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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

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. Source

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

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. Source

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