Showing papers on "Seedling published in 1981"

A comparative study of germination characteristics in a local flora

Abstract: seeds for immediate germination. Of the 403 species examined, 158 failed to exceed 10% germination but 128 attained values greater than 80%. Germination was high in the majority of grasses and low in many annual forbs and woody species. With respect to initial germinability, major families could be arranged in the series Gramineae > Compositae > Leguminosae = Cyperaceae > Umbelliferae. Many small-seeded species were able to germinate immediately after collection and seeds of these species were often elongated or conical and had antrorse hairs or teeth on the dispersule. High initial germinability was conspicuous among the species of greatest abundance in the Sheffield flora. (4) In the majority of species, germination percentage increased during dry storage; this effect was most marked in small-seeded species. Among the seventy-five species which responded to chilling, some germinated at low temperature in darkness whilst others were dependent upon subsequent exposure to light or to higher temperature or to both. Responses to chilling were characteristic of the Umbelliferae. In all of the legumes examined, rapid germination to a high percentage was brought about by scarification. (5) Under the experimental conditions, all of the annual grasses showed the potential for rapid germination. High rates were also observed in many of the annual forbs and perennial grasses. Low rates of germination occurred in the majority of sedges, shrubs and trees, and were particularly common in species of northern distribution in Britain. Rapid germination was characteristic of the species of greatest abundance in the Sheffield flora. Rate of germination showed a progressive decline with increasing seed weight, and, with some exceptions, there was a positive correlation between rate of germination and the relative growth rate of the seedling. (6) In sixteen species, germination in the light was found to be dependent upon exposure to diurnal fluctuations in temperature. Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles. A requirement for relatively high temperature was apparent in sedges, in plants of northern distribution and in a majority of the marsh plants. The range of constant temperatures conducive to germination tended to be wider in grassland plants than in woodland species. Rapid germination over a wide range of temperature occurred in many of the species which attain greatest abundance in the Sheffield flora. 0022-0477/81/1100-1017 $02.00 (?1981 Blackwell Scientific Publications

Osmoregulation, solute distribution, and growth in soybean seedlings having low water potentials.

Abstract: Soybean (Glycine max (L.) Merr.) seedlings osmoregulate when the supply of water is limited around the roots. The osmoregulation involves solute accumulation (osmotic adjustment) by the elongating region of the hypocotyls. We investigated the relationship between growth, solute accumulation, and the partitioning of solutes during osmoregulation. Darkgrown seedlings were transplanted to vermiculite containing 1/8 (0.13 x) the water of the controls. Within 12–15 h, the osmotic potential of the elongating region had decreased to-12 bar, but it was-7 bar in the controls. This osmoregulation involved a true solute accumulation by the hypocotyls, since cell volume and turgor were virtually the same regardless of the water regime. The hypocotyls having low water potentials elongated slowly but, when deprived of their cotyledons, did not elongate or accumulate solute. This result indicated a cotyledonary origin for the solutes and a dependence of slow growth on osmotic adjustment. The translocation of nonrespired dry matter from the cotyledons to the seedling axis was unaffected by the availability of water, but partitioning was altered. In the first 12 h, dry matter accumulated in the elongating region of the 0.13 x hypocotyls, and osmotic adjustment occurred. The solutes involved were mostly free amino acids, glucose, fructose, and sucrose, and these accounted for most of the increased dry weight. After osmotic adjustment was complete, dry matter ceased to accumulate in the hypocotyls and bypassed them to accumulate in the roots, which grew faster than the control roots. The proliferation of the roots resulted in an increased root/shoot ratio, a common response of plants to dry conditions.

Analysis of how ant behaviors affect germination in a tropical myrmecochore Calathea microcephala (P. & E.) Koernicke (Marantaceae): Microsite selection and aril removal by neotropical ants, Odontomachus, Pachycondyla, and Solenopsis (Formicidae).

Abstract: The evolutionary effects of a tropical ant-seed interaction are examined by posing questions about the fate of Calathea seeds carried by neotropical ants. Where do ants take seeds and what do they do with them? How do ant behaviors affect seed germination? Treatment of seeds by ants is determined by a series of seed-fate trials in captive colonies. There is no evidence of seed predation by ants. Odontomachus laticeps, Pachycondyla spp, and Solenopsis geminata rapidly displace seeds to ant nests, determine the microsites of seeds, and remove the seed arils for food. The seed arils are rich in lipids. The effects on germination of microsite selection and aril removal are quantitatively evaluated. Seeds which are immediately taken to a consistently moist spot germinate readily; 72% germinate, with a mean germination speed of 29 days. For such seeds aril removal does not significantly affect germination. In contrast, seeds which experience a delay before encountering appropriate germination conditions seem to exhibit an induced dormancy (sensu, Harper 1977) and a lower germination percentage. They take longer to germinate (up to 85 days) even after conditions become appropriate. It appears that their germination is enhanced by aril removal, which may act as an environmental cue to break dormancy. Such a mechanism would indicate that ant-handling of seeds is predictive of favorable conditions for seedling growth and establishment. The exact nature of such conditions and the effects on plant population dynamics remain to be seen.

Germinable seeds and periodicity of germination in annual grasslands

Abstract: Germinable seed reserves and periodicity of germination of the plant species in annual communities were periodically and intensively sampled from 1974 through 1977 at the Sierra Foothill Range Field Station (SFRFS) and the U.S. Forest Service’s San Joaquin Experimental Range (SJER). One hundred samples of surface soil with accompanying litter were taken every 8 weeks, except when they were taken 1, 3, and 5 weeks after annual initial rains. Few germinable seeds (mostly exotic annual legumes at SFRFS) were carried over from year to year. Dominant annual grasses had virtually no annual carryover. Litterborne and soilborne seed reserves gradually increased as the current year’s crop was dispersed. Through the fall, each species exhibited its own pattern of increased germ inability, which was highly dependent on its inherent afterripening requirements. In years when the initial fall rains resulted in simultaneous germination, the flush of germination began within a week, and by 5 weeks the reserve of germinable seeds was largely exhausted. The seedlings that established in these years accounted for only 20 to 30% of the germinable seeds present in the litter and surface soil before the initial rain. When the communities were subjected to 2 years of extreme drought (1975-76 and 1976-77), established seedling density and subsequent seed reserves dropped dramatically; species composition, however, remained relatively stable. Near-normal moisture conditions in 1977-78 resulted in near-normal communities except that a higher percentage of the seed reserve became established plants than before the drought.

Reliable plantlet formation from embryos and seedling shoot tips of radiata pine

Abstract: A method has been devised for the reliable production of plantlets from embryos and seedling shoot tips of Pinus radiata D.Don (radiata pine). Buds were induced on an agar or liquid Schenk and Hildebrandt (SH) medium containing 5.0 mg/l benzylaminopurine (BAP). Except for some abnormal buds, the buds grew into elongated shoots on an agar SH medium without cytokinin. The transfer of shoots from a SH medium to a Gresshoff and Doy (GD) medium was found to be an important pretreatment which increased the survival of the shoots when they were placed in a peat and pumice mix for root formation. Elongated shoots were induced to form roots under non-sterile conditions in a humid environment with occasional misting. An intervening 5-day treatment of shoots in an agar medium containing 2.0 mg/l indolebutyric acid (IBA) and 0.5 mg/l napthaleneacetic acid (NAA) significantly increased the percentage of shoots forming roots and the number of roots formed per shoot over control shoots placed directly in the peat:pumice mix. An enhanced level of CO2 during root formation had no effect on the time of root formation or on the percentage of shoots forming roots. These results concerning the elongation, growth and rooting of adventitious shoots are now being applied to the development of very large numbers of plantlets starting from cotyledons from partially germinated seeds.

Seed production and spring seedling establishment of diffuse and spotted knapweed.

Abstract: Annual seed production of diffuse (Centurea diffusa) and spotted knapweed (Centurea maculosa) is reduced in dry years by a reduction in the number of viable seeds per seed head and increases when above-normal precipitation occurs by increase in the number of heads/flower stem. Seed production was approximately l,OOOfold that needed to maintain observed levels of infestation. Seedlings emerging in April had a high rate of survival with most plants flowering the following season, while those emerging after May 15 had a very low survival rate and almost no flower stem production the following season. (Table 1). Each site was sampled annually the first week of August in 1973 through 1976. The number of flower stems per unit area was estimated by random counts of m* hoop. Each area was subsampled to determine the number of seed heads/flower stem and the number of mature achenes/flower head. Only seed heads that were in the maturity range of well-developed seed, but had bracts still tightly closed, were counted for the latter measurement. Location and general features of each site are shown in Table 1. Diffuse and spotted knapweed are short-lived perennials of the Centaurea genus that have become major weed problems on semiarid range and pasture lands of the Pacific Northwest. The problem of these weeds, which are continuing to spread into many prime grazing areas, was recently reviewed (Maddox 1979). Control of these species is possible by chemical means (Renney and Hughes 1969) but these measures are not always practical because of economics, terrain, or environmental considerations. Several biotic agents are under study [Maddox (1979); Watson and Renney (1974,] but at present have only a minor impact. Watson and Renney (1974) summarized observations related to the reproduction of these species. In general, they reported that these species under range conditions were capable of producing 400-900 seeds/plant that would germinate under a range of temperatures of 7 to 34O C when optimum moisture was supplied. Some post harvest and light-induced dormancy was measured. We have also observed viability greater than 80% of the seeds still retained in the seed heads of diffuse in April. These normally are fully dispersed by mid June. Both fall and spring seedling emergence is common with these species.

Influence of indole-butyric acid, boron, myo-inositol, vitamin D2 and seedling age on adventitious root development in cuttings of Phaseolus aureus

Abstract: Adventitious roots develop in stem cuttings of Phaseolus aureus Roxb. seedlings when treatment with indole-butyric acid (IBA) is followed by treatment with boron. Root development varies according to the age of seedlings from which cuttings are taken. Increased root number is associated with expansion of the first leaf pair but subsequently declines, whereas root growth increases with increasing seedling age. Removal of leaves furing the first 72 h of treatment impairs root initiation whereas root growth is diminished by removal of leaves at any time during the first 120 h of treatment. IBA stimulates movement of 14C-IAA out of leaves. Vitamin D2 and myo-inositol stimulate rooting of intact cuttings provided cuttings are subsequently supplied with boron. Hypocotyls excised from cuttings pretreated with IBA develop roots in response to myo-inositol in the absence of boron. It is proposed that endogenous auxin, arising in the leaves, and myo-inositol have roles in root initiation whilst the role of boron is suggested as one of initiating or maintaining transport from the leaves.

Morphology of caryopses, seedlings and seedling emergence of the grass Calamovilfa longifolia from various depths in sand.

Abstract: The spikelets of the grass Calamovilfa longifolia (Hook) Scribn. are one flowered and the dispersal unit is composed of a caryopsis (3.5 mm long and 0.9 mm wide) enclosed in lemma and palea. The highest germination of caryopses and emergence of seedlings occurred from 1–2 cm depths and seedling emergence decreased with increasing depth of burial. The maximum depth of sand from which a seedling can emerge is about 8 cm. Seedlings emerging from deep locations had first internodes which were more elongated than those of seedlings from more shallow plantings. Coleoptile lengths of seedlings from shallow or deeply buried caryopses were similar.

Seed Production and Seedling Establishment in the Mayapple, Podophyllum peltatum L.

Abstract: Mayapple (Podophyllum peltatum L), a perennial clonai herb, produces flowering and nonflowering stems. Stem densities per clone are fairly constant from year to year, but fruit and seed production is variable, both among clones and among years. Fruit production is positively correlated with flowering stem density per clone. Seven age-specific mortalities are recognized from flowering to seedling establishment: flower abortion, improper pollination, immature fruit loss, failure of fruits and seeds to be removed from clone area, seed pr?dation, failure of seed germination and seedling competition. Improper pollination is responsible for the largest loss of potential seeds; failure of seeds to be removed from the clonai area is the second most important mortality factor. Eastern box turtles (Terrapene carolina) are the only seed dispersal agents so far identified. Turtle-ingested seeds germinate faster and have a higher probability of success than noningested seeds. The survivorship curve for turtle-ingested seeds is Type II. The negative exponential model for seedling mortality best describes the mayapple and predicts a reduction of the initial seed crop to one plant by the 5th year.

Seed germination and seedling establishment of Calamovilfa longifolia on Lake Huron sand dunes

Abstract: Caryopses ("seeds") of Calamovilfa longifolia (Hook.) Scribn. are dimorphic (brown and white) and are each enclosed in a lemma and palea. The most complete germination was obtained in lighted (fluo...

Relationships between xanthoxin, phototropism, and elongation growth in the sunflower seedling Helianthus annuus L.

Abstract: For phototropic curvature of a green sunflower seedling, only the hypocotyl has to be illuminated; the tip and cotyledons are not involved in stimulus perception. The etiolated seedling is phototropically insensitive, illumination of only the hypocotyl renders it sensitive. It is concluded that the photoreceptor is located within the responding organ. In curving seedlings, the endogenous indoleacetic acid (IAA) remains evenly distributed. However, the inhibitor, xanthoxin (Xa), accumulates on the illuminated side. The degree of phototropic response is generally related to the concentration of Xa. The amount of phototropic curvature is independent of the rate of elongation growth, the former can be changed without affecting the latter, and vice versa. The data conflict with the Cholodny-Went theory, whereas they support the hypothesis of Blaauw that the phototropic reaction is caused by the local accumulation of a growth-inhibiting substance on the irradiated side.

Salinity and waterlogging tolerance of some populations of Melaleuca ericifolia Smith

Abstract: Seed germination of Melaleuca ericifolia (swamp paperbark) is delayed by submergence in water but the final percentage germination after removing seeds from water is unaffected; some seeds will germinate and the cotyledons emerge whilst submerged. Germination is totally inhibited at salinities of 14% and a population which naturally occurs adjacent to coastal saltmarsh was inhibited more by salinities of 6–12% than two other populations from freshwater habitats. Seedling growth may be increased by water‐logging conditions and the degree of response differs for different seed sources. Inundation stimulates root growth and new roots are thick and aerenchymatous. Root systems in the field run horizontally and are shallow, apparently being restricted by clay at depth. All populations studied showed a similar seedling growth‐response to salinity treatments; growth declined at salinities ≤ 13% and was severely restricted at 21%, although no seedlings died after 48 days’exposure to the latter treatment. Copyright © 1981, Wiley Blackwell. All rights reserved

Ecology of Germination and Flowering in the Weedy Winter Annual Grass Bromus japonicus

Abstract: From the time of seed maturity in late June and early July until December when temperatures drop to near freezing, habitat temperatures are within the range of those required for germination of seeds of the winter annual Bromus juponicus. However, a large proportion of the seeds in a given seed crop fail to germinate in the autumn of the year in which they are produced because they are not dispersed until winter. A high percentage of of the winterdispersed seeds is induced into dormancy and must undergo a period of afterripening the following summer before germination can occur the next autumn. Thus, many of the plants that become established at a population site in autumn are from the previous year’s seed crop. Plants overwinter in the field as “rosettes” and require long days for flowering. Nonvernalized plants exposed to natural short photoperiods of late autumn and winter flower under long days in spring, but plants flower much sooner if they are subjected to both low temperatures (vernalization) and short photoperiods during winter. Bromus japonicus Thunb. (Japanese chess) is a native Eurasian winter annual that has been introduced into the United States where it ranges from Vermont to the state of Washington south to North Carolina and California (Hitchcock 1935, Fernald 1950). As is true for some other introduced bromegrasses in the United States, B. japonicus is a problem in wheat fields, in grass and alfalfa seed fields, and in pastures, meadows, and overgrazed range lands (Slife et al. 1960, Finnerty and Klingman 1962, Steyermark 1963). To better understand the ecological life cycle of this weedy winter annual, we have studied (1) the role of temperature in controlling the timing of germination in nature and (2) the influence of vernalization and photoperiod on the timing of flowering. In northcentral Kentucky where we have observed its phenology, B. japonicus begins to flower in early May, and caryopses (hereafter referred to as seeds) are ripe by late June or early July. Plants senesce as the seeds mature, and there are no living plants at a population site during summer. The seeds are retained on the dead erect shoots until autumn and winter. Seed dispersal begins in early October, and continues until the following March, with a high percentage of the seeds being dispersed during November, December, and January. Seed germination occurs in early autumn, and thousands of seedlings may appear at a population site at any time from early September to mid October, depending upon the time when soil moisture conditions become suitable for germination. Only an occasional seedling is found in the field in spring. Since germination occurs before very many of the seeds are shed, population establishment each year results primarily from germination of a reserve of seeds present in and/or on the soil surface. Following germination, each plant produces a “rosette” of 10-l 5

Establishment of Warm- and Cool-Season Native Perennial Grasses on the North-West Slopes of New South Wales. Ii. Establishment and Seedling Survival in the Field

Abstract: Emergence and survival of the seedlings of warm-season native perennial grasses Aristida ramosa R.Br., Bothriochloa macra (Steud.) S . T. Blake, Dichanthium sericeum (R.Br.) Camus, Sporobolus elongatus R.Br., Eragvostis leptostachya Steud. and Chloris truncata R.Br. and the cool-season species Stipa variabilis Hughes and Danthonia linkii Kunth were studied in both native pastures and sown monospecific plots on the north- west slopes of New South Wales. The most favourable period for the successful emergence and establishment of warm-season grasses was from mid summer to early autumn. Cool-season native perennial grasses established best from seedlings that appeared from mid autumn to late winter. Few seedlings were observed to germinate in spring, probably as a result of large variations in temperature, low minimum temperatures or intra and interspecific competition. Seedlings growing in native pasture spent long periods in the vegetative phase compared to the early flowering of seedlings in the sown plots. In the pasture studied only two seedlings flowered over 700 days after emergence, and many others after persisting for up to 2 years died without producing seed. These findings indicate that the seedlings in these native pastures were under considerable stress and that the adult populations of the species examined were relatively stable and little recruitment occurred.

Some effects of different forest litters on seed germination and growth

Abstract: Germination and growth of 12 native herbs, shrubs, and trees were followed in five litter components characteristic of successional stages of the northeastern Minnesota forest Various litter components stimulated or inhibited seed germination and seedling growth of some species Germination and growth were not always similarly affected, suggesting that different factors may be involved Inhibition and lack of inhibition of some species on certain litter components correlate with natural habitat preferences of these species and the nature of the litter in these habitats This information can be of use in improving results of seeding for site reclamation and reforestation

Amino Acid Transport in Germinating Castor Bean Seedlings

Abstract: During germination and early growth of the castor bean (Ricinus communis) nitrogenous constituents from the endosperm are transferred via the cotyledons to the growing embryo. Exudate collected from the cut hypocotyl of 4-day seedlings contained 120 millimolar soluble amino nitrogen and glutamine was the predominant amino acid present, comprising 35 to 40% of the total amino nitrogen. To determine the nature of nitrogen transfer, the endosperm and hypocotyl were removed and glutamine uptake by the excised cotyledons was investigated. Uptake was linear for at least 2 hours and the cotyledons actively accumulated glutamine against a concentration gradient. The uptake was sensitive to respiratory inhibitors and uncouplers and efflux of glutamine from the excised cotyledons was negligible. Transport was specific for the l-isomer. Other neutral amino acids were transported at similar rates to glutamine. Except for histidine, the acidic and basic amino acids were transported at lower rates than the neutral amino acids. For glutamine transport, the Km was 11 to 12 millimolar and the Vmax was 60 to 70 micromoles per gram fresh weight per hour. Glutamine uptake was diminished in the presence of other amino acids and the extent of inhibition was greatest for those amino acids which were themselves rapidly transported into the cotyledons. The transport of amino acids, on a per seedling basis, was greatest for cotyledons from 4-to 6-day seedlings, when transfer of nitrogen from the endosperm is also maximal. It is concluded that the castor bean cotyledons are highly active absorptive organs transporting both sucrose and amino acids from the surrounding endosperm at high rates.

Evidence for amino-acid: proton cotransport in Ricinus cotyledons.

Abstract: During germination and early growth of the castor-bean (Ricinus communis L.), protein in the endosperm is hydrolyzed and the amino acids are transferred into the cotyledons and then via the translocation stream to the axis of the growing seedling. The cotyledons retain the ability to absorb amino acids after removal of the endosperm and hypocotyl, exhibiting rates of transport up to 70 μmol g-1 h-1. The transport of L-glutamine was not altered by KCl or NaCl in low concentrations (0–20 mM). High concentrations of KCl (100 mM) inhibited transport, presumably by decreasing the membrane potential. An increase in the pH of the medium bathing the cotyledons was observed for 10 min following addition of L-glutamine but not with D-glutamine, which is not transported. The rate of proton uptake was dependent on the concentration of L-glutamine in the external solution. Inhibitors and uncouplers of respiration (azide, 2, 4-dinitrophenol, carbonyl cyanide phenylhydrazone and N-ethylmaleimide) inhibited both L-glutamine uptake and L-glutamine-induced proton uptake. Amino acids other than L-glutamine also caused a transient pH rise and the rate of proton uptake was proportional to the rate of amino-acid uptake. The stoichiometry was 0.3 protons per amino acid transported. Addition of sucrose also caused proton uptake but the alkalisation by sucrose and by amino acids were not additive. Nevertheless, when sucrose was added 60 min after providing L-glutamine at levels saturating its uptake system, a rise in pH was again observed. The results were consistent with amino-acid transport and sucrose transport in castor-bean cotyledons both occurring by a proton cotransport in the same membrane system but involving separate carriers.

Physical effects of direct drilling equipment on undisturbed soils. III. Wheat seedling performance and in-groove micro-environment in a dry soil

Abstract: A method of measuring soil relative humidity at the seed-soil zone in direct drilled grooves is described Grooves were formed by several combinations of three selected coulter types and seed covering methods In-groove soil relative humidity was measured at the same time when seeds were growing under controlled constant climatic conditions in a soil initially under severe moisture stress A negative correlation coefficient of r = 075 was found between the in-groove relative humidity and combined counts of seedling emergence and sub-surface unemerged seedling survival The ability of seed grooves to retain moisture vapour was described in terms of'moisture vapour potential captivity' (MVPC) A minimum value of MVPC = 04 was suggested for the dry soil of this experiment A mathematical model relating in-groove relative humidity and seedling emergence plus sub-surface seedling survival was developed Specifications of coulter design and seed covering methods were suggested which might create bett

Presowing Hydration-Dehydration Treatments in Relation to Seed Germination and Early Seedling Growth of Wheat and Ryegrass

Abstract: Seeds of wheat (Triticum aestivum cv. Egret) and annual ryegrass (Lolium rigidum cv. Wimmera) were given a single hydration-dehydration cycle by adding a known amount of water and later air-drying them. Embryos enlarged during this initial hydration, and short periods at high water contents were equivalent to longer periods at lower water contents. After hydration to 145% of seed dry weight (wheat) or to 155% (ryegrass) followed by dehydration back to the original seed weights the speed of germination of both species was approximately doubled because the lag phase of germination was shortened. The proportion of ryegrass seeds that were dark-dormant was reduced if seeds were pretreated in light. Pretreatment did not increase germination synchrony, alter threshold temperatures for germination or enhance seedling growth rates. The viability of pretreated seed declined rapidly at - 15°C and at 50°C. The effect of pretreatment, i.e. early germination, is attributed mainly to embryo enlargement. More rapid imbibition of pretreated seeds may contribute in a minor way to differences in germination time.

Early genetic evaluation of loblolly pine

Abstract: Seedlings of five known fast-growing, open-pollinated loblolly pine (Pinustaeda L.) families and five known slow-growing families were grown from seed to 24 weeks of age in a greenhouse. Each family was subjected to four moisture regimes ranging from high stress levels to little or no stress. Various seedling growth parameters were measured and evaluated to determine their value as predictors of field performance of the same families tested over a range of site conditions. Results showed that the shoot weights and shoot/root ratios of known fast-growing families were significantly greater than those of known slow-growing families at the seedling stage of development. The average shoot/root ratio per family of seedlings grown under unstressed and mildly stressed conditions showed significant positive correlations (r = 0.74 and r = 0.61 respectively) with the average volume superiority of the same families field-tested over a range of sites. (Volume superiority = (volume of family/average volume of plantati...

Regeneration of whole plants from hypocotyl-, root-, and leaf-derived tissue cultures of the pasture legume Stylosanthes guyanensis

Abstract: Callus cultures were established on Murashige and Skoog medium from seedling hypocotyls and roots of Slylosanlhes guyanensis (Aubl.) Sw. cv. Cook and from leaves of 6-month-old) plants. Shoots developed in primary calli derived from seedling tissue with a number of benzyladenine or kinetin and naphthaleneacetic acid combinations. Shoot formation on primary leaf callus, occurred with 2.0 mg/1 benzyladenine and 2.0 or 1.0 mg/l naphthaieneacetic acid. Undifferentiated callus from all three sources was induced and maintained on medium with 2.0 mg/1 kinetin and 2.0 mg/1 2, 4-dichlorophenoxyacede acid in the dark. Shoot formation and regeneration of whole plants from these calli were achieved at high frequencies. The most successful combination of phytohormones for the induction of shoot development in undifferentiated callus, was 2.0 mg/1 benzyladenine and 1.0 mg/1 naphthaleneacetic acid. The regenerated plants showed no phenotypic abnormalities.

Effects of within-row plant uniformity on grain yield of maize

Abstract: Two experiments were conducted over 3 yr to study the effects of variability in intra-row spacing on grain yield of maize; effects of non-uniformity in seedling size were also investigated. Experiment 1 consisted of single-row plots which were thinned in the seedling stage to produce stands of equivalent mean densities (i.e., the same number of plants per plot row), but with different lengths of gaps within the row; two additional treatments involved the selection of seedling plants which were either very uniform, or non-uniform, in height. Yield was unaffected by the presence of gaps up to 1 m long within the row. In general, plots of uniform seedling size outyieldcd those where seedling size was more variable. Experiment 2 involved a comparison of plots seeded to produce one, two, three or four plants per hill at an equivalent mean plant density (same number of plants per plot row). On average, yield was not depressed until the number of plants per hill exceeded two. No treatment effect on the intra-plo...

Effects of Powdery Mildew and Water Stress on CO2 Exchange in Uninfected Leaves of Barley

Abstract: Net photosynthesis is stimulated in third seedling leaves of barley plants whose lower two leaves are heavily infected by Erysiphe graminis f.sp. hordei Marchal. Stimulation is greater in water-stressed than in well-watered plants. In stressed, but not in well-watered plants, stimulation is associated with the maintenance of high leaf water potential and high leaf conductance. A small part of the changes in net photosynthesis is attributable to changes in respiratory metabolism in the third leaf, and other possible causes are discussed.

Studies on some sources of variation in carrot root weight

Abstract: Five investigations were carried out to determine the magnitude of root-size variation within crops of cv. Chantenay Supreme grown under competitive and non-competitive conditions, and to study possible sources of inter-plant variation.In the first experiment root-size variation from crops grown at a high population density (245 plants/m2) and at a low density (25 plants/m2) were compared over a 21-week period from sowing. The c.v.s of root weight were always higher from the high density than from the low density over the harvesting period from 11 to 21 weeks after sowing, and ranged from 74 to 94% and from 50 to 63%, respectively. A second study showed that even with a very low population density (3 plants/m2) the c.v. of root weight at harvest was 58%. The third study showed that 40% of the root weight variation was accounted for by the time of seedling emergence. The results of a pot experiment indicated that when the size of seed, sowing depth, rooting medium and time of seedling emergence were made as uniform as possible, a very uniform population of roots was produced with a c.v. of root weight of 32%. In the final field experiment when time of seedling emergence, seed size and spatial distribution of the plants were the experimental variables, the results confirmed the importance of variability in time of seedling emergence and seedling size in creating variation at an early stage of growth.The results of these studies indicate that competition per se was not a prime source of variation in root size but magnified any initial variation within the crop at the time of seedling establishment. The importance of this early establishment phase in determining the spread of root-size distribution within a crop is discussed together with the factors which influence the time of seedling emergence and seedling size.

Germination and emergence of soybean under crusted soil conditions. I. Effect of crust impedance to seedling emergence

Abstract: Attempts were made to work out the effect of crust impedance to seedling emergence under natural field conditions by photographing a series of positions taken by the emerging hypocotyls. Being epigeal in germination, the seedling had to work through a large volume of soil to pull the cotyledons out of the ground. Since the hypocotyl was brittle, it often collapsed at the stress point between the emerging hypocotyl and the buried cotyledons. A number of seedlings subjected to severe impedance stresses often broke off at the hypocotyl hook when the soil surface ruptured. The emergence force of the varieties tested was closely related to their seed weight. The large seeded variety ‘Bragg’ exerted the greatest emergence force (1.86×105 dynes) and the small seeded variety ‘Type-1’ exerted the least (1.24×105 dynes). The variety ‘UPSS-38’ was intermediate both in hundred seed weight and the force that it exerted (1.49×105 dynes). The time taken to develop the steady maximum force was 78, 67 and 60 hours for Bragg, UPSS-38 and Type-1 respectively.

Method for transplanting of seedlings

Abstract: Disclosed herein is a method and apparatus for mass growing of seedlings in a controlled atmosphere, for later transplanting into a permanent site, e.g. for reforestation. A growing system is disclosed wherein seeds are germinated into seedlings in a growth medium arranged in trays containing compartmentalized recesses or pots all joined together to form a seedling unit. Seedling units in mass growing systems have invariably several pots wherein either the seedlings are dead, or the inserted seeds never germinate; depending on the percentage success of seed germination in the individual pots of each seedling unit, the overall efficiency of utilization of the available room and manpower spent at the growing station is considerably affected. Those pots wherein the seedlings are dead or the seeds have not germinated are identified by automatically scanning the trays; the location of such pots is noted and the pots having no germination nor a usable seedling are emptied automatically and filled with a germinated seedling along with the required growth medium. Having thus ensured that all the pots in all the trays for final stages of growing are occupied by a proper seedling, the efficiency of space utilization is maximized, thereby obviating wastage of manpower, and resulting in increased economy.