Root exudates from lentil (Lens culinaris medic) seedlings in relation to wilt disease

Summary Root exudates from healthy and diseased lentil plants (Lens culinaris) have been investigated in relation to the wilt disease caused byFusarium oxysporum f.lentis. In all ten amino acids and five sugars have been detected. The spore germination of the pathogen in root exudates indicated that 21-days root exudate was inhibitory. Glycine and phenylalanine were detected in 21-days exudate and were found to have an inhibitory effect upon the germination of the spores of the pathogen which may partly explain the lesser disease incidence when plants of more than 3 weeks are inoculated with the pathogen.     

THE EFFECT OF CERTAIN SOIL TREATMENTS ON DIDYMELLA STEM ROT OF TOMATOES PART I. GLASSHOUSE EXPERIMENTS

When tomatoes were planted in steamed soil inoculated with spores of Didymella lycopersici Kleb., a large proportion became infected, but very few became infected in unsteamed soil similarly inoculated. In soil treated with formalin and subsequently inoculated the number of diseased plants was about half that in steamed soil. Reinfecting steamed soil with soil micro-organisms before inoculation with D. lycopersici reduced the amount of disease. Covering steamed soil with a layer of maiden loam filtered out a large proportion of D. lycopersici spores applied in water suspension and reduced the amount of disease. Addition of stable manure either before or after steaming did not affect the number of diseased plants. Steamed soil remained susceptible to infection by D. lycopersici for 4 months. D. lycopersici survived in a glasshouse soil over the winter, but the number of diseased plants was small. Cultivation may lessen the amount of disease by burying most of the infected surface layers of the soil. The peak of infection under glass occurred in May. The amount of disease and the yield were correlated, but with severe infection the yield varied with the time of infection and the distribution of diseased plants.     

Johnsongrass Chlorotic Stripe Mosaic and its Associated Viruslike Particles in Iran1

A mosaic disease of Johnsongrass characterized by the presence of short and long chlorotic stripes in leaves and stunting of plants was found in two locations about 300 km apart in the Fars Province of Iran. The disease occurred in patches or along the irrigation ditches. The disease agent could not be transmitted mechanically or by certain insects and mites. About 0.5% of the seedlings, grown in soil from the root zone of diseased plants, developed the disease after 1–8 months. Electron microscopy, of leaf-dip preparations showed presence of isometric viruslike particles (VLPs) of about 35 nm diameter in unusually high concentrations in diseased plants but not in healthy plants. VLPs from diseased leaves were purified by low-pH clarification followed by differential and densitygradient centrifugation. Purified VLP preparations showed UV absorption spectrum typical of nucleoproteins. A260/A280 was 1.48. High titered antisera obtained by injecting rabbits with purified VLPs reacted with sap from diseased plants but not healthy plants. Purified VLP preparations and sap from diseased plants did not react with antisera to Bermuda grass etched line, Brachypodium sylvaticum, brome mosaic, maize chlorotic dwarf, maize rayado fino, maize white line mosaic and tobacco necrosis viruses.     

Possible Phytoplasma Disease in Papaya (Carica papaya L.) from Baja California Sur: Diagnosis by Scanning Electron Microscopy

The symptoms of possible phytoplasma infection in introduced and local varieties of papaya were first noted in the Mexican state of Baja California Sur (BCS) during field surveys in 2002–2003. Phytoplasma structures were observed using scanning electron microscopy (SEM) in phloem sieve elements in diseased papaya plants, but not in healthy plants. They were rounded structures 400–1600 nm in diameter. This is the first report of the possible association of phytoplasmas with diseased papaya plants in BCS. The use of SEM for the primary detection of disease aetiology is discussed.     

Effect of ascochyta blight (Mycosphaerella pinodes) on yield components of single pea (Pisum sativum) plants under field conditions

Field studies were made in 1992 and 1993 to examine the yield components of pea inoculated with Mycosphaerella pinodes and those of healthy pea (sprayed with a mixture of flutriafol + chlorothalonil), in a split-plot design with the cv. Solara sown at different plant densities. Ascochyta blight was severe on leaves and on internodes of the basal part of the plants; pods had few lesions. The number and length of stems per plant were the same for diseased and healthy plants. The number of reproductive nodes and pods per stem were affected by disease only in 1993. In 1992 and 1993 respectively, disease caused reductions in the number of seeds per stem of 18% and 25%, and in seed size of 13.5% and 16.7%, compared with healthy plants. The harvest index and total biomass were lower in diseased than in healthy plants and seed yield was reduced by 40% in diseased plots. These results show a high relationship between the disease parameters (disease mean on stipules/nodes 8–18/ and on internodes/nodes 5–15/, percentages of stipules or internodes with a disease score 4, and percentage of stems encircled by lesions), plant density and yield reduction.     

Effects of Pratylenchus penetrans and Rhizoctonia fragariae on Vigor and Yield of Strawberry

Microplot and small field-plot experiments were conducted to determine the effects of Pratylenchus penetrans on strawberry yield over several seasons and to evaluate the effects of nematode control on strawberry vigor and yield. Pratylenchus penetrans alone or in combination with the black root rot pathogen, Rhizoctonia fragariae, reduced strawberry yield in microplots over time. There were no differences in effects on yield among R. fragariae anastomosis groups A, G, or I. The interaction of the two pathogens appeared to be additive rather than synergistic. In field plots infested with P. penetrans alone, plant vigor and yield were increased by the application of carbofuran and fenamiphos nematicides. Nematode control was transitory, as P. penetrans populations were initially suppressed but were not different in samples taken 10 months after treatment. These data highlight the error in associating causality between plant damage and nematode populations based on a correlation of root disease with nematode diagnostic assays from severely diseased plants. These findings may help to explain how nematode numbers can sometimes be higher in healthy plants than in severely diseased plants that lack sufficient roots to maintain nematode populations. Because nematode populations from up to a year before harvest are better correlated with berry yield, preplant nematode diagnostic assays taken a year in advance of harvest may be superior in predicting damage to perennial strawberry yield.     

Hummingbirds as vectors of fungal spores in Moussonia deppeana (Gesneriaceae): taking advantage of a mutualism?

Hummingbirds act as vectors of Fusarium moniliforme spores on protandrous flowers of Moussonia deppeana. The resulting interactions between the pathogen and plant-pollinator interactions were investigated in a 4-yr study to determine the pathogen's impact on host flowering phenology, flower longevity, nectar production, and fruit and seed production. We also evaluated hummingbird behavior on healthy and diseased plants and its effectiveness on spore transmission. Individual plants expressed the disease from year to year, and new infected individuals were detected every year. A fraction of the flowers in a plant expressed the disease, and this varied among and within years. Diseased plants produced more inflorescences, buds, and open healthy flowers than did healthy plants. Further, diseased plants bore proportionally fewer pistillate flowers than did healthy plants when considering only healthy flowers. Neither nectar nor fruit production differed between healthy and diseased plants, but healthy plants produced more seeds. Infected flowers were retained longer than uninfected ones, producing an additional 2 mg · μL(-1) · flower(-1) of nectar sugar. Hummingbirds visited more flowers on diseased plants than they did on healthy plants, regardless of number and sexual phase. Most pollen and spores were deposited within plants. These behavioral outcomes may promote geitonogamy and limit fungal spore mixing.     

Comparison of a current eelgrass disease to the wasting disease in the 1930s

A comparison is made of the wasting disease that struck the whole Atlantic population of Zostera marina L. in the 1930s and a current outbreak of a rather similar disease in Z. marina beds along the north-eastern coasts of the U.S.A. Although the disease phenomena on the plants appear to be very similar, disease-related declines of Z. marina are at present still very local. In Europe, diseased plants have been found, but no declines have been observed.

The wasting disease in the 1930s was not investigated before the epidemic reached a devastating stage. Present observations may indicate that a new widespread die-off may be developing. In order to facilitate the study of the current epidemic, a scenario of disease and related decline, with several variants, has been elaborated, based on the existing knowledge of the epidemic of the 1930s, but also clearly showing the gaps in this knowledge.     

The Anther Smut of Sea Campion: A Study of the Role of Growth Regulators in the Dwarfing Symptom

The sympton of dwarfing in the sea campion, Silene vulgaris(Moench) Garcke sub sp. maritima(With.) A. & D. Löveinfected with the anther smut fungus Ustilago violacea (Pers.)Fuckel, a systemic, perennial parasite, has been investigated. Extracts of both healthy and diseased plants contain IAA andGA₃, but diseased plants contain less gibberellins than healthyplants. Neither IAA nor gibberellins were detected in significantquantities in the medium when U. violacea was grown in pureculture, but IAN was present. IAN was also found m extractsof diseased plants and it is tentatively suggested that it isformed by the fungus and may accumulate in the host owing tothe inability of the plant to convert IAN to IAA The exogenousapplication of IAN to healthy plants does not produce any diseasesymptoms. The dwarfing symptom of the diseased plant may be due to thelower levels of gibberellins which it contains compared withhealthy plants since the exogenous application of GA₃, restoresthe diseased plant to normal growth     

粗缩病对玉米产量和籽粒品质的影晌

以6个对玉米粗缩病（MRDV）表现不同抗性的玉米品种为材料,研究了粗缩病对玉米产量性状和籽粒品质的影响。结果表明,在供试品种中,‘青农105’和‘青农8’为抗病品种,‘登海3622’和‘农大108’为中抗品种,‘先玉335’和‘郑单958’为感病品种。感病后,玉米果穗穗长、行粒数、穗粒重和产量显著降低,且损失程度表现为抗病品种〈中抗品种〈感病品种：籽粒中粗淀粉含量显著降低,粗蛋白含量升高,粗脂肪含量变化不明显。回归分析表明,通过旃情指数可以准确预测玉米粗缩病导致的产量损失。     

Changes in the composition of volatile compounds of Spartium junceum induced by the phytoplasmal disease,Spartium witches’‐broom

Abstract

In southern Italy, Spartium junceum (Spanish broom) is severely affected by a phytoplasmal disease, Spartium witches’‐broom (SpaWB). The volatile fractions extracted from flowers of healthy and diseased plants, examined by gas chromatography and gas chromatography–mass spectrometry, appeared to be quantitatively and qualitatively different. In both the healthy and the diseased plants, the main components were n‐alkanes, which occurred at a rate of 55.2% and 38.8%, respectively. The level of aliphatic acids was considerably lower in flowers of the diseased plants than in those of the healthy plants (4.5% vs. 18.7%). Sesquiterpenes were detected only in the diseased plants. It is possible that the changes in the composition of secondary metabolites of diseased plants can be related to plant defense responses.

Abbreviations: AP, apple proliferation; EY, elm yellows; SpaWB, Spartium witches’‐broom     

Development of A Rapid Method for the Diagnosis of Citrus Greening Disease using the Polymerase Chain Reaction

The fastidious bacterium causing citrus greening disease occurs in uneven and low concentrations in the sieve tubes of host plants. A rapid and sensitive assay based on the polymerase chain reaction (PCR) has been developed using the primers derived from the sequences of the cloned DNA fragment of greening fastidious bacterium (GFB) to detect GFB infection in citrus. One set of the primer pairs (named 226-primer pair), which generates a 226 bp GFB-specific fragment from total DNA templates purified from diseased citrus plants, was tested and chosen for PCR amplification. The PCR-based assay using this 226-primer pair effectively detected GFB infection in various citrus cultivars collected from different Asian countries. This detection technique, which can be completed within 6 h, offers a rapid and efficient method for accurate diagnosis of citrus greening disease.     

Mycoplasma-like bodies associated with Rubus stunt disease

Mycoplasma-like bodies were found by electron microscopy in the sieve tubes of blackberry, loganberry and raspberry plants showing symptoms of Rubus stunt disease, but not in those of normal plants. Watering diseased blackberry plants with aureomycin caused remission of the symptoms and greatly decreased the number of mycoplasma-like bodies.     

Microscopic and polyclonal antibody-based detection of yellow leaf disease of arecanut (Areca catechu L.)

Phytoplasma, the pathogen of yellow leaf disease (YLD) of arecanut (Areca catechu L.) was detected by transmission and scanning electron microscopy. Tissues of YLD affected palms contained phytoplasmas in the phloem sieve elements, but not in symptomless healthy palm tissues. Phytoplasma was purified from tissues of diseased palms employing percoll density gradient centrifugation and confirmed by transmission electron microscopy. Using the purified phytoplasma preparation, a polyclonal antiserum was raised in rabbits and used for standardisation of agar gel double diffusion (Ouchterlony) test and DAC-ELISA. Clear precipitin line was observed in Ouchterlony test between the antigen from diseased palms and the pathogen-specific antibodies after 48 h incubation and only undiluted antiserum showed best result in the test. However, in ELISA, 1:10 antigen dilution and 1:400 pathogen-specific antibodies dilution produced sensitive detection of the pathogen with a difference of >3.5 times absorption values between healthy and diseased samples. The results thus confirmed the ability of antiserum to distinguish healthy and infected plants and utility of ELISA for effective diagnosis of YLD.     

The effects of dazomet, fenaminosulf, and soil ridges on red core disease of strawberry

Fenaminosulf applied as a single soil drench soon after planting and growing plants on ridges 305 mm high decreased the incidence and severity of red core (Phytophthora fragariae). Pre-plant treatment with dazomet and growing plants on raised rows 100 mm high were ineffective. The % number of diseased roots was the most useful estimate of disease in evaluating the efficacy of treatments and the interaction of disease and yield. The relationship between disease and yield was highly significant, negative and apparently linear. Disease accounted for a higher proportion of the variation in yield in the first fruiting year than in the second. There was a close correlation between plant size in June and yield in July.     

稀土积累与油菜菌核病发生的关系研究

在试验生态小区的土壤中 ,模拟长期使用稀土 ,以探讨稀土积累与油菜菌核病发生发展的关系 .结果表明 ,0 .5 %、1%、3%、5 %、7%、10 %吸附容量和 0 6kg·hm-2 的稀土以及土壤中 30kg·hm-2 和 0 6kg·hm-2 的稀土复合肥添加剂对油菜菌核病自然发生的病情指数和病株率影响无显著差异 ;对人工接种发病后的病斑绕茎度、病斑扩展速率、单株平均产量和千粒重的影响也无显著差异     

Witches'Broom of Sarothamnus scoparius: A New Disease Associated with a Phytoplasma Related to the Spartium Witches'Broom Agent

In southern and central Italy, a witches’broom and decline disease of Sarothamnus scoparius has been observed. In affected plants, phytoplasmas were detected by PCR amplification of ribosomal DNA. Restriction fragment length polymorphism analysis of PCR-amplified DNA revealed that the diseased plants were infected by a phytoplasma that is closely related to the spartium witches’broom phytoplasma, a member of the apple proliferation group.