Karen Koefoed Petersen

Composition and taste of tomatoes as affected by increased salinity and different salinity sources

SummaryTomato plants were grown in rockwool slabs under glasshouse conditions at different salinities (3–9 mS cm–1) to improve the taste of tomato fruit without reducing their quality in other respects. NaCl or different combinations of major nutrients (comprising Na, K, Ca, Mg, Cl, NO3-N, P and SO4-S) were applied as salinity sources. Increased salinity in the root zone increased the concentrations of dry matter, sugars, titratable acid, vitamin C and total carotene in the tomato fruit, and were in all cases but one independent of salinity source. On a per-fruit basis, no differences in glucose or fructose were found whereas the content of tritratable acid and dry matter decreased with increased salinity. The fruit composition was slightly affected by fruit position within the truss. A trained sensory panel found that NaCl improved the sweetness of tomato fruit more than the other salinity sources. The sensory panel was not able to separate samples from the different treatments by sourness. Fruit firmnes...

Colchicine and oryzalin mediated chromosome doubling in different genotypes of Miscanthus sinensis

Different explant materials were treated with antimitotic agents to induce chromosome doubling in several Miscanthus sinensis clones. In vitro propagated plants established in soil, in vitro shoots, embryogenic callus, shoot apices and leaf explants were treated with different concentrations of colchicine or oryzalin. No tetraploids were obtained after antimitotic treatment of plants established in soil. The percentage of chromosome doubled plants after antimitotic treatment of single in vitro shoots was genotype dependent. Rooted in vitro plantlets were not a suitable target for antimitotic treatment, due to a high frequency of ploidy chimeras. Many tetraploid plants were regenerated after antimitotic treatment at the callus and explant level, but the efficiency was genotype dependent, primarily due to differences in the ability to form regenerable callus and to regenerate plants from embryogenic callus. Treatment of shoot apices with colchicine was the most efficient and reproducible system in the four genotypes tested. It was possible to repeatedly use the same colchicine-containing medium without any reduction in the induction of regenerable callus or in the percentage of tetraploids, thereby minimising the handling of this very toxic compound.

Callus induction and plant regeneration from different explant types of Miscanthus x ogiformis Honda ‘Giganteus’

Different explants of Miscanthus x ogiformis Honda ‘Giganteus’ were tested in order to develop an efficient tissue culture system. Shoot apices, leaf and root sections from in vitro-propagated plants, and leaf and immature inflorescence sections from 6-month-old greenhouse-grown plants were used. The explants were cultured on Murashige and Skoog medium supplemented with 4.5, 13.6, 22.6 or 31.7 μM 2,4-dichlorophenoxyacetic acid. Three types of callus were formed but only one was embryogenic and regenerated plants. Callus induction and formation of embryogenic callus depended on the type and developmental stage of the explants. Shoot apices formed the highest percentage of embryogenic callus. There was a difference in the formation of embryogenic callus between leaf explants from in vitro-propagated shoots and greenhouse-grown plants. The best results were obtained from newly formed leaves of in vitro-propagated shoots and older leaves of greenhouse-grown plants. Immature inflorescences smaller than 2.5 cm produced a higher percentage of embryogenic callus than larger more mature inflorescences. Embryogenic callus derived from immature inflorescences had the highest regeneration capacity. Differences in 2,4-dichlorophenoxyacetic acid concentrations had no significant effect on callus induction, embryogenic callus formation and plant regeneration.

Changes in carbohydrates, ABA and bark proteins during seasonal cold acclimation and deacclimation in Hydrangea species differing in cold hardiness

Cold injury is frequently seen in the commercially important shrub Hydrangea macrophylla but not in Hydrangea paniculata. Cold acclimation and deacclimation and associated physiological adaptations were investigated from late September 2006 to early May 2007 in stems of field-grown H. macrophylla ssp. macrophylla (Thunb.) Ser. cv. Blaumeise and H. paniculata Sieb. cv. Kyushu. Acclimation and deacclimation appeared approximately synchronized in the two species, but they differed significantly in levels of mid-winter cold hardiness, rates of acclimation and deacclimation and physiological traits conferring tolerance to freezing conditions. Accumulation patterns of sucrose and raffinose in stems paralleled fluctuations in cold hardiness in both species, but H. macrophylla additionally accumulated glucose and fructose during winter, indicating species-specific differences in carbohydrate metabolism. Protein profiles differed between H. macrophylla and H. paniculata, but distinct seasonal patterns associated with winter acclimation were observed in both species. In H. paniculata concurrent increases in xylem sap abscisic acid (ABA) concentrations ([ABA](xylem)) and freezing tolerance suggests an involvement of ABA in cold acclimation. In contrast, ABA from the root system was seemingly not involved in cold acclimation in H. macrophylla, suggesting that species-specific differences in cold hardiness may be related to differences in [ABA](xylem). In both species a significant increase in stem freezing tolerance appeared long after growth ceased, suggesting that cold acclimation is more regulated by temperature than by photoperiod.

Yield, Quality, and Nutrient Concentrations of Strawberry (Fragaria ×ananassa Duch. cv. 'Sonata') Grown with Different Organic Fertilizer Strategies.

Four combinations of two solid organic fertilizers (Monterra Malt and chicken manure) applied before planting and two liquid organic fertilizers (broad bean and Pioner Hi-Fruit/K-Max) given through drip irrigation (fertigation) were compared with inorganic fertilization regarding growth, yield, nutrient concentration, and fruit quality of strawberries. Broad bean fertigation combined with Monterra Malt resulted in a similar fruit yield as inorganic fertilizer and a higher yield than Monterra Malt combined with Pioner; however, total soluble solids, firmness, and titratable acid were improved with Pioner fertigation, although these parameters were more affected by harvest time than the applied fertilizers. The concentrations of most nutrients in fruits and leaves were higher in inorganically fertigated plants. The reductions in fruit yield in three of four treatments and fruit weight in all organic treatments may be due to a combination of the following conditions in the root zone: (1) high pH and high NH4(+)/NO3(-) ratio; (2) high EC and/or high NaCl concentration; (3) cation imbalance; and (4) nutrient deficiency.

Polyploidy can Confer Superiority to West African Acacia senegal (L.) Willd. Trees.

Polyploidy is a common phenomenon in the evolution of angiosperms. It has been suggested that polyploids manage harsh environments better than their diploid relatives but empirical data supporting this hypothesis are scarce, especially for trees. Using microsatellite markers and flow cytometry, we examine the frequency of polyploids and diploids in a progeny trial testing four different populations of Acacia senegal, a species native to sub-Saharan regions of Africa. We compare growth between cytotypes and test whether polyploid seedlings grow better than diploids. Our results show that polyploids coexist with diploids in highly variable proportions among populations in Senegal. Acacia senegal genotypes were predominantly diploid and tetraploid, but triploid, pentaploid, hexaploid, and octaploid forms were also found. We find that polyploids show faster growth than diploids under our test conditions: in an 18 years old field trial, polyploid superiority was estimated to be 17% in trunk diameter and 9% in height while in a growth chamber experiment, polyploids grew 28% taller, but only after being exposed to drought stress. The results suggest that polyploid A. senegal can have an adaptive advantage in some regions of Africa.

Low-temperature leaf photosynthesis of a Miscanthus germplasm collection correlates positively to shoot growth rate and specific leaf area.

Background and Aims The C4 perennial grass miscanthus has been found to be less sensitive to cold than most other C4 species, but still emerges later in spring than C3 species. Genotypic differences in miscanthus were investigated to identify genotypes with a high cold tolerance at low temperatures and quick recovery upon rising temperatures to enable them to exploit the early growing season in maritime cold climates. Suitable methods for field screening of cold tolerance in miscanthus were also identified. Methods Fourteen genotypes of M. sacchariflorus, M. sinensis, M. tinctorius and M. × giganteus were selected and grown under warm (24 °C) and cold (14 °C) conditions in a controlled environment. Dark-adapted chlorophyll fluorescence, specific leaf area (SLA) and net photosynthetic rate at a photosynthetically active radiation (PAR) of 1000 μmol m–2 s–1 (A1000) were measured. Photosynthetic light and CO2 response curves were obtained from 11 of the genotypes, and shoot growth rate was measured under field conditions. Key Results A positive linear relationship was found between SLA and light-saturated photosynthesis (Asat) across genotypes, and also between shoot growth rate under cool field conditions and A1000 at 14 °C in a climate chamber. When lowering the temperature from 24 to 14 °C, one M. sacchariflorus exhibited significantly higher Asat and maximum photosynthetic rate in the CO2 response curve (Vmax) than other genotypes at 14 °C, except M. × giganteus ‘Hornum’. Several genotypes returned to their pre-chilling A1000 values when the temperature was increased to 24 °C after 24 d growth at 14 °C. Conclusions One M. sacchariflorus genotype had similar or higher photosynthetic capacity than M. × giganteus, and may be used for cultivation together with M. × giganteus or for breeding new interspecies hybrids with improved traits for temperate climates. Two easily measured variables, SLA and shoot growth rate, may be useful for genotype screening of productivity and cold tolerance.

Nutrient availability, photosynthesis, and growth of parsley fertigated with chicken manure extract and lupin sap

Abstract: A greenhouse experiment with parsley was conducted to investigate the effects of organic liquid fertilizers on biomass yield, photosynthesis, root zone pH, electrical conductivity, and nutrient concentrations of plant tissue and growing medium. Limed peat with 20 kg m-3 composted chicken manure was used as the growing medium. Four organic fertilizer treatments based on chicken manure extract and lupin sap were compared with conventional inorganic liquid fertilizer and no liquid fertilizer (only solid fertilizer). Chicken manure extract resulted in a higher biomass yield than lupin sap (6.7 g dry matter compared with 5.8 g) but lower than inorganic fertigation (8.4 g). Photosynthesis was not influenced by type of fertigation. Growing medium pH was between 7.4 and 8.5 in all organic treatments and one to two units higher than in the inorganic treatment. Electrical conductivity was highest in the lupin sap treatment. The root zone concentrations of NH4, K, Cl, and Na were found to be higher in the organic treatments. Inorganic fertigation, on the other hand, resulted in higher concentrations of NO3, Ca, and Mg. Concentrations of P and most of the micronutrients were at deficit levels in the lupin sap treatment. The addition of extra micronutrients to lupin sap increased the tissue concentrations but not the biomass yield. Among the organic treatments, chicken manure extract showed the most favourable root zone conditions and biomass yield.

Effect of short-term exposure to high-temperature on total gene expression in the leaves of four raspberry (Rubus idaeus L.) cultivars

Summary The effect of high temperature stress (27ºC or 37ºC for 24 h) on total gene expression profiles in the annual-fruiting raspberry (Rubus idaeus L.) cultivars ‘Autumn Bliss’, ‘Autumn Treasure’, ‘Erika’, and ‘Polka’ were evaluated at the floral initiation stage using a customised Rubus microarray. Significantly affected genes were obtained by pairwise t-tests using ‘volcano plots’ for each cultivar × treatment. A 10ºC elevation in temperature altered levels of expression, in at least one cultivar, of 644 differentially expressed genes in total, with ‘Erika’ and ‘Autumn Treasure’ showing elevated expression of 38 genes compared to ‘Autumn Bliss’ and ‘Polka’. We identified 12 common candidate genes that were modulated differentially in ‘Autumn Bliss’ and ‘Erika’ at 37ºC compared to 27ºC. In addition, two aquaporin genes (PIP1 and TIP2) were down-regulated in ‘Autumn Bliss’, but up-regulated in ‘Autumn Treasure’, ‘Polka’, and ‘Erika’ at 37ºC. Other down-regulated genes from the list of 38 genes included those encoding major latex-like proteins, plasma membrane proteins, cysteine rich proteins, and other stress-related proteins. Validation by real-time quantitative RT-PCR (RT-qPCR) indicated subtle changes in differential gene expression, suggesting a mild response to heat stress. This study used molecular tools to increase our understanding of, and to identify candidate genes involved in, the heat stress response of four annual-fruiting raspberry cultivars.

Stepwise incorporation of white clover (Trifolium repens L.) as fertiliser increases nitrogen fixation and improves nitrogen retention when intercropped with leek (Allium porrum L.)

Background and aimsWe investigated whether the incorporation of intercropped white clover as a split-dose fertiliser improves N retention of the plant-soil system in leek production.MethodsWhite clover and leek were grown in pots where clover was stepwise incorporated into soil as fertiliser. Half of the clover was incorporated before leek transplantation (LT), the other half was incorporated 26 (S1) or 41 (S2) days after LT, compared with full incorporation of all clover (F) before LT. 15N injection and leaching studies were performed to investigate interspecific competition and the effects of precipitation on soil N availability.ResultsStepwise incorporations increased or had no effect on leek growth, despite competition for N between white clover and leek. Compared to F, leek grown with stepwise incorporations had similar and lower N accumulation before the second incorporation, but N was higher at the end of the experiment. N2 fixation by white clover increased the total N input into soil and matched N availability with leek N demand and growth rate. Loss of inorganic N by leaching was lowest in S2 and highest in F.ConclusionsStepwise incorporations of white clover improved N retention in the plant-soil system and could be used to increase leek yield.