Effects of cold storage of germinated vegetable seeds prior to fluid drilling on emergence and yield of field crops

Germinated seeds of five vegetable crops were stored at 1 °C in aerated water or humid air for periods of up to 15 days and then fluid drilled in the field. Viability of germinated seed was maintained in carrot and parsnip for a minimum of 15 days, salad onion for 9 days, lettuce for 6 days and cabbage for 3 days. When salad onion, lettuce and cabbage seeds were stored for longer than these times there was a reduction in the number of seedlings emerging. In species where storing seeds for up to 15 days caused a reduction in emergence an adjustment to the seed rate related to the length of storage can be made to achieve the desired population and still retain the advantages of fluid drilling pre-germinated seeds. This is possible because with one exception (an increase in the variation of salad onion stem diameters) the performance of plants from all stored germinated seeds after emergence was similar to plants from freshly germinated seeds.     

The response of carrot (Daucus carota L.) and onion (Allium cepa L.) seedlings to mechanical impedance and water stress at sub-optimal temperatures

The response of pre-emergent shoots of carrot and onion to mechanical impedance, water stress and suboptimal temperature was studied. We used model laboratory systems in which mechanical impedance and water stress could be varied independently of each other and independently of other complicating factors (e.g. aeration and hydraulic conductivity). Our results showed that mechanical impedance reduced the rate and extent of shoot development in both carrot and onion. Roots of both carrot and onion were less sensitive to mechanical impedance than shoots. The recovery of shoot length following the removal of impedance was studied. The data were used to develop a new model of shoot elongation as a function of mechanical stress, water stress, temperature, shoot length and time. Our results also provide a new insight into the physiology of shoot development in strong soils. We contrast the effect of mechanical impedance on pre-emergent seedling development in carrot and onion.     

Effects of Cropping Sequences on Population Densities of Meloidogyne hapla and Carrot Yield in Organic Soil

The influence of various cropping sequences on population densities of Meloidogyne hapla and carrot yield was studied in organic soil under microplot-and field conditions. Spinach, radish, barley, oat, and wheat were poor or nonhosts for M. hapla. Population densities of M. hapla were maintained or increased on cabbage, celery, lettuce, leek, marigold, and potato. Marketable percent-age and root weight of carrots were greater following spinach, oat, radish, and fallow-onion than those following two crops of onion or carrot in microplots. Under field conditions, the carrot-onion-oat-carrot cropping sequence decreased M. hapla population densities and provided a 282% increase in marketable yield of carrot compared to a carrot monoculture. Two consecutive years of onion increased M. hapla population densities causing severe root galling and a 50% yield loss in the following crop of carrot. Based on root-gall indices, carrots could be grown economically for 2 years following radish, spinach, and oat, but not following onion and carrot without the use of nematicides.     

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. II. Seedling emergence and plant growth

Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for two weeks at 15 °C. Seedling emergence was recorded in the field for carrot and onion and in the glasshouse for celery. Compared to the untreated control, priming increased the percentage seedling emergence in certain poorly-emerging seed lots of carrot and celery, but had no effect on onion. Mean emergence times were reduced by priming in all seed lots, by 3–5, 5–8 and 3–9 days in carrot, celery and onion respectively. The largest effects occurred in the slowest-emerging seed lots. There were significant interactions between priming and seed lots within cultivars in carrot and celery and between priming and cultivars in celery and onion. Priming generally reduced the spread of emergence times, but the effects were not statistically significant in carrot. Drying back the primed seeds had no effect on percentage emergence in onion, but reduced it (compared to primed seed which had not been dried-back) in certain carrot and celery seed lots. Primed and dried-back seeds emerged later than primed seeds, by up to 1·5, 2·6 and 2·6 days in carrot, celery and onion respectively. The spread of emergence times was generally larger for primed and dried-back seeds than for primed seeds, but the differences were not always statistically significant. Plant fresh weights were recorded 9, 7 and 12 wk after sowing for carrot, celery and onion, respectively. In each species, mean plant weight was inversely related to seedling emergence time; thus plants grown from primed seed were always heavier than the controls, by up to 33%, 182% and 47% in carrot, celery and onion respectively.     

Effects on the growth of carrots (Daucus carota L.), cabbage (Brassica oleracea var. capitata L.) and onion (Allium cepa L.) of restricting the ability of the plants to intercept resources

The objective of this paper is to assess the size and penetration of edge effects in carrot, cabbage and onion field crops and the extent to which these edge effects are modified by the presence of aerial or soil competition between the crop rows. In all three crops, large weight differences developed between the plants in the edge rows and those in the central rows. There was no indication of plant weight fluctuating between large and small values with each successive row in from the edge, as suggested by others. In carrot and onion, edge effects were greatly reduced by the presence of either white reflective aerial partitions or soil partitions, indicating that these species competed for both light and soil resources in UK field conditions. In cabbage, the mere presence of clear aerial partitions between rows reduced edge effects and there was little effect of soil partitions. This indicates the predominance of shoot over root competition in this species. The differences between species are possibly related to the architectural flexibility of their shoots. These results suggest that, within crops, carrot and onion plants compete for light over a distance of about 20 cm in each direction and for below-ground resources over a distance of about 50 cm in each direction. For cabbage, interactions between plants appeared to be dominated by the requirement for sufficient space to deploy the shoots for efficient light interception.     

Crop and weed emergence patterns in relation to time of cultivation and rainfall

In experiments over 3 years, separate field plots were cultivated once only at 2-wk intervals. Cultivation resulted in a flush of weed seedlings, representing usually less than 6% of the apparently viable seeds in the top 10 cm of soil and with a species composition which varied with the time of year. Subsequent flushes coincided in timing and extent with those on soil which had been undisturbed and were related to significant rainfall events. In each year there were periods when lack of soil moisture restricted emergence. At these times, seeds were released from dormancy by cultivation but germination of some or all of them was delayed. There was a general correspondence in the emergence patterns of weeds and of carrot and onion sown after each cultivation. On occasions when the seedbed was drying out, establishment of the comparatively rapidly-germinating radish and cabbage was greater than that of carrot, onion or weeds. Effective initiation of germination of both crops and weeds was traceable to rainfall events. Emergence was reduced or delayed on more than half of the 45 cultivation occasions during the three growing seasons, and the results emphasise the importance of soil moisture in determining the extent and timing of seedling emergence.     

Viability of VA-mycorrhizal fungi following soil solarization and fumigation

Two field experiments were conducted to examine the effect of soil solarization on the survival of arbuscular mycorrhizal (AM) fungi and root colonization of three crops. The experiments were carried out in a loamy sand soil (Rehovot) and a silty soil (Bet She'an Valley). For both experiments, assessment of indigenous AM fungal populations by the most probable number (MPN) method indicated that populations were reduced to zero after 2 or 4 weeks of solarization treatment. However, Glomus intraradices inoculum applied to the soil prior to solarization remained viable even after 8 weeks of solarization. After soil fumigation with methyl bromide both indigenous and applied AM fungi were nondetectable. Percentage root colonization by the indigenous AM fungal populations, together with plant-growth parameters, were assessed for three crops: onion and wheat (Rehovot), and carrot (Bet She'an). When sown on solarized field plots, onion and carrot seedlings showed a plant growth retardation, whereas wheat showed an increased growth response. Root colonization by indigenous AM fungi was not evident until 6 weeks after seedling emergence. Fumigation with methyl bromide reduced root colonization by indigenous AM populations, and reduced onion and wheat plant development at early growth stages. In a laboratory experiment, a temperature of 45° C for up to 24 h did not affect AM spore viability, indicating that temperatures reached during the solarization treatment cannot solely account for the reduced AM fungi viability in the field. Apparently, soil solarization temporarily delays root colonization by indigenous AM fungi until 6-8 weeks after plant emergence.     

The Possible Involvement of Root-cap Mucilage in Gravitropism and Calcium Movement Across Root Tips of Allium cepa L

Roots of Allium cepa L. grown in aerated water elongate rapidly,but are not graviresponsive. These roots (1) possess extensivecolumella tissues comprised of cells containing numerous sedimentedamyloplasts, (2) lack mucilage on their tips, and (3) are characterizedby a weakly polar movement of calcium (Ca) across their tips.Placing roots in humid air correlates positively with the (1)onset of gravicurvature, (2) appearance of mucilage on tipsof the roots, and (3) onset of the ability to transport Ca polarlyto the lower side of the root tip. Gravicurvature of roots previouslysubmerged in aerated water is more rapid when roots are orientedvertically for 1–2 h in humid air prior to being orientedhorizontally. The more rapid gravicurvature of these roots correlatespositively with the accumulation of mucilage at the tips ofroots during the time the roots are oriented vertically. Therefore,the onset of gravicurvature and the ability of roots to transportCa to the lower sides of their tips correlate positively withthe presence of mucilage at their tips. These results suggestthat mucilage may be important for the transport of Ca acrossroot caps. Allium cepa, root gravitropism, root mucilage, calcium, onion     

Plant-parasitic nematodes associated with semi-temperate vegetables in the highlands of Benguet Province,Philippines

Thirteen genera (Aphelenchoides, Criconemella, Ditylenchus, Globodera, Helicotylenchus, Hoplolaimus, Meloidogyne, Longidorus, Paratrichodorus, Pratylenchus, Trichodorus, Tylenchus and Xiphinema) of plant-parasitic nematodes were found associated with 15 semi-temperate vegetable crops in Benguet Province, Philippines. Among these taxa, Helicotylenchus, Meloidogyne and Pratylenchus were the most predominant. Four taxa that can vector plant viruses were also found: Trichodorus, Paratrichodorus, Longidorus and Xiphinema. The taxa Paratrichodorus, Longidorus and Xiphinema have not been reported previously on semi-temperate vegetable crops in the Philippines. The most predominant nematode species were H. dihystera, P. penetrans and Meloidogyne spp. These nematodes were found abundantly in five out of the nine municipalities surveyed: Atok, Bakun, Buguias, Kibungan and Mankayan. The incidence of Criconemella sp., G. rostochiensis, Hoplolaimus sp., Longidorus sp., Trichodorus sp. and Tylenchus sp. was also recorded in at least one municipality. The predominant nematode species were also found on every vegetable crop examined. More particularly, H. dihystera was highly abundant on cucumber, cauliflower, Chinese cabbage, sweet pepper, snap bean and onion; P. penetrans was highly abundant on carrot, celery, garden pea, broccoli, cabbage, Chinese cabbage, Chinese mustard, onion, potato, radish and lettuce; Meloidogyne spp. were highly abundant on celery, cucumber, Chinese mustard, carrot, sweet pepper and potato. According to the formula by Fortuner and Merny (1973 Fortuner, R and Merny, G. 1973. Les nématodes parasites des racines associés au riz en Basse Casamance (Senegal) et en Gambie, Cahiers de l'Orstom. Série Biologique, 21: 3–20.  [Google Scholar]) for identifying the potential plant pathogens, these predominant nematode species were classified as potential pathogens with the ability to cause economic loss which shows that they are probably important active pathogens of these semi-temperate vegetables. The incidence of other nematode species in the rhizosphere included G. rostochiensis on sweet pepper, garden pea and potato; D. dipsaci on onion; Tylenchus sp. on lettuce, onion and broccoli; A. fragariae on carrot, lettuce, broccoli and onion; Criconemella sp. on cucumber and cauliflower; Longidorus sp. on carrot, celery, cucumber, broccoli, cabbage, cauliflower, Chinese mustard, snap beans, onion, potato and radish; X. americanum on lettuce, broccoli and onion; Paratrichodorus sp. on carrot, lettuce, onion and potato; and Trichodorus sp. on snap bean, potato and radish.     

The impact of mechanical impedance on the emergence of carrot and onion seedlings

The development of a method using wax layers to simulate the effect of strong soil crusts on seedling emergence is described. Wax layers of different strengths were prepared by melting together white soft paraffin and paraffin wax in different proportions. The wax discs were placed above seeds planted in wet, but well-aerated sand in controlled environments. The effect of adding charcoal to the wax discs to prevent transmission of light was also tested. When wax layer penetrometer pressure was 0.2–0.25 MPa, light transmission greatly decreased the final emergence of carrot, but not onion seedlings. Penetrometer pressures above 0.25 MPa greatly decreased emergence through black wax layers in both carrot and onion. The presence of 2–4 mm stones immediately below wax layers (to simulate aggregates) decreased the emergence of onion shoots through wax layers with penetrometer pressures of 0.25 MPa and above. The emergence of carrot and onion seedlings from wax layers was compared to emergence in the field from different soil types and aggregate sizes. In both laboratory and field experiments, carrot gave better emergence than onion when emergence was relatively poor. Results were consistent with the hypothesis that mechanical impedance is a major factor in poor crop emergence in temperate conditions.     

Biochemical Activities and Compounds in Seeds: Possible Tools for Seed Quality Evaluation

The rate and final percentage of field emergence (seed quality)was measured in 55 seed-lots of carrots (Daucus carota L.),45 seed-lots of onion (Allium cepa L.) and 32 seed-lots of cabbage(Brassica oleracea var. capitata), together with the followingbiochemical indices: rates of ATP-synthesis; reduction of tetrazoliumby seed powder; AMP and malate content. Differences in field performance of seed-lots (seed quality)showed some correlation with particular biochemical indices.Seed quality was most significantly correlated with AMP contentand ATP synthesis in carrot, with malate content, reductionof tetrazolium and ATP synthesis in onion and with malate andAMP content and reduction of tetrazolium in cabbage. Daucus carota L., Allium cepa L., Brassica oleracea var capitata, carrot, onion, seed quality, ATP, biochemical indices     

STUDIES OF THE BIOLOGY OF SCLEROTIUM CEPIVORUM BERK.

Sclerotia from 6-week-old pure cultures of Sclerotium cepivorum germinated immediately in soil only after abrasion of their rinds, but after burial in soil for a month or more, unabraded sclerotia became capable of germination.
Marked stimulation of germination occurred in the presence of host plants (onion, leek and shallot). Little or no germination occurred in soil alone or in the presence of non-host plants (barley, cabbage, carrot and white clover). Sclerotial germination was observed in a number of soils of widely differing pH and over a wide range of soil water content. Germination of sclerotia on uninjured onion roots was greatest at the tip region. On artificially injured roots sclerotial germination was enhanced but the effect of position was lost.
Sclerotial germination was independent of contact between roots and sclerotia. It was induced by root extracts of all Allium spp. tested, but of no other plants. Boiling or autoclaving root extracts did not destroy the active principle and it is concluded that under field conditions sclerotia are induced to germinate by a thermostable chemical substance from Allium roots.
The process of germination of sclerotia is described.     

Ethylene-promoted formation of aerenchyma in seedling roots of Zea mays L. under aerated and non-aerated conditions

The role of ethylene in the formation of lysigenous cortical cavities (aerenchyma) in seedling roots of Zea mays L. cv. Capella, has been studied under aerated and non-aerated conditions. Passing roots from air to aerated water or from an aerated nutrient solution to a non-aerated solution, promoted cavity formation and was accompanied by an increase of the endogenous ethylene concentration. When the endogenous ethylene concentration of roots in aerated nutrient solutions, which otherwise would not produce much cavities, was enhanced by applying ethylene gas (0.1 and 1.0 μl 1^-1 in air) or the ethylene precursor 1-aminocyclopropane-1-car-boxylic acid, cavity formation was promoted. When, on the contrary, the endogenous ethylene concentration of the roots was reduced by adding the inhibitors of ethylene biosynthesis, cobalt ions and aminooxyacetic acid, or when the ethylene action was prevented by silver ions, cavity formation was prevented. It is concluded that endogenous ethylene controls the induction of cavity formation in the roots.     

Effects of adding plant nutrients to the gel carrier used for fluid drilling germinating lettuce and onion seeds

Fluid drilled germinating lettuce seeds gave earlier production of larger heads than dry sown natural seeds. The addition of sodium phosphate to the gel with germinating seeds increased seedling growth rate which further advanced maturity and increased head weight. Sodium, ammonium and potassium phosphate added to the gel increased seedling dry weight of onions compared to the germinating seed control which produced larger seedlings than dry seed. However, these early improvements in onion seedling size diminished with time.     

The microflora of stored coleslaw and factors affecting the growth of spoilage yeasts in coleslaw

Saccharomyces dairensis and Sacch. exiguus were isolated as the spoilage flora of coleslaw stored at 5 degrees and 10 degrees C. The growth of these yeasts in mixtures of mayonnaise with vegetable was inhibited by onion. Mayonnaise alone killed the yeasts, primarily because of its content of acetic acid and this effect increased as the temperature was increased and as the pH was decreased. Addition of cabbage or carrot tissue removed the lethal effect of mayonnaise and allowed spoilage, by absorbing acetic acid and increasing the pH.     

Phosphorus Efficiency of Cabbage (Brassica oleraceae L. var. capitata), Carrot (Daucus carotaL.), and Potato (Solanum tuberosumL.)

Plant species and genotypes within the same species may differ in phosphorus efficiency. The objective of this research was to study phosphorus efficiency of cabbage (Brassica oleraceae L.), carrot (Daucus carota L.), and potato (Solanum tuberosum L.) and to quantify the contribution of morphological root characteristics to P uptake of the plant species. An experiment was conducted in a glasshouse with six P levels: 0, 12, 27, 73, 124 and 234 mg P kg^–1 soil, and with six replications. Cabbage attained 80% of its maximum yield already at the level of no P supply, whereas carrot and potato reached only 4 and 16% of their highest yields respectively at this level of P supply. This indicated that cabbage was P-efficient compared to carrot and potato. Root/shoot ratio (cm root g^–1 shoot d. m.) increased in the order of cabbage < carrot < potato, and was enhanced at lower P levels. Root hair length was not affected by P level, and averaged 0.22, 0.03 and 0.18 mm for cabbage, carrot, and potato, respectively. Predicting P uptake by a mechanistic simulation model revealed that root hairs contributed about 50% to the total P uptake of cabbage and potato, but only 0.3% to that of carrot. The relationship between the observed P uptake and the predicted P uptake of the plants revealed that model parameters explained nearly 4/5th of the total P uptake of carrot and potato, but only 2/5th of that of cabbage. This showed that the P uptake of cabbage was strongly under-predicted, whereas that of carrot and potato was predicted well. Therefore, it was hypothesised that cabbage may have the ability to mobilise and take up soil P additionally by other root mechanisms such as exudation of organic acids.     

Growth of Carrot and Tomato from Oxamyl-coated Seed and Control of Meloidogyne hapla

Oxamyl was coated on carrot (Daucus carota L. cv. Spartan Fancy-80) and tomato (Lycopersicon esculentum Mill. cv. Glamour) seeds with a polymer sticker for the control of Meloidogyne hapla. The sticker diluted in water 1:1 delayed carrot seedling emergence. Oxamyl at 40 mg/ml in a 1:5 dilution of sticker lowered the rate of carrot seedling emergence until day 13 and plant growth until day 28. Oxamyl at 20 or 40 mg/ml in a 1:5 dilution of sticker on carrot seeds planted in M. hapla-infested muck soil resulted in fewer galled tap roots and fewer galls per root system 4 weeks after planting. Tap root lengths were greater than those of the control. Tomato seedling emergence was delayed and top and root weights were reduced, relative to the control, at 25 days by the sticker diluted 1:1 to 1:3. Oxamyl at 20 or 40 mg/ml in a 1:5 diluted sticker delayed tomato seedling emergence. Top weights of tomato seedlings from seeds coated with 20 mg/ml of oxamyl in a 1:5 diluted sticker planted in a silt loam were greater than control top weights at 4 and 6 weeks. Root weights were greater than those of the control only at 4 weeks. There were fewer galls per gram of root on seedlings from oxamyl-coated seeds and fewer juveniles per pot of soil, relative to the controls, only at 4 weeks.     

Heterologous C-terminal signals effectively target fluorescent fusion proteins to leaf peroxisomes in diverse plant species

Peroxisomes are functionally diverse organelles that are wholly dependent on import of nuclear-encoded proteins. The signals that direct proteins into these organelles are either found at the C-terminus (type 1 peroxisomal targeting signal; PTS1) or N-terminus (type 2 peroxisomal targeting signal; PTS2) of the protein. Based on a limited number of tests in heterologous systems, PTS1 signals appear to be conserved across species. To further test the generality of this conclusion and to establish the extent to which the PTS1 signals can be relied on for biotechnological purposes across species, we tested two PTS1 signals for their ability to target fluorescent proteins in diverse plant species. Transient assays following microprojectile bombardment showed that the six amino acid PTS1 sequence (RAVARL) from spinach glycolate oxidase effectively targets green fluorescent fusion protein to the leaf peroxisomes in all 20 crops tested, including four monocots (sugarcane, wheat, corn and onion) and 16 dicots (carrot, cucumber, broccoli, tomato, lettuce, turnip, radish, cauliflower, cabbage, capsicum, celery, tobacco, petunia, beetroot, eggplant and coriander). Similarly, results indicated that the 10 amino acid PTS1 sequence (IHHPRELSRL) from pumpkin malate synthase effectively targets red fluorescent fusion protein to the leaf peroxisomes in all four crops tested including monocot (sugarcane) and dicot (cabbage, celery and pumpkin) species. These signal sequences should be useful metabolic engineering tools to direct recombinant proteins to the leaf peroxisomes in diverse plant species of biotechnological interest.     

Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

The microflora of stored coleslaw and factors affecting the growth of spoilage yeasts in coleslaw

Saccharomyces dairensis and Sacch. exiguus were isolated as the spoilage flora of coleslaw stored at 5° and 10°C. The growth of these yeasts in mixtures of mayonnaise with vegetable was inhibited by onion. Mayonnaise alone killed the yeasts, primarily because of its content of acetic acid and this effect increased as the temperature was increased and as the pH was decreased. Addition of cabbage or carrot tissue removed the lethal effect of mayonnaise and allowed spoilage, by absorbing acetic acid and increasing the pH.