Optimisation of the amount of nitrogen enhances quality and yield of pepper

The goals of this study were to explore the characteristics of nitrogen (N) absorption and utilisation of chilli peppers (Capsicum annuum L.), improve the utilisation rate of nitrogen, and provide a theoretical basis for scientific fertilisation. In this experiment, pepper cv. Huoyanjiaowang was used as the material, and potted sand cultures and field randomised block experiments were conducted to study the effects of fertilisation of different forms of nitrogen on the photosynthetic characteristics, chlorophyll, nitrate nitrogen, alkaline nitrogen, capsaicin, dihydrocapsaicin and yield. In the pot experiment, the nitrogen application rates were 0, 10, 100, 320 and 600 mg/L, a level of nitrogen of 100 mg/L significantly inhibited the growth of pepper. With the increase in the application of nitrogen, the photosynthetic capacity gradually decreased, and 10 mg/L was the optimal nitrogen level. Under 0 and 10 mg N/L nitrogen levels in the field experiment, the content of chlorophyll of this group was significantly lower than those of other treatment groups, indicating that the plot lacked nitrogen. With the increase in the level of application of nitrogen, the contents of nitrate nitrogen and alkaline hydrolysis nitrogen in the soil increased. The yield of 153.18 kg/ha and 230 kg/ha nitrogen treatments was relatively high. Therefore, among the five nitrogen treatment levels, treatment with 153.18–230 kg N/ha was the most effective at stimulating the growth and yield of pepper.

Tolerance of extreme salinity in two stem-succulent halophytes (Tecticornia species)

Communities of Tecticornia on the margins of ephemeral salt lakes in Australia often exhibit species zonation, such as at Hannan Lake (Western Australia) where Tecticornia indica subsp. bidens (Nees) K.A.Sheph. and Paul G.Wilson occupies the less saline dune habitat on lake margins and Tecticornia pergranulata (J.M.Black) K.A.Sheph. and Paul G.Wilson subsp. pergranulata occupies both the dunes and the more saline and moist lake playa. Here we tested the hypothesis that these two species differ in tolerance to extreme salinity. Plants were grown in drained sand cultures with treatments of 10–2000 mM NaCl for 85 days. Both species were highly salt tolerant, maintaining growth at treatments of up to 2000 mM NaCl, although the death of two replicates of T. indica at 2000 mM NaCl suggests this salinity is close to the species tolerance limit. Both Tecticornia species maintained a favourable gradient in tissue water potential via osmotic adjustment as external salinity increased, also with reduced tissue water content at very high external salinity. Regulated accumulation of Na+ and Cl–, maintenance of net K+ to Na+ selectivity, high tissue concentrations of glycinebetaine and presumed cellular solute compartmentation, would have contributed to salt tolerance. The growth rate of T. pergranulata was 11–29% higher than T. indica suggesting, in addition to these moderate differences in salinity tolerance, other factors are likely to contribute to species zonation at salt lakes. The higher water use efficiency of the C4 T. indica compared with the C3 T. pergranulata may provide an advantage in the drier dune habitat on salt lake margins. An additional experiment confirmed the hypothesis that survival of T. pergranulata seedlings is enhanced by the duration of reduced salinity after germination, as would occur following significant rainfall, as older seedlings maintained higher growth rates during subsequent increases in salinity.

Characteristics of Cadmium and Lead Phytoextraction by Sunflower (Helianthus annuus L.) in Sand Culture

Higher biomass producing crops such as sunflower have already been considered as a hyperaccumulating candidate. In the present study, Cd and Pb accumulation by sunflower (Helianthus annuus L.), biomass and root exudates changes in sand cultures was analyzed during 90 days. Results demonstrated that ratios of aerial biomass/ root biomass (AW/RW) in Cd or Pb treatments declined with concentrations of Cd or Pb. Optical density (OD) of root exudates at 190 nm and 280 nm observed in Cd and Pb treatments were lower than the control. In single Cd or Pb treatments, bioconcentration factors (BCF) of Cd or Pb increased with time and decreased with concentrations, the highest Cd-BCF and Pb-BCF appeared in Cd5 (21) and Pb50 (7.95), respectively. Cd-BCF or Pb-BCF showed positive correlations with AW/RW ratios and OD values, and they were negative correlated with Cd and Pb concentrations. In the complex of Cd and Pb treatments, the highest values of BCFs were observed in Cd10+Pb100. Cd-BCF values negatively correlated with AW/RW ratios and Cd concentrations; besides, Pb-BCFs were negative with both Cd and Pb concentrations. Translocation factors (TF) fluctuated irregularly with time and concentration of metals in most treatments. Cd-TF values in single Cd treatments were positive correlated with concentrations of Cd. In the complex of Cd and Pb treatments, Cd-TF showed positive correlations with OD at 280 nm, but negative with Pb concentration. Results in this paper may supply useful information for phytoremediation of soil contaminated with cadmium and lead in situ.

Changes in phosphate content and phosphatase activities in rice seedlings exposed to arsenite

The effect of arsenite (As2O3) in situ on the level of the phosphate pool and activities of phosphohydrolytic enzymes was examined in rice (Oryza sativa L.) seedlings grown for 5-20 d in sand cultures. The effects were manifested via a decline in phosphate content and inhibition of the activities of key phosphatases. Application of 50 µM As2O3 in situ resulted in 34 to 77% inhibition of acid phosphatase activity in roots and about 38 to 50% inhibition of activity in shoots of 15-20-d-old seedlings. Similarly, alkaline phosphatase activity was inhibited in shoots under in situ As (III) toxicity. Varietal as well as organ specific differences were observed in the response of inorganic pyrophosphatase activity to in situ As (III) treatment. A moderately toxic in situ As2O3 level of 25 µM as well as a highly toxic level of 50 µM inhibited mitochondrial-ATPase activity whereas 25 µM As (III) stimulated the chloroplastic isoform of ATPase but at a higher level (50 µM) As (III) was inhibitory. The results suggest that exposure of rice plants to arsenite leads to lowering of the phosphate pool and alteration in the activities of key phosphohydrolytic enzymes which might contribute to metabolic perturbations and decreased growth of rice plants in an As (III) polluted environment.

Occurrence of Stem Rot of Basil, Caused by Sclerotinia sclerotiorum, in Coastal California

In January and February 1999, extensive dieback was observed on commercial basil (Ocimum basilicum) being grown in shadecloth greenhouses in coastal California's Salinas Valley. Symptoms were associated with stems that were high in the plant canopy and had cut ends resulting from multiple harvests of the foliage. Stems had brown discoloration extending from the cut ends toward the crown of the plant. Attached petioles and leaves turned brown and wilted. Profuse white mycelia were generally present externally on symptomatic stems, and occasionally large (>5 mm long) black sclerotia were found inside affected stems. In some shade houses approximately 20 to 25% of the plants were diseased. Isolations from mycelia, sclerotia, and symptomatic stems produced colonies of Sclerotinia sclerotiorum. Inocula for pathogenicity tests were produced by growing isolates on potato-dextrose agar, removing the resulting sclerotia, air drying them for 12 h, and placing them onto sterilized sand saturated with sterile distilled water. Sand cultures were incubated at 24 to 26°C in the light. After 4 to 6 weeks, apothecia containing asci with eight uniform ascospores developed from the sclerotia. Apothecial cultures were placed at the base of potted basil plants that had been trimmed to simulate harvest and placed in a humidity chamber. After 4 weeks, stem dieback was observed on test plants and S. sclerotiorum was recovered from symptomatic tissue. This pathogenicity test was repeated and the results were similar. Though this disease has occurred in the state prior to 1999, this is the first report of S. sclerotiorum on basil in California. This disease has been reported in North America from Canada and Louisiana (2,3). In contrast with reports from Europe (1), basal infections were not observed in the California greenhouses. References: (1) A. Garibaldi et al. Plant Dis. 81:124, 1997. (2) G. E. Holcomb and M. J. Reed. Plant Dis. 78:924, 1994. (3) T. C. Paulitz. Plant Dis. 81:229, 1997.

Ion Accumulation and Distribution in Shoot Components of Salt-stressed Eucalyptus Clones

Four clones of Eucalyptus camaldulensis Dehn. (4543, 4544, 4573, and 4590) and one clone of E. rudis Endl. (4501) were grown in greenhouse sand cultures irrigated with waters designed to simulate saline drainage waters present in the San Joaquin Valley of California, and compositions that would result from further concentration of the waters. The drainage waters are typically high in Na+, SO42-, Cl-, and Mg2+. Electrical conductivities of the solutions were 2, 12, and 28 dS·m-1. Ion uptake and distribution patterns in above-ground components were studied in members of these clones grown under treatment for 7 weeks. Results indicated the clones could be separated into two distinct groups by significant differences in leaf-ion relations. Group 1 clones 4543, 4544, and 4573 accumulated less Na+ and more Ca2+ and Cl- in leaves than group 2 clones, 4501 and 4590. Group 2 clones accumulated Na+ under low salinity, but apparently possessed some mechanism for restricting Na+ accumulation by the leaves that was activated as salinity increased. Leaf and stem Cl- concentrations tended to be lower in all clones grown at 28 dS·m-1 than at 2 dS·m-1, despite increases in Cl- concentration in the irrigation waters. Under saline conditions, K+ and P were preferentially accumulated in the youngest leaves in the upper portion of the canopy, whereas Na+, Ca2+, and Mg2+ were retained in the older leaves.