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This study investigated the effect of macrospora leaf spot (MLS), caused by Stenocarpella macrospora, on photosynthetic gas exchange parameters and chlorophyll a fluorescence parameters determined in leaves of plants from two maize cultivars ('ECVSCS155' and 'HIB 32R48H') susceptible and highly susceptible, respectively, to S. macrospora. MLS severity was significantly lower in the leaves of plants from ECVSCS155 relative to the leaves of plants from HIB 32R48H. In both cultivars, net CO2 assimilation rate, stomatal conductance, and transpiration rate significantly decreased, while the internal to ambient CO2 concentration ratio increased in inoculated plants relative to noninoculated plants. The initial fluorescence and nonphotochemical quenching significantly increased in inoculated plants of ECVSCS155 and HIB 32R48H, respectively, relative to noninoculated plants. The maximum fluorescence, maximum PSII quantum efficiency, coefficient for photochemical quenching, and electron transport rate significantly decreased in inoculated plants relative to noninoculated plants. For both cultivars, concentrations of total chlorophyll (Chl) (a+b) and carotenoids and the Chl a/b ratio significantly decreased in inoculated plants relative to noninoculated plants. In conclusion, the results from the present study demonstrate, for the first time, that photosynthesis in the leaves of maize plants is dramatically affected during the infection process of S. macrospora, and impacts are primarily associated with limitations of a diffusive and biochemical nature.

Considering the importance of northern leaf blight, caused by Exserohilum turcicum, to decrease maize yield, this study evaluated electrolyte leakage, content of H2O2, malondialdehyde (MDA), chlorophyll (Chl) a, Chl b, and carotenoids (CAR), and activities of superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, glutathione reductase, glutathione-S-transferase, and glutathione peroxidase, as well as expressions of superoxide dismutase (sod), catalase (cat 1), ascorbate peroxidase (apx 2), peroxidase (pox), glutathione reductase (gr 1), and glutathione-S-transferase (gst 23) genes, and leaf gas exchange and Chl a fluorescence parameters in maize leaves infected with E. turcicum. The content of H2O2 and MDA was high at 15 and 20 d after inoculation (dai) and electrolyte leakage was high from 10 dai onward in infected leaves. Net assimilation rate, stomatal conductance to water vapour, transpiration rate, internal CO2 concentration, maximum quantum yield of photosystem (PS) II, and effective quantum yield of PS II significantly decreased as the disease developed. Quantum yield of regulated energy dissipation significantly increased at 10 and 15 dai but decreased at 20 dai whereas the quantum yield of non-regulated energy dissipation significantly increased at 15 and 20 dai. The content of Chl a, Chl b, and CAR decreased in infected leaves. The activities of the enzymes increased, and the relative expressions of the genes sod, cat 1, apx 2, pox, gr 1, and gst 23 were higher in infected leaves compared to non-infected ones mainly from 10 dai onward. In conclusion, photosynthesis in infected leaves was dramatically affected and a late involvement of the antioxidant metabolism was not sufficiently helpful to counteract the deleterious effects of fungal infection.

Foliar spray of treatments in the control of downy mildew and bulb rot in onionA field experiment was carried out to evaluate the effect of foliar sprays with the following treatments on the downy mildew (Peronospora destructor) and bulb rot (Burkholderia cepacia) in onions: non-treated control, fungicide chlorotalonil/metalaxyl + chlorotalonil, potassium phosphite, foliar fertilizer (03-00-16, N-P-K), bordeaux mixture, bordeaux mixture/potassium phosphite, acibenzolar-S-methyl weekly applied; extract of alga Ulva fasciata and ulvan sprayed every 7, 14 and 21 days. Only the weekly spraying of fungicides and fertilizer (03-00-16, 400 mL/100 L) significantly reduced the mildew severity by 60 and 23%, respectively, but did not increase the bulb yield. The foliar application of potassium rich fertilizers resulted in a higher incidence of rotten bulbs after 5 months in storage. Soluble sugar content and rot incidence of onion bulbs were significantly correlated (-0,629, p ≤ 0,05).

Background In studies of plant stress signaling, a major challenge is the lack of non-invasive methods to detect physiological plant responses and to characterize plant–plant communication over time and space. ResultsWe acquired time series of phytocompound and hyperspectral imaging data from maize plants from the following treatments: (1) individual non-infested plants, (2) individual plants experimentally subjected to herbivory by green belly stink bug (no visible symptoms of insect herbivory), (3) one plant subjected to insect herbivory and one control plant in a separate pot but inside the same cage, and (4) one plant subjected to insect herbivory and one control plant together in the same pot. Individual phytocompounds (except indole-3acetic acid) or spectral bands were not reliable indicators of neither insect herbivory nor plant–plant communication. However, using a linear discrimination classification method based on combinations of either phytocompounds or spectral bands, we found clear evidence of maize plant responses.ConclusionsWe have provided initial evidence of how hyperspectral imaging may be considered a powerful non-invasive method to increase our current understanding of both direct plant responses to biotic stressors but also to the multiple ways plant communities are able to communicate. We are unaware of any published studies, in which comprehensive phytocompound data have been shown to correlate with leaf reflectance. In addition, we are unaware of published studies, in which plant–plant communication was studied based on leaf reflectance.