The efficient breeding and selection of corn (Zea mays L.) genotypes for different climatic regions requires a quantitative understanding of the plant's developmental responses to environmental factors such as temperature and photoperiod. This information is also essential if reliable and meaningful crop simulation models are to be developed. Plants of two corn hybrids, XL45 and W346 were grown in controlled environments under 18 day/night temperature combinations ranging from 16/6 to 38/33°C (12‐h photoperiod) and under three photoperiods (12,14, and 16 h) at two selected temperatures (constant 18 and 28°C). Data defining the temperature response curves, including the minimum and optimum temperature limits, for germination and emergence and for the development periods from sowing to tassel initiation and sowing to anthesis were obtained. A minimum temperature of 9°C was predicted for germination and emergence, and a requirement of 62.5 degree‐days was determined for this growth stage. The optimum temperature was approximately 30°C. Minimum temperatures of 8 and 7°C were determined for tassel initiation and anthesis, respectively, and the optimum temperature for both was 28°C above which the development rates declined. These temperature limits compared with minima and maxima of 10 and 30°C, respectively, used in most current heat‐sum methods. Between the limits of 7 and 28°C, the number of degree‐days required to reach tassel initiation and anthesis were, respectively, 208 and 736 for hybrid W346, and 245 and 816 for XL45. Tassel initiation occurred at approximately one‐third of the time between sowing and anthesis when calculated either on the basis of heat‐sums (degree‐days) or from calendar‐days under the steady‐state temperature conditions used. An increase in photoperiod lengthened both the time between sowing and tassel initiation and that between tassel initiation and anthesis in a similar, almost equal, manner for both cultivars. Sensitivity to the photoperiod response was not altered by temperature.

The prediction of evapotranspiration and canopy photosynthesis, for example in crop simulation modeling and in remote sensing applications, requires a quantitative description of the influence of environmental factors such as temperature and photoperiod on leaf area development. The objectives of this study were to define the temperature response curves and the responses to photoperiod for two components of leaf area development in corn (Zea mays L.), namely leaf‐initiation rate and leaf‐appearance rate. Plants of two corn hybrids, W346 and XL45, were grown in controlled environments under 17 day/night temperature regimes ranging from 16/6 to 38/33°C (12 h photoperiod) and under three photoperiod regimes (12, 14, and 16 h) at two selected temperatures (constant 18 and 28°C). Leaf‐initiation rates, determined from frequent dissections, were constant from seedling emergence until tassel initiation in all treatments. Similarly the appearance rate of the first 12 leaves was constant from seedling emergence onward, but after leaf 12, appearance rate increased, presumably as a consequence of rapid stem elongation and because the upper stem leaves were smaller and required less time to expand. Both cultivars had similar leaf‐initiation and leaf‐appearance rates under each day/night temperature regime. Data from the day/night temperature regimes were used to derive rate of leaf‐initiation (leaf primordia/day) vs. temperature and rate of leaf‐appearance (leaves/day) vs. temperature response curves which could be described by third and fourth‐degree polynomial equations, respectively. Previously published values for leaf‐appearance rates have varied by up to three or four‐fold at any particular temperature, primarily because of different definitions that have been used for appearance rate. Values for the rate of change in leaf appearance rate with temperature within the 16 to 26°C range, however, were more similar ranging from 0.21 to 0.30 leaves day−1°C−1 and were similar to a value of 0.23 leaves day−1°C−1 obtained in this study. Both leaf‐initiation and leaf‐appearance rates increased with an increase in photoperiod, particularly under constant 18°C conditions. Cultivar W346 appeared to be more responsive to photoperiod than XL45.

Container-grown `Delicious', `Golden Delicious', `Braeburn', `Fuji' and `Royal Gala' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees, on Malling 9 (M.9) rootstock, were subjected to a range of different maximum/minimum air temperature regimes for up to 80 days after full bloom (DAFB) in controlled environments to investigate the effects of temperature on fruit expansion, final fruit weight, and fruit maturation. Fruit expansion rates were highly responsive to temperature with those at a mean of 20 °C being ≈10 times greater than those at a mean of 6 °C. All cultivars exhibited the same general response although `Braeburn' consistently showed higher expansion rates at all temperatures compared with lowest rates for `Golden Delicious' and intermediate rates for both `Delicious' and `Fuji'. The duration of cell division, assessed indirectly by measuring expansion rate, appeared to be inversely related to mean temperature (i.e., prolonged under cooler conditions). Subsequently, fruit on trees from the coolest controlled temperature treatment showed greater expansion rates when transferred to the field and smaller differences in fruit size at harvest than would have been expected from the measured expansion rates under the cool treatment. Nonetheless, mean fruit weight from warm postbloom treatments was up to four times greater at harvest maturity than that from cool temperature treatments. Postbloom temperature also markedly affected fruit maturation. Fruit from warm postbloom temperature conditions had a higher soluble solids concentration, more yellow background color, lower flesh firmness, and greater starch hydrolysis than fruit from cooler temperatures.

Temperature effects on the growth and yield of wheat (cv. Gamenya) were studied in controlled environments under three day/night temperature regimes (viz. 25/20, 20/15 and 15/10°C) and at three stages of development, viz. vegetative, ear development and grain growth stages. The most important temperature effects were found during the ear development phase. Plants grown at low temperature at this time had long culms, large flag leaves and more potentially fertile florets in each spikelet. The number of florets which produced harvestable grains, and the weight of these grains at maturity, were affected by temperature during the grain growth stage. Temperature prior to floral initiation was not of major importance to final ear weight in this variety, but it did have an effect on the number of mature ears present at harvest. Grain weight per ear at maturity was found to be highly correlated with the number of grains set (r = 0.96), and hence variation in grain number accounted for most of the variation in ear grain weight. In those treatments where grain numbers were not markedly depressed by the temperature treatments, a hlgh positive correlation was found between flag leaf area duration and total grain yield (r = 0.73).

The role of photoperiod, night temperature, and frequency and severity of frosts on the development of frost hardiness in seedlings of Pinus radiata was studied using controlled environment treatments. In one experiment the specific effects of 9 and 14 h photoperiods and 5 and 15°C night temperatures were examined. In a second experiment, seedlings were sequentially hardened under two simulated early autumn to late winter climates, with the photoperiod and day/night temperatures progressively altered at 11 and 21 day intervals respectively. In addition, half of the seedlings raised in each simulated climate were exposed concurrently to a conditioning frost regime. Frost hardiness of the seedlings in each sequence was determined at regular intervals using a series of evaluation frosts. Frosts of between -3 and -5°C were the most effective factor in controlling the development of frost hardiness. Night temperatures as low as 1°C were also effective but not those above 5°C. A minimum photoperiod requirement of less than 11 h for up to 42 days exposure was required for low-temperature hardening. There appeared to be a response lag in the development of frost hardiness once the critical photoperiod and inductive night temperatures had been imposed. Differences between nursery sites in frost hardiness of seedling stock were attributed to differences in their environments, particularly the incidence of frosts. The final maximum frost hardiness varied between the treatments from - 7.5 to -19°C indicating that Pinus radiata has a greater potential to develop frost hardiness than was previously thought from field observations.