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Analysis of the Profile of Volatile Compounds During the Growing Season in Leaves of Aesculus Trees Differing in Susceptibility to Horse Chestnut Leaf Miner (Cameraria ohridella Deschka & Dimić)
The invasive pest Cameraria ohridella annually colonizes trees of the genus Aesculus across Europe, causing dark brown damage called mines that gradually cover the leaf surface. This study aimed to compare the VOC profiles emitted by chestnut tree leaves with varying susceptibility to the pest and assess whether these profiles change due to larval feeding. The research involved a susceptible tree (Ae. turbinata) and resistant trees (Ae. glabra and Ae. parviflora). Over three growing seasons (2014, 2015, 2016), leaf damage and the profile of VOCs were analyzed biweekly from May to September. Leaf damage increased progressively in Ae. turbinata during all seasons. The VOC profiles differed both qualitatively and quantitatively among the trees and across years. More VOCs were identified in 2014 and 2015 than in 2016. The susceptible Ae. turbinata exhibited the highest VOC diversity in 2014, aligning with severe leaf damage—profiles of VOCs in Ae. turbinata were different from resistant trees. Statistical analysis revealed that in 2014 and 2015, differences in the profile of VOCs between susceptible and resistant trees were apparent near pest-feeding dates. In 2016, VOCs significantly distinguished the profile of susceptible trees that were present before the appearance of the first generation of the pest.
Enhancing Lettuce Drought Tolerance: The Role of Organic Acids in Photosynthesis and Oxidative Defense
The aim of this study was to investigate the effects of maleic acid (MA), salicylic acid (SA), and citric acid (CA) on alleviating the drought stress of a lettuce (Lactuca sativa L.) hydroponic culture. The effect of these organic acids was tested under stress conditions induced by polyethene glycol (PEG 6000) at 5% and 7.5% concentrations. Drought stress reduced the fresh and dry matter yields of plants. The acid treatment caused increasing tendencies in the fresh weight yield:control (SA, MA), PEG 7.5% (SA, MA, CA)) and dry weight yield (control (SA, MA), PEG 5% (MA), PEG 7.5% (SA, MA)). The acid treatment also enhanced the nutrient uptake of stressed plants: SA: N (PEG 7.5%), K (PEG 5 and 7.5%); MA: N, P, K, Ca (PEG 5 and 7.5%). This work found that chlorophyll a and b amounts did not change under applied experimental conditions. Most parameters of chlorophyll fluorescence did not depend on either the level of applied water stress (PEG level) or the type of spraying. Drought stress increased leaf superoxide anion (O2•−) and malondialdehyde (MDA) levels but decreased H2O2. Proline (Pro) and phenolic compounds (TFC), including flavonols (Fla), accumulated more in stressed plants. Drought stress also affected the chlorophyll fluorescence. Our results suggest that acids can improve plant tolerance to drought stress by boosting the antioxidant defence system and reducing the oxidative damage caused by reactive oxygen species.