Investigations on Adult Plant Resistance of Barley Against Erysiphe graminis f.sp. hordei

Spring barley cultivars and lines were tested for 3 years in field studies for adult plant resistance against Erysiphe graminis f.sp. hordei. The cultivars Osiris and Asse were selected for further detailed cytological studies and compared with the susceptible cultivar Peruvian. Under controlled greenhouse conditions, the percentage of conidia that had formed a functional haustorium and secondary hyphae (infection efficiency) was reduced in fifth leaves of the adult plant resistant cultivars. On fifth and flag leaves of adult plant resistant cultivars, papillae were formed more frequently under primary germ tubes and appressoria, and fungal penetration was prevented more often than on the susceptible cultivar Peruvian. In ultrastructural studies various types of papillae were observed, but could not be strictly correlated with penetration success or failure of the fungus.     

Histochemical Studies of the Non‐Host Resistance and the Role of Actin Cytoskeleton in Pepper Against Colletotrichum orbiculare

The penetration process and defence reactions (hypersensitive response, oxidative burst and cell wall fortification) of Colletotrichum orbiculare were studied histochemically on pepper cultivar ‘A11’ (non‐host) and susceptible cucumber cultivar ‘Changchun Thorn’ (host). The results indicate that C. orbiculare could hardly penetrate the non‐host pepper leaves. It was papillae rather than hypersensitive response and H₂O₂ that played an important role in resisting the colonization and development of C. orbiculare on the non‐host pepper. The depolymerization of the actin microfilament weakened the papilla deposition of pepper and allowed successful penetration of the non‐adapted C. orbiculare, suggesting that the actin cytoskeleton of pepper is significant in preventing the invasion of the non‐host pathogen C. orbiculare.     

Mycoparasitic relationships

The mode of attack and the infection structures of the necrotrophic mycoparasite, Pythium acanthicum, as well as the responses of various fungal hosts to parasitism were studied using both electron and light microscopy. Many taxonomically distinct fungal hosts were used, though Phycomyces blakesleeanus, Pythium aphanidermatum, Rhizoctonia solani and a basidiomycete identified as Corticium sensu lato were studied in greatest detail. Parasitism was by direct penetration of the fungal host without appressorium formation by the parasite. The host's cells responded to contact by P. acanthicum by forming papillae. The morphological features of the papillae varied with the particular host. In P. blakesleeanus they were comprised of vesicles and segments of cytoplasm entrapped in a fibrillo-granular matrix, while in R. solani and the Corticium basidiomycete they contained considerable amounts of electron-opaque and electron-translucent material. Evidence for both mechanical and enzymatic penetration of the host fungi by the parasite are presented. Details of host wall and septum penetration by the parasite are presented using time-lapse light microscopy with in vivo systems. Many of these stages of parasitism were examined ultrastructurally. Some comparisons of these mycoparasitic relationships are discussed in relation to what is known from the literature about phytoparasitic interactions.     

Localization of adenylate cyclase activity in Populus: its relation to pollen-pistil recognition and incompatibility

Summary Adenylate cyclase has been localized cytochemically in female and male parents as well as during the pollen-stigma interaction with an original technique employing strontium as the capture ion and adenyl imidodiphosphate as the specific substrate. The specificity of the reaction was checked by using several controls. No final specific reaction product was detected in unpollinated P. deltoides stigmas or in the P. deltoides or P. alba pollen grains used for compatible and incompatible pollinations. In the compatible cross between P. deltoides × P. deltoides, fine dense precipitates were observed in the dictyosomes and the plasma membrane and exterior to the exine of hydrated pollen grains adhering to the stigma surface. Labeling of the stigmatic pellicle was also observed after pollen adhesion and hydration. This was accompanied by a strong reactivity of the cell wall and plasmalemma of the stigma papillae at the sites of pollen tube germination on the stigma surface and at the sites of penetration of pollen tubes between adjacent papillae. In the incompatible cross between P. deltoides x P. alba, adenylate cyclase activity was still present but reduced at the stigma surface following adhesion, hydration, and germination of P. alba pollen. This activity was completely abolished after the penetration of pollen tubes between stigma papillae. These findings suggest that in Populus, adenylate cyclase activity is correlated to pollen adhesion, hydration, and germination at the stigma surface, and that the abolition of this enzyme activity could be one of the cellular events governing the gametophytic phenotype of incompatibility in the cross between P. deltoides and P. alba.     

Cytological studies on rust fungi. (vi) fine structures of infection process of Kuehneola japonica (diet.) dietel

The behavior of rust fungi in their host plants has been elucidated by electron microscopy. However, most of the ultrastructural studies on rust fungi have focused on the uredial stage. In order to elucidate the features of the sporidial stage, we studied the fine structure of Kuehneola japonica, a short-cycle rust, in rose leaves. Infection pegs arising from appressoria penetrated the host walls. Papillae formed at the time of penetration against the outer epidermal cell walls. The papillae which had formed at the penetration sites grew extensively and partially surrounded the intracellular hyphae which were connected with the infection pegs. The intracellular hyphae in the epidermal cells developed further and entered adjacent parenchyma cells. Walls of parenchyma cells either invaginated or thin papillae formed at penetration sites and the invaginated walls or papillae surrounded the necks of the intracellular hyphae. Intracellular hyphae in both epidermal and parenchyma cells were not enveloped by the sheath before 20 days after inoculation. In specimens prepared 20 days after inoculation, some of the intracellular hyphae were enveloped by a sheath in both palisade and spongy parenchyma cells. The sheathed hyphae resembled haustoria of other rust fungi which had been described previously. Teliospore initials were formed in mycelial masses in intercellular spaces between the epidermal cells and palisade parenchyma cells 20 days after inoculation. Uninucleate teliospores developed from teliospore initials 30 days after inoculation.Contribution No. 32.     

Tetrameres (Gynaecophila) aspicula n. sp. (Nematoda: Tetrameridae), a proventricular parasite of the white-faced ibis Plegadis chihi in Argentina

Tetrameres (Gynaecophila) aspicula n. sp. is described from the proventriculus of the white-faced ibis Plegadis chihi (Vieillot) (Ciconiiformes, Threskiornithidae) from Argentina. The new species is characterised by the absence of spicules, by possessing two ventral rows of extremely small spines in males, extending along the second half of body length, and by the tiny, very feebly developed postcloacal papillae. T. (G.) aspicula n. sp. is compared to the remainder of the species in the subgenus as well as to other species of Tetrameres which lack or possess feebly developed spines. The absence of spicules is a character shared with two other species in the genus, T. (G.) gynaecophila and T. (G.) deccani,from which the new species differs in body size, the arrangement of caudal papillae and the somatic spination in males. A pair of somatic papillae, previously unreported in species of this genus, was found just on or ventral to the lateral line at various regions of the body length. The homology of these structures to other paired somatic papillae described in nematodes is discussed.     

Hyperparasitischer Angriff von Epicoccum purpurascens auf den biotrophen Kontakt-Mykoparasiten Gonatobotrys simplex

Hyperparasitic attack of Epicoccum purpurascens on the biotrophic contact mycoparasite Gonatobotrys simplex The in vivo- and in vitro-hyperparazitation of Gonatobotrys simplex (Gs) by Epicoccum purpurascens (Ep) is presented. Ep, showing positive tropism, grows toward the host fungus Gs. After contact Ep penetrates especially the Gs-conidia, more rarely germ tubes and the mycelium. Two types of penetration can be distinguished: 1) direct penetration and 2) penetration after previous formation of appressoria. On this attack Gs reacts with local cell wall appositions (papillae), which mostly can be pierced by the hyperparasite. At the advanced state of parasitism the host fungus finally dies.     

Cuticular structures of the priapulid Halicryptus spinulosus: A scanning electron microscopical study

Summary The surface anatomy and the structures lining the pharynx of Halicryptus spinulosus were examined by scanning electron microscopy (SEM). The structures were compared and contrasted with those reported for other priapulids, particularly those features previously studied with SEM. Buccal papillae and pharyngeal teeth of two types were described. Surface structures observed with SEM were: scalids, abdominal setae, anal papillae, posterior warts and ring papillae. The latter three structures are unique among described priapulids. The anal papillae are composed of several rounded, perhaps pedunculate, structures; the posterior warts are composed of mitriform structures in close association with columnar structures. Both are located in separate depressions in the posterior integument. The ring papillae occur on the annuli close to the posterior end. Halicryptus spinulosus was previously thought to lack these structures.     

Dynamic reorganization of microfilaments and microtubules is necessary for the expression of non-host resistance in barley coleoptile cells

To show the involvement of microfilaments and microtubules in non-host resistance of barley, partially dissected coleoptiles which had been inoculated with a non-pathogen, Erysiphe pisi, were treated with several actin and tubulin inhibitors. If the coleoptiles were not treated with any of the inhibitors, the non-pathogen always failed to penetrate the coleoptile cells. However, when coleoptiles were treated with actin or tubulin polymerization or depolymerization inhibitors, the non-pathogen was able to penetrate successfully and to form haustoria in coleoptile cells of a non-host plant, barley. Actin polymerization inhibitors, cytochalasins, were more effective in causing an increase in penetration efficiency of E. pisi than tubulin inhibitors. The effects of cytochalasins depended on the kind of cytochalasin; the strength of the actin depolymerizing activity correlated significantly with the efficiency of increasing the penetration of the non-pathogen. When both actin and tubulin inhibitors were added simultaneously, the polarization of defense-related responses, such as massive cytoplasmic aggregation, deposition of papillae and accumulation of autofluorescent compounds, at fungal penetration sites was suppressed. Actin inhibitors did not affect arrangement and stability of microtubules and vice versa, and a double treatment of coleoptile cells with both microfilament and microtubule inhibitors showed an additive effect in increasing the penetration efficiency of E. pisi. Furthermore, cytochalasin A treatment allowed other non-pathogens, Colletotrichum lagenarium and Alternaria alternata, to penetrate successfully into the non-host barley cells. These results strongly suggest that microfilaments and microtubules might play important roles in the expression of non-host resistance of barley.     

Scanning and transmission electron microscope studies on the sensory sucker papillae of the fish parasite Entobdella soleae (monogenea)

Summary The ventral surface of the posterior sucker of Entobdella soleae, a monogenean skin parasite of the sole Solea solea, is covered with more than 800 papillae ranging in size from 2.5–19 m in diameter. The papillae are penetrated by nerves which double over themselves to form a stack-like array of lamellae running parallel to the surface of the haptor. No cilia or associated structures are present within these presumed sense organs and the papillae have no opening to the exterior. The much larger sucker papillae of a related species, E. hippoglossi, have been shown to have a similar ultrastructure. The possibility that the papillae may be contact receptors or strain receptors, providing proprioceptive information assisting the coordination of the attachment organ, is discussed and the papillae are compared with vertebrate touch receptors.I should like to thank Colin Ogden of the British Museum of Natural History for the generous assistance with the scanning electron microscopy and the Director and Staff of the Plymouth Laboratory and Ken Mackenzie and Rod Wootten of the Marine Laboratory, Aberdeen for help in obtaining material.     

Correlation Between Induced Resistance and Host Fluorescence in Barley Inoculated with Erysiphe graminis

Resistance was induced in barley by virulent and avirulent Erysiphe graminis f. sp. hordei and by E. graminis f. sp. tritici. The diameters of fluorescent haloes and papillae at the site of the primary germ tube of the inducers were larger until 12 hours after inoculation with E g. f. sp. tritici than in the corresponding periods after inoculation with E. g. f. sp. hordei. Fluorescence at the site of appressorial lobes of the inducers developed, gradually from 10 and 12 hours after inoculation with E. g. f. sp. hordei and E. g. f. sp. tritici, respectively. Penetration success of single infection units of the challenger was reduced in cells with inducer fluorescence, suggesting that resistance is principally localized to cells previously attacked by the inducer. But penetration success was independent of the average distance to the ten nearest inducer fluorescences, and penetration failures did also occur in cells without inducer fluorescence, suggesting that the induced resistance to some extent is translocated to other epidermal cells. The average diameter of the fluorescent papillae at the site of unsuccessful challenger infection units increased as a result of induced resistance.     

Penetration Behaviour of Venturia nashicola,Associated with Hydrogen Peroxide Generation,in Asian and European Pear Leaves

The penetration behaviour of the pathogen Venturia nashicola, which causes scab disease in Asian pears, was studied at the ultrastructural and cytochemical levels in host and non‐host leaves. We show, for the first time, that before V. nashicola penetrated the cuticle of the epidermis of the pear leaf, the appressorial bottom of the pathogen invaginated to form a cavity that contains electron‐dense material. The leaf cuticle beneath the cavity also became highly electron dense following penetration by V. nashicola. The location of these electron‐dense materials at the sites of penetration of the pathogen into plant cell walls suggests that they might be related to enzymes capable of degrading cell walls and that the cavities might be needed for successful penetration of leaves by V. nashicola. The generation of hydrogen peroxide (H₂O₂) was observed in penetration‐related infection structures of V. nashicola, such as appressorial bottoms, infection sacs, penetration pegs and necks of subcuticular hyphae regardless of whether the interaction of V. nashicola with pear plants was compatible or incompatible. Nonetheless, more H₂O₂ was generated at the sites of the structures in scab‐inoculated susceptible leaves than that in scab‐inoculated resistant ones. Furthermore, the decrease in the level of H₂O₂ generation following treatment with the antioxidant ascorbic acid partially prevented the penetration of the cuticle. Therefore, the generation of H₂O₂ from the penetration‐related structures might be a pathogenicity factor that contributes to strengthening the penetration peg of V. nashicola.     

SOME EPIDERMAL CHARACTERISTICS OF PALEAS OF DICHANTHELIUM,PANICUM, AND ECHINOCHLOA

The apical portion of paleas of the perfect (upper) floret of 11 species of Dichanthelium, 10 species of Panicum, and one species of Echinochloa were examined with a scanning electron microscope. The surfaces of the Dichanthelium palea tips uniformly had simple, rounded papillae, widely spaced in regular rows, whereas the palea tips of most Panicum species had irregularly arranged, compound or aggregated papillae. Unusual epidermal features were observed in P. obtusum, P. hians, and P. hemitomon. The Echinochloa crusgalli palea surface exhibited a pattern of papillae or spicule development similar to that of P. hians. Transverse sections of Dichanthelium palea showed the papillae to be little if at all thickened. An electron beam x-ray microanalysis indicated a high concentration of silicon in the papillae.     

Differences in the tolerance of potato cultivars to potato cyst nematodes (Globodera rostochiensis and G. pallida) in field trials with and without nematicides

In field trials Cara, Brio, Maris Piper and Pentland Javelin were consistently more tolerant of damage by Globodera rostochiensis yielding more than Corsair, Pentland Dell, Maris Anchor and Maris Peer, in untreated, heavily infested soil and giving the smallest increases to nematicide treatment. No yield or growth differences were found between plants in untreated and nematicide treated plots at a nematode-free site. The most tolerant cultivars all had a gene (H₁) for resistance to G. rostochiensis derived from Solanum tuberosum ssp. andigena and in soil infested with G. pallida the tolerance of at least one resistant cultivar (Maris Piper) appeared to be lessened. However, some resistant cultivars were comparatively intolerant, even to G. rostochiensis. Early cultivars were generally less tolerant than late maturing cultivars but there were exceptions. Amongst cultivars with resistance derived from Solanum vernei the early cultivar Guardian was more tolerant than the main crop cultivar Corsair. The effect on the yield of several cultivars of a range of densities of G. rostochiensis, produced either by applying different rates of a nematicide or by cropping in the previous year, was examined at two sites. The results indicated that the slope of the regression for yield in relation to nematode density was less for tolerant than intolerant cultivars. At sites infested with G. rostochiensis Maris Piper was found to be consistently more tolerant than Pentland Crown.     

Head morphology and prehensile adaptations in Hedruris spinigera (Nematoda: Spirurida)

Abstract

SEM examination of heads of Hedruris spinigera failed to reveal any posterior pair of papillae as structures that disturb the surface contour of the pseudolabia. In most specimens amphid apertures could not be detected either. All heads examined as transparent en face preparations showed subsurface structures that could be interpreted as ‘papillae’ and amphids. Modifications of the posterior cuticle of both sexes, and associated with the unusual methods of caudal prehension found in this species, are illustrated and discussed.     

Two genes in a pathogenicity gene cluster encoding secreted proteins are required for appressorial penetration and infection of the maize anthracnose fungus Colletotrichum graminicola

To avoid pathogen-associated molecular pattern recognition, the hemibiotrophic maize pathogen Colletotrichum graminicola secretes proteins mediating the establishment of biotrophy. Targeted deletion of 26 individual candidate genes and seven gene clusters comprising 32 genes of C. graminicola identified a pathogenicity cluster (CLU5) of five co-linear genes, all of which, with the exception of CLU5b, encode secreted proteins. Targeted deletion of all genes of CLU5 revealed that CLU5a and CLU5d are required for full appressorial penetration competence, with virulence deficiencies independent of the host genotype and organ inoculated. Cytorrhysis experiments and microscopy showed that Δclu5a mutants form pressurized appressoria, but they are hampered in forming penetration pores and fail to differentiate a penetration peg. Whereas Δclu5d mutants elicited WT-like papillae, albeit at increased frequencies, papillae induced by Δclu5a mutants were much smaller than those elicited by the WT. Synteny of CLU5 is not only conserved in Colletotrichum spp. but also in additional species of Sordariomycetes including insect pathogens and saprophytes suggesting importance of CLU5 for fungal biology. Since CLU5a and CLU5d also occur in non-pathogenic fungi and since they are expressed prior to plant invasion and even in vegetative hyphae, the encoded proteins probably do not act primarily as effectors.     

Cell wall alterations in the leaves of fusariosis-resistant and susceptible pineapple cultivars

Fusariosis, caused by the fungus Fusarium subglutinans f. sp. ananas (Syn. F. guttiforme), is one of the main phytosanitary threats to pineapple (Ananas comosus var. comosus). Identification of plant cell responses to pathogens is important in understanding the plant–pathogen relationship and establishing strategies to improve and select resistant cultivars. Studies of the structural properties and phenolic content of cell walls in resistant (Vitoria) and susceptible (Perola) pineapple cultivars, related to resistance to the fungus, were performed. The non-chlorophyll base of physiologically mature leaves was inoculated with a conidia suspension. Analyses were performed post-inoculation by light, atomic force, scanning and transmission electron microscopy, and measurement of cell wall-bound phenolic compounds. Non-inoculated leaves were used as controls to define the constitutive tissue characteristics. Analyses indicated that morphological differences, such as cell wall thickness, cicatrization process and lignification, were related to resistance to the pathogen. Atomic force microscopy indicated a considerable difference in the mechanical properties of the resistant and susceptible cultivars, with more structural integrity, associated with higher levels of cell wall-bound phenolics, found in the resistant cultivar. p-Coumaric and ferulic acids were shown to be the major phenolics bound to the cell walls and were found in higher amounts in the resistant cultivar. Leaves of the resistant cultivar had reduced fungal penetration and a faster and more effective cicatrization response compared to the susceptible cultivar.     

EPIDERMAL FEATURES AND SILICA DEPOSITION IN LEMMAS AND AWNS OF ZIZANIA (GRAMINEAE)

In four species of Zizania (Gramineae: Oryzeae) epidermal features of pistillate and staminate lemmas, paleas, and awns were studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis. Features observed were silica bodies, siliceous papillae, pitted siliceous papillae, stomata, microhairs, and prickle hairs. Staminate lemmas have all of these features. Pistillate lemmas have silica bodies and prickle hairs, lack stomata, and differ among species in occurrences of microhairs and siliceous papillae and pitted siliceous papillae. Awns of pistillate lemmas have silica bodies, prickle hairs, microhairs, and stomata; therefore, they possess a more complete set of features than their attached lemmas. Shapes of silica bodies on pistillate lemmas differ among species. A taxonomic key based on SEM observation of pistillate lemmas separates the four species by the shapes of silica bodies, arrangement of prickle hairs, and occurrences of microhairs and siliceous papillae. The main silica-containing structures are silica bodies, siliceous papillae, pitted siliceous papillae, and to a lesser extent prickle hairs. Pitted siliceous papillae with circular raised rims are formed by collapse or exfoliation of the tops of siliceous papillae; these have not been previously described in grasses. Comparison of epidermal features in the lemmas and leaves of Zizania shows that the former lack three kinds of nonsilicified papillae and epicuticular wax that are present on the latter but the lemmas have siliceous papillae and pits that are absent in leaves.     

Zoosporic fungi of Oceania. IV. Additional monocentric chytrids

Summary Several monocentric chytrid species of the generaPhlyctochytrium,Rhizidium,Chytridium,Chytriomyces andKarlingia were isolated on various substrata from soils of Oceania. Among these are two new species,Phlyctochytrium megastomum andRhizidium endosporangiatum. The former species is characterized chiefly by sporangia with an usually large apical, subapical, or a lateral exit orifice, the persistence of remnants of the pailla wall at the edge of the exit orifice, and by small zoospores. Rhizidium endosporangiatum is characterized at first primarily by predominantly spherical sporangia which develop 1 to 8 broad papillae. At maturity these papillae give them an angular shape. The exit papillae deliquesce at the tip, and through them protrude prominent arms of an endosporangium which expands and in which the zoospores usually swarm briefly. Willoughby's Chytridium parasiticum occurred abundantly as a parasite ofNowakowskiella sp.,Pythium sp., andPhytophthora sp. and developed epibiotic resting spores like those ofChytriomyces. Accordingly, this parasite is transferred to this genus and renamedChytriomyces willoughbyii because the nameparasiticum is preempted by the author's previously describedChytriomyces parasiticus.This study has been supported by a grant from the National Science Foundation, Washington, D.C.