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The increasing use of new silage-specific corn (Zea mays L.) hybrids, including Leafy types, has created a need for more information on the decision of hybrid choice and time of harvest. A field experiment including dual-purpose and Leafy silage-specific hybrids was conducted for 4 yr (1999–2002) at Ottawa, ON, Canada. Specific objectives were to determine (i) differences in whole plant moisture and dry matter (DM) accumulation after silking, and (ii) the optimum harvest windows of the contrasting corn types. Samples of whole plant moisture and DM accumulation were taken and analyzed at 3- to 7-d intervals from approximately 3 wk after silking to physiological maturity. Our results showed that the rate of decline in silage moisture content varied among the years and hybrid types. On average, 85% of total DM accumulation was achieved when the whole plant moisture was about 65% for all hybrids. Compared to dual-purpose hybrids, the whole plant moisture of Leafy silage-specific hybrids declined more slowly, especially for hybrid ‘Mycogen TMF94’. We concluded that 65% whole plant moisture normally corresponded to the 50% kernel milk line (ML), and occurred between 50 and 60 d after silking under the northeast climate conditions. Silage-specific hybrids had larger windows for harvest than dual-purpose hybrids. However, ML progression was irregular for Leafy hybrids and changed more rapidly for dual-purpose hybrids. Under extreme weather conditions, kernel ML does not correspond to silage moisture content in the same way as under normal conditions, therefore, silage harvest should be based on actual moisture content.

The amount and distribution of leaf area and leaf angles in a crop canopy determine how photosynthetically active radiation (PAR) is intercepted and consequently influences canopy photosynthesis and yield. Factors such as plant shape, plant populations, and row width will affect these leaf distributions and can occur in an almost infinite number of different combinations. To supplement experimentation, a mathematical model was developed to use measurements of leaf area and leaf angles in two dimensions (with height and across the row) to calculate PAR interception and canopy photosynthesis. Maize (Zea mays L.) hybrids with phenotypic differences were planted at several plant populations to produce a wide range of two-dimensional leaf area and leaf angle patterns. The extreme phenotypes, leafy and reduced stature, were included to vary plant height and number of leaves above the ear. Measurements of average PAR at various levels were made in seven different canopies and compared with calculations from the model (R 2 of 0.68 and 0.92 for two sets of data). As well, measurements of PAR at 20-cm increments on transects perpendicular to the row were made in three canopy types at three levels and compared with theoretical calculations (R 2 = 0.74). A simple numerical experiment was run to demonstrate the utility of the model where daily canopy photosynthesis was calculated for two row widths and seven plant types. One result was that depending on row widths, plants with very upright leaves can have both the smallest and largest daily canopy photosynthesis.

The portable chlorophyll meter [Soil Plant Analysis Development (SPAD)] has been used successfully for measuring leaf‐nitrogen (N) of several crops. Determination of the appropriate sample size, in terms of number of plants to be sampled within each plot, has recently become a matter of concern. An insufficient sample size does not allow for the detection of small, but real differences between treatment means, whereas an excessively large sample size constitutes a waste of time and resources. In this study, SPAD meter data were collected at two sites. Each of these two field experiments was organized following a split‐plot design with three blocks and two treatment factors: four nitrogen levels (main plot factor) and six maize (Zea mays L.) hybrids (subplot factor), selected to represent a broad range of canopy types. The approach followed in collecting SPAD meter readings for the determination of an appropriate sample size consisted of sampling one leaf per plant and taking a single reading per ...

Effects of N fertilization have been extensively studied for conventional maize (Zea mays L.) hybrids but not for genotypes bearing the leafy and reduced-stature traits which differ significantly in canopy and root morphology. We tested the hypothesis that genotypes carrying the leafy trait (taller plants with more leaves, greater leaf area development, and greater rooting systems) would show differing responses to N availability in terms of grain yield and yield components from those of conventional maize hybrids. The experimental design was a split-plot in a randomized complete block design with four blocks repeated across two growing seasons at each of two field sites. The treatments were N fertilization rates (0, 85, 170, and 255 kg N ha -1 ) as the main plot factors and genotypes as the subplot factors. The genotypes were leafy reduced stature (LRS), nonleafy normal stature (NLNS), leafy normal stature (LNS), nonleafy reduced stature (NLRS), and conventional hybrid checks of early (P3979) and late maturity (P3905). The latter consistently yielded best and the NLRS hybrid worst; however, the genotypic grain yield ranking varied between sites. Overall, the LRS outyielded its conventional counterpart (P3979) by 12% at one site and by 26% at the other. No significant N x hybrid interactions were detected for grain yield. We inferred that using leafy genotypes in maize production would not require additional N fertilization compared with their conventional maize hybrid counterparts.

To determine if differences exist in the ability of three Fusarium species (F. graminearum, F. verticillioides, and F. subglutinans) to infect maize ears as the silks and kernels mature, one moderately resistant and two susceptible hybrids were inoculated at two points of entry (silk channel and kernels) in 1994 and 1995. Inoculations were conducted nine times for each part of the ear starting from silk emergence. For all three species, the greatest silk channel inoculated disease severities occurred when the ears were inoculated in the early stages of silk development, with a peak in susceptibility around 1-6 days after silk emergence, followed by a rapid decrease in severity. With kernel inoculations, a general decrease in disease severity occurred with time for all species. Fusarium verticillioides had the lowest disease severity of the three species. With silk channel inoculations, F. subglutinans resulted in higher disease severity than F. graminearum; however, the opposite was found with kernel inoculations, with F. graminearum producing the greatest amount of disease symptoms.

Fusarium spp. in maize can contaminate the grain with mycotoxins if environmental conditions are favorable for fungal growth. To quantify the relationship between growth of Fusarium spp. and environmental conditions, a mathematical model was developed to simulate growth of F. graminearum and F. verticillioides on maize ears following silk inoculation in field experiments from 1992 to 1995. Each species was inoculated separately and as a mixture of the two for 3 of the 4 years on one maize hybrid. Disease progress in ears was measured by a visual rating scale that was converted to percent visual infection. Measurements were made at regular time intervals after silks were inoculated 5 days after silk emergence. Differential equations were used to relate growth rates of Fusarium spp. in maize ears to hourly air temperature and relative humidity and to daily precipitation. Integration of these equations over time produced quantitative estimates of fungal growth. Model calculations compared well with measurements (R2 = 0.931, standard error of estimate [SEE] = 2.11%) of percent visual disease infection of maize ears over 3 years. The model was tested against a second set of data (R2 = 0.89, SEE = 5.9%) in which silks were inoculated at nine different times after first silk emergence for each of 2 years (1994 and 1995) with the two species of fungi on the same maize hybrid. At this time, a silk function was developed to account for changes in the susceptibility of silks to disease. F. graminearum responded to wet conditions more than F. verticillioides, and for the conditions of this experiment, grew much faster than F. verticillioides when inoculated separately. When they were inoculated together, F. graminearum growth rates were much lower, indicating some interference by F. verticillioides. During 1993, weather conditions before inoculation reduced the growth of both species in silks.

Temperatures greater than 27°C, in a growth cabinet, have resulted in floral sterility and yield loss in Brassica napus L. Maximum daily temperatures often exceed this in the major canola growing regions. Our objective was to examine the effects of heat stress during flowering on yield and yield components of B. napus, B. rapa L., and B. juncea (L.) Czernj. & Cosson. Cultivars of the three Brassica species were grown in a split-plot design in the field for 3 yr at Ottawa, Canada. Three seeding dates were used each year to obtain different levels of heat stress during flowering. The number of flowers on the main raceme and the first and second branch racemes were counted at anthesis, from 10 plants per plot. At maturity, pods from the sampled plants were counted and seed numbers and weight determined. Two rows of the remainder of each plot was harvested for seed yield. A heat stress index was developed on the basis of the accumulation of daily maximum temperatures greater than a threshold temperature. The threshold temperature during flowering, which resulted in seed yield losses, was 29.5°C for all Brassica species. High mean maximum temperature during vegetative development resulted in a reduction in flower number for all Brassica species. Seed yield decreased as heat stress during flowering increased. The reduction in seed yield was primarily due to a reduction in flower number and in the number and size of the seeds produced per flower. Plant breeders should actively select for heat stress tolerance in future canola cultivars.

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population densi...

The SPAD chlorophyll meter was found to be a reliable, quick, and non-destructive tool used for directly measuring leaf chlorophyll and indirectly assessing the proportional parameter of leaf, and by extension, plant nitrogen (N) status. The meter has been used successfully to assess leaf N in conventional maize crops, but it has not been used with new maize (Zea mays L.) genotypes containing leafy (L) and reduced stature (RS) traits. SPAD meter readings were collected on the uppermost fully developed leaves (before silking) and on the ear leaf (after silking) of field grown maize genotypes with and without the L and RS traits. The experiment was conducted during 1996 and 1997 at two sites in Eastern Canada (Ottawa and Montreal). At each site in each year, a split plot arrangement of two treatment factors was used in a randomized complete block design with four blocks. The main plot treatments were levels of N (0, 85, 170, and 255 kg ha−1), with six maize genotypes as subplot treatments. The hybrids inclu...

Identifying corn (Zea mays L.) genotypes with faster rates of seedling emergence and leaf appearance is important in developing a corn crop with earlier canopy closure and better seasonal light interception. A greenhouse experiment was conducted twice to investigate whether corn genotypes known to vary in canopy architecture and yield potential differed in rates of seedling emergence and leaf appearance. The experiment was arranged in a randomized complete block design utilizing seven genotypes: five of the newly developed Leafy reduced-stature (LRS) types (LRS1, LRS2, LRS3, LRS4 and LRS5), one conventional type [Pioneer 3979 (P3979)], and one late-maturing big-leaf (LMBL) type. Five seeds were planted in each pot and seedling emergence was recorded every day until all seeds emerged. Leaf appearance was recorded from seedling emergence until the plants reached anthesis. There was variability among the genotypes for both seedling emergence and leaf appearance rate. Mean seedling emergence values of greater than 90 % were achieved by four of the five LRS genotypes, and the LRS types generally emerged more rapidly than the others. Leaf appearance rate showed linear increases over time; however, LRS genotypes (in particular LRS3, LRS4 and LRS5) had more rapid leaf appearance rates than the others. The LMBL hybrid ranked last for both seedling emergence (

Weed interference with the growth and yield of corn plants is affected by both mechanical and chemical means of weed control. Recently, corn hybrids accumulating more leaf area, maturing earlier, yielding better in narrower row spacings and tolerating higher plant populations better than conventional hybrids have been developed. Because of more rapid leaf area accumulation during the earliest stages of canopy development and overall canopy architecture, they may be more susceptible to damage due to mechanical weed control. The objective of this study was to assess the response of corn hybrids with a wide range of canopy architectures to chemical and mechanical (rotary hoeing) weed control, with an emphasis on quantifying morphology and grain yield responses. Field experiments were conducted in 1997 and 1998 at Ste. Anne de Bellevue, Quebec. Three hybrids were tested: leafy reduced-stature (LRS1 and LRS2), and the conventional hybrid Pioneer 3979 (P3979). Rotary hoeing alone had very little effect, while herbicide application reduced the interference of weeds with growth and grain yield of all hybrids. Hybrid P3979 had more total leaf area than LRS1 and LRS2, but the percentage of leaf area above the ear was much higher for LRS hybrids (70 %) than for P3979 (51 %). Generally, LRS hybrids were much shorter with more leaf area above the ear than P3979, contributing to the large differences in canopy architecture between the LRS hybrids and P3979. However, morphology and grain yield response of hybrids to rotary hoeing and herbicide weed control was not different, indicating that the new hybrids were not more susceptible to damage caused by mechanical weed control than a corn hybrid with a conventional canopy architecture. Reaktionen von Maishybriden mit unterschiedlich strukturiertem Blatterdach gegenuber chemischer und mechanischer (Hackfrase) Unkrautkontrolle: Morphologie und Ertrag Unkrautwirkung hinsichtlich des Wachstums und Ertrages von Maispflanzen wird sowohl durch mechanische als auch chemische Mittel der Unkrautbekampfung beeinflusst. Kurzlich entwickelte Maishybriden mit groserer Blattflache und Fruhreife brachten in enger Reihenstellung und Toleranz gegenuber hohen Bestandesdichten bessere Ertragleistungen als konventionelle Hybriden. Aufgrund des schnelleren Blattflachenwachstums wahrend der ersten Entwicklung des Blattdaches und der Gesamtstruktur des Blattdaches konnte vermutet werden, dass sie empfindlicher gegenuber Schaden als Folge mechanischer Unkrautkontrolle sein wurden. Ziel dieser Untersuchung war es, die Reaktion von Maishybriden eines weiten Bereiches der Blattdachstruktur gegenuber chemischen und mechanischen (Hackfrase) Unkrautkontrolle wurde gepruft, wobei die Quantifizierung der Morphologie und der Kornertragsreaktionen besondere Beachtung fanden. Die Feldexperimente wurden in den Jahren 1997 und 1998 an der Ste. Anne-de-Bellevue, Quebec durchgefuhrt. Drei Hybriden wurden untersucht: Blatt-reduzierter Typ (LRS1 und LRS2) und konventionelle Hybriden pioneer 3979 (P3979) wurden gepruft. Hackfrasen allein hatte einen geringen Einfluss, wahrend Herbizidanwendung die Auswirkungen der Unkrauter hinsichtlich Wachstum und Kornertrag bei allen Hybriden reduzierte. Die Hybride P3979 hatte eine insgesamt grosere Blattflache als LRS1 und LRS2; der Prozentanteil der Blattflache oberhalb des Kolbens war bei LRS-Hybriden (70 %) erheblich hoher als bei P3979 (51 %). Grundsatzlich kann festgestellt werden, dass LRS-Hybriden wesentlich kurzer mit groserer Blattflache oberhalb des Kolbens als P3979 waren; dies trug zu den grosen Unterschieden in der Blattdachstruktur zwischen LRS-Hybriden und P3979 bei. Allerdings war die Reaktion der Morphologie und des Kornertrages der Hybriden gegenuber Hackfrase-und Herbizidanwendung in der Unkrautkontrolle nicht unterschiedlich; dies lasst vermuten, dass die neuen Hybriden nicht starker-anfallig gegenuber Schaden als Folge mechanischer Unkrautbekampfung sind als Maishybriden mit konventioneller Blattdachstruktur sind.

The Leafy (Lfy) genotype in corn has extra leaves above the ear in comparison to normal non-leafy genotypes and has been shown to increase yields in some geographical areas. In this study, carbohydrate distribution in three Lfy hybrids (two of which were "staygreen") and a normal check (Pioneer 3790) were analyzed in a short-season area (2800 Crop Heat Units, suitable for 85 day Relative Maturity hybrids). Total sugar and starch were determined at all aboveground levels of leaf and stem on 1 August 1990 and this distribution was used to calculate total canopy carbohydrates in two subsequent years from samplings of leaf and stem at only three or four canopy levels bracketing the ear level. Husk, cob and kernel components were also analyzed at three sampling times during grainfill. Major differences in the 2 yr were observed, but in general there was approximately twice the carbohydrate in the canopy at and above the ear in the Lfy genotypes compared to the check. There was also more carbohydrate in the husk and cob in the Lfy lines, but substantially less carbohydrate below the ear in these lines. Rates of grainfill were generally higher in the Lfy hybrids, but the rate of Lfy hybrid A, the early senescent hybrid, was slower in the cooler growing season. Despite the greater amount of carbohydrate in the Lfy hybrids in comparison to the traditional check, their grain yields were not greatly increased, indicating that the kernel component provided a weak sink. This characteristic is probably associated with the long season and tropical origin of the Lfy germplasm. Key words: Maize, grainfill, leafy, carbohydrate distribution, phenology, sink size

Development of maize (Zea mays L.) types that produce leaf area quickly and mature rapidly may increase maize yields in mid- to short-season areas. The leafy (Lfyl) and reduced-stature (rd1) traits each contribute to this objective; however, these two traits have not previously been combined. Our objective was to determine the effect of these traits, alone or in combination, on morphology, reproductive development, and yield of maize hybrids A field experiment including 14 hybrids [two non-leafy reduced-stature (NLRS), four leafy reduced-stature (LRS), eight leafy normal-stature (LNS)], and three commercial hybrid checks [non-leafy normal-stature (NLNS)] was conducted in 1992 and 1993. The following variables were recorded for each hybrid: plant height, internode length, ear height, above-ear leaf number, above-ear leaf area, corn heat units from planting to tasseling, corn heat units from planting to silking, days from tasseling to silking, grain yield (Mg ha -1 ), grain moisture content, husk dry weight, husk moisture content, cob dry weight, cob moisture content, kernel number per row, maximum ear circumference, and ear length. The normal stature hybrids were the tallest plants, with higher ear placement than reduced stature hybrids. The leafy trait was associated with shorter internodes, increased leaf number, and greater above-ear leaf area. The reduced stature hybrids required fewer corn heat units to reach anthesis than the normal stature hybrids. The reduced stature hybrids had the lowest grain moisture (210-270 g kg -1 ), husk moisture, and cob moisture contents at the time of harvesting. The LNS hybrids matured late and had grain moisture contents of 350 to 400 g kg -1 at harvest. In general grain yield, husk dry weight, cob dry weight, kernel number per row, ear length, and maximum ear circumference were higher for the normal stature hybrids than for the reduced stature hybrids. The earlier anthesis and lower grain, husk, and cob moisture contents indicated potential for successful grain production and harvest of leafy reduced-stature hybrids in shorter growing season areas.

Measurement or estimation of leaf area is essential for simulation of light interception and photosynthate production. Leaf shape is an important factor in describing how leaf area is distributed in the canopy. When defined mathematically, leaf shape can be used to calculate leaf area of individual leaves as well as how leaf area varies along the length of the leaf. The objective of this study was to evaluate several methods used to describe leaf shape (the variation in leaf width with distance from the ligule or stem) and to analyze variations in shape coefficients. Measurements of leaf width every 10 cm along fully expanded leaves were made over a number of years, sites, plant densities, and nitrogen treatments with normal, leafy, and reduced-stature hybrids. These measurements were fitted to a number of polynomial equations which related leaf width to distance from the ligule. Leaf area was calculated by integrating these equations. In all, 10 methods were used to calculate areas of individual leaves, but one method, based on a second order polynomial equation which could easily be integrated for total leaf area or area along the leaf, was chosen as a standard. All other methods were compared with this standard and leaf area estimates were found to be similar (R 2 > 0.98). Planimeter measurements of individual leaf area also compared well with estimates using the standard method (R 2 = 0.96) but planimeter measurements had more scatter than estimated values. The most useful equation was the second order polynomial with two dimensionless shape coefficients using maximum leaf width and total length. Integrating this equation produced the well known length × maximum width × alpha equation for calculating leaf area where alpha was 0.743 for all hybrids and 0.734 for normal hybrids. A method was developed to use this equation for calculating leaf area as a function of leaf length.

Maize hybrids which produce more leaves above the ear, with leaf area indices similar to conventional hybrids, which require fewer corn heat units to flowering and maturity, and tolerate higher population densities, should be better adapted for production in short season areas than currently available hybrids. Leafy reduced-stature maize hybrids, which have only recently been developed, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (50 000, 100 000, 150 000, and 200 000 plants.ha−1) on the vegetative growth of one leafy reduced-stature (LRS), one non-leafy reduced-stature (NLRS), and two conventional control hybrids (Pioneer 3979

Maize (Zea mays L.) is a crop of growing importance in Eastern Canada. Modelling the temperature effects on phenological development, crop architecture and disease infection in maize contributes to the development of well-adapted, early-maturing varieties. Details of modelling these three aspects of maize growth were presented. The first focussed on quantifying the effect of air or soil temperature on maize phenological development. Crop growth was divided into two periods: vegetative (planting to silking) and grain filling (silking to maturity). A third period (planting to emergence) was separated within the vegetative period. Heat unit systems based on daily temperature response functions were developed to produce the most consistent heat unit sums for each period. The best fits of these functions were determined by minimizing standard deviations and coefficients of variation of these sums for each thermal period over locations and years. Calculated temperature response functions estimated thermal periods more consistently than growing degree days (GDD) for all three periods. The largest improvement was made in the silking to maturity period.The second aspect was a study of crop architecture. Methods were developed to mathematically characterize the structure of a canopy in terms of leaf area and leaf angle distributions with crop height and across the row. These calculations, in turn, were input to a soil–plant–atmosphere model to calculate interception of photosynthetically active radiation (PAR). Model calculations of PAR interception compared well with measurements for a range of plant types and plant population densities (R2 = 0.76).The third aspect was quantifying growth of Fusarium in maize. Differential equations were used to relate Fusarium rates of growth in maize ears to air temperature, relative humidity and precipitation. Integration of these equations over time produced quantitative estimates of fungal infection. Model calculations were compared to visual ratings of fungal infection for two Fusarium species over three years (R2 = 0.92).In each of the three aspects of this study, modelling tested our understanding of the processes involved and the dominant factors controlling these processes. Thus, modelling was an integral part of the scientific approach, synthesizing experimental data in a quantitative conceptual framework and identifying dominant factors and parameters which required additional focussed experimental evaluation. Key words: Phenological development, crop architecture, Fusarium infection

Development of maize (Zea mays L.) types that produce leaf area quickly and tolerate high plant densities could enhance yields in mid-to short-season environments. The leafy and reduced-stature traits each make contributions to this end, but have not previously been combined. Out objective was to evaluate the effect of plant densities on leafy normal-stature (LNS), non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), and non-leafy reduced-stature (NLRS) inbreds. Twenty-one inbreds were field-grown over 2 yr at low (65 000 plant ha -1 ) and high (90000 plant ha -1 ) densities. Above-ear leaf number, above-ear leaf area, and single plant grain yield were lower for LNS and NLNS at the high, as compared with the low, plant density, but were not affected for LRS or NLRS. The corn heat unit (CHU) requirements from planting to tasseling, and from planting to silking, as well as days between tasseling and silking, were greater under high plant density for LNS and NLNS, but were not affected for LRS or NLRS. Grain yield increased to a greater extent under high density compared with low density for LRS and NLRS than for LNS or NLNS. The LRS inbreds had a shorter vegetative period, longer grain-filling period, highest yields, and were more tolerant of high plant density than the normal-stature genotypes. These characteristics indicate potential both for increased yields and production in areas with lower CHU availability. These advantages are expected to be conferred to LRS hybrids.

Maize hybrids that yield well, mature earlier with low grain moisture contents, tolerate higher population densities and take advantage of narrow row spacings better than the currently available hybrids would be more suitable for production in short-season areas. Leafy reduced-stature maize hybrids, which have only recently been developed, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (65 000 and 130 000 plants ha -1 ) and planting patterns (single rows 76 cm apart and paired rows with 20 cm between rows within a pair of 56 cm between rows of adjacent pairs) on the yield and yield components of two leafy reduced-stature (LRSI and LRS2), one non-leafy reduced-stature (NLRS), and two conventional corn hybrids (Pioneer 3979

The structure of maize (Zea mays L.) canopies influences light interception, photosynthesis, and yield. A recently developed corn phenotype termed Leafy, which has additional leaves above the ear compared with normal phenotypes of the same maturity, is thought to provide a greater source of photosynthates. The objective of this study was to develop a mathematical model to compare hybrid light interception, photosynthesis, carbohydrate storage, and export of carbohydrates from the leaves, based on measured leaf area distribution, leaf photosynthesis, and diurnal changes in leaf sugars and starches. Model simulations were run for two Leafy hybrids and a normal check hybrid, all grown at 6.5 and 3.25 plants m -2 . A series of differential equations described how photosynthate was stored as leaf sugar and starch and then exported to stems. Rate coefficients were used to characterize diurnal changes in leaf carbohydrate concentration during early grain filling for different hybrids and planting densities. Model fits to leaf sugar and starch data were good (0.64 ≤ r ≤ 0.89). Model calculations showed that storage of carbohydrates in leaves was relatively small compared with the total amount of leaf photosynthate produced; more than 90% of the photosynthate was exported directly to the stem. Hybrid and planting density comparisons indicated that rate coefficients for the export of photosynthate from leaves increased with total plant dry matter. Leafy hybrids and hybrids grown at the lower plant density had greater plant dry weights, photosynthetic rates, and leaf export rates than the check or hybrids grown at the higher plant density.

Maize hybrids which yield well, mature earlier and tolerate higher population densities better than the currently available hybrids would be more suitable for production in short-season areas. Leafy reduced-stature maize hybrids, which have only recently become available, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (50000, 100000, 150000, and 200000 plants ha -1 ) on the yield and yield components of one leafy reduced-stature (LRS), one non-leafy reduced-stature (NLRS), and two conventional control hybrids (Pioneer 3979

Development of maize (Zea mays L.) types that produce leaf area and mature quickly would increase production of maize in mid- to short-season areas. The leafy (Lfy1) and reduced-stature (rd1) traits both make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the yield and yield components of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbred lines. The two genes, ‘Lfy1’ and ‘rd1’, were incorporated into a series of inbred lines resulting in a range of canopy architectures. Ten variables were recorded for each of 30 inbred lines over three years. The 10 variables were: corn heat unit requirement from planting to tasselling, corn heat unit requirement from planting to silking, days between tasselling and silking, grain moisture content, husk dry weight, cob dry weight, ear length, maximum ear circumference, grain yield and ratio of grain yield to moisture content. Reduced-stature inbred lines reached anthesis more quickly than normal-stature inbred lines. Grain moisture content was less in reduced-stature inbred lines than normal stature trait groups. Leafy-reduced stature plants had the highest ratio of grain to moisture content and the lowest grain moisture content at harvest. Inbred lines containing the rd1 trait matured more rapidly than other trait groups. The LRS trait group yielded more than the other groups, and showed great potential for use in mid- to short-season environments.

Development of maize (Zea mays L.) types that produce leaf area rapidly and finish vegetative development quickly would increase production of maize in mid- to short-season areas. The Leafy (Lfy1) and reduced-stature (rd1) traits each make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the morphological aspects of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbreds. Two traits, Lfy1 and rd1, were incorporated into a series of inbreds, resulting in a range of canopy architectures. Twelve variables were recorded for each of 30 inbreds over three years. The 12 variables were: seed emergence, above-ear leaf number, below-ear leaf number, dead leaf number at tasselling, live leaf number at tasselling, total leaf number, above-ear leaf area, ear leaf length, ear leaf width, ear height, internode length, and plant height. Inbreds containing the Lfy1 trait had more above-ear leaf area, above-ear leaf number, dead leaf number at tasselling, total leaf number and number of live leaves at tasselling than non-leafy inbred lines. Below-ear leaf number was not different among LRS, LNS, and NLNS inbred lines. LRS and NLRS inbred lines were also not different for below-ear leaf number. Plant height, ear height, and ear leaf length and width were higher in normal-stature than reduced-stature plants. The proportion of the seeds which emerged was higher for LRS inbreds than the other trait groups.

Recent cryo-electron microscopy (cryo-EM) results suggest that sufficient NaCl concentration (> or approximately 0.1 M) and superhelix density (> or approximately-0.05) cause circular DNAs to adopt highly extended, tightly interwound configurations, in which the strands are laterally contiguous along almost their entire length. Millimolar levels of MgCl2 reportedly act synergistically with NaCl to produce similar conformations. However, Monte Carlo simulations with purely repulsive interduplex forces failed to reproduce such structures. In the present work, solution measurements of particular physical properties were performed both to characterize the effects of Na+ and Mg2+ on DNA structure and to provide quantitative tests of Monte Carlo simulations of circular DNAs. Supercoiled p30 delta DNAs in 10 mM Tris plus 0, 0.122, and 0.1 M NaCl, and 0.1 M NaCl plus 4 mM Mg2+ were examined by static and dynamic light scattering (LS and DLS), time-resolved fluorescence polarization anisotropy (FPA) of intercalated ethidium, and circular dichroism (CD) spectroscopy. Upon addition of 0.122 M NaCl, the radius of gyration (Rg) decreased substantially, which indicates that p30 delta adopts a more compact structure. This contradicts the cryo-EM studies, where molecular extension and Rg both increase upon adding 0.1 M NaCl. In 0.1 M NaCl, the torsion constant measured by FPA is practically invariant to superhelix density, and the plateau diffusion coefficient at large scattering vector (Dplat) is likewise nearly the same at both relaxed and native superhelix densities. Such invariance is difficult to reconcile with any transition from relaxed circles to tightly interwound structures with laterally contiguous strands. Metropolis Monte Carlo simulations were performed to generate canonically distributed sets of structures, from which average Do values and scattered intensity ratios, [symbol: see text]I (zero) [symbol: see text]/[symbol: see text] l(k) [symbol: see text], were calculated. Agreement between simulations and experiments in regard to [symbol: see text] I(O) [symbol: see text] /[symbol: see text] I(k) [symbol: see text], D(zero) and the supercoiling free energy, delta Gsc (delta l), is remarkably good for the most extensively studied p30 delta samples. The simulated structures exhibit no sign of very tight interwinding with extensive lateral contacts, but instead exhibit most probable superhelix diameters of 85 to 90 A. When 4 mM Mg2+ was added to native supercoiled p30 delta in 0.1 M NaCl, Rg decreased, D(zero) increased, and the longest internal relaxation rate (1/tau 2(zero)) increased, all of which indicate a further overall contraction of the molecular envelope. The torsion constant exhibited a slight increase that is hardly statistically significant. In this case, agreement between the simulations and experiments was only semi-quantitative for most samples investigated, although the predicted contraction was exhibited by all five samples of p30 delta and one of pBR322 DNA. The simulated structures in 0.1 M NaCl plus 4 mM Mg2+ again showed no sign of extensive lateral contacts. A plausible explanation is proposed for the highly extended, tightly interwound structures seen in cryo-EM, and explicitly tested by Monte Carlo simulations of a 1000 bp circular DNA at +25 and -50 degrees C. Structures identical to those seen in cryo-EM are in fact the equilibrium structures in the simulations at -50 degrees C, and the estimated time for equilibration (2.3 x 10(-6) second) is much smaller than the estimated time for vitrification (1 x 10(-4) second).

Tillage effects on the soil environment suggest that it may influence rooting depth and root distribution. In this study, corn (Zea mays L.) rooting depth and root mass distribution were compared under conventional and conservation (chisel, ridge, no-) tillage on sandy loam and clay loam soils at Ottawa, Ontario. Root depth and distribution in 0.10-m vertical increments during vegetative growth were estimated using a combination of excavation of the surface horizon (0–0.10 m) and 0.05-m diameter cores obtained in the row and midway between two rows over a 3-yr period. An exponential model was used to fit root mass distribution data normalized with respect to total root density summed over all increments and maximum rooting depth in the profile. Soil moisture, temperature, mechanical resistance and bulk density varied with tillage treatment, but differences were not associated with root mass distribution. Rooting depth varied with soil texture, year and tillage, with increased rooting depth associated with increased tillage and decreased moisture in surface soil layers. In contrast, a common exponential model was found to fit normalized root mass distribution data under all tillage treatments. Our data suggest that simulation of root mass distribution under all tillage practices is possible if rooting depth and root mass density of the surface soil layer are known. Key words: Corn, model fitting, root distribution, tillage, Zea mays

Photosynthate contribution to grain yield is complex depending, in part, on the translocation of photosynthate within the plant. A 3-yr field study was conducted to compare the distribution of leaf and stem carbohydrate concentrations of two leafy maize hybrids, both with extra leaves above the ear, vs. a normal hybrid on a loam soil (Typic Eutrochrept) at Ottawa, Canada (45°23'N, 75°43'W). The Leafy 2 hybrid outyielded the Check (both with stay green characteristic), but the Leafy 1 hybrid had yields inferior to the other two. Patterns of leaf and stem carbohydrate concentrations with leaf level varied among hybrids. This genetic variability could be quantified by fitting data to a cubic equation and by calculating mean leaf or stem concentrations for the upper canopy. Patterns in total nonstructural carbohydrates paralleled patterns in sugar concentrations. Leaf carbohydrate concentrations were less than one-third those of stem concentrations, showed more diurnal variation, and appeared to be directly influenced by photosynthate production. Mean stem carbohydrates for both leafy hybrids and the Check showed a small rise during the first 10 to 12 d after pollination (DAP), followed by a decline before 35 DAP, which was largest in Leafy 2. Between 40 and 60 DAP, concentrations in Leafy 1 fell slightly, while those in Leafy 2 and the Check rose. The larger drop in stem carbohydrates in Leafy 2 could be an indication of greater translocation to the grain during early grain fill in this hybrid. The decline in Leafy 1 stem concentrations just before black layer may have provided a later source of carbohydrates to the grain. This study suggests that analysis of canopy carbohydrates may identify the actual photosynthetic contribution of leaf area to grain yield.

Chlorophyll meters have been used to provide a rapid non-destructive method to estimate corn leaf nitrogen (N) concentration, although meter readings plateau at high leaf N levels. Paired chlorophyll meter and leaf N concentration data were obtained for ear level leaves at growth stages ranging from 3 wk before anthesis to 5 wk after anthesis over a 2-yr period at Ottawa, Ontario. Separate quadratic-plus-plateau models best represented chlorophyll meter response to leaf N concentration for pre-anthesis, early grain-fill and late grain-fill stages; chlorophyll meter readings corresponding to the beginning of the plateau increased at later growth stages. Leaf N concentration was estimated well from chlorophyll meter readings up to the plateau range using growth stage specific functions (R2 ≥ 0.77) but chlorophyll meter readings beyond the plateau should not be used to estimate leaf N concentration. Key words: Chlorophyll meter calibration, maize

The value of the twist energy parameter (ET) of pBR322 is determined near zero superhelix density from topoisomer distributions created under various conditions. The resulting value, ET = 1155 +/- 65, at 37 degrees C is essentially unaffected by adding 10 mM Mg2+, or by changing the kind of Topo I from chicken-red-cell to calf-thymus. This value significantly exceeds that (ET = 950 +/- 80) measured for p30 delta DNA under identical conditions by the same method in the preceding paper. Decreasing the temperature from 37 to 21 degrees C yields a slightly larger value, ET = 1340 +/- 130, but the statistical significance of the increase is marginal. Attempts to determine reliable ET values for pBR322 at higher superhelix densities by ethidium binding were frustrated by the fact that good fits of the equilibrium dialysis results could not be achieved using a single value of ET. Moreover, the curves of apparent ET versus binding ratio r vary considerably from one preparation to another, and for a given preparation vary with time after cell lysis up to about seven weeks, after which they settle in to nearly reproducible behavior. The apparent ET values obtained from competitive dialysis experiments are typically rather low (ET approximately 700) for small r and nearly native superhelix density, and rise up to 1300 to 1500 with increasing binding ratio (up to r = 0.055) and decreasing negative superhelix density.(ABSTRACT TRUNCATED AT 250 WORDS)

Field experiments were conducted in summer 1992 on the Central Experimental Farm, Ottawa (45°22'N, 75°43'W) to determine whether a stem infusion technique developed for maize under controlled conditions was applicable to field‐grown maize and to evaluate whether providing sucrose in solution at silking via stem infusion altered plant source‐sink relationships sufficiently to increase kernel set. The higher and more variable evaporative demand and more difficult installation under field conditions dictated modifications to the stem infusion apparatus to prevent leakage and to facilitate assembly prior to field set‐up. A range of several field parameters were tested to identify conditions that would maximize infusion of sucrose solution: raising the syringe barrel height increased the volume of solution uptake; the largest amount of sucrose was taken up using a concentration of 150 g sucrose L‐1, and consecutive multiple infusions of the same plant increased solution uptake. Solution uptake was fou...

The interest in using crop growth simulation models for estimating large area yields in western Canada has led to a requirement for daily values of solar radiation on an historical and a real time basis. Because such data are usually not readily available, an equation was developed which relates solar transmissivity (ζ) (the ratio of incoming global solar radiation at the earth surface (Q) to solar radiation at the top of the atmosphere (Q0)) to daily observations of maximum and minimum air temperature and total precipitation (P):[Formula: see text]where a, b, c and d are empirical coefficients which vary with time of year and ΔT is the range in daily temperature extremes. During the late fall-winter period, correlation coefficients between observed and calculated transmissivities were less than 0.5 with relative large root mean square errors (RMSE). However, during the growing season when the equation would be of most use, correlation coefficients were 0.7 or higher with RMSEs of 0.12 or lower. The coefficients a, b, c and d were found not to be site-specific during the growing season. No significant differences were found between wheat yields estimated with observed solar radiation and those estimated with the calculated solar radiation from the equation. Key words: Solar radiation, transmissivity, crop growth modelling, wheat yield

Leaf area distribution determines the interception of radiation for photosynthesis. A method of analysis was developed to quantify differences in vertical leaf area distribution in a corn (Zea Mays L.) canopy. A third-order polynomial accurately described the relationship between leaf area index (LAI) and plant height (both normalized with respect to their maxima) for a range of normal and leaf licensed and experimental plant lines during the late vegetative and early grainfilling stages (r 2 ≥0.85). The shape of the polynomial reflected the bell shape of individual leaf area versus leaf number curves, with the densest leaf area in the mid-portion of the canopy (...)

Determination of reduction in leaf photosynthesis due to drought conditions is complicated by plant-to-plant variability in the progressive onset of drought stress. In this study a method of analysis was developed to quantitatively compare the reduction in leaf photosynthesis due to drought stress for an old and a new maize (Zea mays L.) hybrid introduced 30 yr apart in Ontario.Key words: Maize, leaf photosynthesis, drought stress, non-linear fitting, hybrid difference

Increased prolificacy and reduced barrenness have been identified as physiological traits in maize (Zea mays L.) hybrids that are tolerant of environmental stresses induced by high plant density. The objective of this study was to investigate ear and kernel formation under a range of plant densities in old and new hybrids. Experiments were carried out during 1987 and 1988 at two locations in Ontario with nine maize hybrids representing three decades of yield improvement in Ontario, grown at 2, 4, 8, 10, and 13 plants m -2 (.)

The vegetative development phase in summer rape (Brassica napus) is characterized by the appearance and expansion of leaves. The objectives of this research were to examine the maximum individual leaf area (LAmax), leaf expansion rate (LAX) and leaf area duration (LAD) of individual leaves as influenced by leaf position and ambient air temperature. Westar summer rape was grown from seed to maturity in controlled environment chambers set at temperatures ranging from 10 to 25 °C. Plants representing each stage of leaf development were selected at random from the population for leaf area determination. Logistic equations were used to relate the area of individual leaves to Growing Degree Days (GDD). Polynomial regression equations were used to fit curves describing the relationship between LAmax, LAX, LAD and leaf position or air temperature. As the air temperature increased the LAmax increased. LAX increased to a maximum which occurred when LAmax was at its maximum. There were no significant differences for LAX among air temperatures ranging from 13.5 to 22 °C. Mean LAX was 0.21 cm2 GDD−1. There were no significant differences in LAD due to leaf position or air temperature. Mean LAD was 140.1 GDD.Key words: Leaf area, leaf expansion rate, leaf area duration, Brassica napus

Understanding of the physiological basis for increased maize (Zea mays L.) yields over the last three decades may contribute to future genetic improvement. Recent maize production systems have tended to increase plant densities to maximize grain yield. The objective of this field study was to determine if there were changes in the response of leaf photosynthetic rates to increasing plant densities in four hybrids grown in Ontario from 1959 to 1989. The four hybrids, numbered from the oldest to most recent hybrid ((1) Pride 5, (2) United 106, (3) Pioneer 3978 and (4) Pioneer 3902) were grown at 20 000, 80 000 and 130 000 plants ha−1. Leaf photosynthetic response to irradiance (PRI) and crop growth rate (CGR) were measured near silking and during late grainfilling, leaf area index (LAI) was measured near silking and total grain yield was measured after maturity. The LAIs of recent hybrids tended to be larger than for old hybrids at comparable plant densities. Leaf photosynthetic rates declined in all hybrids at increasing densities, but the decline occurred at lower LAIs in the older hybrids. As a result, despite the higher LAIs of recent hybrids, they showed an equal or higher PRI at all plant densities. The higher PRI of recent hybrids was correlated with higher CGRs and grain yields. These results suggest that increases in optimum plant density for grain and increases in yield may be attributable, in part, to higher PRI at elevated LAIs in recent hybrids. Key words: Leaf area index, plant density, leaf photosynthesis, Zea mays L.

To investigate the interaction between two major ear-rotting pathogens, maize ears were inoculated with either Fusarium graminearum, F. moniliforme, or an equal mixture of the two. Silk and kernel tissues were periodically harvested throughout the growing season so that a time course of the experimental variables (disease severity, ergosterol content, fungal DNA content, and mycotoxin concentration) could be recorded. Over the 3 years tested (1992 to 1994), the highest levels of disease and ergosterol were found in the F. graminearum treatment, followed by the mixture treatment (F. graminearum plus F. moniliforme) and, finally, the F. moniliforme treatment. Kernel ergosterol content and disease rating were correlated for both pathogens, but the highest correlation coefficients were obtained in the F. graminearum treatment. The DNA analysis revealed that, in the mixed inoculum, F. moniliforme had a greater growth rate than did F. graminearum. In 1994, appreciable F. moniliforme from natural inoculum was found in the F. graminearum treatment. Fumonisin B1 levels did not differ between the F. moniliforme treatment and the mixed inoculum treatment. The effect of temperature on the growth rate of the two species explained some of the field results, with temperatures in the silks being more favorable to F. moniliforme. Data on the growth rate on silks obtained by the incorporation of radiolabeled precursor to ergosterol demonstrated that F. graminearum was able to grow well at 26 to 28°C, whereas F. moniliforme grew well over a broader range, including at higher temperatures.

A physically-based model is described which calculates hard red spring wheat yields for the Canadian prairies given daily weather parameters. The model uses a simple resistance analog to calculate plant water stress and a nonlinear response factor for temperature effects. Yield data on a large area (crop district) basis were used both for calculating coefficients in the model with a nonlinear least squares algorithm and for verification purposes. Weather effects were separated from technological trends using multiplicative and additive non-linear time functions. The model with the additive time trend produced smaller standard errors of estimate (SEE) on all soil types; SEEs between actual and calculated yield averaged 157, 225 and 253 kg ha−1 for the Brown, Dark Brown, and Black soil zones respectively using the additive time trend. Use of the model for predictive purposes is discussed.Key words: Time trends, nonlinear fitting, physical model, crop district scale

Mathematical models of hard red spring wheat (Triticum aestivum L.) were used to account for effects of weather on annual variations in yield and protein content on the Canadian prairies. When weather effects were calculated, other relatively slow-changing trends became much clearer. Results indicate that yields in the three major soil zones have increased an average of 806 kg ha−1, while protein contents have decreased (1.0% from 1961 to 1982). Both trends show the largest change at the beginning of the period (1961) with a levelling off at the end (1982). There seems to be an inverse relationship between yield and protein, with technology contributing to yield increases and at the same time decreasing protein content by dilution although this was not conclusively proved. Decreases in soil organic matter or other soil factors may be contributing to the protein decline but these factors were not required to explain the observed patterns in yield and percent protein. The results indicated that the potential to produce high protein wheats has decreased during the period 1961–1982.Key words: Nonlinear fitting, physical model, technology effects, protein dilution

Measurement of crop canopy light interception data is labor intensive and time consuming, particularly when multi–strata light measurements are required. Different approaches have been used to measure canopy light interception in the field. The use of a manually operated light–bar or multiple light–bars mounted on stationary devices and connected to a datalogger is costly and relatively inflexible. Difficulties with these approaches have led us to develop a portable prototype system for multi–strata measurement of light interception. The ability of the devices to take accurate simultaneous multi–strata canopy light interception measurements was tested on field–grown corn plants produced under a range of N fertilization levels with: (1) hybrids exhibiting a wide range of canopy architectures, and (2) different planting patterns. The device allowed accurate and instantaneous measurement of crop canopy light interception at various depths, allowing calculation of percent light transmitted at various canopy strata. The prototype system could hold up to six 1–m long light–bars, thus simultaneously collecting data at six canopy levels. The prototype showed accurate measurements of light interception in as little as 25% of the time required for a single manually operated light–bar.

Recently, corn ( Zea mays L.) hybrids accumulating more leaf area above the ear, maturing earlier, yielding better in narrower row spacings and tolerating higher population densities than conventional hybrids have been developed. However, no research has been conducted to assess their ability to compete with weeds. The objective of this study was to quantify morphological and grain yield responses of hybrids with differing canopy architectures to the presence and absence of weeds. Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec and in 1996 at Ottawa, Ontario. Three hybrids, leafy reduced-stature (LRS), late maturing big leaf (LMBL), and conventional Pioneer 3979 (P3979), were evaluated at two population densities (normal and high), row spacings (38 and 76 cm) and weed pressure levels (weed-free and weedy). Weed pressure reduced the plant height of LRS less (only 4 cm) than the tall hybrids (average reduction of 26 cm). The overall grain yield of the LMBL hybrid was much greater (12.7 mg ha −1 ) than the LRS (9.6 mg ha −1 ) and P3979 (11.0 mg ha −1 ) hybrids in the absence, but not in the presence (LRS, 6.5; LMBL, 6.7; and P3979, 6.8 mg ha −1 ), of weeds. The yield of early-maturing LRS and P3979 (especially LRS) hybrids, were least affected by weed pressure, suggesting better tolerance of, and competition with, weeds. However, further research with more LRS hybrids is needed, as is the development of better yielding LRS hybrids, before they can be recommended over conventional hybrids.