Etiology and Transmission of Sesame Phyllody in Iran

Phyllody is a destructive disease of sesame (Sesamum indicum L.) in Iran. The major symptoms of the disease are floral virescence, phyllody and proliferation. Other symptoms which sometimes accompany the disease are yellowing, cracking of seed capsules, germination of seeds in the capsules and formation of dark exudates on the foliage. Light microscopy of hand-cut sections of sesame and colza (Brassica napus L. cv. Oro) stems treated with Dienes' stain showed blue areas in the phloem region of phyllody infected plants. Mycoplasma-like bodies were found in the sieve cells of infected sesame stems when thin sections were examined m an electron microscope. Sesame phyllody was successfully transmitted from sesame to sesame by grafting. Among various leafhoppers collected in sesame fields only Neoaliturus haematoceps transmitted the disease. This is the first report on the identification of a Mycoplasma-like organism (MLO) as the cause of sesame phyllody and N. haematoceps as an MLO vector in Iran. In host range studies using the leafhopper vector, only B. napus cv. Oro, Lepidium sativum, Catharanthus roseus, Lactuca sp. and Portulaca oleracea, but not 17 other species, developed symptoms. The species of vector and host range of MLO indicate that sesame phyllody in Iran is different from that reported in India and Upper Volta.     

Dodder Transmission of Pear Decline, European Stone Fruit Yellows, Rubus Stunt, Picris echioides Yellows and Cotton Phyllody Phytoplasmas to Periwinkle

The pear decline, European stone fruit yellows and rubus stunt agents as well as the phytoplasmas causing Picris echioides (bristly oxtongue) yellows and cotton (Gossypium hirsutum) phyllody, respectively, were transmitted from naturally infected plants to the experimental host Catharanthus roseus (periwinkle) via dodder (Cuscuta spp.) bridges. The identities of the dodder-transmitted phytoplasmas were confirmed by restriction length fragment polymorphism analysis of polymerase chain reaction-amplified ribosomal DNA. On the basis of restriction profiles the cotton phyllody agent could be differentiated from the phytoplasma causing faba bean phyllody, a disease previously thought to be induced by the same organism as cotton phyllody.     

Transmission of the hop strain of arabis mosaic virus by Xiphinema diversicaudatum*

Hop plants became infected with the hop strain of arabis mosaic virus (AMV(H)) when grown in hopfield and woodland soil in which infected plants had been growing. Infection occurred in soil infested with the dagger nematode Xiphinema diversicaudatum, but neither in uninfested soil nor in soil previously heated to kill nematodes. X. diversicaudatum transferred direct from hop soils transmitted AMV(H) to young herbaceous plants and to hop seedlings; some of the hop seedlings developed nettlehead disease. A larger proportion of plants was infected using X. diversicaudatum obtained from a woodland soil and then given access to the roots of hop or herbaceous plants infected with AMV(H). AMV(H) was transmitted by adults and by larvae, in which the virus persisted for at least 36 and 29 wk, respectively. Difficulties were encountered in detecting AMV(H) in infected hop plants, due partly to the delay in virus movement from roots to shoots. Infection of hop shoots was seldom detected until the year after the roots were infested and sometimes nettlehead symptoms did not appear until the third year. Isolates of arabis mosiac virus from strawberry did not infect hop. The results are discussed in relation to the etiology and control of nettlehead and related diseases of hop.     

An Infectious Agent Associated with Amebas of the Genus Naegleria*

A study of amebas of the genera Naegleria, Acanthamoeba, Polysphondylium, and Didymium shows that a cytopathogenic agent that is filterable and passageable is present only in the strains of the Naegleria whether they are obtained free-living from soil samples (N. gruberi) or as pathogens from humans (N. fowleri). The agents obtained from the different Naegleria strains are similar in amount and in their cytopathogenic interaction with chick cultures. The agent has characteristics that distinguish it from the known viruses.     

Maceration of Clover and Grass Leaves by Lachnospira multiparus

A strain of Lachnospira multiparus, a pectin-hydrolyzing bacterium from the rumen, was incubated in nutrient media in the presence of surface-disinfected clover leaflets. When the culture flasks containing the leaflets together with Lachnospira were shaken after overnight incubation, extensive maceration of the leaflets was seen, although uninoculated control leaflets remained intact during a similar treatment. Examination of inoculated leaflets by transmission electron microscopy showed extensive invasion of intercellular areas of the mesophyll tissue but only minor invasion of vascular tissue. Cutting the leaves before incubation greatly increased the ability of L. multiparus to colonize and macerate the leaflets. Similar experiments with grass leaves are also described, and the possible role of maceration in the digestion of plant material in the rumen is discussed. Although Lachnospira stains gram variable and often gram negative, the ultrastructure of the cell wall was that of a gram-positive bacterium.     

Effects of Daylength on Floral Characteristics of Six White Clover (Trifolium repens) Varieties

The effect of daylength upon floral initiation, flower position,and associated features was measured in six white clover (Trifoliumrepens) varieties Most plants initiated flowers in the longest days (16 h). Thevarieties of more southerly origin and with large leaves hada greater spread of response to daylength. Increasing daylength increased the number of buds becoming inflorescencesin all varieties except Milkanova in which the reverse was true.Peduncle length and nectar production were both greatest inthe longest days. Trifolium repens, white clover, daylength, flower initiation, flower position     

Determination of the Antigenic Protein Size Associated with Faba Bean Phyllody MLO by Using (SDS-PAGE) Electrophoresis and Immunotransfer

The antigenic proteins of MLO associated with faba bean phyllody (FBP) occurring in the Sudan were studied by using SDS-PAGE electrophoresis followed either by silver nitrate staining or by transferring to nitrocellulose membrane probed with specific polyclonal antiserum. No remarkable differences between healthy and FBP infected plants were observed when the gel was colored with silver nitrate. In contrast, after probing the transferred membrane with the specific polyclonal FBP antisera, band formation was only detected with FBP infected plants. These results were treated through an image analyser using a BIOLAB logicial. The analysed proteins measure approximately 18,000 and 36,000 daltons with regard to the protein molecular weight niarkers used (Bio-Rad). Possibility of the existence of a dimer is discussed. The localization of the bands is the same whatever the origins of FBP: Vicia faba or Crotalaria saltiana. However, the partial purification of the MLO including differential centrifugations followed by precipitation with polyethylene glycol (PEG) and passage through a column of Sepharose 4B were found to be essential for having clear electrophoretic profiles.     

Infection of Subterranean Clover (Trifolium subterraneum) by Kabatiella caulivora

Kabatiella caulivora is a serious pathogen of clover ( Trifolium ) spp. Subterranean clover ( T. subterraneum ) cv. Woogenellup was inoculated with K. caulivora , to study the attachment and germination of conidia, germ-tube penetration of the plant surface, and histochemistry and ultrastructure of changes in the host associated with lesion development. The foliar architecture caused the conidia to concentrate at the base of leaflets and on the petiolules (between the leaflets and petioles). Epidermal cells immediately beneath conidia and, occasionally, also adjacent cells developed a yellow-brown discoloration 1 day post-inoculation. Penetration appeared to be directly through the cuticle, characterized by constricted hyphae at the point of entry. No appressoria were observed. In leaves, invasion was restricted to the area proximal to the petiolule and leaf mid-rib. In petioles and petiolules, the hyphae initially remained between the epidermal cells and first layer of mesophyll cells before moving intercellularly through the mesophyll tissue towards phloem tissues. The cuticle was occasionally degraded in petiole and petiolule infections, the loss of epidermal and mesophyll cell wall components was detected, and chloroplasts and starch grains were disrupted. Plants developed macroscopic symptoms 10–11 days post-inoculation with necrotic lesions occurring on leaves, petioles and petiolules. Sporulation occurred approximately 15–18 days post-inoculation when affected plants collapsed. This information may be useful for breeding programmes aimed at selecting varieties with improved resistance to the clover scorch disease.     

Role of Extracellular Phosphatases in the Phosphorus-Nutrition of Clover

This paper examines the relationship between the ability ofsubterranean clover to use P-esters as sources of P for growth,and the enzymatic hydrolysis of those P-esters at the root surface.Trifolium subterraneum (cv. Mt. Barker) was grown under sterileconditions in porous agar containing either KH₂PO₄ (P₁), 2',3'-cyclicadenosine monophosphate (cAMP) or inositol hexaphosphate (IHP)as the source of P in the medium. Subterranean clover used cAMPas well as P¹ as a source of P for growth, but made little useof IHP. This preference in the use of P-esters was associatedwith differences in the substrate specificities of the externallyaccessible root phosphatases; roots of P-deficient clover grownunder sterile conditions had high hydrolytic activity againstcAMP but not IHP. These results are discussed in terms of anhypothesis on the function of the externally accessible phosphatases,i.e. that the phosphatases are present to recapture P from organicP compounds leaked from the cells. Key words: Organic P, extracellular phosphatase, roots, P uptake, clover     

Competence of Cimex lectularius Bed Bugs for the Transmission of Bartonella quintana,the Agent of Trench Fever

Background Bartonella quintana, the etiologic agent of trench fever and other human diseases, is transmitted by the feces of body lice. Recently, this bacterium has been detected in other arthropod families such as bed bugs, which begs the question of their involvement in B. quintana transmission. Although several infectious pathogens have been reported and are suggested to be transmitted by bed bugs, the evidence regarding their competence as vectors is unclear.ConclusionThe present work demonstrated for the first time that bed bugs can acquire, maintain for more than 2 weeks and release viable B. quintana organisms following a stercorarial shedding. We also observed the vertical transmission of the bacterium to their progeny. Although the biological role of bed bugs in the transmission of B. quintana under natural conditions has yet to be confirmed, the present work highlights the need to reconsider monitoring of these arthropods for the transmission of human pathogens.     

Dodder infection induces the expression of a pathogenesis-related gene of the family PR-10 in alfalfa

A full-length cDNA, PPRG2, representing a gene highly expressed in dodder (Cuscuta trifolii Bab et. Gibs)-infected alfalfa (Medicago sativa L.) stems was isolated by differential screening. The predicted protein contains 157 amino acids and belongs to the PR-10 family of the pathogenesis-related genes with putative ribonuclease activities. Northern hybridizations showed that PPRG2 is transcribed in root and crops of uninfected alfalfa and is induced not only by dodder attack but also by bacterial infections and a large variety of environmental stresses.     

Cyclical Transmission of Trypanosoma brucei rhodesiense and Trypanosoma congolense by Tsetse Flies Infected with Culture-Form Procyclic Trypanosomes*

SYNOPSIS. Culture procyclic forms of Trypanosoma brucei rhodesiense and Trypanosoma congolense were fed to Glossina morsitans morsitans through artificial membranes. A very high percentage of the flies so fed produced established midgut infections, a proportion of which went on to develop into mature metacyclic trypanosomes capable of infecting mammalian hosts. The method offers a safe, clean way of infecting tsetse flies with African trypanosomes which reduces the need for trypanosome-infected animals in the laboratory.