Chondrogenic differentiation of rat mesenchymal stem cells on silk fibroin/chondroitin sulfate/hyaluronic acid ternary scaffolds

Cartilage repair is a challenge in bone tissue reconstruction. In this study, silk fibroin (SF), chondroitin sulfate (CS) and hyaluronic acid (HA) were employed to fabricate scaffolds for tissue engineered cartilage by freeze drying technique. The secondary pores were formed in the main pores of SF/CS/HA scaffold which improved the pore connectivity and equilibrium swelling of the scaffold. Furthermore, rat bone marrow mesenchymal stem cells were seeded on the scaffolds to evaluate the cell adhesion and proliferation. Results of hematoxylin/eosin staining and cell counting kit-8 assay showed that the cells migration and differentiation of SF/CS/HA (80/15/5) scaffold were better than that of SF/CS/HA scaffolds with different ratios after 7 days culture. Moreover, immunohistochemistry and scanning electron microscope demonstrated that large amounts of collagen II and proteoglycans of the cells were expressed in the SF/CS/HA 3D scaffold, while the expression of collagen I was barely visible by immunohistochemistry. Abound of extracellular matrix was formed to morphologically round and distributed uniformly throughout the scaffolds. The 3D ternary scaffold could promote the cells chondrogenic differentiation without using any inductive agent and offer potential for cartilage tissue regeneration.     

The effect of growth regulators on tuberisation of cultured stem pieces ofSolanum Tuberosum

Summary The effect of growth regulators on tuberisation of potato (var.British Queen) stem cuttings has been investigated. It was found that indoleacetic acid and maleic hydrazide promoted tuberisation while gibberellic acid strongly inhibited the formation of tubers. The behaviour of stem pieces on a low sugar medium was also investigated and it was found that the application of growth regulators did not cause tuberisation when an adequate supply of carbohydrate was not available. It is suggested that tuberisation is regulated by the interplay of carbohydrate supply, gibberellins and antigibberellin-like substances.     

Fabrication of hollow nanofibrous structures using a triple layering method for vascular scaffold applications

This study aims to develop a new approach for fabricating hollow nanofibrous yarns by engineering a triple-layer structure (polyvinyl alcohol (PVA) multifilament core surrounded by a layer of PVA nanofibers and a polylactic acid (PLA) nanofiber outer layer). After fabrication of this 3-layer structure, the core portion was extracted, leaving the outer layer intact after dissolving the PVA nanofibers in water. To determine the optimum thickness of the outer layer, hollow nanofiber yarns with five different thicknesses were produced. A hollow nanofiber yarn was also produced using a common method to enable comparison of the methods. In the common method, a core sheath yarn consisting of a PVA multifilament core and a PLA nanofiber outer layer was fabricated, and a hollow yarn was produced by placing the core yarn in hot water. The results revealed facilitation of core extraction from the yarn body of the new 3-layer structure, which occurred due to rapid dissolution of the middle layer. The wicking behavior in the hollow yarn fabricated using the novel method followed the Locus Washburn equation and that of the hollow yarn produced from the core sheath yarn deviated from it. The results demonstrated that tensile properties of hollow nanofiber yarns were improved by increasing the thickness. Furthermore, hemolysis and cytotoxicity assays indicated that the fabricated hollow nanofibrous structure is non-toxic and blood compatible, indicating its potential for use in biomedical applications such as vascular scaffolds.     

Impact of vitronectin concentration and surface properties on the stable propagation of human embryonic stem cells

The standard method for culturing human embryonic stem cells (hESC) uses supporting feeder layers of cells or an undefined substrate, Matrigel(?), which is a basement membrane extracted from murine sarcoma. For stem cell therapeutic applications, a superior alternative would be a defined, artificial surface that is based on immobilized human plasma vitronectin (VN), which is an adhesion-mediating protein. Therefore, VN adsorbed to diverse polymer surfaces was explored for the continuous propagation of hESC. Cells propagated on VN-coated tissue culture polystyrene (TCPS) are karyotypically normal after >10 passages of continuous culture, and are able to differentiate into embryoid bodies containing all three germ layers. Expansion rates and pluripotent marker expression verified that a minimal VN surface density threshold is required on TCPS. Further exploration of adsorbed VN was conducted on polymer substrates with different properties, ranging from hydrophilic to hydrophobic and including cationic and anionic polyelectrolyte coatings. Despite differing surface properties, these substrates adsorbed VN above the required surface density threshold and were capable of supporting hESC expansion for >10 passages. Correlating wettability of the VN-coated surfaces with the response of cultured hESC, higher cell expansion rates and OCT-4 expression levels were found for VN-coated TCPS, which exhibits a water contact angle close to 65°. Importantly, this simple, defined surface matches the performance of the benchmark Matrigel, which is a hydrogel with highly complex composition.     

Adhesion, proliferation, and gene expression profile of human umbilical vein endothelial cells cultured on bilayered polyelectrolyte coatings composed of glycosaminoglycans

This study characterized human umbilical vein endothelial cell (HUVEC) adhesion, proliferation, and gene expression on bilayered polyelectrolyte coatings composed of an outermost layer of glycosaminoglycans (hyaluronan, heparin, or chondroitin sulfate), with an underlying layer of poly-L-lysine or chitosan. The proportion of cells that adhered to the various polyelectrolyte coatings after 1 and 2 h incubations was quantified by the WST-8 assay. Interchanging poly-L-lysine with chitosan resulted in significant differences in cellular adhesion to the outermost glycosaminoglycan layer after 1 h, but these differences became insignificant after 2 h. The proliferation of HUVEC on the various bilayered polyelectrolyte coatings over 10 days was characterized using the WST-8 assay. Regardless of whether the underlying layer was poly-L-lysine or chitosan, HUVEC proliferation on the hyaluronan outermost layer was significantly less than on heparin or chondroitin sulfate. Additionally, it was observed that there was more proliferation with poly-L-lysine as the underlying layer, compared to chitosan. Subsequently, real-time polymerase chain reaction was used to analyze the expression of seven genes related to adhesion, migration, and endothelial function (VWF, VEGFR, VEGFA, endoglin, integrin-α5, ICAM1, and ICAM2) by HUVEC cultured on the various bilayered polyelectrolyte coatings for 3 days. With poly-L-lysine as the underlying layer, biologically significant differences (greater than twofold) in the expression of VWF, VEGFR, VEGFA, endoglin, and ICAM1 were observed among the three glycosaminoglycans. With chitosan as the underlying layer, all three glycosaminoglycans displayed biologically significant differences in the expression of VWF and VEGFR compared to the chitosan control. CT-HA displayed the highest level of expression of VWF, whereas expression levels of VEGFR were almost similar among the three glycosaminoglycans.     

The effect of stem population on tuber yield in a trial with single-stem seed pieces

Summary Excised eyes on 5 g of seed tuber tissue were used to grow plants with single stems. These were transplanted in the field at densities of 120 000, 180 000 and 240 000 plants/ha, with in-row spacings of 16 or 33 cm. Total tuber yield was not affected, although more tubers were produced at the high densities. Tuber numbers did not increase in proportion to the number of stems. This was due to the fact that the number of tubers per stem decreased from a mean of 4.8 to 2.9 with increasing stem populations.     

Methods of testing fungicides for controlling skin spot (Polyscytalum pustulans) on potatoes during storage

Summary Suspensions of 12 fungicides were evaluated for controlling skin spot on stored potatoes in two experiments. Tubers produced from seed tubers inoculated withPolyscytalum pustulans (Experiment 1) or tubers wounded with pin pricks before dipping in mycelial suspensions ofP. pustulans (Experiment 2) were immersed for 5 minutes in suspensions of different fungicides at 10 mg l. 100 mg 1 or 1 g l a.i. After incubation in sealed plastic bags at 5°C the numbers of skin spots developed at random over the tuber surface (Experiment 1) or at pin pricks (Experiment 2) were recorded after 20 or 24 weeks. In both experiments carbendazim, thiabendazole and thiophanate methyl and in one experiment thiophamine were most effective in decreasing incidence of skin spots. Imazalil, prochloraz and sisthane also had highly significant effects at higher concentrations (100mg l. l g l a. i).

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Zusammenfassung Es wurden 12 Fungizide auf ihre Wirkung auf das Myzelwachstum vonPolyscytalum pustulans und auf das Auftreten der Tüpfelfleckenkrankheit an gelagerten Kartoffelknollen geprüft. Formulierte Fungizide wurden in Konzentrationen von 0.3 bis 80 mg l in 2%igen, auf pH 7 abgepufferten Malzagar inkorporiert. Der durchmesser der Kolonien wurde nach 4-w?chiger Inkubation bei 15°C gemessen, die meisten Verbindungen ergaben niedrige Hemmkonzentrationen (IC₅₀, Tabelle 1). Die Prüfung der Fungizide erfolgte in 2 Versuchen durch 5-minütige Immersion von Knollen in Suspensionen von 10 mg 1, 100 mg 1 und 1 g l Wirkstoff. In Versuch 1 wurden die Knollen von Saatgut, welches zur Pflanzung mitP. pustulans inokuliert worden war. 5 Tage nach der Rodung behandelt. In Versuch 2 wurden 8 Wochen lang gelagerte Knollen gewaschen und dann mit einem Ger?t, mit 25 Nagelspitzen (1 mm lang, 0,5 mm Durchmesser an der Basis) in 3 mm Abstand in einer Platte (20 mm × 20 mm × 3 mm) mit Handgriff, verletzt (Abb. 1). Das Ger?t wurde an 2 Stellen in die Knollen gedrückt, die verletzten Knollen wurden unmittelbar danach in eine Suspension von 10 Wochen alten mazerierten Kulturen vonP. pustulans von 2%igem Malzagar getaucht. Am n?chsten Tag wurden die Knollen mit den Fungiziden behandelt. In beiden F?llen wurden die Knollen nach Abtropfen luftgetrocknet und bei 5°C in drahtverschlossenen Plastikbeuteln gelagert. Ermittelt wurde die Zahl der Tüpfelflecken (Abb. 1) bei zuf?lligem Auftreten (Versuch 1, 20 Wochen) und nach Verletzung mit Nagelspitzen (Versuch 2, 24 Wochen). Carbendazim, Thiabendazol, Thiophanatmethyl und Thiophamine waren die effektivsten Verbindungen zur Verhinderung von Tüpfelflecken an gelagerten Knollen (Tabellen 2 und 3). Imazalil, Prochloraz und Sisthane hatten bei h?heren Konzentrationen ebenfalls hochsignifikante Wirkung. Die Knollenbesch?digung verursacht neue Verwundungen, an denen sich Tüpfelflecken bilden k?nnen, deshalb sind Fungizidprüfungen offensichtlich auch zu anderen Zeitpunkten als unmittelbar nach der Rodung m?glich, wie dies bei natürlich infizierten Knollen erforderlich ist. Ausserdem war das Auftreten von Tüpfelflecken zwischen Proben besch?digter Knollen weniger variabel als bei Knollen aus inokuliertem Pflanzgut.

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Résumé Douze fongicides ont été testés afin d'observer leur action sur la croissance mycélienne dePolyscytalum pustulans et l'incidence de l'oosporiose sur les tubercules en conservation. Des formulations de fongicides ont été incorporées dans la gélose avec 2% d'extrait de malt tamponné à pH 7 à des concentrations variant de 0,3 à 80 mg/l. Le diamètre des colonies a été mesuré à 15°C après 4 semaines d'incubation. La plupart des produits ont donné une inhibition à des concentrations faibles (IC₅₀, tableau 1). Deux expérimentations ont été mises en place pour tester les fongicides après immersion des tubercules pendant 5 minutes dans des suspensions de 10 mg/l, 100 mg/l et 1 g/l de matière active. Dans la première expérimentation, les tubercules provenant de plants inoculés avecP. pustulans à la plantation ont ètè traités 5 jours après l'arrachage. Dans la deuxième expérience, les tubercules ont été conservés pendant 8 semaines, puis la vés et blessés à l'aide d'une plaque (fig. 1) en laiton (20 mm×20 mm×3 mm) munie de 25 pointes (1 mm de long 0,5 mm de large à la base) espacees de 3 mm chacune. Chaque tubercule est blessé de deux endroits et immergé immédiatement dans une suspension contenant une culture deP. pustulans agée de 10 semaines et macérée dans une solution d'extrait de malt à 2%. Les tubercules ont été traités avec les fongicides le jour suivant. Dans les deux expérimentations, les tubercules traités ont été ressuyés puis séchés et mis dans des sacs en plastique. Les sacs sont fermés et stockés à 5°CC. Le nombre de taches sur les tubercules, soit présentes sur toute la surface après 20 semaines dans la première expérimentation, soit aux endroits des blessures après 24 semaines dans la deuxième expérimentation, a été enregistré (fig. 1). Le carbendazime, le thiabendazole, le méthyl thiophanate et la thiophamine ont été les produits les plus efficaces vis à vis de l'oosporiose sur tubercules en conservation (tableaux 2 et 3). L'imazalil, le prochloraz et le sisthane ont eu des effets significatifs aux concentrations les plus élevées. Les tubercules blessés pour l'expérimentation provoquent des conditions favorables au développement de l'oosporiose; il est donc suggéré de tester les fongicides à d'autres dates que celle de l'arrachage où l'on utilise obligatoirement des tubercules infectés naturellement. De plus, en ce qui concerne l'expression des sympt?mes, les échantillons de tubercules blessés présent nt une variabilité moins importante que des tubercules provenant de semences inoculées.

     

Determination of the potential land for securing double-rice cropping in the Cambodian Mekong Delta,based on a sub-area based modeling of flood inundation

Inundated areas of the Mekong Delta are the most important regions for agricultural production in both Cambodia and Vietnam. With population growth and increasing water demand in the dry season, effectively managing available water in the region is vital for crop production. This study is aimed at developing a sub-area based modeling of flood inundation model in order to analyze flood inundation processes in the Cambodian Mekong Delta as a basis for introducing semi-flood control for new cropping systems such as double-rice cropping. The simulated results of the flood inundation model from 2002 to 2003 were utilized for estimating land appearance in the dividing sub-area, and the potential of securing land for double-rice cropping was determined based on the period of land appearance and the cropping schedule. In order to realize the available water for double cropping, consideration of the effect of operating canal gates for controlling the early and receding inundation are crucially necessary. By considering the operation of control gates facilities, the potential land for securing double-rice cropping exceeded about 50 km² compared to the 34 km² of the actual land used for recession rice (about 30 and 20% of the total selected area, respectively). The study confirms that the sub-area based modeling of inundation model can be a helpful tool for water management in the Cambodia Mekong Delta.     

Host range of Alternaria alternata—a potential fungal biocontrol agents for waterhyacinth in India

The host ranges of Alternaria alternata and fungi native to India and pathogen of waterhyacinth (Eichhornia crassipes) were evaluated using 29 plant species (some with several cultivars tested) representing 18 families of economic and ecological importance. The results showed that only waterlettuce (Pistia stratiotes), another common weed in India, was infected by A. alternata. The use of these pathogens in the biological control of waterhyacinth would not be expected to affect plants of economic and ecological importance in India.     

Use of 2-aminobutane as a fumigant for control of gangrene,skin spot and silver scurf diseases of potato tubers

Summary Fumigation of tubers with 2-aminobutane (sec-butylamine) gas at a dosage of 200 mg/kg in simply made fumigation chambers gave very good control of the diseases gangrene (caused byPhoma exigua var.foveata) and skin spot (Oospora pustulans) if treatment was done within 14 days of harvesting. Some control of silver scurf disease (Helminthosporium solani) was also obtained, but results were always poorer than with gangrene or skin spot. Fumigation did not control tuber blight (Phytophthora infestans), dry rot (Fusarium solani var.caeruleum) and did not kill the sclerotia ofRhizoctonia solani. Since chemical analysis of treated peeled and boiled tubers, and crisps, granules and flakes made from treated tubers showed that they contained substantial residues of 2-aminobutane, the treatment can only be used on seed tubers. There were no significant residues in crops grown from treated tubers.

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Zusammenfassung Jedes Jahr k?nnen Pilzkrankheiten an Kartoffelknollen betr?chtliche Verluste verursachen. In Schottland ist die Phoma-Knollenf?ule, verursacht durch den PilzPhoma exigua var.foveata, die bedeutendste Krankheit, doch ist die Tüpfelfleckenkrankheit, hervorgerufen durchOospora pustulans, ebenfalls wichtig, vor allem weil sie die Keime bef?llt. Silberschorf, verursacht durchHelminthosporium solani, ist sehr verbreitet, aber obwohl er die Keime nicht bef?llt, werden durch ihn die Knollen missgebildet, und er verursacht Welke infolge des Wasserverlustes durch die besch?digte Schale. Begasung von Knollen mit 2-Aminobutan (sek-Butylamin)-Dampf in einer Dosierung von 200 mg/kg innerhalb 14 Tage nach der Ernte wurde als ein sehr gutes Mittel zur Bek?mpfung von Phoma-Knollenf?ule und Tüpfelfleckigkeit (Tabelle 5) befunden. In zwei Versuchen ergab die Begasung eine bessere Bek?mpfung von Phoma-Knollenf?ule als das Eintauchen in eine L?sung von Quecksilbermethoxy?thylchlorid, das 100 mg/kg Quecksilber enth?lt (Tabelle 6). Eine gewisse Bek?mpfung der Silberschorfkrankheit wurde mit 2-Aminobutan erzielt (Tabelle 7), aber die Ergebnisse waren immer schlechter als bei Phoma-Knollenf?ule und Tüpfelfleckigkeit. Phytophthora-Knollenf?ule (Phytophthora infestans) und Fusarium-Trockenf?ule (Fusarium solani var.caeruleum) wurden durch die Begasung nicht bek?mpft, und auch auf die Sklerotien vonRhizoctonia solani hatte, die Begasung keinen Einfluss. Die Beurteilung der F?ulen wurde an zwei Terminen vorgenommen, einmal im Februar und dann wieder im April, w?hrend die Schalenkrankheiten, Tüpfelfleckigkeit und Phoma-Knollenf?ule im April an gewaschenen Mustern von 50 oder 100 Knollen beurteilt wurden. Der Bau der Gaskammern (dargestellt in Abb. 1 und 2) wird kurz beschrieben und der Vorgang der Begasung diskutiert. Die Kammern sind für Gas-Innenkreislauf eingerichtet, das System ist verbunden mit einem Gebl?se und einem Verdampfer. Da das 2-Aminobutan-Luftgemisch durch einen losen Kartoffelhaufen dringt, wird die Chemikalie von den unteren Knollenschichten aufgenommen; aber da der Innenkreislauf anh?lt, findet eine Abgabe und Wiederaufnahme statt, so dass der Wirkstoff, wie sich bei Rückstandsanalysen gezeigt hat, m?glicherweise gleichm?ssig im Haufen verteilt wird. Es wurde festgestellt, dass bei einer Dosis von 200 mg/kg in 30–40 Minuten und bei Luftumw?lzung w?hrend weiteren zwei Stunden die Rückst?nde in Knollenmustern von unten und oben im Haufen ?hnlich waren (Tabelle 1). Rückst?nde von 2-Aminobutan waren in signifikantem Ausmass vorhanden in gesch?lten (Tabelle 2) und gesottenen Kartoffeln sowie in Chips (Tabelle 3), ferner in Flocken und Granulaten, die aus begasten Kartoffeln hergestellt wurden, so dass das Verfahren nur bei Pflanzkartoffeln angewendet werden kann. Analysen des Nachbaus von behandelten Knollen zeigte, dass sie keine signifikanten Rückst?nde enthalten (Tabelle 4). 2-Aminobutan wird leicht verdampft (Siedepunkt 63°C) und ist schwach giftig; die Giftigkeit beruht in erster Linie auf seiner Alkalinit?t. Gewisse Vorsichtsmassnahmen müssen getroffen werden, wenn diese Substanz zur Begasung von Kartoffeln verwendet wird; sie sind in einer formellen Gebrauchsanweisung beschrieben, die von den Autoren bezogen werden kann.

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Résumé Les maladies fongiques des tubercules de pomme de terre peuvent occasionner des pertes annuelles considérables. En Ecosse, la gangrène, causée par le champignonPhoma exigua var.foveata, est la maladie la plus grave mais, l'oosporiose, causée parOospora pustulans, est également importante, spécialement quand elle attaque les germes. La gale argentée, causée parHelminthosporium solani, est très commune, mais bien que n'attaquant pas les germes, elle détériore l'aspect des tubercules et provoque leur ramolissement par suite de la perte d'eau au travers de la peau endommagée. On a trouvé que la fumigation des tubercules avec la vapeur de 2-aminobutane (sec-butylamine), à la dose de 200 mg/kg dans les 14 jours qui suivent l'arrachage avait une très bonne efficacité dans la lutte contre la gangrène et l'oosporiose (tableau 5); de plus, dans deux essais, le résultat du traitement contre la gangrène a été supérieur au trempage dans une solution du chlorure de méthoxyethylmercurique à 100 mg/kg de mercure (tableau 6). Le 2-aminobutane a donné certains résultats dans le traitement de la gale argentée (tableau 7), mais ceux ci sont toujours inférieurs à ceux obtenus contre la gangrène et l'oosporiose. La fumigation n'a aucun effet contre le mildiou du tubercule (Phytophthora infestans) et la pourriture sèche (Fusarium solani var.caeruleum), pas plus que contre les sclérotes duRhizoctonia solani. La détermination des pourritures a été faite deux fois, une première fois en février et une seconde en avril, tandis que les déterminations des maladies de la peau, oosporiose et gangrène, ont été effectuées en avril sur des échantillons lavés de 50 ou 100 tubercules. Les auteurs décrivent brièvement la construction des chambres de fumigation (voir fig. 1 et 2) et expliquent le mécanisme de fumigation. Les chambres sont équipées pour la circulation forcée du gaz, grace à un ventilateur et un vaporisateur. Au moment où le mélange air — 2-aminobutane traverse le tas de pommes de terre, la substance chimique est absorbée par les couches inférieures de tubercules, mais grace à la circulation forcée, il se produit des phénomènes de ‘désaborption’ et de ‘réabsorption’ de telle sorte que, finalement, la substance chimique se répartit d'une mainière égale dans la masse de tubercules, comme l'indique l'analyse des résidus. Il a été démontré que si on applique la dose de 200 mg/kg pendant 30–40 minutes et qu'on réalise la circulation forcée pendant un minimum de 2 heures, les résidus dans les échantillons de tubercules sont identiques de la base au sommet du tas (tableau 1). Les résidus de 2-aminobutane sont présents en quantités significatives dans les tubercules pelés (tableau 2), bouillis et transformés en chips (tableau 3), de même dans les flocons et granulés fabriqués à partir de pommes de terre traitées, de sorte que le traitement ne peut s'appliquer qu'aux plants. L'analyse des récoltes issues de plants traités ne révèle aucune quantité significative de résidu (tableau 4). Le 2-aminobutane se vaporise aisément (63°C), est modérément toxique, la toxicité étant due en premier lieu à l'alcalinité. Il y a lieu de prendre certaines précautions dans l'emploi de cette substance dans la fumigation des pommes de terre, qui sont décrites dans le code d'emploi officiel que les auteurs peuvent fournir.

     

Possible mechanisms of size hierarchy among tubers on one stem of a potato (Solanum tuberosum L.) plant

Summary The tubers on one potato stem vary greatly in size and their size distribution may be described by their number and their average size and its variation. These components are mutually and closely related. The variation is partly caused by stolon characteristics, including their date of initiation, position and size. Tuber size is therefore partly determined before tuberization. Tuber-specific factors, such as the position and activity of the tuber initial also play a role, but the date of initiation of an individual tuber is not crucial. Later on, during tuber bulking, the activity of enzymes involved in starch metabolism, the levels of hormones, the mineral composition and the turgor potential are associated with the tuber growth rate. The growth characteristics of individual tubers may also vary since they are exposed to different conditions because of differences in position or growing period.     

A commercially acceptable assessment technique for improved control of cabbage stem flea beetle feeding on winter oilseed rape

Highly significant relationships between the percentage of leaves showing Psylliodes chrysocephala (L.) feeding scars and the mean number of larvae per plant during autumn, were established from 457 fields (over five different years) in England and Wales, and used to define an index of leaf scarring as an alternative assessment method for control decisions. The index was tested in conjunction with autumn samples using datasets from 786 fields (six years). An action threshold of 50% leaves scarred resulted in similar treatment advice to the current plant dissection method in over 98% of cases. During spring, the relationship between percentage leaves scarred and mean number of larvae per plant was not consistent between years and the index cannot be used for population assessment at this time of year.     

Effect of crop management on epidemics of phomopsis stem canker (Diaporthe helianthi) for susceptible and tolerant sunflower cultivars

Phomopsis stem canker (Diaporthe helianthi) is a worldwide fungal disease which is responsible for high yield losses in sunflower crop in the main regions of production. Field data on the influence of crop management on the incidence and severity of stem canker were reported by Debaeke et al. (2003) but a more thorough study was required to analyse step-by-step the spread of the fungus within the canopy from spore deposition on leaves to stem injury.In a 2-year study (2000–2001), the effects of crop management (plant density, N fertilization, and irrigation) and genotypic tolerance (susceptible vs tolerant cultivars) on the epidemics of Diaporthe helianthi were monitored under conditions of reinforced inoculum. The incidence and severity of leaf and stem symptoms were closely related to canopy development (leaf area index) and microclimatic conditions (relative humidity) resulting from different crop management options. Increasing plant density resulted in a greater proportion of girdling stem lesions, detrimental to yield, because of earlier infection under dense canopies. The number of girdling lesions per plant was maximal with high N fertilization but more leaves were infected without N fertilization.The field data were used to evaluate satisfactorily the epidemiological Asphodel model regarding the main periods of leaf infection. The relative humidity within the canopy (observed), the number of leaf infection events (simulated by Asphodel) and the final proportion of stem lesions (observed) were positively related which clearly demonstrated the key role of crop management in the development of stem canker in sunflower.     

Intercropping potatoes in early spring in a temperate climate. 3. The influence of planting date, row width and temperature change on the potential for intercropping

Summary The effects of planting date and row width on canopy development, intercepted radiation and yield were studied in two experiments, with the variety Wilja in 1988 and Cara in 1989. Planting dates were between mid March and early May and were combined with row widths of 0.75 and 1.25 m. Increasing the row width decreased intercepted radiation and yields in both years. Delayed planting reduced the yield of Cara, but not of Wilja. Early planting increased radiation use efficiency of Cara. It is argued that intercropping in spring without potentially reducing tuber yield might be favoured by delaying the planting of a determinate variety such as Wilja but by increasing the row width for an indeterminate variety such as Cara. Trends in mean monthly and soil 10 cm temperatures however suggest that opportunities for intercropping potatoes in the spring in a temperate climate may become more restricted.     

Bacteriophages with potential for inactivation of fish pathogenic bacteria: survival, host specificity and effect on bacterial community structure

Phage therapy may represent a viable alternative to antibiotics to inactivate fish pathogenic bacteria. Its use, however, requires the awareness of novel kinetics phenomena not applied to conventional drug treatments. The main objective of this work was to isolate bacteriophages with potential to inactivate fish pathogenic bacteria, without major effects on the structure of natural bacterial communities of aquaculture waters. The survival was determined in marine water, through quantification by the soft agar overlay technique. The host specificity was evaluated by cross infection. The ecological impact of phage addition on the structure of the bacterial community was evaluated by DGGE of PCR amplified 16S rRNA gene fragments. The survival period varied between 12 and 91 days, with a higher viability for Aeromonas salmonicida phages. The phages of Vibrio parahaemolyticus and of A. salmonicida infected bacteria of different families with a high efficacy of plating. The specific phages of pathogenic bacteria had no detectable impact on the structure of the bacterial community. In conclusion, V. parahaemolyticus and A. salmonicida phages show good survival time in marine water, have only a moderated impact on the overall bacterial community structure and the desired specificity for host pathogenic bacteria, being potential candidates for therapy of fish infectious diseases in marine aquaculture systems.     

Fungicide treatment of seed tubers infected with thiabendazole-resistantHelminthosporium solani andPolyscytalum pustulans for controlling silver scurf and skin spot on stored progeny tubers

Summary Seed tubers, cv. Désirée, derived from stocks treated annually with thiabendazole were infected with thiabendazole-resistant strains ofHelminthosporium solani andPolyscytalum pustulans. Samples of seed tubers were either untreated or immersed for 5 min in fungicide suspensions of thiabendazole, imazalil or thiabendazole plus imazalil and planted on four farms in 1988 and 1989. After harvest, tuber samples from each treatment were treated with thiabendazole and stored for 6 months. Applying imazalil or thiabendazole plus imazalil to seed tubers decreased the severity of silver scurf and skin spot on stored progeny tubers. Thiabendazole applied to seed tubers or to progeny tubers after harvest did not affect the severity of either disease, but post-harvest treatment decreased the incidence of black scurf after storage.     

Selection for individual traits in the early generations of a potato breeding program dedicated to producing cultivars with tubers having long shape and russet skin

Early generation selection in a potato breeding program involves visual assessment of economic worth based on appearance. Efficiency could be improved by using individual characteristics with defined selection behavior. This study was done to define the selectability of visible traits used for selection in the early generations of potato breeding. Twenty-seven traits were evaluated through three clonal generations using two hundred clones, twenty from each of ten crosses, taken from a population created to produce cultivars with long tuber shape and russet skin. Genotype × environment interactions, heritabilities, correlation coefficients among generations and locations, and rejection pattern analysis were used to quantify the consistency of expression for each trait. The chosen traits showed a wide range of heritabilities and consistency of expression. Traits were divided into three categories: those amenable to positive selection, those appropriate for negative selection, and those which should be ignored. The study showed positive selection to be possible for degree of skin russetting, and the incidence and severity of skin defects. It showed negative selection to be appropriate for incidence of second growth, growth cracks, tuber malformations, tuber curvature, pointed ends, the incidence and severity of russet patchiness, eye depth, tuber shape, yield, tuber number, average tuber weight, and flatness. To a lesser extent, negative selection could be used to reduce eyebrow prominence, degree of eye covering, and prominence of internodes. Traits too inconsistent for use in selection in early generations included uniformity of skin russetting, uniformity of tuber shape, and uniformity of tuber size. Severity ratings for second growth, growth cracks, tuber malformations, tuber curvature, and pointed ends were inconsistent and should not be used in lieu of incidence scores for the same traits.     

The effect of two planting dates on the physiological age and yielding potential of seed potatoes grown in a warm temperate climate in Argentina

Summary The effect of two planting dates upon the physiological age of seed tubers, measured by their incubation period, and their yielding potential was studied during a three-year period with two medium-early and one medium-late cultivar. Although seed tubers of the December planting were physiologically significantly younger than those obtained from the November planting in two of the three seasons studied, no reliable effect upon tuber yield was found. Reasons for this lack of relation are discussed. The accumulated day-degrees above 17°C (daily mean temperature) during the bulking period of the seed crop modified the incubation period of the tubers clearly.

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Zusammenfassung Der Einfluss zweier Pflanztermine auf das physiologische Alter von Pflanzkartoffeln und ihr Ertragspotential wurde w?hrend einer Dreijahresperiode an zwei mittelfrühen Sorten, Spunta und Kennebec, und einer mittelsp?ten Sorte, Bonaerense la Ballenera MAA, in warmer gem?ssigter Klimazone in Argentinien geprüft. Saatbest?nde aus November- und Dezemberpflanzungen von 1979, 1980 und 1981 wurden im November 1980, 1981 und 1982 in vergleichenden Ertragsversuchen gepflanzt. Das physiologische Alter der Knollen wurde bei der Pflanzung durch die Inkubationsperiode (Claver, 1973, 1975) gemessen. Abb. 1 zeigt die meteorologischen Daten der vier Vegetationsperioden. Es ergaben sich signifikante Unterschiede im physiologischen Alter zwischen den Sorten und den Pflanzterminen (Tab. 1). Bei Lagerung der Saatkartoffeln in Mieten im Feld beschleunigte sich das physiologische Alter (Tab. lc). Die Gesamtknollenertr?ge schwankten zwischen den Sorten in 1980/81 und 1982/83 (Tab. 2a und 2c), es ergaben sich jedoch keine signifikanten Unterschiede zwischen Pflanzgut der beiden Pflanztermine, obwohl sich zwischen beiden Pflanzterminen Unterschiede im physiologischen Alter ergaben. Der Gesamtknollenertrag war 1982/83 am h?chsten (Tab. 2c), obwohl die Pflanzknollen physiologisch die ?ltesten waren. Es ist unwahrscheinlich, dass eine hohe prozentuale Infektionsrate mit PLRV und PVY der Pflanzknollen von Spunta und Kennebec aus der Dezemberflanzung den Einfluss des physiologischen Alters auf den Ertrag derart überdeckte, dass keine signifikanten Unterschiede mehr gefunden werden konnten (Abb. 2). Weil die Unterschiede im physiologischen Alter innerhalb einer Sorte jedoch klein waren, waren andere ertragsbestimmende Faktoren offensichtlich wichtiger als die Unterschiede im Alter. Die akkumulierten Tagesgrade über einer t?glichen Temperatur von 17°C w?hrend der Periode des Knollenansatzes hatten eine klare ?nderung der Inkubationsperiode zur Folge.

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Résumé L'effet de deux dates de plantation sur l'age physiologique de tubercules de semence et sur leur rendement potentiel a été étudié durant une période de trois années avec deux variétés demi-hatives, Spunta et Kennebec, et une demi-tardive, Bonaerense la Ballenera MAA, cultivées dans un climat chaud d'Argentine. Les plants récoltés en novembre et décembre des années 1979, 1980 et 1981 ont été plantés en novembre 1980, 1981 et 1982 selon des essais comparables de rendement. L'age physiologique des tubercules était évalué à la plantation par la période d'incubation (Claver, 1973, 1975). Les relevés météorologiques pour les quatres saisons sont donnés dans la fig. 1. On observait des différences significatives dans l'age physiologique entre les variétés et les dates de plantation (tabl. 1). Quand les tubercules de semence étaient conservés en silo au champ, l'age physiologique était avancé (tabl. lc). Le rendement total en tubercules était différent entre variétés pour 1980/81 et 1982/83 (tabl. 2a et 2c) mais il n'y avait pas de différences significatives entre les plants des deux dates de plantation bien qu'il y ait des différences significatives dans leur age physiologique. Le rendement total en tubercules était plus élevé en 1982/83 (tabl. 2c) malgré des tubercules de semence physiologiquement plus vieux. Il est peu probable que le taux important d'infection par les virus de l'enroulement et Y des semences de Spunta et Kennebec observé de l'age physiologique des plants sur les rendements, ceux-ci ne présentant aucune différence significative (fig. 2). De plus, parce que les différences d'age physiologique des semences au sein d'une variété sont-faibles, d'autres facteurs déterminants que le rendement doivent avoir été plus importants que la différence d'age. Le cumul jour-degrés au-dessus de la température journalière de 17°C durant la période de tubérisation des tubercules de semence modifie sensiblement la durée d'incubation des plants (fig. 3).