Nickel supplementation effect on the growth,urease activity and urea and nitrate concentrations in lettuce supplied with different nitrogen sources

Effect of nickel (Ni) in the nutrient solution on yield, N metabolism, and nitrate content of leafy vegetables is poorly understood. The aim of this nutrient solution culture experiment was to investigate the effects of Ni supplementation on the nitrogen (N) metabolism and growth of lettuce (Lactuca sativa L. cv. Baker) with either urea or nitrate as the N source. Nickel supplement at 0.04 μM reduced urea toxicity to the urea-fed plants. Addition of Ni to the nutrient solution significantly increased the leaves and root growth of the urea-fed lettuce plants while it increased the growth of lettuce plants fed with nitrate only at N level of 20 mM. At N level of 20 mM, the leaves fresh weight of the urea-fed plants promoted by Ni supplement was comparable with the nitrate-fed plants untreated with Ni. Nickel supplementation increased the leaf total N concentrations in the urea-fed plants, although the nitrate-fed plants accumulated greater N in their leaves compared with urea treated plants at without Ni treatment. Nickel addition decreased the concentrations of leaf urea-N in the urea-fed plants and NO₃-N in the nitrate-fed plants. Nickel addition enhanced urease activity in the leaves of urea-fed plants. The results indicated Ni supplementation enhances the growth of the urea-fed lettuce plants while it has role in decreasing leaf nitrate concentration and thus, improving the health quality of the nitrate-fed plants.     

Accumulation of phytotoxic organic acids in reused nutrient solution during hydroponic cultivation of lettuce (Lactuca sativa L.)

Proper nutrient solution management in the root zone is the first consideration for the adoption of a closed hydroponic system. Plant roots often exude numerous organic acids, which are known to inhibit growth. To investigate the accumulation of these phytotoxic organic acids as root exudates, lettuce (Lactuca sativa L.) was hydroponically grown in reused nutrient solution. Organic acids were extracted with diethyl ether from the reused nutrient solutions (RNS), root residues, and activated charcoal (AC) then quantified by GC/MS. Five individual organic acids were identified from the root residues and seven from the reused nutrient solutions. After 90 days of lettuce cultivation, in the treated AC in 3RNS, benzoic, phenylacetic, cinnamic, p-hydroxybenzoic, lauric, phthalic, vanillic, palmitic, and stearic acids were identified. In contrast, little or no organic acids were detected in the 3RNS treated with AC (3RNS/AC). Artificially applied pure organic acids ranging from 25 to 200 μM inhibited lettuce growth in a concentration-dependent manner. Lettuce growth was also greatly reduced in the nutrient solutions containing a externally applied, simulated mixture of the organic acids as in the 3RNS. Lettuce growth was not inhibited following the addition of AC (2.5 g/L) to the nutrient solution containing the mixture of organic acids. Our results demonstrated that organic acids were accumulated in reused nutrient solutions and were phytotoxic to lettuce growth. Also, this study showed that the addition of AC reduces the phytotoxic effects by eliminating the organic acids.     

Nutritional quality of greenhouse lettuce at harvest and after storage in relation to N application and cultivation season

The effect of five levels of nitrogen fertilization on the growth and nutritional quality of Cos lettuce (Lactuca sativa L. cv. Parris Island) at harvest and after storage was studied during autumn and winter in South-West Greece. Plants were cultivated hydroponically in a greenhouse and the nitrate, chlorophyll and ascorbic acid (vitamin C) concentrations within the plant tissues were measured at harvest and following storage at 5 or 10 °C for 10 days. Nitrate accumulated in the leaves with increasing amounts of N within the nutrient solution and was higher in the winter than in the autumn. At the lowest N level (20 mg L⁻¹), the inner leaves accumulated more nitrate than the outer leaves, whereas at higher N levels (140, 200 or 260 mg L⁻¹) nitrate accumulation was higher in the outer leaves. Overall, the highest nitrate concentrations were detected in the petiole and the proximal end of the leaf, but at the lowest N application rate (20 mg L⁻¹) nitrate accumulated in the distal region of the leaf too. Although the nitrate concentrations within the leaves did not change significantly during 10 days storage at 5 or 10 °C, the chlorophyll and vitamin C concentrations decreased. Chlorophyll loss was higher in lettuce that was grown under low N levels and was higher at 10 °C than at 5 °C, but was reduced by enclosure of the lettuce in polyethylene film. It is concluded that the optimum N application rate for Cos lettuce grown hydroponically under cover during autumn and winter in South-West Greece, and in other areas with a similar climate, is 200 mg N L⁻¹ because at this N rate yield is satisfactory and leaf nitrate concentrations are below the maximum acceptable level for human consumption. Nutritional value (vitamin C concentration) and market quality (chlorophyll content) are highest at harvest and decrease during storage, but quality in terms of nitrate concentration does not change.     

Effect of application methods of organic fertilizer on growth,soil chemical properties and microbial densities in organic bulb onion production

This study was carried out to maximize the fertilization efficiency of mixed organic fertilizer (OF) for organically managed onion (Allium cepa L.) production during the one growing season of 2005–2006. The organic fertilizer was made of organic materials like sesame oil cake, rice bran and molasses and minerals like illite and mountainous soil. Four organic topdressing treatments, which all followed the same basal fertilization with solid OF, consisted of solid OF without mulch (OF/OFnM), liquid organic fertilizer without mulch (OF/LOFnM), liquid organic fertilizer under mulch (OF/LOFuM) and liquid organic fertilizer over mulch (OF/LOFoM). Chemical fertilizer (CF) and no fertilizer (NF) were treated as controls. The solid organic fertilization base was 2.0 ton ha⁻¹, and 4.57 ton ha⁻¹ and was used for topdressing. The total amount of liquid organic fertilization was 133.2 ton ha⁻¹, which was divided into 6 applications from February through March. The OF/LOFuM and OF/LOFoM topdressings did not reduce onion height, leaf number or bulb diameter as compared to chemical fertilizer, whereas no mulch treatments made onion growth significantly poorer. Onion top weight in CF was significantly higher than that in OF groups at the peak growth stage, while there was not much difference in bulb weight between the CF and OF/LOFoM treatment. Finally, the onion marketable yield was 45.9 ton ha⁻¹ in the OF/LOFoM treatment, which exceeded that in the CF treatment by up to 1.9 ton. Furthermore, OF/LOFoM was the most effective among all the treatments in transferring the nutrients from sink to source. CF made the soil pH more acidic than OF did, and the electrical conductivity (EC) remained higher with CF than OF as well. While organic fertilizer helped to keep the NO₃-N content stable throughout the growing season, the concentration rapidly oscillated up and down according to CF fertilization. Organic fertilizer increased population number of soil microorganisms like aerobes, actinomycetes in the field.     

Dynamic relationships between field temperatures and romaine lettuce yield and head quality

Romaine lettuce (Lactuca sativa L. var. longifolia Lam.) has great potential as a winter alternative crop in coastal South Carolina. Apache (A), Darkland (D), Green Tower (GT), Green Forest (GF), Ideal Cos (IC), and Tall Guzmaine (TG) romaine lettuce cultivar transplants were planted on 9 different planting dates in Charleston, South Carolina (SC) on monthly intervals from September to April from 1998 to 2001. The objective was to determine romaine's yield and quality responses to different growing season climates. Growing season mean (GSM) minimum or maximum temperatures (temps) were determined by averaging daily min and max temps from planting date to harvest date. The growing season for the September planting date (PD) was the warmest, followed by the April PD. The coldest growing season was the December PD, followed by January and November PDs. Collectively, GSM max temps ranged from 17 to 27 °C and GSM min temps ranged from 5 to 15 °C with these planting dates. The total accumulated heat units (Base 4.5 °C) were similar for all 8 PD growing seasons. The harvest maturities were similar between: September versus April PDs; October versus March PDs; and November versus February PDs. The December PD growing season required the greatest number of days to reach harvest from transplanting followed by the January PD growing season, with every 1 °C decrease in GSM min or max temps, days to harvest increased by 5 days. GSM min temperature affected number of marketable heads produced per plot more than GSM max temps for A, D, GT and TG but not GF and IC. Individual marketable head weight, however, was unaffected by GSM min and max temps. When all cultivar data were pooled and regressed, we found that from about 3 to 6 °C GSM min temps, the number of culls produced dropped steeply, but then plateaued from about 6 to 11 °C, and then decreased rapidly from 11 to 14 °C. The major cull defect was loss due to field rots. Generally, the pooled cultivar mean indicated that with an increase in GSM min temps from 3 to 6.5 °C, the rate of field rot production accelerated, but from 6.5 to 14 °C, field rot production was much slower in contrast.     

Effect of nitrogen form and radiation on growth and mineral concentration of two Brassica species

Three greenhouse experiments were carried out to determine the growth, yield, nitrate, total N and S concentration in shoots, and water uptake of hydroponically grown Brassica rapa L. subsp. nipposinica var. chinoleifera and Brassica juncea L. In each experiment, daily photosynthetically active radiation (PAR) level was 5.0 mol m⁻² (low), 6.8 mol m⁻² (medium) or 9.0 mol m⁻² (high). Plants were supplied with nutrient solutions having equal N concentrations of 11 mM in different forms: 100% NH₄, 50% NH₄ + 50% NO₃, and 100% NO₃. Nitrogen supplied as 100% NH₄ reduced fresh and dry shoot biomass, leaf area, and leaf number in both Brassica species, especially at low and medium PAR levels. In both Brassica species, S concentrations were highest, while nitrate concentrations were lowest in leaves of plants grown at N supplied as 100% NH₄. No differences in leaf nitrate concentrations were observed between 50% NH₄ + 50% NO₃ and 100% NO₃ treatments. Low and high PAR levels increased the nitrate concentrations and decreased the N/S ratio in leaves of both crops compared to medium PAR level. Fresh shoot biomass was maximized in Brassica rapa when PAR level was above the medium value and nitrate was supplied in the nutrient solution as NO₃ or as a mixture of 50% NO₃ and 50% NH₄. The highest fresh shoot biomass of Brassica juncea was observed in all nutrient solution treatments at high PAR level.     

Effect of fruit-load on the growth,absorption, and partitioning of inorganic nutrients in young ‘Fuyu’ persimmon trees

Tree growth and the increase in inorganic nutrients during a growing season were studied in 3-year-old, container-grown ‘Fuyu’ persimmon trees with different levels of fruit-load. Fruit-load was varied by adjusting the leaf–fruit ratio to 10, 20, 30, and 60 on July 5. Some trees were completely defruited. The whole trees were harvested on November 5 of that year, and increases in dry weight and inorganic elements in different tree parts during the season were measured. A lower leaf–fruit ratio resulted in a higher yield but also decreased fruit weight, soluble solids, and fruit color. Dry weight of the aerial woods and root increased significantly with a greater ratio. However, total dry weight including the fruits was higher in the lower ratio trees than in the higher ratio trees; the weight of a tree that maintained the ratio of 10 was 35% higher than a tree without fruit. Fruits accounted for 62% of total dry weight when the ratio was 10 and 27% when the ratio was 60. The leaf–fruit ratio did not significantly alter the total increase in P, K, Ca, and Mg content. N tended to decrease with an increasing leaf–fruit ratio. Of the total increases of N, P, and K during the season, the fruits accounted for 30%, 50%, and 54% at the ratio of 20, respectively, and the percentages increased to 44, 81, and 74 at the ratio of 10. The inorganic element content in the aerial woods and root tended to increase with greater ratios, especially in the root. When trees were defruited, N and K increases in the root accounted for 44% and 35% of the total increase, respectively. These results indicated that persimmon orchard fertilization programs with different fruit-load levels should accommodate the proportion of nutrients partitioned to fruits that are removed permanently from the tree.     

Effect of smoke-water and a smoke-isolated butenolide on the growth and genotoxicity of commercial onion

Smoke-water and a biologically active butenolide compound (3-methyl-2H-furo[2,3-c]pyran-2-one) derived from burning plant material, show stimulating effects on a number of agricultural and horticultural crops. In these trials, onion (Allium cepa L.) plants were treated (drenched) with either a 1:500 (v/v) smoke-water solution or a butenolide solution of 10⁻¹⁰ M under greenhouse conditions. Onion plants supplied with smoke-water and butenolide solution exhibited a significantly greater number of leaves, increased leaf length, and a higher fresh and dry leaf weight than untreated plants at 175 days after seed sowing (DASS) (third harvest). In addition, smoke-water and butenolide-treated onion plants exhibited a significantly higher bulb diameter and bulb weight than untreated plants, when these plants were harvested at 175 DASS. Overall, smoke-water was more effective than butenolide and achieved the highest harvest index. Genotoxicity was not detected in the bulbs of onion when they were treated with either smoke-water or butenolide.     

Effect of co-cultivation and crop rotation on corm rot disease of Gladiolus

Field and pot experiments were conducted to evaluate the effect of co-cultivation and crop rotation on the growth and corm rot disease of gladiolus (Gladiolus grandiflorus sect. Blandus) cv. Aarti caused by Fusarium oxysporum f.sp. gladioli (Massey) Snyd. and Hans. In the field experiment, gladiolus was co-cultivated with 10 agricultural/horticultural crops viz. Allium cepa L., Brassica campestris L., Capsicum annuum L., Eruca sativa Mill., Helianthus annuus L., Tagetes erectus L., Zea mays L., Vinca rosea L. and Rosa indica L., in a soil infested with F. oxysporum. All the crops except V. rosea and R. indica reduced disease incidence. The effect of H. annuus and T. erectus was significant and more pronounced than other co-cultivated crops. In general, root and shoot dry biomass, corm fresh weight, number of cormlets and number of flowers per spike decreased as compared to the un-inoculated monoculture gladiolus treatment (negative control) but these parameters enhanced as compared to the F. oxysporum inoculated monoculture gladiolus treatment (positive control). In a pot experiment, all the crops of the field experiment except V. rosea and R. indica were sown in rotation with gladiolus. Pot grown plants of different species were harvested at maturity and the soil was inoculated with F. oxysporum. Gladiolus was cultivated 1 week after inoculation. Disease incidence was significantly suppressed in all the treatments ranging from 29% to 53%. The highest suppression of disease incidence was recorded in T. erectus (53%) followed by B. campestris (49%). The effect of preceding crops on various vegetative parameters was similar in the pot experiment to that of the field experiment. The present study suggests that corm rot disease of gladiolus can be managed by mixed cropping of H. annuus and T. erectus or cultivation of T. erectus and B. campestris in rotation.     

Allelopathic effect of ginger on seed germination and seedling growth of soybean and chive

The rhizome, stem and leaf aqueous extracts of ginger were assayed at 10, 20, 40, and 80 g l⁻¹ for their effects on seed germination and early seedling growth of soybean and chive. All aqueous extracts at all concentrations inhibited seed germination, seedling growth, water uptake and lipase activity of soybean and chive compared with the control, and the degree of inhibition increased with the incremental extracts concentration. The degree of toxicity of different ginger plant parts can be classified in order of decreasing inhibition as stem > leaf > rhizome. The results of this study suggest that rhizome, stem and leaf of ginger contain water-soluble allelochemicals which could inhibit seed germination and seedling growth of soybean and chive. The rhizome is the main harvested part of ginger. The residue (mainly stems and leaves) of the ginger plant should be removed from the field so as to diminish its inhibitory effect. Further work is needed to specify and verify the allelochemicals produced by this plant. The results of this study suggest that ginger allelochemicals are heterotoxic, and thus intercropping should not be practiced using ginger.     

Effects of conventional and organic fertilization on spinach (Spinacea oleracea L.) growth,yield, vitamin C and nitrate concentration during two successive seasons

Current experiment was laid out in order to compare different kinds of organic manure and chemical fertilizer application in growing spinach under the open-field conditions in two successive seasons. Matador type spinach (Spinacea oleracea L.) was cultivated organically and conventionally and spinach growth, yield, vitamin C and nitrate concentrations were checked throughout two successive seasons (autumn and winter). Commercial chemical fertilizer was used as conventional application, and chicken manure (CM), farmyard manure (FM) and blood meal (BM) were used as organic manure applications as a single and as mixtures at different quantities by aiming to receive 150 kg N ha⁻¹ for each, totally 19 applications. In general, autumn season gave the better results in terms of spinach growth, yield and resulted in lower nitrate concentration, whereas the vitamin C concentration was found to be higher in winter season. Reasonable applications to be recommended should be as follows with regard to the seasons; 3.5 ton ha⁻¹ CM and 0.6 ton ha⁻¹ BM + 0.85 ton ha⁻¹ CM + 4.0 ton ha⁻¹ FM for spinach growth; 3.5 ton ha⁻¹ CM and 5.0 FM + 1.2 CM + 0.4 BM applications for spinach yield; 5.0 ton ha⁻¹ FM + 2.5 ton ha⁻¹ CM and 15.0 ton ha⁻¹ FM for vitamin C and nitrate concentration in the autumn and the winter season, respectively. In conclusion, FM and CM can be used effectively in growing organic spinach especially in the autumn season and can be transferred successfully into an asset.     

The conjunctive use of compost tea and inorganic fertiliser on the growth,yield and terpenoid content of Centella asiatica (L.) urban

The conjunctive use of a compost tea (CT) and an inorganic fertiliser (NPK) on the growth, yield and terpenoid content of Centella asiatica (L.) urban was evaluated. CT and NPK applied at half the recommended concentration resulted in the significant enhancement of vegetative growth, yield and antioxidant content. The synergistic effect of CT₅₀ and NPK₅₀ was highly pronounced on the bioactive components Asiatic acid, madecassoside and asiaticoside. The distribution of the total antioxidants was highest in roots (80%), followed by leaves (66%) and petioles (54%). There was a strong positive correlation (r = 0.990) between fertility and total antioxidant content, suggesting an enhanced synthesis of bioactive components resulting from the treatment. This response by C. asiatica to the integrated experimental treatment suggests a viable option for the commercial cultivation of the herb. Augmenting the vegetative biomass production and bioactive components will increase the availability of this medicinal herb for the treatment of various human ailments.     

Effect of different girdling dates on tree growth,fruit characteristics and reserve accumulation in a late-maturing persimmon

Trunks of 8-year-old vigorous ‘Fuyu’ persimmon (Diospyros kaki Thunb.) were girdled to a 1 cm width on April 20 and June 10 2004. Tree growth and fruit characteristics were monitored for two years, with special emphasis on the carry-over effect in 2005. Girdling reduced trunk and shoot growth especially of April-girdled trees over two consecutive years. However, the most significant effect of girdling was in the occurrence of water sprouts: a control tree had 29.5 in 2004 and 27.3 in 2005, whereas the April-girdled trees had only 0.3 and 5.3, respectively. Girdling increased fruit set by nearly 50% and enhanced fruit colour in 2004 only. Girdling date did not significantly affect fruit size and soluble solids for two years. Fruit flesh of girdled trees in 2004, especially in the April-girdled trees, had lower N and P concentrations. The levels of starch, soluble sugars, and inorganic elements in flower-bearing distal buds measured just before new growth in 2005 were not significantly altered by the girdling in 2004.     

Phytochemical accumulation and antioxidant capacity at four maturity stages of cranberry fruit

Specific components of cranberry fruit are being associated with human health attributes, such as maintenance of urinary tract health and antioxidant status. Some of the chemical properties and antioxidant capacity of cranberry (Vaccinium macrocarpon Ait. cv. Pilgrim) fruits were investigated at light green, blush, light red and dark red maturation stages. Fruit total phenolics, total monomeric anthocyanins, soluble solids, titratable acidity and individual organic acids were examined. Antioxidant capacity of fruits were determined by both the ferric reducing antioxidant power (FRAP) and trolox equivalent antioxidant capacity (TEAC) assays. The fruit color was measured using a portable chromameter. A converse relationship was found between total phenolics and anthocyanin as fruits mature. Total phenolic concentration was declined from 7990 to 4745 mg GAE/kg fw, while total monomeric anthocyanin content was increased from 0.8 to 111.0 mg/kg fw from green to dark red stage. Brix was increased from 6 to 9.3% as well. The main organic acid was citric acid determined by the HPLC method. The antioxidant capacity of cranberries decreased to light red stage; when a fruit accumulates more anthocyanin the activity increased again in both FRAP and TEAC methods. Averaged antioxidant capacity measured was 12.61 and 17.48 mmol TE/kg fw by FRAP and TEAC methods.     

Determination of the uptake and translocation of nitrogen applied at different growth stages of a melon crop (Cucumis melo L.) using N isotope

In order to establish a rational nitrogen (N) fertilisation and reduce groundwater contamination, a clearer understanding of the N distribution through the growing season and its dynamics inside the plant is crucial. In two successive years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to determine the uptake of N fertiliser, applied by means of fertigation at different stages of plant growth, and to follow the translocation of N in the plant using ¹⁵N-labelled N. In 2006, two experiments were carried out. In the first experiment, labelled ¹⁵N fertiliser was supplied at the female-bloom stage and in the second, at the end of fruit ripening. Labelled ¹⁵N fertiliser was made from ¹⁵NH₄¹⁵NO₃ (10 at.% ¹⁵N) and 9.6 kg N ha⁻¹ were applied in each experiment over 6 days (1.6 kg N ha⁻¹ d⁻¹). In 2007, the ¹⁵N treatment consisted of applying 20.4 kg N ha⁻¹ as ¹⁵NH₄¹⁵NO₃ (10 at.% ¹⁵N) in the middle of fruit growth, over 6 days (3.4 kg N ha⁻¹ d⁻¹). In addition, 93 and 95 kg N ha⁻¹ were supplied daily by fertigation as ammonium nitrate in 2006 and 2007, respectively. The results obtained in 2006 suggest that the uptake of N derived from labelled fertiliser by the above-ground parts of the plants was not affected by the time of fertiliser application. At the female-flowering and fruit-ripening stages, the N content derived from ¹⁵N-labelled fertiliser was close to 0.435 g m⁻² (about 45% of the N applied), while in the middle of fruit growth it was 1.45 g m⁻² (71% of the N applied). The N application time affected the amount of N derived from labelled fertiliser that was translocated to the fruits. When the N was supplied later, the N translocation was lower, ranging between 54% at female flowering and 32% at the end of fruit ripening. Approximately 85% of the N translocated came from the leaf when the N was applied at female flowering or in the middle of fruit growth. This value decreased to 72% when the ¹⁵N application was at the end of fruit ripening. The ammonium nitrate became available to the plant between 2 and 2.5 weeks after its application. Although the leaf N uptake varied during the crop cycle, the N absorption rate in the whole plant was linear, suggesting that the melon crop could be fertilised with constant daily N amounts until 2–3 weeks before the last harvest.     

Differences in onion pungency due to cultivars,growth environment,and bulb sizes

This study was conducted to determine the effects of genetic and environmental factors on onion pungency, estimated as pyruvic acid levels. Genetically identical clones were grown at three different field locations and in a greenhouse. Onion pungency was significantly influenced by clone type, location, and their interaction. Genetic differences were the major determining factor of onion pungency (81.3% of total variation). Location, including all environmental factors, and the clone × location interaction comprised 11.4% and 7.3% of the total variation, respectively. The magnitude of the pungency difference among field-grown onions was about 1.5 μmol/ml. The pungency levels were not positively correlated with soil sulfur nutrition levels, which ranged from 16 to 97 ppm. Within clones, onion pungency levels were loosely inversely correlated with increasing bulb weight. The clones proved to have the most uniform pungency (8% CV), followed by hybrids (10.6% CV) and open-pollinated cultivars (21.3% CV). We have demonstrated that genetic factors were determinant of onion pungency. Environmental factors influenced pungency to a lesser degree. Therefore, choosing cultivars with low pungency, ideal growing environments and proper sulfur nutrition control, are key factor in producing sweet onions.     

Effect of hydrogen cyanamide,mineral oil and thidiazuron in combination with tip pruning on bud break,shoot growth and yield in ‘Bourjasotte Noire’, ‘Col de Damme Noire’ and ‘Noire de Caromb’ figs

Commercial fig production is relatively new to the Mediterranean-type climate Western Cape Province of South Africa. A lack of lateral branch development impedes tree structure development and therefore adequate yields of quality fruit. The chemical rest breaking agents, Lift^® (thidiazuron 3 g L⁻¹) at 6%, Dormex^® (hydrogen cyanamide, 520 g L⁻¹) at 4%, mineral oil at 4% and a combination of mineral oil and Dormex^® at 2% each were evaluated in a split plot design in combination with tip-pruning vs. no-pruning to overcome apical dominance and increase complexity (Experiment 1). During the 2008/2009 season, an additional investigation was conducted to evaluate the use of thidiazuron and hydrogen cyanamide for harvest scheduling (Experiment 2). Dormex^® at 3% and Lift^® at 6%, were applied to dormant trees on 30 June 2008, 3 August 2008, 15 August 2008 or 30 August 2008. In general, Lift^® can be used to increase the number of buds breaking in ‘Bourjasotte Noire’ and ‘Col de Damme Noire’, while tip pruning decreased bud break with a resultant increase in shoot length. Dormex^® and oil combined decreased bud break in these two cultivars but was effective on ‘Noire de Caromb’. Where bud break was increased the resultant N + 1 shoot length was decreased. RBAs increased the number of fruit in both the breba and main crop of ‘Noire de Caromb’, but decreased fruit size of the breba crop. Our data are not conclusive as to what the reason for low lateral bud break might be but leans towards strong AD in seasons with 400 Utah CU or more, but might include some delayed foliation response in seasons with less than 200 Utah CH.     

Silicon supplementation ameliorated the inhibition of photosynthesis and nitrate metabolism by cadmium (Cd) toxicity in Cucumis sativus L.

The effects of silicon (Si) application on plant growth, pigments, photosynthetic parameters, chlorophyll a (Chl a) fluorescence parameters and nitrogen metabolism were studied in Cucumis sativus L. under cadmium (Cd) toxicity. Compared with the control, 100 μM CdCl₂ treatment caused dramatic accumulation of Cd in cucumber leaves, greatly induced chlorosis, and the transmission electron microscope (TEM) analysis indicated that Cd treatment cucumber chloroplast showed obvious swollen, thylakoids and chloroplast membrane were seriously damaged, and could not be observed clearly. Application of Si reversed the chlorosis, protected the chloroplast from disorganization, and significantly increased the pigments contents, which might be mainly responsible for the higher photosynthetic rate and accumulation of biomass under Cd stress. Further investigation of chlorophyll a fluorescence indicated that Cd treatment decreasing photosynthesis was not due to stomatal restriction, while was closely related integrity damage or function lost of the photosynthetic machinery which can be concluded from the higher intercellular CO₂ concentration (Ci) and lower F_v/F_m and ΦPSII. Application of Si alleviated the inhibited level of photosynthesis and F_v/F_m and ΦPSII by Cd, which might imply that Si plays important roles in protecting photosynthetic machinery from damaging. The Cd treatment also greatly inhibited the enzymes of nitrogen metabolism including nitrogen reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), and Si supply decreased the inhibiting effects of Cd.     

DNA sequencing reveals false positives during the detection of aster yellows phytoplasmas in leafhoppers

During the summer of 2001 and 2002, 850 and 865 carrot plants and 926 and 2584 leafhoppers associated with aster yellow (AY)-type disease were collected from five fields in Manitoba, Canada. DNA was extracted from 999 individual leafhoppers and 381 leaf tissues from both apparently healthy and AY-like infected carrot plants. All DNA samples were examined by PCR for the presence of phytoplasmas using three universal primer pairs P1/P6, P1/P7 and R16F2n/R2 derived from phytoplasma rDNA sequences. DNA amplification with these three primer pairs generated the expected amplification products of 1.7, 1.5 and 1.2 kb, respectively. Diluted PCR products obtained using universal primer pair P1/P6 were nested with R16F2n/R16R2n. The latter set of primers amplified DNA samples from 92 carrot plants and 83 leafhopper samples. In order to assess the diversity among insect and plant phytoplasmas, nested PCR products from all 92 carrot and 83 leafhopper samples were subjected to RFLP analysis using restriction endonucleases KpnI, MseI, and HhaI. This RFLP analysis showed similar patterns among carrot and leafhopper samples. Phytoplasmas detected in most samples belonged to the subgroup 16Sr-IA. To understand why the R16F2n/R16R2n of primers did not amplify the PCR product obtained from the first PCR in the remaining samples, four PCR products of P1/P6 from two plants (representing 16Sr-IA and 16Sr-IB) and two leafhopper samples that did not amplify with nested PCR, were used for DNA sequencing. ¹ The BLAST analysis of the obtained sequences showed that the PCR amplicons from the two carrot samples precisely matched with the GenBank sequences of known phytoplasmas. Alignments of these two sequences have shown very slight variations (transition/transversion ratio mean of 0.539) that would correspond to the minor differences at the 16S level between the 16Sr-IA and 16Sr-IB phytoplasma subgroups. The sequences of PCR products obtained from the two insect samples had similarity (>98%) with the sequences of phytoplasma in carrot except that their length differed from the carrot samples by 6 bp. They actually matched bacterial sequences from the GenBank, indicating that a single PCR using P1/P6 was not enough to detect phytoplasma in leafhoppers.     

Quality and volatile attributes of attached and detached ‘Pluk Mai Lie’ papaya during fruit ripening

The ‘Pluk Mai Lie’ papaya (Carica papaya L.) is a promising cultivated fruit for use in fresh and processed products due to its firm flesh, but the aroma it releases is flat. Changes in quality and volatile profiles were analyzed during on- and off-tree fruit ripening. Detached fruit ripened faster than attached fruit, accumulating high internal ethylene levels. Aside from peel color, which was redder in on-tree ripened fruit, most quality attributes changed similarly in the two ripening situations. A slight increase in total soluble solids (TSS) was measured from the onset of the preclimacteric stage, whereas titratable acidity (TA) remained stable throughout the development. Whereas 2-ethyl-1-hexanol was found specifically in green fruit, ethyl octanoate emerged only in fully-ripe fruit. Furthermore, benzyl isothiocyanate was the most abundant volatile and was present in fruit at every stage except full ripening. The production of total esters, highly correlated with a loss of firmness and an increase in cavity ethylene accumulation, was about 10-fold higher in off-tree ripened fruit. The levels of methanol and ethanol sources in fruit increased steadily throughout ripening, with esters formed from ethyl alcohol predominating from the half-ripe through the senescence phases. The alcohol dehydrogenase activity in the mesocarp increased dramatically during the early ripening stages, whereas alcohol acetyltransferase was active throughout ripening. No difference in volatile profiles was found in the papaya fruit during on-tree and postharvest ripening.