Induced Resistance in Tomato Against Corynebacterium michiganense pv. michiganense by Prior Inoculation with Pseudomonas syringae Pathovars

Prior inoculation of wounded tomato petioles with a minimum concentration of 5 × 10⁴ cells per wound of various Pseudomonas syringae pathovars completely protected plants against subsequent infection with Corynebacterium michiganense pv. michiganense inoculated on the same site. Only living cells induced effective protection. In protected tissue, cells of Corynebacterium michiganense pv. michiganense remained localized at the inoculation site and their multiplication was restricted. Irrespective of the cell number introduced, initial population decreased slowly and then levelled off below the initial inoculum level. This level remained constant throughout the experimental period (15 days). Similarly, the, cell number of the inducer Pseudomonas syringae pv. phaseolicola levelled off at ca. 10⁶ cells per plant. The protection was not systemic and could be eliminated by removing the upper 5 mm of the inoculated wound tissues containing, the inducer.     

Survival ofXanthomonas campestris pv.vesictoria in pepper seeds and roots in symptomless and dry leaves in non-host plants and in the soil

Summary A population ofXanthomonas campestris pv.vesicatoria developed as endophytes in the leaves and rhizosphere of apparently symptomless plants grown under mist but not under dry conditions. The pathogen survired for long periods on, and could be isolated from, the surface of infested dried seeds, inoculated sandy loam soil, dried leaves, and the rhizosphere of pepper and of other non-host plants. In addition, small numbers of the pathogen survived for 18 months in a field previously cropped with pepper diseased with bacterial scab. Healthy nursery or mature plants developed symptoms while growing in soil containing infested leaves, either buried or placed on the soil surface.     

Systemic spread of downy mildew in basil plants and detection of the pathogen in seed and plant samples

Downy mildew on sweet basil (Ocimum basilicum L.) occurs worldwide. Contaminated seeds are considered as the primary inoculum source. So far no strategy to control the disease is available. Hence, the use of pathogen-free seeds is the only alternative to prevent disease outbreaks. Therefore, a rapid diagnostic method for seed testing is urgently needed. The sensitivity of a specific PCR method for direct detection of the downy mildew pathogen Peronospora belbahrii on basil samples, particularly on seeds, was evaluated. The applied PCR method proved to be very sensitive for direct detection of the pathogen on seeds and plant samples. The PCR detection limit of P. belbahrii in artificially infested seeds corresponded to the DNA amount of a single spore per seed. Additionally, the systemic spread of the pathogen from naturally infected seeds was investigated. The experiments showed that outgrowing basil plants were latently infected with the downy mildew pathogen, and the infection continued within the plant. Contaminated seeds were harvested from symptomless latently infected plants. These results support the implementation of PCR-based detection in a seed certification scheme and the necessity to control the pathogen on seeds. The PCR method can also be used for evaluation of pathogen control on seeds based on detection of the pathogen in outgrowing plants.     

Leakage of solutes from leaf discs of alfalfa plants susceptible and resistant to bacterial wilt caused byCorynebacterium michiganense pv.insidiosum

Seven day- and six week-old alfalfa (Medicago sativa L.) plants, susceptible and resistant to bacterial wilt, were inoculated withCorynebacterium michiganense pv.insidiosum (McCulloch) Dye & Kemp. Leakage of solutes absorbing UV light from leaf discs into distilled water was investigated. The bacterial infection did not affect solute leakage rate from unifoliate and trifoliate leaves of either susceptible or resistant plants at an early stage of the disease. This may indicate that cell membrane integrity in alfalfa leaf tissues was not impaired.     

Inheritance and sources of resistance to bacterial speck of tomato caused by Pseudomonas syringae pv. tomato

Inheritance of resistance to bacterial speck of tomato was determined by analysing F₁ F₂ and backcross progenies of crosses involving a susceptible (VF-198) and a resistant cultivar (Rehovot-13). The results fit the hypothesis that resistance is controlled by a single dominant gene in interaction with minor genes. Cultivar susceptibility to Pseudomonas syringae pv. tomato was tested under greenhouse conditions under high inoculum pressure using infested tomato seeds together with infested soils and spray-inoculated wounded plants. Of 21 species, cultivars and lines, Rehovot-13, Ontario 7710 and Lycopersiconpimpinellifolium P.I. 126927 were found to be resistant to the pathogen. VF-198 and Tropic-VF were the most susceptible. Extra Marmande, Saladette, Acc.339944–3 and the wild type Lycopersicon esculentum var. cerasiforme were moderately resistant.     

Inhibition of Seed Germination and Root Development Caused by Xanthomonas campestris pv. vesicatoria in Pepper and Tomato

Inoculation of pepper seeds with the leaf pathogen Xanthomonas campestris pv. vesicatoria inhibited pepper germination. The inhibitory effect, which was stronger in non-sterilized light textured soils, decreased with time, and after 20, days or more, there was no difference between inoculated and non-inoculated seeds. Inhibitory substance(s) within the cytoplasmatic fraction of pathogen cells inhibited the germination of non-host tomato seeds. No relationship between pathogenicity to pepper leaves and inhibition of pepper seed germination was detected. The inhibitory substance(s) was found in two out of four X. campestris pv. vesicatoria strains. Heat-killed bacteria suppressed growth of pepper but not tomato seedlings. It is, therefore, suggested that the inhibition of seed germination and the decrease in root development are different modes of X. campestris pv. vesicatoria pathogenesis toward pepper plants.     

Inoculum Sources for the Spread of Leaf Scald Disease of Sugarcane Caused by Xanthomonas albilineans in Guadeloupe

Leaf scald of sugarcane, caused by Xanthomonas albilineans, is thought to be spread mainly in infected cuttings and transmitted on infested cutting implements. Several observations made in Guadeloupe indicated that other means of spreading also occur. The dispersal of the pathogen outside sugarcane was investigated with plants inoculated by an antibiotic-resistant marked strain of X. albilineans and with plants naturally infested with wild strains of the pathogen. The bacteria were isolated in water droplets (rain or dew) on the surface of sugarcane leaves at dawn. It was also detected on the surface of dry leaves during the day by leaf imprinting onto a selective culture medium. The bacteria were much more frequently isolated from the surface of symptomatic leaves than from symptomless ones. Aerial dispersal of X. albilineans was investigated by placing Petri dishes containing selective culture medium between sugarcane plants but without direct contact with the leaves. The pathogen was isolated in four out of 270 dishes which were randomly set 3–14 h in a diseased field. These results indicated that the pathogen exuded from the leaves and then was spread by aerial means (rain, insects, …) or by leaf contact. The bacteria were also found in roots and rhizospheric soil of infested sugarcane stools suggesting that X. albilineans could be transmitted by root to root contact or by the soil. Finally, isolations of the pathogen in sugarcane inflorescences were positive. So, fuzz transmission may also occur.     

Inoculum Sources for the Spread of Leaf Scald Disease of Sugarcane Caused by Xanthomonas albilineans in Guadeloupe

Leaf scald of sugarcane, caused by Xanthomonas albilineans, is thought to be spread mainly in infected cuttings and transmitted on infested cutting implements. Several observations made in Guadeloupe indicated that other means of spreading also occur. The dispersal of the pathogen outside sugarcane was investigated with plants inoculated by an antibiotic-resistant marked strain of X. albilineans and with plants naturally infested with wild strains of the pathogen. The bacteria were isolated in water droplets (rain or dew) on the surface of sugarcane leaves at dawn. It was also detected on the surface of dry leaves during the day by leaf imprinting onto a selective culture medium. The bacteria were much more frequently isolated from the surface of symptomatic leaves than from symptomless ones. Aerial dispersal of X. albilineans was investigated by placing Petri dishes containing selective culture medium between sugarcane plants but without direct contact with the leaves. The pathogen was isolated in four out of 270 dishes which were randomly set 3-14 h in a diseased field. These results indicated that the pathogen exuded from the leaves and then was spread by aerial means (rain, insects,…) or by leaf contact. The bacteria were also found in roots and rhizospheric soil of infested sugarcane stools suggesting that X. albilineans could be transmitted by root to root contact or by the soil. Finally, isolations of the pathogen in sugarcane inflorescences were positive. So, fuzz transmission may also occur.     

Transmission of seed-borne infection of chilli by Burkholderia solanacearum and effect of biological seed treatment on disease incidence

Abstract

A survey of chilli fields in the state of Karnataka, India, showed the presence of bacterial wilt disease in important chilli growing regions. The disease incidence ranged from 26?–?32%. The pathogen was isolated from infected plant material and seeds. Infected plant material showed the release of milky white bacterial ooze. Burkholderia solanacearum was detected from chilli seeds by liquid assay and its identity was confirmed by biochemical tests, hypersensitive reaction and pathogenicity tests. Seed transmission of the pathogen up to 45% was observed in seeds artificially infested with the pathogen. Among different tissues of the seed, endosperm showed the presence of the pathogen. Biological seed treatment with antagonistic Pseudomonas fluorescens significantly (p?=?0.05) improved the seed quality parameters under laboratory conditions and drastically reduced the bacterial wilt incidence under field conditions. Seed-borne nature, transmission and effect of Pseudomonas fluorescens in both the forms of pure culture and formulation on seed quality parameters and bacterial wilt incidence are discussed in the present work.     

The Hydroxyproline Content in Cell Wall of Resistant and Susceptible Alfalfa Plants Inoculated with Wilt Pathogens

The changes of hydroxyproline (Hyp) content in cell wall after inoculation with Corynebacterium michiganense pv. insidiosum or Verticillium albo-atrum in 8 cultivars of alfalfa (Medicago sativa) were studied. In our experiments cultivars ‘Trek’ and ‘Vernal’– resistant, ‘Du Puits’ and ‘Vertus’– susceptible to C. michiganense;‘Vela’ and ‘Maris Kabul’– resistant to V. albo-atrum, ‘Sabilt’ and ‘Lahontan’– susceptible to V. albo-atrum were used. In resistant plants inoculated with C. michiganense none or a small increase of Hyp content in comparison with control plants was registered. On the other hand, inoculated susceptible plants showed markedly increase of Hyp content in comparison with the control plants. The differences in Hyp content between control and inoculated resistant and susceptible plants with V. albo-atrum were not markedly expressed in comparison with the alfalfa –C. michiganense pair. The changes had similar tendency both in C. michiganense and V. albo-atrum.–alfalfa pairs.     

Effect of Alfalfa Wilts on the Hydroxyproline Content in Cell Wall

The Hyp content was studied in cell wall of alfalfa susceptible and resistant strains on the 3rd, the 7th and on the 14th day after inoculation with Verticillium albo-atrum or Corynebacterium michiganense pv. insidiosum. The changes of Hyp content after inoculation with both pathogens were markedly expressed in alfalfa roots. Resistant plants of R 337 strain responded to inoculation with V. albo-atrum or C. michiganense pv. insidiosum by the decrease of Hyp content mainly on the 3rd and on the 7th day. On the 14th day after inoculation Hyp content practically did not differ from that of the control. Susceptible plants of S 354 and S 321 srains responded to inoculation with wilt pathogens by the slight decrease of Hyp content at the 3rd day after inoculation. A significant increase of Hyp content was found on the 7th and mainly on the 14th day after inoculation in comparison with control plants. The cell wall Hyp content was also determined with 7 R-strains and 7 S-strains at 120 days after inoculation with both pathogens. In each R and S strain two categories of plants were used for chemical analyses: Wilt-free plants (0 to 1 classes) and diseased, wilted plants (2 to 6 classes). In the resistant alfalfa strains no differences in Hyp content between the wilt-free and diseased plants were found. In the susceptible alfalfa strains the Hyp content was significantly higher in roots of diseased plants comparing with the wilt-free ones. Only negligible changes in Hyp content were registered in the overground parts of all inoculated alfalfa strains.     

Behavior of the tachinid parasitoid <Emphasis Type="Italic">Exorista japonica</Emphasis> (Diptera: Tachinidae) on herbivore-infested plants

Odors from corn plants infested with the larvae of the noctuid herbivore Mythimna separata (Walker) attract tachinid fly, Exorista japonica Townsend, females; and odors from corn plants artificially damaged also attract this fly. We investigated the responses of flies to herbivore-infested, artificially damaged, and undamaged plants before and after arrival at the target plants to measure timing of the behavioral sequence. The behavior of the flies for 10 min after takeoff from a release point was observed in a wind-tunnel bioassay. The percentage of flies attracted to the plants was higher in infested and artificially damaged plants than in undamaged plants. Latency before takeoff was longer in undamaged plants, and time from takeoff to arrival at the plant was also longer in undamaged plants. Moreover, flies stayed longer on infested and artificially damaged plants. Flies walked longer on infested plants than on artificially damaged and undamaged plants. In this paper, we summarize the behavioral data and discuss the host-searching behavior of E. japonica females.     

Suppression of Root Rot on Peas, Beans and Beetroots Caused by Pythium ultimum and Rhizoctonia solani through the Amendment of Growing Media with Composted Organic Household Waste

In pot experiments under controlled environmental conditions, composted organic household waste showed a suppression of soilborne plant pathogens. The addition of 8 %, 10 % and 30 % compost to the potting material which was artificially infested with Pythium ultimum or Rhizoctonia solani considerably reduced the incidence of disease in different varieties of host plants. It became evident that the degree of protection provided by compost depends upon the amount of compost added and upon the vulnerability of the host plant to infection. In an experiment using increasing levels of inoculum, the compost proved suppressive to the pathogen even under extreme disease conditions. This suppressive effect was still evident in compost which had been stored for prolonged periods.     

The effects of inoculum density and physical factors on the assessment of disease caused by Sclerotium rolfsii

Greenhouse and laboratory experiments were conducted to determine the effects of various physical factors on the assessment of disease caused by Sclerotium rolfsii using field and artificially infested soils. Lentil(Lens esculenta Moench) seedlings growing in trays or pots with sand were inoculated by surrounding them with a layer of soil infested with the pathogen. The number of dead plants was maximal within a 10-day period following inoculation. Seedling mortality increased with the number of sclerotia in the soil to a maximum that depended on seedling spacing, depth of the soil layer, and soil type.     

Effect of sorghum phenology on the control of Chilo partellus with Nosema marucae (microspora: Nosematidae)

An aqueous suspension of Nosema marucae spores was sprayed on foliage of sorghum plants that had been infested with neonate Chilo partellus larvae at 3, 5, 7 and 9 weeks after (plant) emergence (WAE). These periods corresponded to plants at the tillering, early booting, soft dough and late maturation phenological stages, respectively. The extent of borer infestation and plant damage was monitored until crop harvest, and compared with plants which had been similarly infested but not sprayed with the pathogen, and with plants in insect‐free control plots. When applied early, infestation with neonate borer larvae caused most damage to the plants and the greatest reduction in yield in the untreated plots. Early treatment with N. marucae spores at 3 and 5 WAE resulted in the greatest reduction in damage to plants and the highest improvement in yield of seeds. It is apparent, therefore, that for maximum crop protection the microsporidian needs to be applied when sorghum is in an early phenological stage.     

Origin of Early Attacks of Sclerotinia Stem Rot on Winter Oilseed Rape (Brassica napus sub. sub. sp. oleifera var. biensis) in the UK

Studies in artificially infested field plots of winter oilseed rape showed that mycelia originating from both sclerotia and ascospores of Sclerotinia sclerotiorum can initiate early attacks of sclerotinia stem rot. Disease symptoms appeared in early November in plots previously infested with sclerotia in September. There was a 6–7 week period from artificially inoculating plants with ascospores in October to observing disease symtoms in December. The primary sites of infection for both typesof inocula were the laminae and petioles of senescent and frost-damaged leaves. Following primary infection, mycelia of the pathogen spread by plant to plant contact, causing secondary infections of neighbouring plants. Sclerotia developed on diseased plants and high numbers were returned to the soil. The importance of these findings to the epidemiology of the disease are discussed.     

Preliminary Investigations about the Mode of Transmission and Spread of Xanthomonas campestris pv. graminis on Forage Grasses

Extensive studies showed that no disease was caused when seeds of different forage grasses were inoculated with Xanthomonas campestris pv. graminis. The disease could easily be induced by infecting the plants in the root system, leaves or flower. The inoculation site in the leaf proved to be of vital importance for the development of the disease. Wilting symptoms were quickly induced when the pathogen was inoculated near the leaf base. Plants in root-contact with diseased plants showed disease symptoms. It is not known whether these symptoms were caused by the bacteria or by toxins released by nearby diseased plants. Cross inoculation trials on different grass varieties revealed that different pathovars exist in the group of xanthomonads, pathogenic to forage grasses. Some have a broad host range whereas others are more limited to a single plant genus. Field trials suggest that in Belgian climatic conditions, the losses caused by bacterial wilt are rather limited.     

Bacterial blight pathogen concentration in cotton seeds; its role in seed quality parameters of fuzzy and acid delinted seeds

Abstract

The adverse effects of increasing concentration of Xanthomonas axonopodis pv. malvacearum on cotton seed quality parameters, seedling dry weight and on defense-related enzyme, Phenylalanine Ammonia Lyase (PAL) were studied. Different concentrations of pathogen (1×10² to 1×10⁸ CFU/ml) were treated on both fuzzy and acid delinted seeds and subjected to the standard blotter method to study the effect of the pathogen on seed quality parameters. The seedling symptom test following the roll towel method, the modified germination test to study the blight incidence and the field emergence test were carried out to discover the field planting value and disease incidence under laboratory and field conditions. From these experiments, it was found that the decrease in the seed quality parameters like seed germination, seedling vigour, and the dry weight of seedlings when X. axonopodis pv. malvacearum concentration was increased. Whereas the bacterial blight incidence increased with an increase in pathogen concentration, in both greenhouse and field conditions. Phenylalanine ammonia lyase activity was found to increase along with the pathogen concentrations, but total phenol content decreased as pathogen concentration increased. The effect of X. axonopodis pv. malvacearum load on seed quality parameters, PAL enzyme activity of fuzzy and acid delinted cotton seeds are discussed in the present study.     

Soybean seed damage by different species of stink bugs

Abstract

• 1 Damage caused by the three main species of stink bugs occurring on soybean Nezara viridula (Linnaeus), Piezodorus guildinii (Westwood) and Euschistus heros (Fabricius) was compared in field cages and in greenhouses. Infestation levels of 4 stink bugs/m row of plants (field cages) and 2 stink bug/plant (greenhouse) for 15 days during the pod filling stage are reported. At harvest, the yield and seed quality were evaluated.
• 2 In the field, there was no difference in yield between infested and insect‐free plants, but damage to seed quality varied with stink bug species. Plants damaged by P. guildinii had the lowest quality seeds. From 50 g seed samples harvested in the field, the mean weight of seeds classified as ‘good’ was 37.3 g in plants infested with P. guildinii, compared to 41.8, 44.2 and 46.6 g in plants infested with E. heros, N. viridula and the control, respectively.
• 3 Plants infested with P. guildinii showed the highest number of seeds damaged by stink bugs, whereas those infested with E. heros showed the lowest damage.
• 4 Plants infested with P. guildinii had 18.5% damaged seeds, higher than the 3.6% and 3.4% damaged seeds from plants infested with the two other species and 0.1% in control plants. The percentage of non‐viable seeds due to stink bug damage was 5.7% for P. guildinii but lower for the other two species.

     

Induced androgenesis in tomato (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> Mill.). III. Characterization of the regenerants

We present data on the morphological, cytological, biochemical and genetic characteristics of tomato regenerants obtained through anther culture. As a result of induced androgenesis, more than 6,000 rooted regenerants were developed that differed both from the donor plants and among each other with respect to habitus and leaf, flower and inflorescence morphology. Cytological analysis revealed a great variability in chromosome number in the cells of the regenerated plants. While most of the regenerants were mixoploid, the majority of the cells had a haploid chromosome number. R₁ and R₂ progenies were tested for their resistance to Clavibacter michiganense subsp. michiganense (Cmm 7). Some of the regenerants were resistant to the pathogen. A biochemical analysis of fruit from R₃ and R₄ plants showed a higher content of dry matter, sugars and vitamin C in the regenerant plants obtained from the hybrids than in those from the cultivars and control plants. The values of the parameters of hybrid regenerants grown in the greenhouse were about 1.5-fold higher than those of the hybrid regenerants grown in the field, and this trend is clearly expressed in all of the hybrid regenerants. The results obtained suggest that induced androgenesis and gametoclonal variation may be used as an additional tool to create a large range of new forms. The application of the latter in breeding programs would accelerate the development of tomato lines and varieties that would be more productive, disease-resistant, highly nutritive and flavour-acceptable.Abbreviations BAP N⁶-Benzylaminopurine - Cmm Clavibacter michiganense subsp. michiganense - cfu Colony-forming units - GA ₃ Gibberellic acid - IBA Indole-3-butyric acid - ms Male sterility - PDA Potato dextrose agar Communicated by H. Lörz