple leaves is unclear. In the present study, the penetration and colonization processes of C. fructicola were characterized on apple (cv. Gala) leaves using light and transmission electron microscopy. C. fructicola conidia produced germ tubes 4 hours post-inoculation (hpi) and appressoria at 8 hpi. In melanized appressoria, funnel-shaped appressorial cones formed around the penetration pore. At 12 hpi, C. fructicola produced secondary conidia. After penetration, C. fructicola began to develop infection vesicles at 36 hpi. At 48 hpi, the primary hyphae of C. fructicola were produced from infection vesicles within host epidermal cells; the host epidermal cell plasma membrane remained intact, indicating a biotrophic association. Subsequently, secondary hyphae penetrated epidermal cells and destroyed cell components, initiating necrotrophic colonization. C. fructicola also produced biotrophic subcuticular infection vesicles and hyphae. Together, these results demonstrate that C. fructicola forms special infection structures and colonizes apple leaves in a hemibiotrophic manner, involving intracellular as well as subcuticular colonization strategies. Detailed characterization of the infection process of C. fructicola on apple leaves will assist in the development of disease management strategies and provide a foundation for studies of the molecular mechanism of the C. fructicola–apple leaf interaction.     

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.     

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。     

Infection of wheat spikes by <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> and alterations of cell wall components in the infected tissue

The infection process of Fusarium avenaceum on wheat spikes and the alteration of cell wall components in the infected host tissue were examined by means of electron microscopy and cytochemical labelling techniques following spray inoculation at growth stage (GS) 65 (mid-flowering). Macroconidia of the pathogen germinated with one to several germ-tubes 6–12 h after inoculation (hai) on host surfaces. The germ-tubes did not penetrate host tissues immediately, but extended and branched on the host surfaces. Hyphal growth on abaxial surfaces of the glume, lemma and palea was scanty 3–4 days after inoculation (dai) and no direct penetration of the outer surfaces of the spikelet was observed. Dense mycelial networks formed on the inner surfaces of the glume, lemma, palea and ovary 36–48 hai. Penetration of the host tissue occurred 36 hai by infection hyphae only on the adaxial surfaces of the glume, lemma, palea and upper part of ovary. The fungus penetrated the cuticle and hyphae extended subcuticularly or between the epidermal wall layers. The subcuticular growth phase was followed by penetration of the epidermal wall, and hyphae spread rapidly inter- and intracellularly in the glume, lemma, palea and ovary. During this necrotrophic colonization phase of the wheat spike, a series of alterations occurred in the host tissues, such as degeneration of cytoplasm and cell organelles, collapse of host cells and disintegration of host cell walls. Immunogold labelling techniques showed that cell walls of spike tissues contained reduced amounts of cellulose, xylan and pectin near intercellular hyphae or infection pegs compared to walls of healthy host tissues. These studies suggest that cell wall degrading enzymes produced by F. avenaceum facilitated rapid colonization of wheat spikes. The different penetration properties of abaxial and adaxial surfaces of the spikelet tissues as well as the two distinct colonization strategies of host tissues by F. avenaceum are discussed. The penetration and colonization behaviour of F. avenaceum in wheat spikelets resembled that of F. culmorum and F. graminearum, although mycotoxins produced by F. avenaceum differed from those of the latter two Fusarium species.     

Studies on Botrytis spp. occurring on onions (Allium cepa) and leeks (Allium porrum)

Botrytis byssoidea (mycelial neck rot) was more prevalent than B. allii (sclerotial neck rot) on the leaves of field onions and the bulbs of stored onions grown in some of the areas where onions or onions and leeks had previously been grown sequentially.
B. byssoidea and B. porri were also isolated from leeks. Spores of B. allii, B. byssoidea (from onions and leeks), B. porri , and B. squamosa caused infection of seedlings of salad (green) and bulb onions.
Inoculation with B. squamosa spores caused severe infection of seedling leaves, but inoculation with mycelial discs caused little damage to onion bulb tissue. By comparison, mycelial discs of the remaining species were highly pathogenic to bulbs.
The practical implications of disease transfer of certain of these species between onions and leeks are discussed.     

Light and scanning electron microscopy studies on the infection process of melon leaves by Colletotrichum lagenarium

Colletotrichum lagenarium is the casual agent of anthracnose disease of melons. Light and scanning electron microscopy were used to observe the infection process of C. lagenarium on the leaves of two melon cultivars differing in susceptibility. On both cultivars conidia began germinating 12 h after inoculation (hai), forming appressoria directly or at the tips of germ-tubes. By 48 hai appressoria had melanised and direct penetration of host tissue had begun. On the susceptible cultivar, infection vesicles formed within 72 hai and developed thick, knotted primary hyphae within epidermal cells. By 96 hai C. lagenarium produced highly branched secondary hyphae that invaded underlying mesophyll cells. After 96 hai, light brown lesions appeared on the leaves, coincident with cell necrosis and invasion by secondary hyphae. While appressoria formed more quickly on the resistant cultivar, fewer germinated to develop biotrophic primary or invasive necrotrophic secondary hyphae than on the susceptible cultivar. These results confirm that C. lagenarium is a hemibiotrophic pathogen, and that resistance in melons restricts colonisation by inhibiting the development of necrotrophic secondary hyphae.     

Microscopical studies of the infection of gerbara flowers byBotrytis cinerea

The formation of lesions on ray florets of gerbera flowers caused by single conidia ofBotrytis cinerea was studied in two cultivars infected by two isolates of the pathogen. No differences in reaction after inoculation with conidia of either isolate were seen on either cultivar. The conidia produced usually one germ tube not longer than 10 m, but conidia with five germ tubes were also seen. Direct penetration of germ tubes through the upper cuticle of ray florets was observed. No appressoria or other specialised structures were observed before penetration, and degradation of the cuticle did not occur. Germination of conidia and subsequent flower infection was dependent on the availability of free water, but not on the addition of external nutrients.Between 18 to 25°C, fungal development usually stopped after cuticle penetration, two to four cells around the site of penetration becoming necrotic. This number did not increase when inoculated flowers were subsequently placed at 4°C, conditions conductive for the formation of spreading lesions. When flowers were incubated constantly at 4°C, lesions became visible 3 days after inoculation as a group of 10 to 14 cells. Initially from a vesicle-like structure, mycelium spread subcuticularly or in the lumen of epidermal cells resulting in the death of 40 to 50 cells at 18 days after inoculation. Ungerminated conidia and conidial germlings which has not yet penetrated the cuticle did not cause any visible symptoms in underlying epidermal cells.     

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.     

Characterization of three Colletotrichum acutatum isolates from Capsicum spp.

Colletotrichum acutatum causes anthracnose on peppers (Capsicum spp.), resulting in severe yield losses in Taiwan. Fungal isolates Coll-153, Coll-365 and Coll-524 collected from diseased peppers were found to differ in pathogenicity. Pathogenicity assays on various index plants revealed that Coll-524 was highly virulent and Coll-153 was moderately virulent to three commercially available pepper cultivars. Both isolates induced anthracnose lesions and produced abundant conidia. Coll-365 was only weakly virulent on pepper fruit, where it caused small lesions and hardly produced conidia on pepper fruit. However, Coll-365 was highly pathogenic to tomato fruit and mango leaves, where it caused anthracnose lesions and formed acervuli and conidia. All three isolates showed similar abilities in the attachment and germination of conidia, formation of highly branched hyphae and appressoria, penetration of cuticles, and infection of epidermal cells on chili peppers. Coll-365 accumulated less turgor pressure in appressoria but produced higher levels of cutinase and protease activity than Coll-153 and Coll-524 did. All three isolates invaded the neighbouring cells through plasmodesmata in chili peppers and showed similar pectinase or cellulase activities in culture. However, the most virulent strain Coll-524 expressed stronger laccase activity and was more resistant to capsaicin compared to Coll-153 and Coll-365. The three isolates are different in numbers and sizes of double-stranded RNAs. Depending on the cultivar genotypes, cellular resistance of chili pepper to C. acutatum might rely on the ability to restrict penetration, colonization, or conidiation of the pathogen. We conclude that the differences in pathogenicity among the three C. acutatum isolates of pepper are attributed to their ability to colonize the host plant.     

苹果炭疽叶枯病病原Glomerella cingulata及其侵染过程

为明确苹果炭疽叶枯病病原菌围小丛壳Glomerella cingulata的侵染致病特征,在分离获得该病原菌的基础上,采用形态学观察、ITS序列分析和致病性测定对其进行了鉴定,并利用光学和扫描电子显微镜对病原菌在嘎啦苹果叶片上的侵染过程进行了研究.结果表明,在陕西咸阳地区分离获得的9株病原菌均为围小丛壳G.cingulata.25 ℃下接种9 h后,分生孢子中间产生隔膜,双胞化,并萌发产生芽管和附着胞;24 h后分生孢子的2个细胞均可萌发并形成芽管及附着胞,部分芽管顶端可产生次级分生孢子;48 h后次级分生孢子萌发形成附着胞;72 h后,附着胞下形成的侵染钉可直接入侵寄主,在表皮细胞内形成初生菌丝和次生菌丝,此时叶片表面已出现褐色斑点.接种7 d后叶片病斑处出现分生孢子盘和子囊壳.表明陕西省近年出现的苹果炭疽叶枯病病原菌为围小丛壳G.cingulata,该病菌在嘎啦叶片上的一些特殊侵染行为可能是导致该病害易在短时间内暴发的重要原因.     

Investigation of the host ranges of the leaf blotch pathogens of onion (Cladosporium allii-cepae) and leek (C. allii)

Inoculation of a range of Allium species and two non-alliaceous species with isolates of Cladosporiumallii-cepae and C. allii , obtained from onion and leek, respectively, demonstrated that the two pathogens had distinct host ranges. Conidia of C. allii-cepae, applied either dry or in aqueous suspension, infected A. altaicum, A. fistulosum (Japanese bunching onion), A. cepa (bulb onion), A. cepa var. ascalonicum (shallot), A. galanthum, A. pskemense and A. vavilovii . Dry conidia of C. allii applied at a high concentration caused atypical necrosis on A. altaicum, A. fistulosum, A. cepa var. ascalonicum, A. galanthum, A. pskemense, A. vavilovii, A. sativum (garlic), A. ampeloprasum and A. porrum (leek). Only A. ampeloprasum and A. porrum became typically infected following inoculation with conidia applied dry at low concentration or in aqueous suspension. Isolates of C. allii from leek failed to infect A. vineale, the type host. The length of conidia of a single isolate of C. allii-cepae varied significantly on different Allium spp.     

Histopathology of Infection and Colonization of Susceptible and Resistant Port-Orford-Cedar by Phytophthora lateralis

ABSTRACT Port-Orford-cedar (POC) root disease, caused by Phytophthora lateralis, continues to kill POC in landscape plantings and natural forests in western North America. POC trees resistant to P. lateralis have been identified and propagated. Cytological observations of P. lateralis in susceptible and resistant roots and stems were made with light and transmission electron microscopy to identify resistance mechanisms. No differences in infection pathway and initial colonization were observed between susceptible and resistant roots, although there were differences in the rate and extent of development. Germ tubes formed appressoria, and penetration hyphae grew either between or directly through epidermal cell walls; inter- and intracellular hyphae colonized the root cortex. In susceptible roots, hyphae penetrated into the vascular system within 48 h of inoculation. In contrast, hyphae in roots of resistant seedlings grew more slowly in cortical cells and were not observed to penetrate to the vascular tissues. In resistant roots, infection was marked by general thickening of cortical cell walls, wall appositions around penetrating hyphae, collapse of cortical cells, and accumulation of osmophillic granules around hyphae. In susceptible stems, hyphae grew inter- and intracellularly in all cells of the secondary phloem except fiber cells, but were concentrated in sieve and parenchyma cells in the functional phloem. The pattern of penetration and colonization of hyphae was similar in the resistant stems, except that hyphae were found in the fiber cells of the xylem. In resistant stems, there were fewer hyphae in the functional phloem, and cytological changes such as damaged nuclei and disintegrated cytoplasm were evident. Structural changes in resistant stems included collapsed cells, wall thickening, secretory bodies, apposition of electron dense materials, and crystals in cell walls.     

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.     

The development of different pathotype groups of Mycosphaerella pinocles in susceptible and partially resistant pea leaves

The progress of infection by high- and low-virulence isolates of Mycosphaerella pinodes was examined in susceptible and partially resistant pea leaves. Conidia germinated with one or more germ tubes which frequently branched and formed appressorium-like structures on the leaf surface. Penetration occurred through the epidermal walls. A structure similar to an infection vesicle was formed, lying partly in the epidermal wail and partly in the cell lumen. From this structure, a penetration hypha was derived which initiated the development of the intra- and intercellularly-growing fungal colony. Infections led to rapid tissue collapse in both susceptible and resistant interactions. In resistant interactions, the formation of infection vesicles and penetration hyphae was reduced, and the development and spread of lesions was retarded.