The survival on chrysanthemum roots of epiphytic mycelium of Mycosphaerella ligulicola

Mycosphaerella ligulicola has been shown to survive as epiphytic mycelium on the root surface of chrysanthemum cuttings: such survival could continue throughout the life of the glasshouse crop. Symptomless surface colonization of roots of cuttings could be induced in non-sterile soil from an inoculum of (a) mycelium and sclerotia or (b) conidia (Ascochyta state); the colonization could spread upwards over the root surface. After 12 weeks survival as an epiphyte on chrysanthemum roots the fungus was still pathogenic to unrooted cuttings. Although the root surfaces of twelve other plants could be colonized by M. ligulicola the fungus survived on these roots for not more than 8 weeks.     

Host range and variation in virulence of Mycosphaerella ligulicola

A soil-borne inoculum of Mycosphaerella ligulicola was found to be mildly pathogenic to leaves or stems of globe artichoke, rudbeckia, zinnia, sunflower and dahlia, but severely pathogenic to lettuce. This is the first report of an infection by this fungus of plants other than chrysanthemum or pyrethrum. It was found that, with successive passages of the fungus through lettuce and chrysanthemum respectively, an increase in virulence to these hosts occurred. After a single passage through lettuce a reduction in virulence to chrysanthemum resulted, but with further passages through lettuce there was no further reduction in virulence to chrysanthemum.     

Effect of regurgitant from Leptinotarsa decemlineata on wound responses in Solanum tuberosum and Phaseolus vulgaris

The effect of regurgitant from Leptinotarsa decemlineata Say larvae on wound-induced responses was studied using two plant species, Solanum tuberosum L. and Phaseolus vulgaris L. Wounding of one leaf of intact S. tuberosum plants differentially affected ethylene production and activities of peroxidase and polyphenol oxidase. Only polyphenol oxidase activity was stimulated by wounding in both wounded and systemic leaves. Peroxidase activity was not affected by wounding. Wounding caused only a transient increase of ethylene production from wounded leaves. The application of regurgitant to wound surfaces stimulated ethylene production as well as activities of peroxidase and polyphenol oxidase in both wounded and systemic leaves. Wounding significantly enhanced ethylene production and polyphenol oxidase activity in wounded and systemic leaves of P. vulgaris . The application of regurgitant caused an amplification of ethylene production, peroxidase activity, and polyphenol oxidase activity, in both wounded and systemic leaves of bean plants. Several substances were tested for their role as possible endogenous signals in P. vulgaris . Hydrogen peroxide and methyl jasmonate appeared as potential local and systemic signals of ethylene formation in wounded bean plants. Local ethylene production in leaf discs was differentially affected by the regurgitant application in potato versus bean plants. While all tested concentrations of regurgitant caused stimulation of ethylene formation from potato leaf discs, ethylene production was completely inhibited by increasing concentrations of the regurgitant in bean leaf discs. Our data present evidence that ethylene may play an important role in the interaction between plants and herbivores at the level of recognition of a particular herbivore leading to specific induction of signalling cascades.     

Réactions histologiques de blés, résistants ou non àľinfection par Pseudocercosporella herpotrichoïdes

Histological reactions of wheat resistant or sensitive against infection of Pseudocercosporella herpotrichoides The microscopic observations reveal important histological differences between the sensitive or resistant varieties. The disease rapidly affect the whole of the first three leafsheath tissues in the “Étoile de Choisy” variety; in the “Roazon” variety, it only affects the first two sheaths. The inter- or intracellular mycelia can be observed both under the form of filaments more or less dilated or under the form of dense segments in the sensitive variety. However in the resistant variety, only short segments can be observed. The tissues of those two varieties are gradually destroyed when they are in contact with P. herpotrichoides hyphae, whereas the hyphae remain undamaged. In “Etoile de Choisy” the hyphae develop in great quantity whereas in “Roazon”, the development remains limited. In the variety Ae. ventricosa no. 11, which is very resistant, the parasite rarely penetrates into the more external cell layers of the first leaf sheath,‘those invaded host cells are destroyed by the mycelium but, at the same time, the mycelian hyphae degenerate and dilate. Thus, the Ae. ventricosa no. 11 tissues seem to be the seat of a strong fungic toxic reaction.     

White rust of chrysanthemums

Teleutospores of Puccinia horiana Henn. germinate and discharge sporidia between 4 and 23 °C. At the optimum temperature of 17 °C sporidia discharge starts within 3 h. Maximum germination of the sporidia takes place within 2·5 h between o and 30 °C, there being no clear optimum. High humidity and a film of moisture appear to be necessary for germination of both teleutospores and sporidia. Sporidia can penetrate either leaf surface of chrysanthemum to cause infection between 4 and 24 1°C and within the optimum temperature range, 17–24 °C, effectively penetrate within 2 h. The sporidia are very sensitive to desiccation at below 90 % relative humidity. Methods are described, using leaf discs and whole plants, for screening chrysanthemum cultivars for susceptibility to white rust. Cultivars were placed in five classes ranging from susceptible to immune. Leaf discs of immune cultivars can be distinguished within 30 h by a brown discolouration at the point of inoculation. The early stages of development of the fungus in susceptible, resistant and immune hosts are described. The incubation period in susceptible plants is normally 7–10 days, teleutospores being formed a few days later. Leaves become less susceptible with age but the oldest leaves on 5-month-old plants could still be infected. The maximum survival time of teleutospores in the sori on detached leaves was 8 weeks but was considerably less under moist conditions or buried in soil. Low doses of a mancozeb with zineb fungicide controlled infection by preventing penetration rather than by inhibiting sporidial germination.     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

Leaf curl disease of Almond caused byTaphrina deformans (Berk.) Tul.

Summary The host/parasite relationship ofTaphrina deformans (Berk.) Tul. on Almond,Prunus dulcis (Miller) D. A. Webb (=Prunus amygdalus Stokes), has been studied with the light microscope by clearing and sectioning infected leaves.A quantitative study of the host reaction shows that the presence of the fungus causes immediate cell division (hyperplasia) followed by cell enlargement (hypertrophy) and cell differentiation. The epidermal and bundle sheath cells in infected regions contain anthocyanin.The vegetative mycelium is located in intercellular spaces in three distinct leaf regions. The sub-epidermal and intercellular hyphae are morphologically similar, consisting of an irregularly branching network of cells separated by unusual septa. Sub-cuticular hyphae have a more regular shape and become short and wide during development of the disease.Infection margins illustrate changes in the healthy leaf caused byT. deformans and observations indicate that the fungus spreads in the upper leaf regions.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.): Susceptibility of proximal and distal parts of leaves from different stalk positions on intact and topped field plants in relation to free amino nitrogen and carbohydrate content*

The area covered by visible mycelium of E. cichoracearum on the upper surface of leaves 4, 8, 12 and 16 of tobacco plants in field plots in Rhodesia was expressed as percentages of the proximal and distal halves at weekly intervals. Free amino nitrogen and carbohydrate in discs from proximal and distal halves of the same leaves were analysed when each leaf was expanding rapidly and was not infected, and several weeks later, when the rate of expansion had slowed down and there was slight infection. On two other occasions, similar leaf discs were inoculated with conidia, to measure the percentage germination and hyphal length from individual conidia after incubation for 2–3 days at constant temperature and humidity; duplicate discs were chemically analysed. Leaves were not susceptible until at least 6 weeks after they had emerged from the bud. Soluble carbohydrate increased and free amino nitrogen decreased during the change from resistance to susceptibility. Proximal parts of leaves were usually infected first; they initially contained less amino nitrogen and soluble carbohydrate than distal parts. All parts of the leaf seemed to be equally susceptible later, when there were no differences in their amino nitrogen or soluble carbohydrate. Upper leaves of intact plants had more natural infection than those from corresponding leaves from topped plants. More conidia germinated on discs from them and produced longer hyphae. The discs from intact plants contained less free amino nitrogen and more soluble carbohydrate than those from topped plants. The accuracy of visual assessments of susceptibility was, generally, confirmed by measurements of percentage germination and length of hyphae from individual conidia on leaf discs. Regressions of hyphal length on leaf composition showed that susceptibility was apparently related inversely to free amino nitrogen and water content and directly to insoluble carbohydrate per unit dry matter.     

Production and characterisation of the intergeneric hybrids between Dendranthema morifolium and Artemisia vulgaris exhibiting enhanced resistance to chrysanthemum aphid (Macrosiphoniella sanbourni)

Aphids represent the most destructive of chrysanthemum pests to cultivation. Reliable variety sources of resistance and control methods are limited, so development of highly resistant breeding lines is desirable. An intergeneric hybrid between Dendranthema morifolium (chrysanthemum) variety ‘Zhongshanjingui’ and Artemisia vulgaris (mugwort) ‘Variegata’ was attempted. Most of the hybrid embryos aborted at an early developmental stage. Embryo rescue allowed the generation of hybrid plants, whose hybridity was confirmed by a combination of morphological, cytological and GISH analysis. The hybrids were vigorous, flowered normally, and their flower and leaf shape resembled those of the chrysanthemum more than those of the mugwort parent. The hybrids showed much higher resistance to chrysanthemum aphid (Macrosiphoniella sanbourni) than maternal chrysanthemum by inoculation test. The leaves of the hybrid developed a higher density of trichomes and secretory glands compared to the maternal chrysanthemum. GC–MS analysis revealed that ~51% of the essential oil in the hybrid leaves were monoterpenoids and sesquiterpenoids, while the proportion in the chrysanthemum was ~37%, and in the mugwort was ~90%. It is inferred that higher aphid resistance in the hybrid mainly owed to the leaf micromorphology and bioactive essential oil content.     

Transposition of the maize transposable element Ac in Solanum tuberosum

Summary The maize transposable element Ac has been introduced into potato via the T-DNA (transferred DNA) of Agrobacterium tumefaciens. Ac was inserted within the untranslated leader region of a neomycin phosphotransferase II (NPT-II) gene such that excision restored NPT-II activity. Two approaches to monitor Ac excision were used. (i) Using an Agrobacterium strain harbouring plasmid pGV3850::pKU3, leaf discs were selected on kanamycin (Km) after exposure to Agrobacterium. (ii) Using a strain containing plasmid pGV3850HPT::pKU3, the leaf discs were selected on hygromycin (Hm) and the resulting shoots were checked for NPT-II expression. Thirteen kanamycin resistant shoots transformed with pGV3850::pKU3 were isolated, suggesting that Ac had excised from the NPT-II gene. Out of 43 hygromycin resistant shoots transformed with pGV3850HPT::pKU3, 22 expressed the NPT-II gene, indicating that Ac had undergone excision in approximately 50% of the hygromycin resistant shoots. Southern analysis revealed that all kanamycin resistant plants contained the DNA restriction fragments expected when Ac excises from the NPT-II gene. The presence of Ac at new locations within the genomic DNA of several transformants was also detected.     

The significance of temperature during sporulation on the biology of pycnidiospores of Mycosphaerella ligiilicola

The germination, infectivity and survival of pycnidiospores obtained from cultures of Mycosphaerella ligulicola grown at 15 and 26 °C were compared. Spores formed at 26° (‘26° spores’) were less able to germinate at low relative humidities and showed a narrower temperature range for maximum germination after 6 h. At high spore densities 26° spores showed self-inhibition of germination and, over a range of lower densities, growth of their germ tubes was checked, which resulted in lower infection of leaf discs compared with 15° spores in which this phenomenon did not occur. The fungus could be recovered from un-sterile compost over a longer period after inoculation with 15° spores. Only after storage at a temperature well below zero was there a difference in viability between 15° and 26° spores. It is thought that the potential advantage of producing larger numbers of spores at 26° would be realized only under optimum conditions for dispersal and infection. The smaller number of spores produced at 15° are likely to be successful under natural conditions.     

THE PATHOLOGY OF HYPODERMELLA LARICIS ON LARCH,LARIX OCCIDENTALS

A study of the larch needle disease caused by Hypodermella laricis provided information on the mode of infection, the manner of spread, and the relationship between the parasite and its host, Larix occidentalis. Infection by spores occurs in early spring as soon as the leaves emerge, but there is no evidence that hyphae invade the dwarf shoots. The fungus disrupts the normal abscission mechanism, and the fructifications and spores of H. laricis develop on the leaves which remain attached to the dwarf shoots. The time of precipitation is a decisive factor in the initiation of the disease, i.e., infection occurs only when precipitation coincides with the emergence of young leaves. However, vulnerability to infection diminishes rapidly as the leaves mature. By observing leaf size and noting the time of rainfall, the severity of infection can be accurately predicted. Several adaptive mechanisms related to successful parasitism in H. laricis are discussed.     

Variation for Resistance to <i>Alternaria tenuissima</i> and Potential Structural Mechanism among Different Cultivars of <i>Chrysanthemum morifolium</i>

Black spot disease, caused by the necrotrophic fungus Alternaria tenuissima (Fr.) Wiltsh (A. tenuissima), is considered a highly destructive disease of Chrysanthemum (Chrysanthemum morifolium Ramat.). A set of 17 accessions of commercial chrysanthemum cultivars were evaluated for resistance to A. tenuissima by seedling artificial inoculation. It was found that the reaction of the accessions to artificial inoculation ranged from resistant to highly susceptible. Five varieties of chrysanthemum (‘Zhongshan Taogui’, ‘Jinba’, ‘Zhongshan Jinguan’, ‘Jinling Wanhuang’ and ‘Jinling Yangguang’) were resistant; two varieties of chrysanthemum (‘Zhongshan Xinggui’ and ‘Zhongshan Jinkui’) were moderately resistant; and others were susceptible to various degrees, four varieties of chrysanthemum (‘Zhongshan Zihe’, ‘Zhongshan Jiuhong’, ‘Zaoyihong’ and ‘Jinling Jiaohuang’) were highly susceptible, especially. Some leaf morphological features of two resistant and two highly susceptible cultivars were further researched. Trichome density, length, height, gland size and stomata density were found to be associated with plant passive resistance. Resistant varieties that were identified in present study will be promising germplasm for exploitation of breeding programmes aimed at developing A. tenuissima-resistant cultivars and increasing genetic diversity.     

Monitoring of Virulence in Populations of Pbytophthora infestans Using a Schwarzbach Spore Trap

A modified Sehwarzbach jet spore trap was used to sample Phytophthora infestans populations in small crops of potato within polyethylene tunnels and in the field. Airborne sporangia were eaptured in the trap and deposited upon potato leaf discs, of a cultivar lacking race-specific resistance genes, contained within the trap. Virulence characters of isolates captured in the spore trap were determined by subculturing the isolates on leaf discs of a range of potato genotypes with race-specific resistance (R-genes), incubating them and then recording compatible and mcompatible reactions, reactions. For four isolates of P. infestans the levels of sporulation on the differential leaf discs were noted and although cultivar × isolate interactions were inconsistent, variable light and temperature conditions had no significant effect on the reactions of the cultivars.     

Resistance of roses to pathotypes of Diplocarpon rosae

Colonies of Diplocarpon rosae derived from single conidia were isolated on malt extract agar, multiplied (at 23°C) and stored (at ?20°C) on surface‐sterilised leaf discs of a universally susceptible rose, ‘Frensham’. The resistance of 16 species and cultivars of Rosa to different isolates of D. rosae was assessed using surface‐sterilised leaf discs. Four pathotypes of D. rosae were distinguished on the basis of host range. One species and one hybrid were resistant to all pathotypes. Two species and two cultivars were susceptible to all pathotypes. Four species and six cultivars were interpreted as having vertical resistance because they were strongly resistant to some but not all pathotypes. Only species and hybrids of the section Cinnamomeae were resistant to the pathotype identified as CW1 whereas only roses of other origins were resistant to the pathotype DA2.     

A Simple Technique for Determining the Reaction of Barley Genotypes to Pyrenophora graminea

An in vitro technique was used to determine the reaction of 10 barley genotypes to Pyrenophora graminea, the seed‐borne pathogen causing barley leaf stripe disease. Determination was based on the percentage of inoculated seeds that produced fungal hyphae when cultured on potato dextrose agar. The technique allows low, intermediate and absolute levels of resistance to leaf stripe to be determined. Genotypes CI‐5791 and Banteng were resistant, Thibaut, Igri and PK (30‐531) were moderately resistant, Gollf was moderately susceptible, and WI2291, Arabi Abiad, Furat 1 and Arrivate were susceptible. The in vitro and in field assessments were significant (correlation coefficient r=0.96), results indicating that repeated measurements for infected seeds by this in vitro method were very similar to those of field assessments.     

马铃薯对晚疫病水平抗性的组织细胞学观察

以马铃薯晚疫病水平抗性品种LBr-12和感病品种费乌瑞它为材料,采用普通光学和电子显微镜技术,系统研究了马铃薯与晚疫病菌(致病疫霉)互作的组织细胞学反应特征。观察结果显示:(1)接种后,水平抗性材料LBr-12出现过敏反应,病菌被限制在侵染点的几个细胞中,菌丝产生较少的分支和吸器。(2)感病品种费乌瑞它被侵染细胞呈蔓延趋势,菌丝产生较多的分支和吸器。(3)电镜观察发现,抗病品种上病菌的胞间菌丝、吸器母细胞、吸器在细胞和亚细胞水平均发生了一系列异常变化,包括原生质的电子致密度加深、液泡增多变大、菌丝细胞壁不规则增厚、细胞器排列紊乱及解体、吸器母细胞及吸器形态异常、病菌最终畸形坏死,同时发现抗病品种受病菌侵染时可迅速产生结构防卫反应,形成的细胞壁沉积物使胞壁极度增厚或细胞膜上产生乳突状结构。     

Synergistic interactions of begomoviruses with Sweet potato chlorotic stunt virus (genus Crinivirus) in sweet potato (Ipomoea batatas L.)

Three hundred and ninety‐four sweet potato accessions from Latin America and East Africa were screened by polymerase chain reaction (PCR) for the presence of begomoviruses, and 46 were found to be positive. All were symptomless in sweet potato and generated leaf curling and/or chlorosis in Ipomoea setosa. The five most divergent isolates, based on complete genome sequences, were used to study interactions with Sweet potato chlorotic stunt virus (SPCSV), known to cause synergistic diseases with other viruses. Co‐infections led to increased titres of begomoviruses and decreased titres of SPCSV in all cases, although the extent of the changes varied notably between begomovirus isolates. Symptoms of leaf curling only developed temporarily in combination with isolate StV1 and coincided with the presence of the highest begomovirus concentrations in the plant. Small interfering RNA (siRNA) sequence analysis revealed that co‐infection of SPCSV with isolate StV1 led to relatively increased siRNA targeting of the central part of the SPCSV genome and a reduction in targeting of the genomic ends, but no changes to the targeting of StV1 relative to single infection of either virus. These changes were not observed in the interaction between SPCSV and the RNA virus Sweet potato feathery mottle virus (genus Potyvirus), implying specific effects of begomoviruses on RNA silencing of SPCSV in dually infected plants. Infection in RNase3‐expressing transgenic plants showed that this protein was sufficient to mediate this synergistic interaction with DNA viruses, similar to RNA viruses, but exposed distinct effects on RNA silencing when RNase3 was expressed from its native virus, or constitutively from a transgene, despite a similar pathogenic outcome.     

Interactions Between Hyphosphere-Associated Bacteria and the Fungus <Emphasis Type="Italic">Cladosporium herbarum</Emphasis> on Aquatic Leaf Litter

We investigated microbial interactions of aquatic bacteria associated with hyphae (the hyphosphere) of freshwater fungi on leaf litter. Bacteria were isolated directly from the hyphae of fungi from sedimented leaves of a small stream in the National Park “Lower Oder,” Germany. To investigate interactions, bacteria and fungi were pairwise co-cultivated on leaf-extract medium and in microcosms loaded with leaves. The performance of fungi and bacteria was monitored by measuring growth, enzyme production, and respiration of mono- and co-cultures. Growth inhibition of the fungus Cladosporium herbarum by Ralstonia pickettii was detected on leaf extract agar plates. In microcosms, the presence of Chryseobacterium sp. lowered the exocellulase, endocellulase, and cellobiase activity of the fungus. Additionally, the conversion of leaf material into microbial biomass was retarded in co-cultures. The respiration of the fungus was uninfluenced by the presence of the bacterium.     

Temporal and spatial patterns of 1, 3-β-glucanase and chitinase induction in potato leaves infected by Phytophthora infestans

Infection of potato (Solarium tuberosum L.) leaves with the fungal pathogen Phytophthora infestans caused a similar, strong and coordinated induction of 1, 3-β-glucanases and chitinases in compatible (plant susceptible) and incompatible (plant resistant) interactions of two selected plant cultivars with appropriate races of the fungus. The temporal and spatial patterns of 1, 3-β-glucanase induction were studied in further detail by immunohistochemical and in-situ hybridization methods. Accumulation of the protein was preceded by progressive activation of the corresponding gene, commencing near infection sites and spreading rapidly throughout the whole infected leaf as well as to adjacent, non-infected leaves. Protein and mRNA distribution patterns were nearly identical in compatible and incompatible interactions. In comparison with 1, 3-β-glucanase mRNA, phenyl-alanine ammonia-lyase mRNA accumulated more rapidly and remained restricted to the vicinity of fungal infection sites, in addition to its constitutive occurrence in the vascular bundles. Even more rapid than any detectable mRNA induction was the accumulation of auto fluorescing material in plant cells immediately surrounding fungal structures, particularly and invariably in incompatible interactions and less frequently in compatible interactions. It is concluded that cultivar-race-specific resistance is established early in the interaction of potato leaves with P. infestans and hence the observed massive accumulation of 1, 3-β-glucanase and chitinase is presumably not involved in determining this specificity.