Gibberellic acid (GA3) increases berry size of "Emperatriz" seedless grape, the response depending on the phenological stage of vine at treatment date and on the concentration applied. From berry fruit set to 21 days later, 80 mg/L GA3 increased commercial berry weight by 50%-90%, depending on the year, reaching similar size to that of "Aledo" seeded grape, used as comparison. This effect takes place through: a) a larger berry growth rate; b) an early glucose, fructose and sucrose uptake; c) an increase of absolute glucose and fructose content (mg/berry) of seedless berries up to similar values to those of seeded berries; and d) an increase of absolute berry water content but not of relative content to fresh weight, thus water potential and osmotic potential are not significantly modified by treatments. GA3 does not affect berry pericarp cell number but increases pericarp cell diameter.
Chitosan and acibenzolar-S-methyl could directly inhibit the growth of Botrytis cinerea in vitro and confer resistance on grapes against grey mould. Pretreatment with these compounds could be an alternative to traditional fungicides in post-harvest disease control in grapes.
Ultrastructural alterations in epidermal and mesophyll cells and variations in endogenous zeatin riboside (ZR) concentrations were studied in leaves of Hedera helix, Pelargonium zonale, Pru-nus avium, and Rubus ulmifolius infected by Colletotrichum trichellum, Puccinia pelargonii-zonalis, Cercospora circumscissa, and Phragmidium violaceum, respectively. Infected tissues showed a marked increase in vesicles, myelin-like structures, and electron-dense bodies associated with plasma membranes. The main changes to the chloroplast included thylakoid swelling and disruption of the chloroplast envelope. The ZR content of the green islands was always higher than that of the yellow, senescent parts of the same leaves; the highest levels of ZR were observed in the green areas of infected Prunus avium (462.2 pmol g-1 fresh weight [FW]) and Rubus ulmifolius (441.6 pmol g-1 FW), followed by Pelargonium zonale (263.8 pmol g-1 FW) and Hedera helix (219.8 pmol g-1 FW); the yellow zones of the same leaves had lower ZR contents (78.3, 73.9, 73.6, and 18.1 pmol g-1 FW, respectively). The green islands had almost the same ZR content as the controls (green healthy leaves). These results suggest a relationship between ultrastructural alterations and ZR content of these plant species (blackberry, cherry, English ivy, geranium) in reacting to this type of biotic stress and could confirm the role of cytokinins as senescence-delaying hormones.
-Experiments were conducted to study the susceptibility to infection by two fungal pathogens, Cryphonectria parasitica or Phomopsis spp. of undisturbed holm oaks (Quercus ilex) and the resprout from the stump of trees after excision of the shoot. Leaf gas-exchange and chlorophyll a fluorescence were recorded on plants growing in natural conditions for two years, as markers of disease progress at the first stages of infection. In infected plants, pathogen-induced stomatal closure limited photosynthesis and increased contribution of energy dissipating processes protecting PSII integrity, as shown by higher non-photochemical quenching (NPQ). Excision treatment reduced susceptibility to infection and favoured water availability in resprouts, which showed higher gasexchange rates.Quercus ilex / Cryphonectria parasitica /Phomopsis spp. / gas-exchange / chlorophyll fluorescence Résumé -Effet de l'infection fongique sur les échanges gazeux et la fluorescence de la chlorophylle chez Quercus ilex. Le but de ce travail est l'étude de la susceptibilité des plants élagués (cas du chêne vert), à l'infection par Cryphonectria parasitica et Phomopsis spp. Pendant deux années, les échanges gazeux et la fluorescence de la chlorophylle d'un groupe de plants croissants dans des conditions environnementales naturelles ont été étudiés. Ces paramètres ont été des marqueurs convenables de l'évolution de la maladie durant les premières étapes de l'infection. Chez les plants infectés, le progrès de la maladie a été mis en évidence par la réduction de l'assimilation de CO 2 et l'augmentation de la participation des processus de dissipation thermique de l'énergie révélée par un NPQ élevé (Non-photochemical quenching). L'élagage induit une diminution de la susceptibilité à l'infection et permet une haute disponibilité hydrique chez les rejets assurant ainsi des taux élevés d'échanges gazeux.
Quercus ilex / Cryphonectria parasitica / Phomopsis
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