Interspecific hybridization in <i>Cucumis </i>leads to the divergence of phenotypes in response to low light and extended photoperiods

With the aim of improving shade tolerance of cucumber, Cucumis ×hytivus, a newly synthesized allotetraploid, was obtained by crossing a shade tolerant wild relative, C. hystrix, with a cultivated cucumber, C. sativus L. ‘BejingJietou’. The results show that the new C. ×hytivus only partly is an intermediate hybrid and it has not only chlorophyll deficiency, which recovers during leaf development, but also lower carotenoid content. Three light conditions with the combination of different light intensities and photoperiods were employed to investigate the photosynthetic response of these three Cucumis species to low light and long photoperiod. The consistent order of Pmax and DWS being lowest in C. hystrix, medium in C. ×hytivus and highest in ‘BejingJietou’ suggests the three species to have genetically different photosynthetic efficiency, which relates well with the natural habitats of the parent species and the hybrid as intermediate. C. ×hytivus appears to be inhibited by the low light levels to the same extent as the cultivated ‘BeijingJietou’, which indicates neither improvement of shade tolerance nor hypothetical heterosis effect in C. ×hytivus. However, unexpectedly, the PSII of C. hystrix was affected by the long photoperiod in the long term, suggested by the decrease of Fv/Fm. This sensitivity towards day length has not been passed on to C. ×hytivus

Phylogeography reveals a potential cryptic invasion in the Southern Hemisphere of Ceratophyllum demersum, New Zealand's worst invasive macrophyte

Ceratophyllum demersum (common hornwort) is presently considered the worst invasive submerged aquatic macrophyte in New Zealand. We explored the global phylogeographic pattern of the species, based on chloroplast and nuclear DNA, in order to identify the origin of the invasive populations in New Zealand and to clarify if there were multiple introductions. The phylogeographic study identified geographically differentiated gene pools in North America, tropical Asia, Australia, and South Africa, likely native to these regions, and a recent dispersal event of a Eurasian-related haplotype to North America, New Zealand, Australia, and South Africa. At least two different invasive genotypes of this Eurasian-related haplotype have been found in New Zealand. One genotype is closely related to genotypes in Australia and South Africa, while we could not trace the closest relatives of the other genotype within our C. demersum sample set. Contrasting spectra of genetic distances in New Zealand and in a region within the native range (Denmark), suggest that the invasive population was founded by vegetative reproduction, seen as low genetic distances among genotypes. We also discovered the introduction of the same Eurasian-related haplotype in Australia and South Africa and that a cryptic invasion may be occurring in these continents

Inherent trait differences explain wheat cultivar responses to climate factor interactions: New insights for more robust crop modelling

Climate change predictions foresee a combination of rising CO2, temperature and altered precipitation. Effects of single climatic variables are well defined, but the importance of combined variables and genotypic effects is less known, although pivotal for assessing climate change impacts, for example, with crop growth models. This study provides developmental and physiological data from combined climatic factors for two distinct wheat cultivars (Paragon and Gladius), as a basis to improve predictions for climate change scenarios. The two cultivars were grown in controlled climate chambers in a fully factorial setup of atmospheric CO2 concentration, growth temperature and watering regime. The cultivars differed considerably in their developmental rate, response pattern and the parameters responsible for most of their variation. The growth of Paragon was linked to climatic effects on photosynthesis and mainly affected by temperature. Paragon was overall more negatively affected by all treatment combinations compared to Gladius. Gladius was mostly affected by watering regime. The cultivars' acclimation strategies to climate factors varied significantly. Thus, considering a single factor is an oversimplification very likely impacting the accuracy of crop growth models. Intraspecific crop variation could help understanding genotype by environment variation. Cultivars with high phenotypic plasticity may have greater resilience against climatic variability.</p

Low air humidity during cultivation promotes stomatal closure ability in rose

In greenhouse horticulture, evaporative demand varies between seasons. For instance, plants are typically exposed to low relative air humidity (RH) during summer, whereas elevated RH prevails in winter. Since high RH during cultivation impairs stomatal functioning, some opposite changes might be expected, when plants are subjected to long-term low RH. To investigate this, Rosa hybrida ‘Pasadena’ was cultivated at 40, 60 or 90% RH. Plant performance, transpiration, stomatal closing ability and anatomy were recorded. As RH increased from 40 to 60% as well as from 60 to 90%, plants showed larger leaf area and thinner leaves. Plant water loss was mainly determined by ambient RH in the growing environment, with stomatal conductance (gs) being of secondary importance. With increasing RH, plant transpiration declined at growth environment. Larger stomata were found at 90% RH, as compared to 40 or 60%. Stomatal physiology was considerably affected by 90% RH, including reduced gs oscillations within the photoperiod, attenuated opening response following dark/light transition, as well as reduced closing response upon darkening. The plants cultivated at 90% RH had a reduced ability to control water loss upon water deprivation, compared to those grown at 60%. In contrast, cultivation at 40% RH resulted in stomata, which were much more responsive to water stress, compared to 60% RH-grown plants. This superiority was dual: lower transpiration rate combined with less severe leaf drying to induce stomatal closure. In conclusion, low RH during cultivation, which is typical during summer, leads to thicker leaves with very responsive stomata.</p

Stomatal anatomy and closing ability is affected by supplementary light intensity in rose (Rosa hybrida L.)

Increasing the light level in protected cultivation of ornamental crops via supplementary lighting is critical to enhance both production and external quality especially during the periods of low light availability. Despite wide applications the effects of light intensities were not previously addressed on water loss pathways. In this study rose plants were cultivated at 100, 200 or 400 μmol/(m2 s) photosynthetic photon flux density (PPFD). The stomatal responsiveness to desiccation, stomatal anatomical features and cuticular transpiration were determined. Plant biomass as well as photosynthesis response to light and CO2 were also assessed. Increasing growth PPFD led to a considerable increase in plant biomass (85 and 57% for 100 to 200 and 200 to 400 μmol/(m2 s) respectively). Photosynthesis was marginally affected by increasing growth PPFD from 100 to 200 μmol/(m2 s) while a further rise to 400 μmol/(m2 s) considerably increased photosynthetic rate at high light intensities. Higher PPFD during cultivation generally led to larger stomata with bigger pores. A PPFD increase from 100 to 200 μmol/(m2 s) had a small negative effect on stomatal closing ability whereas a further rise to 400 μmol/(m2 s) had a substantial stimulatory effect. Cultivation at a PPFD higher than 100 μmol/(m2 s) led to lower rates of cuticular transpiration. In conclusion, high growth PPFD (> 200 μmol/(m2 s)) enchanced both photosynthetic and stomatal anatomical traits. High light intensity (> 200 μmol/(m2 s)) also led to a better control of water loss due to more responsive stomata and decreased cuticular permeability

Differential effects of elevated air humidity on stomatal closing ability of Kalanchoë blossfeldiana between the C₃ and CAM states

High relative air humidity (RH ≥ 85%) impairs stomatal functionality, attenuating plant capacity to cope with abiotic stress. Previous studies were limited to C3 species, so the RH effect on stomatal physiology of CAM plants remains unexplored. We addressed the topic through comparisons of C3 and CAM states in a facultative CAM species. These states were validated by diel measurements of net assimilation rate and malate level. In the first two experiments, three Kalanchoë interspecific hybrid cultivars were exposed to moderate (60%) or high (90%) RH. Both leaves that expanded at high RH and leaves that had expanded at moderate RH and were subsequently exposed to high RH (for nine days) showed increased stomatal conductance. In the third experiment, both C3 and CAM state plants of one K. blossfeldiana cultivar were exposed to low (40%), moderate (60%) or high (90%) RH. Plant transpiration during night-time was inversely related to ambient RH in either state, whereas during day-time a significant effect was only noted at 90% RH. Kalanchoë leaves showed a very effective control of water loss upon water deprivation, especially in the CAM state. Following a single week exposure to 90% RH, detached leaves showed increased rates of water loss during desiccation in C3 state plants. No effect of high RH on stomatal response to desiccation was noted in leaves detached from plants in CAM-state. It is concluded that the negative effect of either growth or one-week exposure to high RH is restricted to the C3 state in Kalanchoë.</p

Incorporating cultivar-specific stomatal traits into stomatal conductance models improves the estimation of evapotranspiration enhancing greenhouse climate management

The effect of considering cultivar differences in stomatal conductance (gs) on relative air humidity (RH)-related energy demand was addressed. We conducted six experiments in order to study the variation in evapotranspiration (ETc) of six pot rose cultivars, investigate the underlying processes and parameterise a gs-based ETc model. Several levels of crop ETc were realised by adjusting the growth environment. The commonly applied Ball–Woodrow–Berry gs-sub-model (BWB-model) in ETc models was validated under greenhouse conditions, and showed a close agreement between simulated and measured ETc. The validated model was incorporated into a greenhouse simulator. A scenario simulation study showed that selecting low-gs cultivars reduces energy demand (≤5.75%), depending on the RH set point. However, the BWB-model showed poor prediction quality at RH lower than 60% and a good fit at higher RH. Therefore, an attempt was made to improve model prediction: the in situ-obtained data were employed to adapt and extend either the BWB-model, or the Liu-extension with substrate water potential (Ψ; BWB-Liu-model). Both models were extended with stomatal density (Ds) or pore area. Although the modified BWB-Liu-model (considering Ds) allowed higher accuracy (R2 = 0.59), as compared to the basic version (R2 = 0.31), the typical lack of Ψ prediction in greenhouse models may be problematic for implementation into real-time climate control. The current study lays the basis for the development of cultivar specific cultivation strategies as well as improving the gs sub-model for dynamic climate conditions under low RH using model-based control systems