Robert Pokluda

Quality changes in organic and conventional Hokkaido pumpkin (Cucurbita maxima Duch.) during storage

Abstract Organic production of vegetables has increased in recent years. Pumpkin is a well-known edible plant, which has substantial nutritional properties due to the presence of unique natural substances. Pumpkin is one of the most commonly grown organic vegetables in the Czech Republic. The aim of this work was to compare the quality of organic and conventional Hokkaido pumpkin (Cucurbita maxima Duch.) during storage in terms of colour changes (Lab colour space), loss of mass, concentrations of ascorbic acid and total carotenoid. BIO (from organic farming) and CONV (from conventional farming) variants were tested at monthly intervals over three (2013) and four (2014) months storage after harvest. In 2013, the average loss of mass reached 19% in BIO and 23% in CONV and in 2014 it reached 12% in BIO and 20% CONV. Differences of loss of mass between BIO and CONV were only significant in 2014. In all variants and in both years, a gradual reduction in ascorbic acid (AA) during storage was noted. The reduction in concentration of ascorbic acid (AA) was slower in BIO than in CONV variants, and in both years BIO variants also showed smaller changes in concentrations of total carotenoids compared to CONV variants. The BIO pumpkins maintained their red colour (a*) better during storage than the CONV pumpkins, but the evaluation of the total colour difference (TCD) showed significant differences over time in both variants in both years.

Impacts of chilling on photosynthesis and chlorophyll pigment content in juvenile basil cultivars

The objective of this study was to examine several cultivars of Ocimum basilicum L. (green, red, cinnamon, lettuce leaf, lemon, and Thai basils) for photosynthetic performance, chlorophyll a fluorescence, and chlorophyll content under chilling stress conditions of 6°C in comparison to non-stressed controls (18°C). The basil plants were grown in a peat substrate for 8 weeks and then exposed to chilling for 8 or 16 days, under a 300 μmol•m-2•s-1 photosynthetic photon flux. After chilling, significant reductions in both the transpiration (E) and net photosynthetic (PN) rates were observed in basil plants, while the intercellular CO2 concentration (Ci) was higher in the plants treated with 6°C in comparison to the controls. The decrease in PN and E was associated with decreased water use efficiency (WUE) and stomatal conductance (gs). The greatest impairment of photosynthesis for Thai basil leaves was observed after 8 days of chilling, and for green basil after the 16-day low temperature treatment. The photosystem II (PSII) activity (Fv/Fm) and variable-to-initial chlorophyll fluorescence (Fv/F0) were decreased after chilling. PSII activity was most affected in lettuce leaf basil after 8 days, and in Thai and red basil plants after the prolonged temperature treatment. Low temperatures did not significantly alter the chlorophyll concentration but did increase the Chl a/b ratio in leaves of basil. The results indicated that the decrease in photosynthesis was not attributable mainly to damage to PSII, but rather to chilling-induced photoinhibition of PSI. The knowledge gained in this study on the genotypic variation in basil response should be helpful for future selection of plants with low chilling sensitivity.

Sequential abiotic stress applied to juvenile eggplant modifies the seedlings parameters, plant ontogeny and yield

Sękara A., Bączek-Kwinta R., Gawęda M., Kalisz A., Pokluda R., Jezdinský A. (2016): Sequential abiotic stress applied to juvenile eggplant modifies the seedlings parameters, plant ontogeny and yield. Hort. Sci. (Prague), 43: 149–157. The main goal of this study was to evaluate eggplant (Solanum melongena L.) susceptibility to a sequence of stress factors during plant ontogeny based on seedling morphological, biochemical and physiological parameters and the subsequent assessment of yield characteristics. After germination, seedlings at the radical stage were exposed to chilling, heat, osmotic or oxidative stress. Four weeks after development in standard conditions in a greenhouse, the seedlings were again subjected to chilling stress in a growth chamber. A non-chilled Control was implemented. Then, the yield and physiological characteristics were assessed after field cultivation. Generally, stress application after germination resulted in better plant acclimation to chilling at the 4-week-old seedling phase, evaluated on the basis of photosynthetically active pigment contents, chlorophyll fluorescence and some morphological characteristics. The comparable time to reach successive phenological stages by stressed and Control plants in the field suggests that stress pretreatment does not retard eggplant development. These results also confirm the thesis that stress memory can be induced in eggplant by stressor application during the early stages of development.

The physiological status and stress biomarker concentration of Coriandrum sativum L. plants subjected to chilling are modified by biostimulant application

Abstract This study investigated the effects of biostimulant treatment and chilling applied during the young phase of growth on stress indicators, antioxidant compounds and physiological status of coriander leaves. Coriander transplants were sprayed three times with Asahi SL or Goëmar Goteo (Arysta Life Science). After the last spraying, 6-week-old plants were placed in vegetative chambers at 6 °C (chilling stress) and 18 °C (control) for 6 days, and then stress biomarkers, total antioxidant activity, photosynthetic pigment concentration, chlorophyll fluorescence and photosynthetic activity were determined in leaves. In chilled conditions, biostimulant application significantly decreased electrolyte leakage from leaf tissues to the level determined for non-chilled plants. The comparison of hydrogen peroxide and malondialdehyde concentrations for control and biostimulant-treated plants did not confirm the protective effect of biostimulants against stress molecule accumulation in chilling conditions. Biostimulants increased maximal photochemical efficiency of photosystem II, the rate of transpiration and stomatal conductance but decreased intercellular carbon dioxide concentration. L-ascorbic acid, total phenolic concentration and total antioxidant activity increased as a result of biostimulant application to chilled plants. The increased values of most photosynthesis and stress indicators in coriander leaves after 6 days chilling showed that plants were in a phase of acclimation to low temperature. The results indicate that biostimulants can affect selected metabolic pathways, accelerating the adaptation of chilled coriander plants. The precise use of plant growth regulators with application of chilling can be a method for controlling nutritionally important compounds in coriander foliage.