Use of the Weibull Function to Calculate Cardinal Temperatures in Faba Bean

The onset of germination of faba bean seeds at constant temperaturewas progressively delayed as that temperature diverged froman optimum of 25.5 ?C. At temperatures below 10 ?C, or above28 ?C, the maximum germination percentage fell to below 90%.There was no germination at 39 ?C. Positive and negative linearrelationships were established between the constant temperaturesand the rates of progress of germination to different percentiles,at sub-optimal and supra-optimal temperatures, respectively.Like germination rates, base temperature (T_b) declined from3.71 to –0.83 ?C as the percentile value increased from10% to 80%. Caution was urged in extrapolating beyond the experimentaldata set. Differences in the ceiling temperature (T_c) with percentilecould not be discerned. Cumulative germination progress curves at each temperature weremodelled by the Weibull, logistic, and cumulative normal distributionfunctions. Cardinal temperatures (T_b and T_c) calculated fromthese data reasonably approximated the actual data. The Weibullfunction demonstrated a good approximation at all percentilelevels, while the logistic and cumulative normal distributionfunctions, as a result of their inherent symmetry, deviatedat the extreme percentiles. It was concluded that the Weibullfunction not only accurately modelled cumulative germinationbut could also be used in the calculation of cardinal temperatures. Key words: Seed germination rate, cardinal temperatures, faba bean, Weibull function, probit and logic scales     

Calcium as a plant nutrient

Abstract. Calcium occurs as a relatively large, divalent ion which readily enters the apoplast and is bound in exchangeable form in cell walls and on the exterior surface of the plasmalemma. It occurs in only very low concentrations in the cytoplasm and chloroplasts and appears to have a limited role as an enzymatic cofactor. The soil solution usually provides an adequate supply of Ca to plants. The well known physiological disorders resulting from localized Ca deficiencies within the plant are thus attributable to poor Ca distribution rather than restriction in uptake. Calcium is moved largely in the xylem and only to a very limited extent in the phloem. The phloem/xylem ratio of the solute input can be particularly critical in organs which are naturally low in Ca, such as fruits and young leaves. Factors which influence the distribution of Ca such as humidity, root pressure, phytohormone activity, can also affect the occurrence of these disorders.     

The response of an autumn-sown determinate faba bean to different plant distributions

The response of an autumn-sown determinate selection, 858 , to different plant distribution patterns was examined in field trials during the two seasons 1985/86 and 1986/87 at the University of Nottingham. Plants were sown at two densities (20 and 40 plants per m2) and at three different row widths (11.9, 23.8 and 47.6 cm) in the autumn of each season. Plant numbers and combined yields were greater in 1986/87 than in 1985/86. Grain yield was unaffected by differences in inter-row spacing and this was ascribed to the early attainment of complete ground cover even when plants were grown in widely spaced rows. Yield was most strongly correlated with seed numbers per m². An examination of yield on a per plant basis suggested that narrow inter-row spacings were more productive at low plant densities, while yield per plant was greater at higher densities if the crop was grown on wider inter-row spacings. It was concluded that autumn-sown determinate forms of faba bean were able to compensate for large changes in plant distribution and consequently yield was unaffected.     

Response of Populations of Lolium perenne cv. S 23 with Contrasting Rates of Dark Respiration to Nitrogen Supply and Defoliation Regime: 1. Grown as Monocultures

Simulated swards of two populations of perennial ryegrass cv.S 23 selected for contrasting rates of mature leaf tissue respirationwere grown in a glasshouse. From establishment, the swards weresubject to three levels of nitrogen supply (14.5, 32 and 173.5ppm N) and from the first harvest 7 weeks after sowing, to threecutting frequencies (at intervals of 1, 3, and 6 weeks). Throughout the 18-week experiment, the herbage yield and themean tiller weight of the slow-respiring population were 10%greater on average than those of the fast-respiring population.Increasing nitrogen supply (from 14.5 to 173.5 ppm N) enhancedthe yield advantage of the slower-respiring population—moreso under infrequent cutting (from nothing to 22%) than underfrequent cutting (from 6 to 13%). Both maximum absolute yields,and the greatest yield advantage of the slow-respiring populationover the fast, were achieved when high nitrogen was combinedwith infrequent defoliation. Lolium perenne, perennial ryegrass cv. S23, respiration, nitrogen defoliation, simulated sward, dry-matter production, monoculture, population     

Effect of Nitrogen Supply on the Growth and Senescence of Leaves of Lolium perenne with Contrasting Rates of Leaf Respiration

Respiration rates remain high during senescence which is anenergy demanding process. Different rates of senescence mayexplain the contrasting respiration rates of mature leaves oftwo populations of perennial ryegrass cv. S23. This hypothesiswas tested by measuring the lengths of elongating and senescingleaves of plants of two populations (GL72, a slow and GL66,a fast respiring population) for 76 d following the transplantationof the seedlings into soil-filled pots in a growth room. Nitrogenwas supplied at two different rates at the beginning of theexperiment and again at day 36. At high levels of nitrogen supply the slow respiring populationhad a faster elongation rate and so a greater leaf length thanthe fast respiring population. There was no difference betweenthem in the rate of leaf senescence or in the duration of leafgrowth. Consequently, the fast respiring population is consideredprofligate in its use of carbon. By contrast, under low nitrogensupply both elongation and senescence rates were higher in thefast respiring population, although there was no differencein final leaf length. Therefore the longevity of leaves of thefast respiring population was reduced. It is argued that theleaves of the fast respiring population may turn-over mineralsmore rapidly than those of the slow, which may be more advantageousin conditions of low nitrogen supply and offset the benefitsof a more conservative use of carbon normally seen under conditionsof high nitrogen supply. Lolium perenne L., perennial ryegrass cv. S23, nitrogen supply, respiration rate, leaf senescence rate, leaf elongation rate, leaf longevity, population     

Response of Populations of Lolium perenne cv. S 23 with Contrasting Rates of Dark Respiration to Nitrogen Supply and Defoliation Regime 2. Grown as Mixtures

Two populations of perennial ryegrass cv. S 23, selected forcontrasting rates of mature leaf tissue respiration, were grownin 50: 50 replacement mixtures to investigate their relativecompetitive abilities in a range of conditions. The 18 mixedsimulated swards were subject to three levels of nitrogen supply(14.5, 32 and 173.5 ppm) from establishment, and to three cuttingfrequencies (at 1-, 3- and 6-week intervals), 7 weeks aftersowing. The slow-respiring population yielded more than the fast. Thissuperiority was greater in mixtures (50%) than in monocultures(10%). Its superiority was as great in weekly-cut swards (51%), where there was little or no aerial competition, as in 6-weekly-cutswards (50%), where shoot interference was maximal, indicatingthat its advantage lay in below-ground competition. The limitingresource for which competition occurred could not be positivelyidentified. Lolium perenne, perennial ryegrass cv. S 23, population, simulated sward, defoliation, nitrogen, respiration, dry-matter production, 50: 50 replacement mixture     

The response of determinate and semi-determinate faba bean varieties to different sowing dates in the spring

Field trials conducted during 1986 and 1987 at the University of Nottingham compared the growth and development of two varieties of faba bean, Alfred and Ticol, in response to three different dates of sowing in the spring. Grain yields were greater the earlier the crop was sown. This difference was attributed to the larger canopy size, especially at the pod-filling stage of the earlier sown crops. This probably reflected the influence of temperature on the expansion and senescence of leaves during development. A semi-determinate variety of faba bean, Alfred, yielded 31% more than a determinate variety, Ticol. This difference was not attributable to any particular yield component. In 1986, it was correlated with pods per podding node and in 1987 with the number of seeds per pod. Three reasons can be advanced to explain this greater yield. Firstly, Ticol branched more than Alfred and so a greater proportion of its total reproductive nodes were borne on the branches rather than the mainstem. Branches were shown to be inferior in terms of yield production. Secondly, it was demonstrated that Ticol was probably less able to transfer stored assimilates from the stem to the developing pod than Alfred. Thirdly, Alfred had a larger canopy during pod development than Ticol.     

Effect of tannin content of faba bean (Vicia faba) seed on seed vigour, germination and field emergence

Differences in seed vigour of zero- and high-tannin faba beans were investigated using 25 seed lots of 12 cultivars following earlier reports of poor emergence in the zero-tannin types. Field emergence ranged from 54–96% indicating differences in seed vigour between cultivars all having high laboratory germination (>91%). Seed from zero-tannin accessions with poor emergence had a higher incidence of testa and cotyledon cracking, a smaller percentage of hard seeds, more rapid water uptake, a lower percentage of vital staining of cotyledons and a greater leaching of solutes than high-tannin types. Nevertheless, variation in these characteristics existed between cultivars and lines of both types. Seeds with more cracks in the seed coat and fewer hard seeds imbibed water more rapidly and consequently showed lower levels of vital staining and more cracks in the abaxial surface of the cotyledons. Slower imbibition in polyethylene glycol lessened the incidence of these deleterious characteristics and may provide a practical resolution to the problem of poor field emergence in zero-tannin lines of faba bean with low seed vigour.     

Effects of Nitrate Withdrawal and Resupply on the Assimilation of Nitrate in Leaves of Tomato

Nitrate reduction in leaves of tomato occurred at the same ratein plants grown in 8.0 mol m^–3 nitrate as in plants grownin 2.0 mol m^–3 nitrate, but at a much slower rate in plantsgrown in 0.1 mol m^–3 nitrate. However, the plants grownin 8.0 mol m^–3 nitrate had a larger leaf system than theplants grown in 2.0 mol m^–3 nitrate, and so the totalcapacity to assimilate nitrate was greater in the plants grownin the higher concentration. It was shown that plants grownin 8.0 mol m^–3 nitrate were better buffered against nitratewithdrawal than plants grown in 2.0 mol m^–3 nitrate asthe rate of nitrate reduction declined more slowly when plantswere transferred to 0.1 mol m^–3 nitrate from the higherconcentration than from the lower concentration. Furthermore,leaf expansion continued in the plants transferred from thehigher concentration, whereas it ceased abruptly in the plantstransferred from the lower concentration. It was concluded thatboth continuing expansion and continuing nitrate reduction wereaccompanied, and possibly caused by, a release of nitrate fromstorage pools in the lower part of the stem or the roots. Duringwithdrawal of nitrate the leaves were shown to maintain potentialactivity of the enzyme nitrate reductase although there wasno nitrate to be reduced. When nitrate was resupplied it couldbe reduced very quickly and reduction in the leaves was seento increase within 5 h of resupply. By 3 d after resupply furtherenzyme activity had been induced. Key words: Lycopersicon esculentum Mill, nitrate assimilation, nitrate reductase activity, nitrate withdrawal     

Free amino acids and alkaloids of South American, Asian and Australian Crotalaria species

Free amino acids in seeds of 22 species of Crotalaria (Leguminosae) which grow in South America, Asia and Australasia have been identified. The position of these species in recent classifications of the genus is assessed on the basis of the distribution offree amino acids and alkaloids in their seeds as well as on the basis of morphological characters. The alkaloid 1-methylenepyrroiizidine is shown to occur in seeds of 4 species in which it has not been identified previously.