Rate Of Phenological Development Research Articles

An empirical and a dynamic-empirical model for the estimation of maize seedbed temperature

Soil temperature is the main factor in determining the germination of maize seeds and the emergence time of the crop. It controls the rate of phenological development while the meristem is underground, which is until the V6 (six leaf collar) stage of maize. The research performed by the authors aimed to model maize seedbed temperatures at sowing depth (soil temperature at 5 cm depth) during the sowing-emergence-early development period. The research is based on measurements in ploughed plots of the maize experiments at the Látókép Experiment Site of the University of Debrecen (Eastern Hungary) in two growing seasons of 2021–2022. Two types of empirical models were established, a multilinear regression model (M1) and a dynamic-empirical model (M2), where the daily increase and decrease of soil temperature are determined by multilinear regression. Candidates for input variables for both models were various, easily available daily meteorological parameters. M2 model performed better than M1 when applied to an independent database of 2022. This is particularly valid for the maximum and minimum soil temperatures. It was found that both M1 and M2 can be used to predict the soil temperature of the maize seedbed before shading by the plants. For daily mean temperature, M1 and M2 give a similarly good estimation, while the dynamic-empirical model has to be preferred for the maximum and minimum temperatures. M2, which is based on daily temperature, global radiation and wind speed data, predicts the daily mean (RMSE = 1.4 °C), maximum (RMSE = 2.2 °C), and minimum (RMSE = 1.6 °C) of seedbed temperature not worse than many earlier soil temperature models do, even hybrid or mechanistic ones with a large number of parameters.

Model-based climate change adaptational potential and productivity of some cowpea genotypes and its sensitivity to bias adjustment

Grain legumes are essential for the protein supply to an ever-growing population in Africa. However, little is known about the adaptational potential and thus resilience to abiotic stress of major grain legumes under future climatic change for the evaluation of climate change impact and adaptation. This study assessed the adaptation potential of some cowpea genotypes to future climate change in the moist (Kumasi—Ghana) and dry savanna (Ouagadougou—Burkina Faso) biomes of West Africa based on a validated process-based SIMPLACE model using the output of four global circulation models (GCMs) for two shared socioeconomic pathways (SSPs, i.e., ssp126 and 585). In addition, it assesses the sensitivity of the cowpea model to bias corrections of the GCM outputs. In comparison of future socioeconomic pathways with historic time series, the use of bias-corrected climate model output slightly increased the rate of the phenological development of the genotypes in the future period except in Ouagadougou, in the ssp585 scenario. Without bias correction, this increase of the rate of phenological development in the future scenarios was less pronounced. With bias correction, the total aboveground biomass and yield of all genotypes were reduced in both SSPs. The change in the average water stress and phosphorous stress were genotype specific. Despite a general yield decline in both SSPs, the genotypes Asontem and GH6060 exhibited the adaptational potential to future climate change in the moist and dry savanna biomes. This is by a higher accumulation of total aboveground biomass, higher yield, and tolerance to high temperature as well as high water use and photosynthetic efficiency due to higher atmospheric carbon dioxide concentrations, despite faster phenological development.

The contrasting role of climate variation on the population dynamics of a native and an invasive insect pest.

Since 2008, spotted-wing drosophila, Drosophila suzukii, has become a major pest of soft, thin-skinned fruits in the USA, causing significant annual yield losses. Historically, the native blueberry maggot fly, Rhagoletis mendax, has been a key blueberry pest in eastern North America and a driver of insecticide usage. After its invasion in 2011 into New Jersey (USA), D. suzukii has supplanted R. mendax as the main target of insecticide applications in the state. However, the impact of D. suzukii on the native R. mendax has not been documented, particularly in relation to local climate. Historical monitoring data from New Jersey blueberry farms were used to assess the role of climate on R. mendax and D. suzukii populations. Seasonal trap captures of R. mendax adults have decreased after D. suzukii invasion, while D. suzukii trap captures have increased. Similarly, D. suzukii first captures have occurred earlier each year, while R. mendax has been captured later in the growing season. Winter freezing and summer growing degree days were found to significantly correlate with D. suzukii activity. Using downscaled climate simulations, we projected that D. suzukii will arrive in New Jersey blueberry fields up to 5 days earlier on average by 2030 and 2 weeks earlier by 2050 with warming temperatures, exacerbating yield losses and insecticide usage. As regional temperatures are projected to warm and the invasive range continues to expand, we predict the rate of phenological development of the invasive D. suzukii and its impact on native insects to change noticeably, bringing new challenges for pest management strategies.

A comparison of soybean maturity groups for phenology, seed yield, and seed quality components between eastern Ontario and southern Manitoba

The expansion of soybean [ Glycine max (L.) Merr.] production onto the Canadian Prairies has resulted in new environmental constraints that affect soybean phenology, seed yield, and seed quality. This study examined these factors for 10 soybean cultivars differing in maturity group (MG) rating from 000.9 to 1.3 in southern Manitoba (MB) and eastern Ontario (ON). Detailed climate and phenological data collected at both locations were used to explore the environmental factors and differences in measurements among MG and between locations. In MB, more time was spent in vegetative growth and less time developing flowers and seeds than in ON. The longer vegetative growth stage in MB resulted in more leaves produced on the main stem at flowering than in ON. The leaf appearance rate was consistent between locations and the rate of phenological development in the vegetative stage was greater in ON because of its warmer mean temperature and shorter photoperiod. In MB, seed yield was positively correlated with precipitation in all growth stages and had a strong correlation with precipitation during reproductive development. In ON, increasingly warmer temperatures during reproductive development had the greatest influence on seed yield, particularly in the seed development stage. This study is a baseline for soybean phenology, seed yield, and seed quality components for early MG and will aid in the optimization of soybean breeding and production in the Canadian Prairies.

Interactions of Spring Cereal Genotypic Attributes and Recovery of Grain Yield After Defoliation.

Dual-purpose crops are grazed during their vegetative phase and allowed to regrow to produce grain. Grazing slow-developing winter cereals (wheat, barley, and triticale) is common, but there is also potential to graze faster-developing spring cereals used in regions with shorter-growing seasons. Defoliation in faster-developing genotypes has risks of larger yield penalties, however, little is known about genotypic characteristics that may improve recovery after grazing. Four experiments examined 7 spring wheat and 2 barley cultivars with differing physiological attributes (phenological development rate, putative capacity to accumulate soluble carbohydrates, and tillering capacity) that may influence the capacity of spring wheat to recover after defoliation. Defoliated and undefoliated crops were compared to assess physiological differences between cultivars including recovery of biomass, leaf area and radiation interception at anthesis, and subsequent crop grain yield and yield components. All genotypes had similar responses to defoliation treatments indicating that the physiological attributes studied played little part in mitigating yield penalties after defoliation. Despite some differences in yield components amongst cultivars, defoliation did not adversely affect cultivars with different yield component combinations under non-water limited conditions. Later and intense defoliation (around GS30/31) resulted in large yield penalties (40%) which reduced both grain number and kernel mass. However, earlier defoliation (before GS28) induced small or insignificant yield penalties. Defoliation often reduced canopy radiation interception and crop biomass at anthesis but this rarely translated into large yield penalties. These studies further demonstrate that shorter season spring cereals can provide valuable forage (up to 1.2 t DM/ha) for grazing during early vegetative growth without inducing large yield penalties. This study suggests that beyond appropriate phenology, there were no other specific characteristics of cultivars that improved the recovery after grazing. Hence farmers don’t need specific dual-purpose cultivars and can still focus on those that optimize grain yield potential for a particular environment and sowing date. The timing and intensity of defoliation appear to be larger drivers of yield recovery in spring cereals and better understanding of these relationships are needed to provide grazing management guidelines that mitigate risk of yield penalties in dual-purpose cereal crops.

Variation in rate of phenological development and morphology between red clover varieties: Implications for clover proportion and feed quality in mixed swards

AbstractRed clover (Trifolium pratense) grown in mixtures with grasses often constitutes a lower proportion of total yield in spring than in summer growth. A more even red clover proportion between the harvests would benefit forage quality and management at feeding. We investigated whether inclusion of early versus late‐maturing red clover varieties could reduce this disproportionality. In a two‐year field trial harvested three times per season, each of six red clover varieties was grown in two grass mixtures. Rate of phenological development did not differ during spring growth, but did so in regrowth after first and second cuts. Here, the earliest varieties constituted the highest proportion. At all harvests, the early varieties had lower crude protein concentrations and a higher content of neutral detergent fibre (NDF) and indigestible NDF than the late varieties. Clover proportion was higher in swards with a mixture of timothy and meadow fescue than in swards with perennial ryegrass during the first year and lower in the second year. It is concluded that developmental rate should be explored further as a key character for red clover competiveness in spring growth of rapidly elongating grasses.

Quantitative Trait Loci Associated with Phenological Development, Low-Temperature Tolerance, Grain Quality, and Agronomic Characters in Wheat (Triticum aestivum L.).

Plants must respond to environmental cues and schedule their development in order to react to periods of abiotic stress and commit fully to growth and reproduction under favorable conditions. This study was initiated to identify SNP markers for characters expressed from the seedling stage to plant maturity in spring and winter wheat (Triticum aestivum L.) genotypes adapted to western Canada. Three doubled haploid populations with the winter cultivar ‘Norstar’ as a common parent were developed and genotyped with a 90K Illumina iSelect SNP assay and a 2,998.9 cM consensus map with 17,541 markers constructed. High heritability’s reflected large differences among the parents and relatively low genotype by environment interactions for all characters considered. Significant QTL were detected for the 15 traits examined. However, different QTL for days to heading in controlled environments and the field provided a strong reminder that growth and development are being orchestrated by environmental cues and caution should be exercised when extrapolating conclusions from different experiments. A QTL on chromosome 6A for minimum final leaf number, which determines the rate of phenological development in the seedling stage, was closely linked to QTL for low-temperature tolerance, grain quality, and agronomic characters expressed up to the time of maturity. This suggests phenological development plays a critical role in programming subsequent outcomes for many traits. Transgressive segregation was observed for the lines in each population and QTL with additive effects were identified suggesting that genes for desirable traits could be stacked using Marker Assisted Selection. QTL were identified for characters that could be transferred between the largely isolated western Canadian spring and winter wheat gene pools demonstrating the opportunities offered by Marker Assisted Selection to act as bridges in the identification and transfer of useful genes among related genetic islands while minimizing the drag created by less desirable genes.

Increased Temperatures Have Dramatic Effects on Growth and Grain Yield of Three Maize Hybrids

Core Ideas Projected Corn Belt temps by the end of the 21st century increase the rate of phenological development. Temperature increases reduce grain production but not vegetative production. There were differences in corn hybrid response to yield impacts. Rising temperatures under climate change are projected to have negative impacts on crop growth and production. These conclusions are not based on direct observations but on projected model results. A study conducted comparing normal seasonal temperatures (1980–2010) for Ames, IA, to a normal + 4°C environment with the same water vapor deficit evaluated the impacts of temperature on maize (Zea mays L.) development and production. The rate of phenological development increased at higher temperatures; however, the relationship of leaf collar and leaf tip appearance to growing degree days was the same between temperature regimes. There was no effect on total leaf area or vegetative dry matter production, but grain yields decreased from 84 to 100% because of exposure to high nighttime temperatures and disruption of the pollination process as evidenced by the large reduction in kernels per ear. Projected increases in temperature will negatively affect grain production and threaten food security.

Temperature extremes: Effect on plant growth and development

Temperature is a primary factor affecting the rate of plant development. Warmer temperatures expected with climate change and the potential for more extreme temperature events will impact plant productivity. Pollination is one of the most sensitive phenological stages to temperature extremes across all species and during this developmental stage temperature extremes would greatly affect production. Few adaptation strategies are available to cope with temperature extremes at this developmental stage other than to select for plants which shed pollen during the cooler periods of the day or are indeterminate so flowering occurs over a longer period of the growing season. In controlled environment studies, warm temperatures increased the rate of phenological development; however, there was no effect on leaf area or vegetative biomass compared to normal temperatures. The major impact of warmer temperatures was during the reproductive stage of development and in all cases grain yield in maize was significantly reduced by as much as 80−90% from a normal temperature regime. Temperature effects are increased by water deficits and excess soil water demonstrating that understanding the interaction of temperature and water will be needed to develop more effective adaptation strategies to offset the impacts of greater temperature extreme events associated with a changing climate.

Phenomorphological Characterization of Vegetable Soybean Germplasm Lines for Commercial Production

ABSTRACTGrowing demand for vegetable soybean [Glycine max (L.) Merr.] has renewed interest in producing the crop in the United States, a significant importer of vegetable soybean despite being the world's largest producer and exporter of grain‐type soybean. Field studies were conducted over 3 yr to(i) compare phenomorphological traits of vegetable and grain‐type soybean and (ii) identify candidate lines for vegetable soybean production in the North Central United States, the nation's leading soybean‐producing region. A total of 136 vegetable soybean entries from 22 sources were compared to 14 grain‐type cultivars representing a range of maturity groups. Germination and emergence of vegetable soybean were poorer than grain‐type entries. Seedling growth traits and rate of phenological development were higher in vegetable soybean. However, by the time of crop harvest (i.e., R6 growth stage), vegetable soybean produced shorter, smaller plants than grain‐type soybean. Seed mass accounted for some of the variation in emergence and seedling traits. Filtering entry responses by criteria essential to viable commercial production, including a sensory evaluation, 12 entries from eight seed sources were identified as the most promising candidate lines for use in the North Central United States. By comparing vegetable soybean responses to grain‐type soybean, this work puts into perspective the agronomic performance of vegetable soybean germplasm available to growers in the United States and points to specific areas of future research and crop development.

Phenological development of East African highland banana involves trade-offs between physiological age and chronological age

The phenology of East African highland banana (Musa acuminata AAA-EA, hereafter referred to as ‘highland banana’) is poorly understood. We tested three hypotheses: (1) the physiological age at flowering is independent of site effects, (2) there is no difference in threshold size at flowering between sites with different growth potential, and (3) morphological and physiological components of highland banana relative growth rate (RGR) contribute equally to mitigate growth reduction in response to limiting supply of water, K or N. The physiological age of highland banana plants from field trials at Kawanda (central Uganda) and Ntungamo (south-western Uganda) was computed from daily temperature records. Growth analysis was conducted using RGR, net assimilation rate (NAR), specific leaf area (SLA) and leaf mass ratio (LMR) estimated from allometry. Growth response coefficients were used for quantifying the relative contribution of NAR, SLA and LMR to RGR. Physiological age at flowering was delayed by 739°Cd at Kawanda compared with that at Ntungamo whose chronological age at flowering was in turn 51d older. At both sites a threshold total dry mass of 1.5kg per plant was required for flowering. Faster absolute growth rate and NAR fostered by wet conditions, K input and cooler temperatures enabled plants at Ntungamo to attain the threshold total dry mass sooner than those at Kawanda, hence the phenotypic plasticity in age at flowering. Net assimilation rate contributed at least 90% to RGR increase due to wet conditions at both sites. The contribution of NAR to RGR increase in response to K at Kawanda reduced to 38% while that for SLA increased to 49%. Net assimilation rate contributes more to highland banana RGR modulation than SLA except when warmer conditions reduce NAR. Differences in crop growth rate cause phenotypic plasticity in highland banana rate of phenological development.

Identification of genomic regions determining the phenological development leading to floral transition in wheat (Triticum aestivum L.)

Autumn-seeded winter cereals acquire tolerance to freezing temperatures and become vernalized by exposure to low temperature (LT). The level of accumulated LT tolerance depends on the cold acclimation rate and factors controlling timing of floral transition at the shoot apical meristem. In this study, genomic loci controlling the floral transition time were mapped in a winter wheat (T. aestivum L.) doubled haploid (DH) mapping population segregating for LT tolerance and rate of phenological development. The final leaf number (FLN), days to FLN, and days to anthesis were determined for 142 DH lines grown with and without vernalization in controlled environments. Analysis of trait data by composite interval mapping (CIM) identified 11 genomic regions that carried quantitative trait loci (QTLs) for the developmental traits studied. CIM analysis showed that the time for floral transition in both vernalized and non-vernalized plants was controlled by common QTL regions on chromosomes 1B, 2A, 2B, 6A and 7A. A QTL identified on chromosome 4A influenced floral transition time only in vernalized plants. Alleles of the LT-tolerant parent, Norstar, delayed floral transition at all QTLs except at the 2A locus. Some of the QTL alleles delaying floral transition also increased the length of vegetative growth and delayed flowering time. The genes underlying the QTLs identified in this study encode factors involved in regional adaptation of cold hardy winter wheat.

Interactions among factors regulating phenological development and acclimation rate determine low-temperature tolerance in wheat.

Exposure to low temperatures (LT) produces innumerable changes in morphological, biochemical and physiological characteristics of plants, with the result that it has been difficult to separate cause and effect adjustments to LT. Phenotypic studies have shown that the LT-induced protective mechanisms in cereals are developmentally regulated and involve an acclimation process that can be stopped, reversed and restarted. The present study was initiated to separate the developmental factors determining duration from those responsible for rate of acclimation, to provide the opportunity for a more in depth analysis of the critical mechanisms that regulate LT tolerance in wheat (Triticum aestivum). The non-hardy spring wheat cultivar 'Manitou' and the very cold-hardy winter wheat cultivar 'Norstar' were used to produce reciprocal near-isogenic lines (NILs) in which the vrn-A1 (winter) alleles of 'Norstar' were inserted into the non-hardy 'Manitou' genetic background and the Vrn-A1 (spring) alleles of 'Manitou' were inserted in the hardy 'Norstar' genetic background so that the effects of duration and rate of LT acclimation could be quantified. Comparison of the acclimation curves of the NILs and their parents grown at 2, 6 and 10 degrees C established that the full expression of LT-induced genetic systems was revealed only under genotypically dependent optimum combinations of time and temperature. Both duration and rate of acclimation were found to contribute significantly to the 13.8 degrees C difference in lowest survival temperature between 'Norstar' and 'Manitou'. Duration of LT acclimation was dependent upon the rate of phenological development, which, in turn, was determined by acclimation temperatures and vernalization requirements. Rate of acclimation was faster for genotypes with the 'Norstar' genetic background but the ability to sustain a high rate of acclimation was dependent upon the length of the vegetative stage. Complex time/temperature relationships and unexplained genetic interactions indicated that detailed functional genomic or phenomic analyses of natural allelic variation will be required to identify the critical genetic components of a highly integrated system, which is regulated by environmentally responsive, complex pathways.

EVOLUTIONARY POTENTIAL OF CHAMAECRISTA FASCICULATA IN RELATION TO CLIMATE CHANGE. II. GENETIC ARCHITECTURE OF THREE POPULATIONS RECIPROCALLY PLANTED ALONG AN ENVIRONMENTAL GRADIENT IN THE GREAT PLAINS

Climate change will test the evolutionary potential of populations. Information regarding the genetic architecture within and among populations is essential for prediction of evolutionary outcomes. However, little is known about the distribution of genetic variation for relevant traits in natural populations or alteration of genetic architecture in a changing environment. In this study, pedigreed families from three populations of the annual prairie legume Chamaecrista fasciculata were reciprocally transplanted in three environments across a broad latitudinal range in the Great Plains. The underlying premise of this work is that northern populations will in the future experience climates similar to current-day climates further south. Estimates of narrow-sense heritability ranged from 0.053 to 0.481, suggesting the potential for evolutionary change is possible for most traits. In general, the northern population harbored less genetic variation and had lower heritability for traits than the southern population. This population also experienced large reductions in fitness, as measured by estimated lifetime fecundity, when raised in either the intermediate or the southern climate, whereas the difference between the intermediate and southern population was less extreme. For fecundity, the pattern of cross-environment additive genetic correlations was antagonistic to evolutionary change in four of six cases when native and nonnative sites were compared. Six additional antagonistic positive correlations were found for the rate of phenological development and leaf thickness. Overall, the data suggest that if climate changes as predicted, the northern population will face a severe evolutionary challenge in the future because of low heritabilities, cross-environment genetic correlations antagonistic to selection, and demographic instability due to lower seed production in a hotter and drier climate.

Developmental traits affecting low-temperature tolerance response in near-isogenic lines for the Vernalization locus Vrn-A1 in wheat (Triticum aestivum L. em Thell).

Investigation of low-temperature (LT) tolerance in cereals has commonly led to the region of the vyn-A1 vernalization gene or its homologue in related genomes. Two cultivars, one a non-hardy spring wheat and one a very cold-hardy winter wheat, whose growth habits are determined by the Vrn-A1 (spring habit) and vrn-A1 (winter habit) alleles, were chosen to produce reciprocal near-isogenic lines (NILs). These lines were then used to determine the relationship between rate of phenological development and the degree and duration of LT tolerance gene expression. Each allele was isolated in the genetic backgrounds of the non-hardy spring wheat 'Manitou' and the very cold-hardy winter wheat 'Norstar'. The effects of each allele on phenological development and low-temperature tolerance (LT50) were determined at regular intervals over a 4 degrees C acclimation period of 0-98 d. The vegetative/reproductive transition, as determined by final leaf number (FLN), was found to be a major developmental factor influencing LT tolerance. Possession of a vernalization requirement increased both the length of the vegetative growth phase and LT tolerance. Similarly, increased FLN in spring Norstar and winter Manitou NILs delayed their vegetative/reproductive transition and increased their LT tolerance relative to Manitou. Although the winter Manitou NILs had a lower FLN than the spring Norstar NILs, they were able to extend their vegetative stage to a similar length by increasing the phyllochron (interval between the appearance of successive leaves). Cereal plants have four ways of increasing the length of the vegetative phase, all of which extend the time that low-temperature tolerance genes are more highly expressed: (1) vernalization; (2) photoperiod responses; (3) increased leaf number; and (4) increased length of the phyllochron.

Photoperiod and Temperature Responses in Early‐Maturing, Near‐Isogenic Soybean Lines

While photoperiod responses have been studied in soybean [Glycine max (L.) Merr.] isolines, identification of temperature and photo–thermal responses are lacking in early‐maturing soybean. This study was conducted to quantify photoperiod and temperature responses of early‐maturing soybean. Six ‘Harosoy’ isolines with different combinations of alleles at the E1, E3, E4, and E7 loci were grown in growth cabinets with 10‐, 12‐, 14‐, 16‐, and 20‐h photoperiods and with either 18 or 28°C constant temperature. Under the most inductive conditions (10 and 12 h, 28°C), all isolines flowered in about 26 d. Under the least inductive conditions (20 h, 28°C), there was a 50 d difference in flowering time between the early‐ and late‐flowering isolines. Interestingly, the late‐flowering isolines flowered earlier under cool than under warm temperatures. A mathematical model was developed to quantify the effects of temperature and photoperiod on days to first flower. This model related the rate of phenological development from planting to flowering to temperature, photoperiod and the interaction between temperature and photoperiod. The equation was integrated analytically, resulting in an inverse time (1/time) equation, or numerically resulting in the development of a Growing Photothermal Day (GPTD) similar to a heat unit. The model had a base temperature (5.8°C) below which the rate of phenological development was zero, a critical or base photoperiod (13.5 h) below which photoperiod had no effect, and two genetic coefficients, one of which varied with isoline. The isoline photoperiod sensitivity coefficient was linearly related to the number of dominant (late flowering, photoperiod sensitive) alleles. The model fit the observed data well (R2 = 0.96).

Germination, Growth, and Development of Herbicide Resistant and Susceptible Populations of Rigid Ryegrass (Lolium rigidum)

Rate of seedling emergence, relative growth rate (RGR), and phenological development were compared in several accessions of rigid ryegrass belonging to three distinct resistance classes. The aryloxyphenoxypropionate resistant (AOPP-R) class had a faster and less variable seedling emergence than the sulfonylurea resistant (SU-R) and susceptible (S) classes. However, even the fastest of the AOPP-R accessions was within the range of the S and SU-R classes. No significant differences were detected among the resistant classes in seed dormancy, RGR, and the rate of phenological development. The rate of spike emergence, irrespective of the resistance class, was related to the latitude of the origin of the accessions, suggesting adaptation to the local climates since introduction. Due to considerable variation among weed populations for most biological attributes, the need to include several R and S accessions, in studies similar to the one reported here, is of vital importance. Because of the means and variances of the three resistance classes, at least four accessions from each resistance class would have been required to detect the observed differences between emergence rates of the AOPP-R and S classes with a confidence of 95%.

Photosynthetic and Respiratory Characteristics of Peanut Cultivars Adapted to Varying Night Temperatures1

Abstract Relatively mild night temperatures can reduce leaf carbon dioxide exchange rates (CER) and dry matter (DM) accumulation in peanut (Arachis hypogaea L.). To investigate differences among cultivars in response to long-term exposure to a range of night temperatures, three peanut cultivars (OAC Ruby, Chico, and Early Bunch) with known differences in chilling sensitivity were grown in controlled-environment cabinets at the University of Guelph, Ontario. Effects of long-term exposure to night temperatures from 9 to 20 C were assessed in terms of leaflet and whole plant CER, DM accumulation, and phenological development. Effects of night temperature on rate of phenological development and DM accumulation were consistent with differences in accumulation of degree-days. Cultivars did not differ in daytime leaf CER response to all night temperatures except 9 C, at which CER for OAC Ruby was higher than for Early Bunch or Chico. CER in the 9 C treatment was 92% of the CER at 20 C for OAC Ruby and 80% for Early Bunch and Chico. Continuous exposure to night temperatures of 10C reduced CER sensitivity to low daytime temperature in OAC Ruby, but Early Bunch was unaffected. Specific respiration rates were higher for plants of OAC Ruby than Early Bunch in the 10 C treatment, with indications that these differences were due to increased maintenance requirements. The ability of OAC Ruby to adapt to cool-night conditions may have a significant impact on crop performance in cooler environments.

Forecasting flowering dates of lawn species with air temperature: Application boundaries of the linear approach

A modelling analysis was performed on the phenological data collected for three years in a lawn located at the Operational Meteorological Centre of S. Pietro Capofiume, Bologna, Italy. The data concern the flowering of up to 56 wild species and were taken according to a seven-stage phenological key. The analysis was performed in order to verify the predictive limits of the degreeday model, an approach assuming a linear functional relationship between air temperature and the rate of phenological development. The procedure we followed consists in the heuristic assessment of the three parameters characterizing the linear model, that is the starting date before which the temperature has no influence on the anthesic development, the base temperature, and the temperature sum. With that in mind, we determined the temperature sums for all the pairs of parameter values taken in the range (− ÷ 15° C) for base temperatures, and in the range (January Im ÷ flowering date) for starting dates. Not all the species examined produced stable parameter sets but a test of the latter against independent data showed data, where applicable, the linear approach provides a reliable forecasting tool. The linear approach was also applied in order to determine the existence of leading species, that is species whose flowering dates could represent the staring date of temperature accumulation in order to forecast the flowering date of later species. In this case the determination of base temperatures and temperature sums derives from the assumption that when the leading species attains flowering the predicted one has reached an unknown but fixed fraction of its own phenological development. We applied this procedure to all the possible pairs of species and in this case the stability test produced a drastic selection among them.

Maize hybrid response to tillage under irrigated and dryland conditions

The popularity of reduced-tillage cropping systems has emphasized the need to determine if maize ( Zea mays L.) developed under conventional tillage systems (moldboard plow, disk, and harrow) is readily adaptable to conservation production systems (greater than 30% residue cover after planting). Past research has indicated that crops grown under conservation production systems are subjected to cooler and wetter soil conditions than crops grown with conventional tillage practices. Information is needed to determine if a significant interaction exists between tillage and hybrid in maize. Field experiments were conducted in 1982 and 1983 near Lincoln, Nebraska, U.S.A., on an Abruptic Argiaquoll and in 1983 near Gothenburg, Nebraska, U.S.A., on a Typic Haplustoll under dryland and irrigated conditions, respectively, to evaluate the response of eight hybrids to several tillage practices. Tillage practices studied were moldboard plow, tandem disk, and no-tillage. Tillage practice had a significant effect on only plant emergence at Lincoln during 1983 and dry matter production at Lincoln in 1982 and Gothenburg in 1983. Hybrids differed in plant population at harvest, rate of phenological development, leaf area and dry matter production, and grain yield. A significant tillage × hybrid interaction was observed for dry-matter production at the tasseling stage at Lincoln during 1983; however, no significant interactions were observed for grain-yield among the hybrids and tillage systems investigated. Results indicate that for the adapted hybrids tested, relative grain-yield comparisons will be maintained with both conservation and conventional tillage practices.