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A series of field experiments were undertaken at three locations in Khyber PukhtunKhwa (KPK) Province, Pakistan to assess the effects of low temperatures and phytohormone applications on chickpea ( Cicer arietinum L.) growth and yield. These trials showed that ABA application (10 −4 M) to 40-day-old plants (before the first seasonal frost) offset low temperature-induced growth and yield depression at harvest (200-day-old plants) by up to 17%. These yield improvements were mainly due to an increase in the number of seeds pod −1 . Growth room experiments were carried out under controlled environmental conditions to establish how foliar application of 10 −4 M ABA to 40-day-old plants might improve seed production at harvest. The foliar application of 10 −4 M ABA had no detectable effect on endogenous shoot or root ABA levels four-days after spraying or on biomass when plants were maintained in warm conditions. When exposed to night temperatures of −2 °C, however, the endogenous ABA levels increased dramatically in both control and ABA-treated plants, but this rise was more rapid after ABA application ( p p

Robust calibration of phenological models requires long term field observations, which are not always available or sufficiently widespread. This has motivated the evaluation of short-term experiments using cuttings under semi-controlled conditions as an alternative data source. Single-node cuttings from two grapevine cultivars were exposed to variable chilling durations and allowed to sprout in a growth room. The observed budburst dates and temperature series were used to calibrate two budburst models, which were validated against a 39-year field observation dataset by means of a fuzzy-logic based integrated index (FI). Satisfying validation scores were obtained, ranging from 0.262 to 0.411 on a 0-1 scale (best-worst response). The experiment was then inverted, using field data for calibration and cuttings for validation, and FI scores ranging between 0.352 and 0.495 were obtained. On this occasion however, the models were not able to estimate budburst occurring after short chilling exposures, where they returned either high overestimations or failed completely. This was due to the narrow winter length variability in the field dataset, which made the optimization algorithm converge towards unrealistically high chilling requirements and artifactual descriptions of the temperature effects on dormancy. Cutting-based calibration on the other hand produced parameterizations that were more consistent with available experimental knowledge. Despite this difference between them, the two approaches proved to be equivalent under the climatic conditions present, but not when tested on projected scenarios of climate change over the period 1990–2090, where cutting-calibrated models, which are more sensitive to decreasing winter length, predicted higher variations of the budburst dates.

Total number of initiated leaves and duration from sowing to silking increases when photoperiod is increased during the photoperiod-sensitive phase in maize ( Zea mays L.). Little is known, however, about possible other effects of photoperiod and incident photosynthetic photon flux density (PPFD) on rate of development and duration of life cycle. A study was undertaken to quantify effects of photoperiod and incident PPFD from sowing to the 15-leaf stage on rate of leaf appearance and duration of the grain-filling period. The short-season maize hybrid Pioneer 3902 was grown in growth cabinets from sowing to the 15-leaf stage with either (i) a 10 h photoperiod at high PPFD (650 μmol m −2 s −1 ), (ii) a 20 h photoperiod consisting of 10 h of high PPFD followed by 10 h of low PPFD (5–50 μmol m −2 s −1 ), or (iii) a 20 h photoperiod of high PPFD. From the 15-leaf stage to maturity the plants were placed under a 16 h photoperiod in a growth room. Increasing photoperiod from 10 to 20 h increased final number of initiated leaves and delayed silking but did not affect rate of leaf appearance. Doubling incident PPFD to a value similar to that under Ontario field conditions during the summer resulted in a 16% increase in rate of leaf appearance and in a significant increase in total number of initiated leaves. Differences in final number of initiated leaves and in rate of leaf appearance from sowing to the 15-leaf stage among treatments resulted in a 4-day difference in silking date between the 10 h photoperiod treatment and the two 20 h photoperiod treatments. Duration of the grain-filling period did not differ among the three treatments.

A simple, relatively inexpensive, and effective method for the control of relative humidity in an environmental chamber was developed and evaluated. Relative humidity was maintained at 90% ± 0.4% and 95.2% ± 0.5% through the use of a micrologger-controlled ultrasonic mister that cycled between relatively narrow set points. To maintain consistent relative humidity, misters were activated at approximately 5- and 3-min intervals at 90% and 95% relative humidity, respectively. Air temperatures of 20–28°C were maintained at ±0.5°C by regulation of growth room controls. This environmental chamber has considerable utility for investigations of the influence of relative humidity and water potential on plants and plant-associated microorganisms.

Regeneration of normal carrot plants has been achieved from cultures kept in an inactive state for up to 2 years. Suspensions of embryoids plated onto an agar mineral medium lacking sucrose remained viable under growth room conditions (25°, 16 h photoperiod) but did not grow. On supplying sucrose, spherical and heart stage embryoids germinated. In some cases torpedo stage embryoids formed fresh embryoids at the root pole, but did not themselves germinate. Callus did not survive. Over the 2-year period the parent cultures, sub-cultured at approximately 6-weekly intervals, lost the ability to regenerate plants.

Exogenous growth substances (GA4+7, IAA, PBA, and ABA) alone and in combination were applied as leaf dips to young ‘Golden Delicious’ apple trees in a growth room at 21 °C. All treatments containing GA4+7 accelerated the incidence of physiological leaf spot over treatments without GA4+7, ABA alone delayed the appearance of leaf spot. PBA, PBA + GA4+7, and PBA + GA4+7 + IAA retarded the abscission of spotted leaves. GA4+7 and GA4+7 + PBA also accelerated leaf spot development in bearing ‘Golden Delicious’ trees in the orchard. Fumigation of apple trees with ethylene at 2, 10, and 20 ppm had no influence on the occurrence of leaf spot or premature abscission.

Summary Attached ears and flag leaves of spring wheat plants were exposed to 0, 300 and 800 vpm CO2 in a growth room in plexiglass cuvettes. The increased assimilate production at 800 vpm CO2 in no case was connected with enhanced grain growth or enhanced grain yield of the ears compared to the controls. Inhibition of photosynthesis by a 5-day exposure to 0 vpm CO2 yielded a decrease in grain growth of 20 % in such cases only, in which the lower parts of the plant were darkened. Otherwise a more than 5-day exposure of the upper parts to CO2 free air was necessary to induce a relatively small decrease in grain growth. It was concluded from the results that assimilate production and accumulation in the kernels are uncoupled by the existence of a relatively large pool of free assimilates in the culm. Therefore, growth of the reproductive organs, the caryopses, is possible also under conditions unfavourable for photosynthesis.