Paul Hadley

Bio: Paul Hadley is an academic researcher from University of Reading. The author has contributed to research in topics: Germplasm & Theobroma. The author has an hindex of 39, co-authored 150 publications receiving 4614 citations. Previous affiliations of Paul Hadley include University of Adelaide.

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Abstract: Winter wheat (Triticum aestivum L. cv. Hereward) was grown in the field inside polyethylene-covered tunnels at a range of temperatures at either 380 or 684 μmol mol -1 CO 2 . Serial harvests were taken from anthesis until harvest maturity. Grain yield was reduced by warmer temperatures, but increased by CO 2 enrichment at all temperatures. During grain-filling, individual grain dry weight was a linear function of time from anthesis until mass maturity (attainment of maximum grain dry weight) within each plot. The rate of progress to mass maturity (the reciprocal of time to mass maturity) was a positive linear function of mean temperature, but was not affected by CO 2 concentration. The rate of increase in grain dry weight per ear was 2.0 mg d -1 greater per 1 °C rise, and was 8.0 mg d -1 greater at 684 compared with 380 μmol mol -1 CO 2 at a given temperature. The rate of increase in harvest index was 1.0% d -1 in most plots at 380 μmol mol -1 CO 2 and in open field plots, compared with 1.18% d -1 in all plots at 684 μmol mol -1 CO 2 . Thus, the increased rate of grain growth observed at an elevated CO 2 concentration could be attributed partly to a change in the partitioning of assimilates to the grain. In contrast, the primary effect of warmer temperatures was to shorten the duration of grain-filling. The rate of grain growth at a given temperature and the rate of increase in harvest index were only independent of the number of grains per ear above a critical grain number of 23-24 grains per ear (∼20 000 grains m -2 ).

Growth and yield of winter wheat (Triticum aestivum) crops in response to CO2 and temperature.

Abstract: Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at either c. 350 or 700 μmol mol -1 CO 2 in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45 % greater at elevated CO 2 in the first year due to more tillers, and was 30 % greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO 2 treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6-31% greater at elevated compared with normal CO 2 and was also affected by a positive interaction between temperature and CO 2 in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO 2 concentrations. A 7-44 % greater seed dry weight at elevated CO 2 in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72 % at elevated CO 2 , because grain numbers per ear did not decline with an increase in temperature at elevated CO 2 . Grain numbers were reduced by temperatures > 31°C immediately before anthesis at normal atmospheric CO 2 in 1992/93, and at both CO 2 concentrations in 1991/92. To quantify the impact of future climates of elevated CO 2 concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO 2 and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO 2 concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO 2 doubling are offset by an increase in mean seasonal temperature of only 1.0 °C to 1.8 °C in the UK.

Low relative humidity triggers RNA-directed de novo DNA methylation and suppression of genes controlling stomatal development

Abstract: Environmental cues influence the development of stomata on the leaf epidermis, and allow plants to exert plasticity in leaf stomatal abundance in response to the prevailing growing conditions. It is reported that Arabidopsis thaliana ‘Landsberg erecta’ plants grown under low relative humidity have a reduced stomatal index and that two genes in the stomatal development pathway, SPEECHLESS and FAMA, become de novo cytosine methylated and transcriptionally repressed. These environmentally-induced epigenetic responses were abolished in mutants lacking the capacity for de novo DNA methylation, for the maintenance of CG methylation, and in mutants for the production of short-interfering non-coding RNAs (siRNAs) in the RNA-directed DNA methylation pathway. Induction of methylation was quantitatively related to the induction of local siRNAs under low relative humidity. Our results indicate the involvement of both transcriptional and post-transcriptional gene suppression at these loci in response to environmental stress. Thus, in a physiologically important pathway, a targeted epigenetic response to a specific environmental stress is reported and several of its molecular, mechanistic components are described, providing a tractable platform for future epigenetics experiments. Our findings suggest epigenetic regulation of stomatal development that allows for anatomical and phenotypic plasticity, and may help to explain at least some of the plant’s resilience to fluctuating relative humidity.

Effect of Temperature

Abstract: A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

The effect of drought and heat stress on reproductive processes in cereals.

Abstract: As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.