Infected Bulbs Research Articles

Xanthomonas hyacinthi . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas hyacinthi . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Hyacinthus orientalis and Scilla tubergeniana ( Liliaceae ); by artificial inoculation: Galtonia candicans, Muscari armeniacum and Scilla hispanica ( Liliaceae ). DISEASE: Yellow disease of hyacinth. Initially, small dark green spots develop on leaves, which may coalesce and develop into streaks, mainly at the leaf margin. Streaks blacken to produce a distinctive 'black rim'. On bulbs, bacterial exudate can be seen between scales, which appear glassy and discoloured. Wet and windy weather, generally followed by dry, hot periods, increases the disease incidence. Similarly, frost, mist and hail can induces similar effects. Bacterial entry into healthy plants is generally through natural openings such as hydathodes and stomata or through wounds. Between 0.7-2.4% of hyacinth bulbs can be infected with yellow disease (VAN DOORN & ROEBROECK, 1993). The disease can be controlled by heat-treating the bulbs (VREERBURG et al. , 1986) or the application of bactericidal foliar sprays (KOSTER et al. , 1988). GEOGRAPHICAL DISTRIBUTION: ASIA: Japan. NORTH AMERICA: USA (Connecticut, Massachusetts, Michigan, Minnesota, New Jersey, Texas, Washington). AUSTRALASIA: Australia (New South Wales, Tasmania, Victoria). EUROPE: Austria, Denmark, Finland, Former Yugoslavia, Germany, Hungary, Ireland, Italy, Netherlands, Poland, Romania, Russian Federation, Sweden, United Kingdom. TRANSMISSION: By the movement of infected bulbs. Localised spread by the action of wind-blown water droplets, animal movements and the use of infected tools and bulb sorting equipment.

First Report of a Bulb Decay of Onion by Enterobacter cloacae in Colorado.

Sweet Spanish onion cultivars (Allium cepa L.) in northern Colorado displayed symptoms of postharvest bulb rot during September to November of 1999. This disease appears identical to that reported from infected onions in California in 1988 and is presumably associated with high temperature stress (1). Mature, firm bulbs harvested from scattered fields in Weld County exhibited a brownish discoloration and breakdown of inner scales. Gram negative, rod-shaped, cream-colored bacteria were consistently recovered from infected bulb tissue on nutrient agar. Physiological tests showed that the bacteria utilized glucose in an oxidative and fermentative manner and were catalase positive and oxidase negative. A representative strain was identified by Microbe Inotech Laboratories (St. Louis, MO) as Enterobacter cloacae (Jordan) Hormaeche & Edwards (2) using Biolog analysis, with a similarity index of 0.81. To confirm pathogenicity, a 0.5- to 1.0-ml suspension of bacteria (108 CFU/ml sdw) was injected into firm onion bulbs (7.5 to 10.0 cm diameter). After incubation for 14 days at 22°C in closed plastic bags in the dark, bulbs were cut in half and evaluated. Tan to brown discoloration and initial dry rot, similar to that observed postharvest, was observed in inoculated bulbs. The pathogen was reisolated from six of eight bulbs inoculated with the representative strain. No discoloration or disease developed on eight control bulbs injected with water. To our knowledge, this is the first report of E. cloacae from onion grown in Colorado.

BREEDING FOR RESISTANCE TO FUSARIUM OXYSPORUM IN FLOWER BULBS

Cultivation of the major flower bulb crops, e.g., lily, narcissus, gladiolus and tulip, is threatened by the soil-borne fungus Fusarium oxysporum. Fusarium infected bulb lots have lower yields and cause significant problems for bulb export and cut flower production. Besides cultivation practices and chemical protection, resistant cultivars can play an important role in preventing this disease. To breed Fusarium resistant cultivars, screening and selection tests have to be developed and genetic variation in the host and in the pathogen determined. Information about the inheritance can be helpful in selecting the parents with the best breeding value for Fusarium resistance. Clonal screening tests under standardized conditions (e.g., concerning temperature, inoculum concentration and duration of the test) are developed for lily, narcissus, gladiolus and tulip using artificially infested soil or bulbs. By using a clone of a genotype, levels of resistance can be determined accurately. Severity of the disease is mainly observed by using disease ratings or the percentage of diseased bulbs. Partial resistance to Fusarium is present in all four crops. In Narcissus and Gladiolus even species with absolute resistance were identified. Resistant species are used in interspecific breeding programmes with commercial cultivars. Variation in virulence of Fusarium was investigated for f.sp. lilii, f.sp. gladioli and f.sp. narcissi. In all these formae speciales indications for race-formation were observed. Comparison of different sizes of bulbs within genotypes showed that screening immature bulbs is possible. Tests of individual plants in the seedling stage also gave promising results for a more efficient selection system. The use of indirect selection by molecular markers was investigated in the lily-Fusarium interaction. Inheritance of resistance in all four crops was mainly of a polygenic nature. Breeding values of parents determined after diallel analysis correlated well with resistance levels determined in clonal tests.

The potential for the biological control of basal rot of Narcissus by Streptomyces sp.

Glasshouse experiments were conducted over 2 years to study the control of basal rot of Narcissus by a biological product based on a Streptomyces sp. In year 1, 88% of untreated bulbs of the susceptible cv. Golden Harvest were infected and artificial inoculation did not increase disease incidence. The Streptomyces sp. dip (0.1%) did not control the disease. In Year 2, natural infection of Golden Harvest was 15% and artificial inoculation increased infection of untreated bulbs to 53%. The Streptomyces dip (0.01%) supplemented with spray applications controlled basal rot as effectively as thiabendazole hypochlorite. Natural infection of cv. Carlton was 19–20% and artificial inoculation increased the percentages of infected bulbs to 64% (Year 1) and 71 % (Year 2). In Year 1, the Streptomyces dip (0.1 %) reduced disease for cv. Carlton by 24%. In Year 2, all Streptomyces treatments reduced the disease incidence in this cultivar. The combination of 0.01% dip and spray was most effective, reducing infection to 18.7%. Basal rot resulting from natural or artificial infection of the resistant cv. Ice Follies was too low to determine the effectiveness of treatments. The Streptomyces sp. did not control natural infection originating from bulbs. The results suggest that the Streptomyces sp. has potential as a component of an integrated control strategy for basal rot.

A rapid serological test for detecting Fusarium oxysporum f.sp. narcissi in Narcissus

SUMMARYPolyclonal antiserum was elicited against a strain of Fusarium oxysporum f.sp. narcissi (GCRI80/26) and a specific and sensitive enzyme‐linked immunosorbent assay developed. Antiserum raised to cell wall fractions gave better recognition than that to cytoplasmic fractions. Recognition was equally good in artificially and naturally infected bulbs. Little cross‐reactivity in bulb tissue was shown by three other bulb‐rotting fungi. Nine isolates of F. oxysporum f.sp. narcissi from a wide geographic area gave similar results in an indirect ELISA of mycelial extracts, although some cross‐reactivity was observed with two other Fusarium spp. Four Fusarium spp. and four other fungi showed little cross‐reactivity. Ten days after inoculation the pathogen was readily detected in the base plate area of three Narcissus cultivars and points remote from the inoculation site in the most susceptible cultivar. A direct correlation was observed between positive results in the enzyme‐linked immunosorbent assay and recovery of the pathogen on selective medium.

A storage soft rot of New Zealand onions caused byPseudomonas gladiolipv.alliicola

Abstract A bacterium, isolated from infected bulbs of onion (Allium cepa L.) in store, was identified as Pseudomonas gladioli pv. alliicola (Burkholder 1942) Young et al. 1978, and was confirmed as a soft rot pathogen of onion by completion of Koch's postulates. P. gladioli pv. alliicola was first reported as an onion pathogen in New Zealand by Hale in Pennycook (1989). This paper documents the evidence for that record.

An electron microscopical study of the infection of the nematode Panagrellus redivivus by the endoparasitic fungus Verticillium balanoides

The infection of nematodes by the endoparasitic fungus Verticillium balanoides was studied by means of optical and electron microscopical techniques. Conidia of this fungus adhere randomly in high numbers to the entire cuticle surface of the nematode Panagrellus redivivus . Adhesion is accomplished by means of a tri-layered adhesive pad located at the apical end of the conidium, the outermost layer of which shows a radiated substructure. After attachment an appressorium which grows through the adhesive pad and establishes a firm contact between the fungal cell wall and the nematode cuticle is formed. Penetration of the cuticle by means of a hyphal outgrowth on the appressorium is followed by the formation of an infection bulb from which trophic hyphae develop that invade the nematode. Approximately 60 h after infection conidiophores develop outside the nematode, producing numerous conidia.

Ultrastructure of Infection of Cyst Nematode Eggs By the Nematophagous Fungus Verticillium Suchlaspori Um

Ultrastructural studies showed that strains of Verticillium suchlasporium isolated from eggs of Heterodera avenae, infected in vitro eggs of H. avenae and Globodera pallida. In H. avenae, V suchlasporium formed appressoria at the point of infection. In serial sections it was observed that a narrow penetration hypha perforated the egg-shell and formed an infection bulb. Other types of penetration hyphae and germinating conidia were also found. Areas of low electron-density were frequently observed, suggesting the secretion of enzymes by V. suchlasporium to weaken the egg-shell. Penetration of eggs of G. pallida was similar to that described for H. avenae, but the egg-shell of G. pallida was twice as thick as that of H. avenae (approximately 500 nm). Ultrastructure of infection of cyst nematode eggs by V. suchlasporium has features in common with other nematophagous fungi.

Detection of tobacco rattle virus by ELISA and test plants in main sprouts of tulip bulbs during storage at different temperatures

The detectability of tobacco rattle virus (TRV) in the main sprouts of primarily and secondarily infected tulip bulbs of cv. Apeldoorn stored at different temperatures from the lifting in July up to February is described. Detection by ELISA was not affected by the size of the main sprout, nor by the size of the bulbs. The rates of TRV-infected bulbs found by ELISA were highest during storage at 13, 9 or 5°C continuously, and when temperatures were lowered from 20 or 17°C to 5°C in October. The percentages detected via test plants, but undetectable by ELISA were also lowest at these temperatures. The unfavourable effect of continuous storage at 20, 17, or 2°C as expressed in low ELISA absorbances not significantly different from the mean value of healthy bulbs, was largely overcome during long storage by the change of temperature down to 5°C from 20 and 17°C or upwards from 2°C. The reverse from 5°C upwards to 17 and 20°C affected the detectability by ELISA unfavourably. The rate of detection via test plants in the main sprout and in the small sprouts from different positions in bulbs was only possible at low percentages. The effect of some factors, like different temperatures during storage, detectability of different TRV serotypes, interference of irregular occurrence of TRV in the removed scale and basal-plate tissue with the main sprout, and variable recurrence of TRV in progeny bulbs, is discussed in view of its impact on routine testing of bulbs during storage.

Embellisia allii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Embellisia allii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Allium sativum (white garlic). DISEASE: Garlic bulb canker; lesions occur on the bulbs of white garlic on the back and edges of the cloves where they touch other cloves. Lesions are seen as a dark layer underneath the epidermis. The fungus then penetrates the parenchyma causing a breakdown of the cells to form lacunae in which the fungus can sporulate. The leaves and flower stems of garlic can also be attacked by the fungus. GEOGRAPHICAL DISTRIBUTION: Africa: Egypt, Zimbabwe. Asia: Israel. Australasia & Oceania: Australia (NSW), New Zealand. Europe: Bulgaria, Italy, Romania, Spain, UK, Yugoslavia. North America: Mexico, USA (Louisiana, Massachussetts, New Mexico). Central & South America: Argentina. Brazil, Chile. Puerto Rico, Venezuela. TRANSMISSION: The fungus overwinters in the plant debris, soil and infected bulbs.

Embellisia hyacinthi . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Embellisia hyacinthi . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Hyacinthus orientalis, Freesia refracta, Scilla sibirica, Muscari sp. DISEASE: Skin spot of bulbs. Leaf lesions also occur as spots. above which the leaves yellow and die. GEOGRAPHICAL DISTRIBUTION: Europe: Germany, The Netherlands, UK. North America: USA. TRANSMISSION: The fungus overwinters in the plant debris, soil and infected bulbs.

Sclerotinia narcissicola . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Sclerotinia narcissicola . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Narcissus spp. DISEASE: Smoulder, grey mould. Infection may reduce bulb yield and flower size (55, 3617). Symptoms may include: rot of the bulbs and leaves at ground level, brown lesions on the leaves and flower buds, distortion and failure of emergence. GEOGRAPHICAL DISTRIBUTION: Asia: Iraq, USSR; Australasia: Australia (Tasmania, Victoria), New Zealand; Europe: Channel Islands (Guernsey, Jersey), Denmark, Eire, England, Germany, Northern Ireland, The Netherlands, Norway, Scotland, Sweden, USSR, Wales, West Germany; North America: Canada (British Columbia, NS, Ontario, PEI); USA (North Carolina, New York, Oregon, Virginia, Washington State) (see CMI Distribution Maps of Plant Diseases , No. 315). TRANSMISSION: The disease may come from planting of infected bulbs or from infected soil; sclerotia in the soil may be viable for up to nine months (61, 7053). In vitro conidial suspensions did not cause infection except of wounded or damaged tissue; mycelial inoculation consistently caused lesions on detached leaves and bulb scales (61, 5797).

Penetration and Population Growth of the Robine Bulb Mite, Rhizoglyphus robini CLAPAREDE(Acari:Acaridae), on Healthy and Fusarium-Infected Rakkyo Bulbs

Differences in population growth of the Robine bulb mite (Rhizoglyphus robini CLAPAREDE) were observed using three types of rakkyo (Allium chinense G. DON) bulbs; healthy, injured (by mechanical cutting), and Fusarium-infected bulbs. Within the short period of 14 days, bulb mites penetrated the infected bulbs and showed and exponential population growth. On the other hand, few mites could penetrate healthy bulbs and population increase was low even at 35 days after release. It required 60 to 90 days for the mites to finally penetrate the healthy bulbs and show an exponential population growth. On the injured bulbs, the population increase of mites was higher than on the healthy ones, but much lower than that on the fungi-infected bulbs. These results suggest that earlier penetrations of mites result in a faster population growth of subsequent infestations.

Significance of electron dense microbodies in trap cells of the nematophagous fungus Arthrobotrys oligospora.

We have studied the fate of electron dense microbodies in nematode-trapping organs (traps) of the fungus A. oligospora during the initial hours following nematode capture. The interaction studies were performed with isolated traps which had captured a nematode under conditions where the fungal cells had no access to external energy sources. Video enhanced contrast microscopy showed that under these conditions the number of dense bodies present in the trap cell that formed the penetration tube, rapidly decreased. During subsequent penetration and development of the infection bulb this decrease continued while at this time common cell organelles such as mitochondria and vacuoles were formed. This was confirmed by electron microscopy which also revealed that the dense bodies were degraded by means of an autophagic process. The organelles were degraded individually and finally turned into compartments which, based on ultrastructural criteria, were considered vacuoles. Fusion of such vacuoles into larger organelles frequently occurred. The degradation process was initiated early in the interaction since initial stages were already evident within 15 min after capture. Generally it took 1-2 h before the infection bulb had fully developed and trophic hyphae formation started. During this time the original trap cell, characterized by numerous dense bodies, was transformed into an active vegetative hyphal cell containing typical cell organelles such as nuclei, mitochondria, a strongly proliferated endoplasmic reticulum, vacuoles and "normal" microbodies but lacked dense bodies. This disappearance of dense bodies was confined to the cell that penetrated the nematode and--less frequently--its two neighbouring cells in the hyphal loop. In the other cells, constituting the trap, the dense bodies remained unaffected. As will be discussed, the present results support our current view that traps of A. oligospora contribute to the survival of the organism in its natural environment.

Occurrence and metabolic significance of microbodies in trophic hyphae of the nematophagous fungus Arthrobotrys oligospora.

This paper describes the results of an ultrastructural study on the subcellular events occurring in nematode-infecting (trophic) hyphae of the nematophagous fungus Arthrobotrys oligospora. In early stages of the infection process (30 min-4 h), the infection bulb and developing trophic hyphae are characterized by a highly proliferated endoplasmic reticulum (ER). Its membranes often appeared vesiculated and occur in close association with the cell membrane of the cells. Upon further invasion of the nematode, lipid droplets developed in the trophic hyphae; these droplets were first observed 4-5 h after the infection but were abundantly present after 24-36 h. Along with the formation of lipid droplets proliferation of microbodies was observed. These organeles were characterized by the presence of catalase and thiolase and were frequently observed in close association with the lipid droplets. Later on the lipid droplets disappeared. During this period new vegetative mycelium developed from the trap that had originally captured the nematode. Our results suggest that part of the nutrients released from the nematode are first converted into lipids by the fungus which in turn are degraded via the beta-oxidation pathway and further metabolized to support growth of new vegetative hyphae.

Agronomic evaluation of virus-free and virus-infected garlic (Allium sativumL.)

SummaryThe yield from virus-free bulbs of five garlic cultivars (Rosé du Var, Moulinin, Printanor, Blanc de la Drôme and Isles of Scilly) was substantially higher than that from comparable infected stocks. Growth, measured by leaf length, was significantly greater for virus-free plants of these cultivars at mid-season, and at harvest the virus-free bulbs contained a higher proportion of bigger cloves than infected bulbs. In contrast, the yield from virus- free bulbs of cv. Fructidor was similar to infected bulbs, as was the amount of mid-season growth and the proportion of large to small cloves. Infected stocks of cvs Rosé du Var and Moulinin that had been selected to remove the most severely diseased plants gave better yields than unselected infected stocks, but less than virus-free stocks. The yield of selected stocks of cv. Fructidor was significantly less than unselected infected stocks.

TOWARDS A RAPID AND RELIABLE DETECTION METHOD FOR IRIS SEVERE MOSAIC VIRUS IN IRIS BULBS

Detection of iris severe mosaic virus (ISMV) in ISMV-infected iris bulbs during storage, by either ELISA or electron microscopy has been problematic. We have applied different storage-temperature treatments and a cutting method as possible procedures to enhance ISMV detection in stored iris bulbs cv. Professor Blaauw. While at lifting ISMV could not be detected in the bulbs, gradually the virus became detectable in time when bulbs were stored at about 17°C. Better results were obtained when the cutting method was employed. Using ELISA, a 100 ␜core was obtained for infected bulbs that were cut 1 month prior to testing. The virus could be detected only in tissue adjacent to the cut surface. These results offer good prospects for the development of a reliable detection method for ISMV in iris bulbs.

Detection of tobacco rattle virus in different parts of tulip by ELISA and cDNA hybridisation assays

Different parts of tulips cv. Apeldoorn were assayed for the presence of tobacco rattle virus (TRV) by means of ELISA, cDNA hybridisation and immuno-electron microscopy. Assays were periodically performed during the growing season and upon storage of the bulbs, During the growing season in the field the relative TRV concentrations detected by ELISA and cDNA were highest mainly in the basal stem-parts and basal leaf-parts, respectively. When, during storage, infected bulbs were divided into a number of sections, TRV could be detected only in some of the sections, irrespective of the test used. However, nearly all sprouts of infected bulbs, stored at 5°C for 7 months, appeared to contain detectable amounts of TRV upon testing with ELISA and cDNA. Thus, testing of sprouts may offer a possibility to develop a routine test for TRV in tulip bulbs in due course. Verschillende delen van tulp cv. Apeldoorn werden getoetst op de aanwezigheid van tabaksratelvirus (TRV) met behulp van ELISA, cDNA-hybridisatie en immuno-elektronemicroscopie. Tijdens het groeiseizoen en de bewaring van de bollen werden regelmatig toetsingen uitgevoerd. Gedurende het groeiseizoen op het veld werden de relatief hoogste TRV concentraties voornamelijk gevonden in het basale deel van de stengel en het okselgedeelte van het blad met respectievelijk ELISA en cDNA-hybridisatie. TRV bleek gelokaliseerd aanwezig te zijn in een of meer stukjes van een gedeelde bol, onafhankelijk van de gebruikte toetsmethode. Bijna alle spruiten van geinfecteerde bollen die gedurende 7 maanden bij 5°C bewaard waren, bleken bij het toetsen met behulp van ELISA en cDNA aantoonbare hoeveelheden van TRV te bevatten. Het toetsen van spruiten biedt de mogelijkheid te zijner tijd een routinetoets voor TRV in tulpebollen te ontwikkelen.

Histopathology of Oil Palm Seedlings Infected by, Pathogenic Fusarium oxysporum Isolates from Africa

AbstractOil palm seedlings (one‐leaf stage) grown from Malaysian seed were inoculated with six African isolates of Fusarium oxysporum f. sp. elaeidis and one African isolate of Fusarium oxysporum var. redolens. All the isolates induced similar symptoms and anatomical responses in the inoculated palms. The pathogen invaded the root, bulb, leaf bases and leaves in that sequence. In the root and bulb, infection resulted in plugging of xylem elements with mycelium, conidia, tyloses and gums, disintegration and plugging of phloem tissues, disintegration of plugged vascular elements forming gaps and cavities, and collapse of cortical tissues leading to the isolation of the infected vascular tissues. Formation of hypertrophic or hyperplastic cells in the xylem parenchyma was not observed. Anatomical changes in the infected leaf bases and petioles were similar to those occurring in the infected bulb; except that tyloses were formed less frequently. Generally there was no sign of the pathogen in the wilted leaf blade, but the epidermal, hypodermal and mesophyll cells appeared shrunken or to have collapsed. No hyphae or anatomical changes were observed m the tissues of symptomless inoculated palms.

Control of stem nematode, Ditylenchus dipsaci, in tulip bulbs with aldicarb and oxamyl

In the Netherlands complete elimination of the stem nematode Ditylenchus dipsaci (Kühn, Filipjev) in tulip by destruction of infested lots and sterilization of infested soil is the aim of the Plant Protection Service. Elimination of stem nematode in narcissus bulbs is achieved by hot-water treatment, but this treatment is not appropriate for tulip bulbs because these are damaged at temperatures of 43 · 5°C and higher. As the effects of the systemic nematicides aldicarb and oxamyl looked promising, these were investigated further. Aldicarb, 6 kg a.i./ha, was applied once in the autumn and once in spring. Oxamyl, 2 · 88 kg a.i./ha, was applied three times in spring. The efficacy of these nematicides was shown not only by a reduction in the numbers of infested bulbs but also by a reduction in nematode numbers in the bulbs, shown here in the frequency distribution of infested bulbs over nematode numbers. However in some bulbs, probably those which had the highest number of nematodes before planting, a few stem nematodes could still be detected, having survived high dosages of nematicides. Therefore, complete elimination of stem nematodes from infected bulbs with very high nematode numbers is probably impossible. It is expected, however, that repeated treatment will increase the percentage of nematode-free bulbs and will lead to almost healthy tulip-bulb stocks.