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Buenos Aires, Argentina

Insausti P.,Catedra de Fruticultura | Insausti P.,CONICET | Ploschuk E.L.,Catedra de Cultivos Industriales | Izaguirre M.M.,Catedra de Fruticultura | Podworny M.,Catedra de Fruticultura
European Journal of Plant Pathology | Year: 2015

Sooty molds are a lineage of follicolous fungi that cover the upper surface of leaves with black mycelia. Sooty molds do not infect plants, but grow on surfaces where honeydew deposits accumulate. It causes a reduction of incident sunlight by physical obstruction and in some species it interferes with photosynthesis. However, there are no studies proving that light interception by the sooty mold mycelia affects photosynthesis in orange plants. The aim of this study was to experimentally evaluate changes in the interception of sunlight caused by the black coating of sooty mold formed on orange leaves and to investigate its effects on the leaf chlorophyll content, stomatal conductance and photosynthetic rate. To facilitate the measurements, orange leaves with and without sooty mold colonies were selected. On a clear day, the sooty mold mycelia intercepted between 44 and 74 % of the total incident photosynthetic photon flux density (PPFD). However, even on leaves covered by the sooty mold mycelia, the measured PPFD was sufficient to saturate maximum net photosynthesis rate (Amax) for much of the day. No differences were found in Amax or leaf conductance, but there were increases in chlorophyll content and quantum yield in leaves infested by sooty mold, revealing a clear acclimation response. This study is the first to experimentally assess the direct effects of sunlight interception by sooty mold on chlorophyll content and net photosynthesis in orange leaves. © 2015, Koninklijke Nederlandse Planteziektenkundige Vereniging.

Gimenez R.,Catedra de Cultivos Industriales | Sorlino D.M.,Catedra de Cultivos Industriales | Bertero H.D.,Catedra de Produccion Vegetal FAUBA | Bertero H.D.,CONICET | Ploschuk E.L.,Catedra de Cultivos Industriales
Industrial Crops and Products | Year: 2013

The lifecycle of the facultative biennial oilseed-crop evening primrose (Oenothera biennis) is a major constraint for its commercial production under different growing conditions, as a variable proportion of plants fails to flower during the first season and remains as vegetative rosettes (biennial behavior). The aim of this work was to understand how flowering is regulated in this species and to identify the main determinants of its biennial behavior.Different planting dates and manipulative treatments (seed vernalization, photoperiod extension and fertilization) were employed to analyze if: (i) biennial behavior occurs when obligate requirements for vernalization or photoperiod are not satisfied; and (ii) responses to these environmental cues depend on the size and/or growth rate of rosettes.Our results indicate that O. biennis has an obligate long-day requirement for flowering and a facultative vernalization response. There is no minimum size requirement for vernalization response (as very small seedlings responded to the vernalization treatment) and the rate of development toward flowering under inductive photoperiods was strongly affected by rosette's growth rate. The incidence of high temperatures just before the onset of reproduction is proposed as an inhibitory factor that prevents reproduction under otherwise photo-inductive conditions. This last factor would explain the high incidence of biennial behavior frequently observed in spring/summer sowing in this crop. © 2012 Elsevier B.V.

Ploschuk E.L.,Catedra de Cultivos Industriales | Bado L.A.,Catedra de Cultivos Industriales | Salinas M.,Catedra de Cultivos Industriales | Wassner D.F.,Catedra de Cultivos Industriales | And 3 more authors.
Environmental and Experimental Botany | Year: 2014

Jatropha curcas is a promissory species for biodiesel production. Chilling and freezing stress are major environmental constraints for its establishment as a result of the injury provoked on leaf photosynthetic apparatus. This study is aimed at evaluating the impact of chilling (40h at 4°C) and freezing (2h at -1, -2 and -3°C) on maximum leaf photosynthesis (Amax), in relation to stomatal conductance (gs) and photochemical activity. Two similar experiments were conducted in pots outdoors; treatments were performed in climate chambers at the stage of four expanded leaves per plant, and then returned outdoors. Leaf gas exchange, water status and fluorescence variables were measured at 1 and 30 days after the end of the treatments (DAT). At 1 DAT, Amax and gs were reduced up to 75% and 100% in chilling and freezing treatments, respectively. However, the intercellular CO2 concentration (Ci) showed an inverse pattern, discarding a determinant role in Amax reductions. A lower efficiency electron use for photosynthesis was detected for plants subjected to chilling and freezing stress. The potential efficiency of PSII (Fv/Fm), chlorophyll content (Chl) and relative water content (RWC) were only affected by the lowest freezing treatments, while chilling and intermediate freezing plants showed an increase of the non photochemical quenching (NPQ). Leaf death occurred in the lowest freezing treatments, while several residual effects on Amax, gs and electron transport rate (ETR) were also observed at 30 DAT in the survival plants. This work sheds light on the determinant processes involved in the depletion of photosynthesis by chilling and freezing injuries, revealing that low temperatures have persistent and detrimental effects on J. curcas crop establishment. © 2014 Elsevier B.V.

Windauer L.B.,Catedra de Cultivos Industriales | Martinez J.,Catedra de Cultivos Industriales | Rapoport D.,Catedra de Cultivos Industriales | Wassner D.,Catedra de Cultivos Industriales | Benech-Arnold R.,Catedra de Cultivos Industriales
Annals of Botany | Year: 2012

•Background and Aims: Jatropha curcas is a drought-resistant tree whose seeds are a good source of oil that can be used for producing biodiesel. A successful crop establishment depends on a rapid and uniform germination of the seed. In this work we aimed to characterize the responses of J. curcas seeds to temperature and water availability, using thermal time and hydrotime analysis,•Methods: Thermal and hydrotime analysis was performed on germination data obtained from the incubation of seeds at different temperatures and at different water potentials.•Key Results: Base and optimum temperatures were 14·4 and 30 °C, respectively. Approximately 20 of the seed population displayed absolute dormancy and part of it displayed relative dormancy which was progressively expressed in further fractions when incubation temperatures departed from 25 °C. The thermal time model, but not the hydrotime model, failed to describe adequately final germination percentages at temperatures other than 25 °C. The hydrotime constant, θH, was reduced when the incubation temperature was increased up to 30 °C, the base water potential for 50 germination,Ψ b(50), was less negative at 20 and 30 °C than at 25 °C, indicating either expression or induction of dormancy. At 20 °C this less negative Ψ b(50) explained satisfactorily the germination curves obtained at all water potentials, while at 30 °C it had to be corrected towards even less negative values to match observed curves at water potentials below 0. Hence, Ψ b(50) appeared to have been further displaced to less negative values as exposure to 30 °C was prolonged by osmoticum. These results suggest expression of dormancy at 20 °C and induction of secondary dormancy above 25 °C. This was confirmed by an experiment showing that inhibition of germination imposed by temperatures higher than 30 °C, but not that imposed at 20 °C, is a permanent effect.•Conclusions: This study revealed (a) the extremely narrow thermal range within which dormancy problems (either through expression or induction of dormancy) may not be encountered; and (b) the high sensitivity displayed by these seeds to water shortage. In addition, this work is the first one in which temperature effects on dormancy expression could be discriminated from those on dormancy induction using a hydrotime analysis. © The Author 2011.

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