M. C. Van Labeke

Chlorophyll fluorescence as a tool for evaluation of drought stress in strawberry

The effect of water deficit on chlorophyll fluorescence, sugar content, and growth parameters of strawberry (Fragaria×ananassa Duch. cv. Elsanta) was studied. Drought stress caused significant reductions in leaf water potential, fresh and dry masses, leaf area, and leaf number. A gradual reduction of photochemical quenching (qP) and quantum efficiency (ΦPS2) was observed under drought stress while non-photochemical quenching (qN) increased. Maximum efficiency of photosystem 2 (Fv/Fm) was not affected by drought stress.

Application of chlorophyll fluorescence to screen eggplant (Solanum melongena L.) cultivars for salt tolerance

The objective of this study was to investigate the relative salt tolerance of four eggplant cultivars (Solanum melongena L.) by studying chlorophyll (Chl) fluorescence parameters during the vegetative growth stage under increasing salinity levels. The plants were grown in pots filled with peat under controlled conditions and were subjected to the salt stress ranging from 0 (control), 20, 40, 80, and 160 mM NaCl for 25 days. The results showed that the increasing NaCl concentration affected hardly the maximum quantum yield of photosystem (PS) II. The quantum yield of PSII (ΦPSII) decreased significantly in ‘Adriatica’ and ‘Black Beauty’ under the salt stress. The photochemical quenching decreased in ‘Black Beauty’ and nonphotochemical quenching increased in ‘Adriatica’ under the salt stress. The Chl fluorescence parameters did not change significantly under the salt stress in ‘Bonica’ and ‘Galine’, revealing their tolerance to salinity. After 25 days of the salt stress, the plant growth was reduced in all cultivars, however, this decline was more pronounced in ‘Adriatica’ and ‘Black Beauty’. Additionally, a significant correlation between the biomass and ΦPSII was observed in ‘Adriatica’ and ‘Black Beauty’. Our results suggest that ΦPSII can be used as a diagnostic tool to identify salt-tolerant egg-plant cultivars.

Diurnal cycle of chlorophyll fluorescence in Phalaenopsis

Chlorophyll (Chl) fluorescence of warm day/cool night temperature exposed Phalaenopsis plants was measured hourly during 48 h to study the simultaneous temperature and irradiance response of the photosynthetic physiology. The daily pattern of fluorescence kinetics showed abrupt changes of photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of photosystem II electron transport (ΦPSII) upon transition from day to night and vice versa. During the day, the course of ΦPSII and NPQ was related to the air temperature pattern, while maximum quantum efficiency of PSII photochemistry (Fv/Fm) revealed a rather light dependent response. Information on these daily dynamics in fluorescence kinetics is important with respect to meaningful data collection and interpretation.

Nondestructive determination of nitrogen and chlorophyll content in olive tree leaves and the relation with photosynthesis and fluorescence parameters

For Tunisian olive tree orchards, nitrogen deficiency is an important nutritional problem, in addition to the availability of water. Establishment of relationships between nutrients such as nitrogen and ecophysiological parameters is a promising method to manage fertilisation at orchard level. Therefore, a nitrogen stress experiment with one-year-old olive trees (Olea europaea L. ‘Koroneiki’ and ‘Meski’) was conducted with trees respectively subjected to four nitrogen supply regimes (23.96 meq l−1, 9.58 meq l−1, 4.79 meq l−1 and 0 meq l−1 NO3−1).The current paper focuses on the use of the SPAD-502 portable chlorophyll (Chl) meter, a nondestructive method for fertilisation management under nitrogen stress conditions of olive trees. Maximum net photosynthetic assimilation rates, chlorophyll fluorescence parameters and the SPAD Chl index were therefore measured simultaneously and the Chl and nitrogen content of the leaves were analysed. Significant correlations were established in the olive tree leaves between SPAD-502 readings on the one hand and Chl content, nitrogen content, photosynthetic assimilation rate, and Chl fluorescence parameters (ΦPSII and ETR) on the other hand.

Seasonal variation of photosynthesis and photosynthetic efficiency in Phalaenopsis

Nowadays, a quest for efficient greenhouse heating strategies, and their related effects on the plant’s performance, exists. In this study, the effects of a combination of warm days and cool nights in autumn and spring on the photosynthetic activity and efficiency of Phalaenopsis were evaluated; the latter, being poorly characterised in plants with crassulacean acid metabolism (CAM) and, to our knowledge, not reported before in Phalaenopsis. 24-h CO2 flux measurements and chlorophyll (Chl) fluorescence analyses were performed in both seasons on Phalaenopsis ‘Hercules’ exposed to relatively constant temperature regimes, 25.5/24.0°C (autumn) and 30/27°C (spring) respectively, and distinctive warm day/cool night temperature regimes, 27/20°C (autumn) and 36/24°C (spring), respectively. Cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10–16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. Nevertheless, a distinctive warm day/cool night temperature regime seemed to induce photorespiration. Although photorespiration is expected not to occur in CAM, the suppression of the leaf net CO2 exchange during Phase II and Phase IV as well as the slightly lower efficiency of carbon fixation for the distinctive warm day/cool night temperature regimes confirms the involvement of photorespiration in CAM. A seasonal effect was reflected in the leaf net CO2 exchange rate with considerably higher rates in spring. In addition, sufficiently high levels of photosynthetically active radiation (PAR) in spring led to an efficiency of carbon fixation of 1.06–1.27% which is about twice as high than in autumn. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative.

Effects of Nitrogen Deficiency on Leaf Chlorophyll Fluorescence Parameters in Two Olive Tree Cultivars ‘Meski’ and ‘Koroneiki’

Effects of nitrogen (N) deficiency on photosynthetic carbon dioxide (CO2) assimilation, photosystem II (PSII) photochemistry and photoinhibition were investigated in young trees of two olive cultivars ‘Meski’ and ‘Koroneiki’ grown in a greenhouse under controlled conditions. The trees were subjected to four different levels of N supply. N deficient trees had a significantly smaller CO2 assimilatory capacity, but showed little changes in maximum quantum efficiency of PSII photochemistry. However, modifications in PSII photochemistry induced by N deficiency were observed. This was reflected in decreases in quantum yield of PSII electron transport (ΦPSII) and efficiency of excitation energy capture by open PSII reaction centres (Fv’/Fm’) and in an increase in non-photochemical quenching (NPQ). These results suggest that modifications in PSII photochemistry might be a mechanism to down-regulate photosynthetic electron transport so that production of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). would be in equilibrium with the decreased demand in the Calvin cycle in the N deficient trees. Therefore, both CO2 assimilation rate and total electron flow (Jt) with its compound electron flows devoted to either carboxylation (Jc) or oxygenation (Jo) can be considered as useful tools to assess the N nutrition status of the trees. Clear relationships were found between Amax and the nitrogen nutrition index (NNI) on the one hand, and between Jt and NNI on the other hand. The results demonstrate that ‘Meski’ is more efficient than ‘Koroneiki’ when subjected to N deficiency.

Parameters Influencing Preference by Sheep in Soft Leaved Tall Fescue Genotypes

An important disadvantage of tall fescue (Festuca arundinacea Schreb.) is its low voluntary intake, resulting in suboptimal performances of cattle grazing tall fescue. Ideally selection for this trait is done by animals themselves, but the use of grazing animals in large breeding programmes is laborious. Repeatable, stable and quantifiable parameters that can be linked to animal preference could ease tall fescue breeding. We established a trial to find relations between the grazing preference of sheep and other plant parameters. Twenty clones were selected from a breeding programme and swards of 2 m2 were planted with three replications for each clone. On four different occasions in 2014, sheep were allowed to graze the clones and grazing preference was determined visually. Prior to the grazing, multiple morphological and chemical parameters were measured. Parameters that were correlated with sheep preference were digestibility (r = 0.86), water soluble carbohydrate content (r = 0.74) crude fiber content (r = −0.67), leaf blade width (r = 0.57) and sward height (r = −0.53).

Production and Characterization of Intergeneric Hybrids between Anemone coronaria and Ranunculus asiaticus

Anemone coronaria L. and Ranunculus asiaticus L. are common cut flowers which belong to the Ranunculaceae. Between these species a high degree of variation can be found in leaves, flower morphology and flower colour. Therefore intergeneric crossings between these species might result in new interesting hybrids. Crosses between these genera were performed in the greenhouse and pre- and post-zygotic barriers were examined. Two to five weeks after pollination, immature achenes were harvested and rescued in vitro. The obtained F1 generation was investigated on morphological, molecular and cytogenetic level. The F1 plants had very similar flowers to the mother plants and although the limited molecular paternal contribution, AFLP analyses confirmed the hybrid character of the F1 plants. Chromosome counts showed that the F1 plants were mixoploids, composed of cells with different chromosome numbers.

Development, maturation and germination of horse chestnut somatic embryos.

Somatic embryogenesis could represent a way to clonally propagate mature elite trees of horse chestnut. However, while a number of protocols describe successfully the induction and proliferation of somatic embryos a low frequency of embryos converted successfully into plants. The objective of this research was to identify a maturation medium that could contribute to the outcome of more efficient germination results. Therefore, in a first approach the effects of sucrose 3 and 6%, and maltose 3%, were evaluated on somatic embryo maturation, in terms of subsequent somatic embryo germination. Carbon source and concentration had a marked influence on maturation, and subsequent germination of horse chestnut somatic embryos, with sucrose 6% promoting the highest frequency of germinated embryos larger than 1 cm.