Field studies of leaf development and expansion in the leek (Allium porrum)

An analysis of leek leaf development and expansion was carried out over three seasons using field-grown plants of three varieties which were directly sown at different dates or transplanted from controlled conditions. In all cases, successive leaves appeared (tip visible) at equal intervals of accumulated temperature. Detailed analysis of a single sowing in 1985 showed that the regularity of leaf appearance was a consequence of the coordinated response to accumulated temperature of leaf initiation (plastochron 100°C days > 0°C) and leaf blade and sheath extension. For each successive leaf, an additional 32°C days were required between initiation and appearance to allow for the linear increase in ‘sheath’ height, giving a phyllochron of 132°C days. Direct measurement of leaf extension before and after leaf appearance, and of the length of the leaf extension zone, confirmed that the rate of leaf extension, in terms of accumulated tempeature, was constant, and independent of leaf number. However, there were differences between seasons and between varieties in the responses of leaf appearance, leaf extension and ‘sheath’ length to accumulated temperature. It was concluded that the simple ontogenetic increase in leaf dimensions, which was a feature of all the crops studied, was a consequence of the progressive increase in the duration of leaf expansion.     

The influence of temperature on leaf development and growth in potatoes in controlled environments

Three controlled environment experiments were conducted at different temperatures to determine the relation between temperature and leaf development and growth in the potato (cv. Maris Piper). Developmental stages are defined for the appearance and duration of leaf extension in the potato and comparisons made with other temperate zone crops. The rate of leaf appearance was linear over the temperature range (9–25°C) and above 25°C there was no further increase in the rate. The temperature coefficient for the rate of appearance of leaves was 0.032 leaves (degree days)^-1 using a base temperature of 0°C. The duration of extension of an individual leaf decreased with increase in temperature up to 25°C such that the thermal duration was constant at 170 degree days using a base temperature of 0°C for leaf positions 4–10 on the main stem. At higher leaf positions the thermal duration was similar or greater. The advantages and limitations of controlled environment work as a parallel to field experimentation are discussed.     

Daylength change and leaf appearance in winter wheat

Abstract In the field successive leaves of winter wheat appear at a rate which varies because it depends strongly upon temperature. When plotted against ‘thermal time’, however (temperature accumulated above a fixed base of 0°C), leaf appearance was a strictly linear function of temperature. The mean rate of leaf appearance in thermal time, R′, was faster for a spring sowing than for an autumn sowing. The variation in R′ between sowings was better correlated with the rate at which daylength was changing when the plants emerged than with the mean daylength while leaves were appearing.     

The prediction of leaf canopy expansion in the leek from a simple model dependent on primordial development

In an analysis of leaf development of leek plants grown in the field in 1988, successive leaves initiated, appeared (tip and ligule) and senesced at equal intervals of accumulated temperature/thermal time. These intervals corresponded to a plastochron of 92°C days and phyllochrons of 135 (tip) and 233 (ligule) °C days. The rate of appearance of ligules was exactly equal to the rate of leaf senescence, with the result that the number of fully-expanded leaves per plant remained constant at 1.4. These data, which were compatible with results from previous seasons, were used to develop a model of the interrelationships between primordium initiation at the shoot apex and subsequent events in the development of individual leaves. Primordium initiation is considered to be the primary controlling event in the life of a leaf, and the processes of tip appearance, ligule appearance and death can be predicted from knowledge of the number of primordia which have been initiated, without reference to the environment. A model of canopy expansion, based on the central role of the shoot apex, was developed using the temperature relations of primordium initiation and additional data on leaf expansion and leaf dimensions. Leaf area indices computed in this way provided a satisfactory simulation of the thermal-time course of leaf area index observed in a previous season, 1985.     

The effect of temperature on leaf appearance and canopy establishment in fibre hemp (Cannabis sativa L.)

The effects of temperature on the development and growth of hemp (Cannabis sativa L.) have never been quantified. Therefore, to establish the effect of temperature on leaf appearance and canopy establishment of fibre hemp under controlled and field conditions, plants were grown in growth chambers at 11 regimes with average temperatures between 10°C and 28°C, and three cultivars were sown in the field in March, April and May in 1990, 1991 and 1992. In the field, thermal time (base 0°C) between sowing and emergence ranged from 68°Cd to 109.5°Cd (average 88.3°Cd). Rates of leaf appearance and stem elongation increased linearly with temperature between 10°C and 28°C. The base temperature for leaf appearance was 5.7°C from the growth chamber experiments and 1°C from the field experiments. In the field, the base temperature for the relationship between light interception by the canopy and thermal time was 2.5°C, and thermal time, calculated at the appropriate base temperature, accounted for about 98% of the variance in the number of leaves and for 98.6% of the variance in the proportion of light intercepted by the canopy. Days from emergence accounted for less of the variance in both parameters than thermal time. Interception of 90% of light was attained on average at 465°Cd (base 0°C) after emergence. It is concluded that thermal time is a simple and accurate tool to describe leaf appearance and light interception in fibre hemp.     

Spring Wheat Leaf Appearance and Temperature: Extending the Paradigm?

Extensive research shows temperature to be the primary environmental factor controlling the phyllochron, or rate of leaf appearance, of wheat (Triticum aestivum L.). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 degrees C above the ambient soil temperature (denoted +0C). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +0C plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominantly controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.     

An analysis of leaf growth in sugar beet.

The responses of leaf appearance and expansion to temperature in sugar beet were measured under controlled conditions, using ruler and auxanometers, to establish a basis for a subsequent analysis of leaf growth in field crops. The studies showed that leaf appearance rate responded linearly to temperature above 1°C, that leaf expansion rate responded likewise above 3°C and that both rates were zero below these base temperatures. Auxanometer measurements of leaf extension showed that daily rates of expansion of leaf area increased linearly with the daily integral of temperature. However, hourly rates of extension in length alternated with those in width during each 24 h cycle in patterns that were not clearly related to hourly changes of temperature or to the day/night sequence.     

Variation in growth attributes of contrasting populations of Trifolium repens

A range of growth attributes was measured in seedlings of 10 Trifolium repens populations, differing in leaf size and origin, grown in three temperature and two glasshouse environments. Growth rates of large leaf types of Mediterranean origin were higher than those of smaller leaf types at 10°C. However, the greater temperature response of the smaller leaf types resulted in higher growth rates for S.100 and S.184 than for a large leaf type from Israel at 20°C. The increase of growth rate with temperature was associated with changes in leaf area ratio and net assimilation rate between 10° and 15°C but only with changes in net assimilation rate between 15° and 20°C. Within each temperature environment, population differences in growth rate were related to differences in net assimilation rate rather than leaf expansion. At low temperature a greater proportion of dry matter was distributed to leaf tissue in large leaf types particularly those of Mediterranean origin but they showed a proportionately smaller increase in allocation to leaves with increasing temperature compared with small leaf types. In the glasshouse environments growth rates in spring were more than double those in the autumn. This difference was associated with net assimilation rates which were about five times greater in the spring environment. However, leaf area ratios in the spring were only half those in the autumn. These differences in leaf area ratio between the glasshouse environments were closely related to differences in specific leaf area but not to differences in distribution of dry matter to leaf tissue which was greater in the spring environment.     

Effect of sowing date on the temperature response of leaf emergence and leaf size in barley

Abstract Rate of leaf emergence of barley grown in the field in each of 2 years was affected by sowing date and, where direct comparisons were possible, it was found that leaves on late-sown plants emerged more quickly. Rate of leaf emergence fluctuated throughout the season, slowing almost to zero in the winter. Much of this variation in rate was removed when the number of leaves was plotted against accumulated temperature rather than time. When emergence rates for each sowing were calculated using a common base temperature they were found to be well correlated with rate of change of daylength. However, it was (bund that base temperature as well as temperature response was affected by date of sowing. The pattern of change of size of leaves was also affected by date of sowing. It appeared that in low temperatures and short days, there was no increase in leaf size from leaf position to leaf position. The responses of leaf emergence, extension and final size to date of sowing appear to adapt the plant to grow quickly when sown early but to cease growth and possibly frost-harden at low temperatures.     

Analysis of leaf appearance,leaf death and phoma leaf spot,caused by Leptosphaeria maculans,on oilseed rape (Brassica napus) cultivars

Development of phoma leaf spot (caused by Leptosphaeria maculans) on winter oilseed rape (canola, Brassica napus) was assessed in two experiments at Rothamsted in successive years (2003–04 and 2004–05 growing seasons). Both experiments compared oilseed rape cultivars Eurol, Darmor, Canberra and Lipton, which differ in their resistance to L. maculans. Data were analysed to describe disease development in terms of increasing numbers of leaves affected over thermal time from sowing. The cultivars showed similar patterns of leaf spot development in the 2003–04 experiment when inoculum concentration was relatively low (up to 133 ascospores m⁻³ air), Darmor developing 5.3 diseased leaves per plant by 5 May 2004, Canberra 6.6, Eurol 6.8 and Lipton 7.5. Inoculum concentration was up to sevenfold greater in 2004–05, with Eurol and Darmor developing 2.4 diseased leaves per plant by 16 February 2005, whereas Lipton and Canberra developed 2.8 and 3.0 diseased leaves, respectively. Based on three defined periods of crop development, a piece-wise linear statistical model was applied to the progress of the leaf spot disease (cumulative diseased leaves) in relation to appearance (‘birth’) and death of leaves for individual plants of each cultivar. Estimates of the thermal time from sowing until appearance of the first leaf or death of the first leaf, the rate of increase in number of diseased leaves and the area under the disease progress line (AUDPL) for the first time period were made. In 2004–05, Canberra (1025 leaves ×°C days) and Lipton (879) had greater AUDPL values than Eurol (427) and Darmor (598). For Darmor and Lipton, the severity of leaf spotting could be related to the severity of stem canker at harvest. Eurol had less leaf spotting but severe stem canker, whereas Canberra had more leaf spotting but less severe canker.     

Field Studies of Cereal Leaf Growth: I. INITIATION AND EXPANSION IN RELATION TO TEMPERATURE AND ONTOGENY

Measurements of leaf initiation, appearance, and expansion arepresented for winter wheat and spring barley crops. For winterwheat, these processes occurred during periods of several weekswhen fluctuating temperatures influenced process rates. Analysisof these measurements was facilitated by plotting variablesagainst the time integral of temperature above an appropriatebase temperature (O °C), here called thermal time with unitsof °C d. Leaf primordial number and appearance stage increasedlinearly with thermal time for both winter wheat and springbarley which initiated 12 and 9 leaves respectively. When plottedagainst thermal time 90% of laminar and leaf length growth and80% of laminar width growth was satisfactorily described bya straight line for both species. This enabled an average extensionrate and duration of linear growth to be defined for each leaf.When expressed in thermal time, wheat leaves had a similar durationof linear growth (210 °C d; s.d. 30 °C d) with insolationexerting a negligible influence. The first seven barley leaveshad a shorter duration of linear growth (151 °C d; s.d.8 °C d). For wheat, final leaf length and laminar widthincreased with leaf number and were not apparently associatedwith changes in apical development stage. Changes of barleyleaf dimensions with leaf number were more complex.     

Temperature Effects on Phenological Development and Yield of Muskmelon

Our goal was to construct a simple muskmelon phenology modelthat could be run with easily obtainable weather station dataand used by growers to quantify phenological development andaid in projecting harvest dates. A growth chamber experimentwas conducted with two cultivars of muskmelon (‘Gold Rush’and ‘Mission’) to determine how main vine leaf appearancerates responded to temperature. We identified three cardinaltemperatures for leaf appearance rate: the base temperature(10 °C) at which leaf appearance rate was zero; an optimumtemperature (34 °C) at which the rate of leaf appearancewas maximal; and an upper threshold temperature (45 °C)at which leaf appearance rate returned to zero. Using thesethree cardinal temperatures, we constructed a simplified thermalunit accumulator for hourly measurements of air temperature.Main vine plastochron interval (PI), thermal time to harvest,and final yield were determined for three cultivars of muskmelon(‘Explorer’, ‘Gold Rush’ and ‘Mission’)grown in the field at Overton, TX, USA, over six transplantingdates from March to June 1998. PI was calculated for each cultivarx transplanting date combination as the reciprocal of the slopeof main vine node number vs. accumulated hourly thermal units(     

Variation in cardinal temperatures for germination among wheat (Triticum aestivum) genotypes

In most tropical regions where wheat is grown under irrigation, high temperatures at sowing adversely affect crop establishment and subsequent seedling survival. The objective of this study was to compare wheat (Triticum aestivum) genotypes for their ability to germinate and grow at high temperatures during the seedling stage. Twenty-five seeds each of 14 spring wheat cultivars were placed on moist filter paper at different temperatures (5°C to 40°C) in a one-way thermogradient plate to determine the cardinal temperatures for germination. Rate of germination at each temperature for each genotype was computed as the inverse of time taken for 50% of the seeds to germinate. Rate of germination for each genotype at different temperatures was modelled with temperature to determine the base (t_b), and optimum (t_opt) temperatures. Response of germination to temperature for each genotype was calculated as the slope of a linear regression of the rate of germination on temperature below t_opt. Genotypes differed in their optimum temperatures and Mexipak (= Kalyansona) had the lowest. Range in base temperature among the genotypes was between 0°C and 2°C differences but were not statistically significant though they might be biologically significant. Genotypes differed in their response to temperature with Gomam having the lowest rate, implying that it was slow to respond to increasing temperatures. Debeira and Cham 6 showed a similar response. Three lines which had performed well in spring wheat evaluation trials for moderate rainfall areas under heat stress had the highest response rate. It is concluded that combining higher optimum temperatures with faster response rates would result in better-adapted germplasm for regions where high temperatures persist at sowing.     

Influence of day length and temperature on number of main stem leaves and time to flowering in lupin

A growth chamber experiment was carried out to investigate the influence of day length and temperature on the development of flowering in eight varieties of the three grain lupin species Lupinus albus (Wat and C3396), L. angustifolius (Gungurru, Polonez and W26) and L. luteus, (Juno, Radames and Teo). The plants were grown at two temperatures, 10°C and 18°C, in combination with five daylength regimes: 10, 14, 18, 24 h day at full light intensity and 10 h full light extended with 8 h low intensity light. Increased daylength decreased days from sowing to flowering in all varieties, but had little effect on thermal time to flowering in most varieties. However, C3396, W26 and Radames had a significantly longer thermal time to flowering at high, non‐vernalising temperature (18°C) at short daylengths. Low light intensity daylength extension did not significantly influence thermal time to flowering. For flower initiation, measured as number of leaves on the main stem three types of response were found. All varieties formed fewer leaves on the main stem at 10°C than at 18°C, although the two thermo‐neutral varieties of L. luteus, Juno and Teo, gave only a small response to temperature and daylength. In Polonez, Gungurru and Wat, low temperature decreased leaf number, but there was only a small response to changes in daylength. Three varieties, C3396, W26 and Radames, showed longer thermal time to flowering at 18°C with short daylengths. This could be explained by a greater number of main stem leaves formed at short daylength at non‐vernalising temperatures. Increased daylength decreased leaf number in these varieties, but never to a smaller number than for plants grown at 10°C. In these varieties, low intensity extension of the daylength had a similar (W26, Radames) or decreased (C3396) effect compared to full light extension. The hastening of time to flowering by long days could be separated into two effects: a high light energy effect hastened development by increasing the rate of leaf appearance in all varieties, while low light energy in thermo‐sensitive varieties was able to substitute for vernalisation by decreasing leaf number.     

The Growth and Development of Maize (Zea mays L.) at Five Temperatures

The objectives of this work were to measure growth and developmentrates over a range of temperatures and to identify processeswhich may limit vegetative yield of maize (Zea mays L.). Twosingle cross Corn Belt Dent maize hybrids were grown from sowingin a diurnal temperature regime of 16/6 °C day/night andin constant temperature environments of 16, 20, 24 and 28 °C.The 16/6 °C environment was close to the minimum for sustainedgrowth and 28 °C was near the optimum. Entire plants wereharvested at stages with 4, 6, 7 and 8 mature leaves in alltemperature treatments except 20 °C in which the final twoharvests were carried out at 9 and 10 mature leaves. Mean totalleaf number varied between 19.5 and 16.0 with the maximum occurringat 16/6 °C. Although harvests were carried out at comparableleaf numbers, and hence at similar developmental stages, thetime interval between sowing and harvest decreased considerablyas temperatures increased. The relative rates of dry weight and leaf area accumulationwith time increased with a Q₁₀ of 2.4 between 16 and 28 °C,while leaf appearance rate increased with a Q₁₀ of 2.9 overthe same range; both rates were highest at 28 °C. Althoughdry matter partitioning to the shoots increased with temperature,the area of individual leaves varied in a systematic patternwhich resulted in maximum leaf area, leaf area duration andconsequently dry weight being realized at 20 °C for anygiven stage of development. Zea mays, corn, low temperature stress, temperature response, growth, development     

Developmental Base Temperature in Different Phenological Phases of Wheat (Triticum aestivum)

The linear relationship between temperature and developmentrate has been widely recognized and it has been suggested thatthermal units (the summation of daily mean temperature abovea base temperature) can predict the phenological developmentof a crop. The aim of this paper was to determine the base temperaturefor different phenological phases of wheat. Two mediterraneanwheat cultivars and five sowing dates were used to obtain differentmean temperatures during development and different developmentalrates. The linear regression of development rate against meantemperatures for each period indicated that there were no uniquebase temperatures for all stages of the life span and valuesclose to 4°C and to 9·5°C were found to be bestfits for base temperatures before and after the terminal spikeletstage of both cultivars. A model to predict wheat developmentwas validated with another data set, which included differentwheat cultivars and sowing dates. Estimates of the error indevelopmental prediction by using a single base temperatureof 0°C is discussed as a function of separate developmentstages. Key words: Wheat development, base temperature, thermal time, Triticum aestivum     

The effect of temperature on the rate of sprout growth and development within stored onion bulbs

In order to understand better the effects of storage temperature on the time to visible sprouting in stored onions, sprout growth was measured by regularly dissecting samples from bulbs stored at 1, 10, 15 or 25°C for 243 days. The dry-weight of the shoot or sprout within stored onion bulbs increased exponentially with time. The rate of increase of sprout dry weight, as well as the rate of leaf initiation by the shoot apex was faster at 17° than at 10 or 25°C, and almost zero at 1°C. The rate of loss of dry weight from storage tissue was similar at 17°C and 25°C but slower at 10°C and slower still at 1°C.     

Estimating temperature‐dependent developmental rates of potato tuberworm,Phthorimaea operculella (Lepidoptera: Gelechiidae)

Abstract The potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is the most destructive pest of potato, Solanum tuberosum L. (Solanaceae), in tropical and subtropical regions in both field and storeroom situations. The modeling of temperature‐dependent development can be useful in forecasting occurrence and population dynamics of the pests. Published developmental parameters for this pest vary greatly for many reasons. We determined temperature‐dependent development of P. operculella at seven constant temperatures (16, 20, 24, 28, 32, 34 and 36 °C). Developmental period of whole immature stage (egg to the end of the pupal stage) varied from 75.5 days at 16 °C to 17 days at 32 °C. The population failed to survive at 36 °C. The observed data was modeled to determine mathematical functions for simulating P. operculella development in each stage of development and overall. Two linear models, ordinary linear regression and the Ikemoto linear model were used to describe the relationship between temperature and development rate of the different stages of P. operculella and estimating the thermal constant and lower temperature threshold. The lower temperature threshold (t) and thermal constant (k) of whole immature stage were estimated to be 11.6 °C and 338.5 DD by Ikemoto linear model, and the estimated parameters were not substantially different with those estimated by ordinary linear models. Different models provided a better fit to the various developmental stages. Of the eleven nonlinear models fitted, the Beriere‐1, Logan‐6 and Lactin‐1 model was found to be the best for modeling development rate of egg, larva and pupa of P. operculella, respectively. Phenological models based on these findings can be part of a decision‐support tool to improve the efficiency of pest management programs.     

Determination of the Length of the Vegetative and Pre-floral Stages in the Day-Neutral Plant Helianthus annuus by Chilling Pulses

Helianthus annuus seedlings grown in an 18 h day at 28 ?C wereexposed to one 6 d chilling pulse of 12 ?C, at spaced timesduring the first 21 d from sowing. At 2 d intervals, the terminalbuds of 5 plants were dissected to determine leaf number andto score the vegetative or flowering state of the shoot apex.It was found that, while the rate of leaf initiation was reducedequally by each chilling pulse, pulses commencing on days 9or 12 reduced the total leaf number from 30 to 26, while pulsesapplied earlier had little effect. This variation is interpretedin terms of the time available for leaf production. The apicesof control plants commenced the visible transition to flowering16 d after sowing. Chilling pulses applied from days 3 or 6delayed this transition by about 5 d, whereas later pulses causedonly a 1•5 d delay. In a second experiment, where the chillingwas reduced to 2 d duration, it was again found that chillingdelayed flowering during the first 8 d and was progressivelyless effective when applied later. From this variation in temperaturesensitivity it is proposed that chilling sunflower plants immediatelyafter sowing delays flowering by extending the vegetative phaseof growth and so delaying the attainment of a ‘ripenessto flower’ state that appears to coincide with the expansionof the first pair of leaves. From day 8 onwards processes leadingto flowering that are relatively temperature insensitive apparentlybecome dominant in the apex and result in visible signs of flowering8 d later, although during this transitional stage leaf primordiacontinue to be initiated on the flanks of the apex.