The effect of temperature on leaf appearance and canopy establishment in fibre hemp (Cannabis sativa L.)

The effects of temperature on the development and growth of hemp (Cannabis sativa L.) have never been quantified. Therefore, to establish the effect of temperature on leaf appearance and canopy establishment of fibre hemp under controlled and field conditions, plants were grown in growth chambers at 11 regimes with average temperatures between 10°C and 28°C, and three cultivars were sown in the field in March, April and May in 1990, 1991 and 1992. In the field, thermal time (base 0°C) between sowing and emergence ranged from 68°Cd to 109.5°Cd (average 88.3°Cd). Rates of leaf appearance and stem elongation increased linearly with temperature between 10°C and 28°C. The base temperature for leaf appearance was 5.7°C from the growth chamber experiments and 1°C from the field experiments. In the field, the base temperature for the relationship between light interception by the canopy and thermal time was 2.5°C, and thermal time, calculated at the appropriate base temperature, accounted for about 98% of the variance in the number of leaves and for 98.6% of the variance in the proportion of light intercepted by the canopy. Days from emergence accounted for less of the variance in both parameters than thermal time. Interception of 90% of light was attained on average at 465°Cd (base 0°C) after emergence. It is concluded that thermal time is a simple and accurate tool to describe leaf appearance and light interception in fibre hemp.     

Diurnal variation in the temperature response of leaf extension of two bunchgrass species in the field

The effect of temperature on short-term leaf extension rates was studied for two cool-season tussok grasses, Agropyron desertorum and Pseudoroegneria spicata, growing in the field under a variety of water stress and defoliation conditions. Leaf extension rates and air temperatures were monitored every half hour during numerous 12- to 65-h periods in three growing seasons using auxanometers constructed of precision resistors. For both species, a three-phase relationship between leaf extension rate and temperature was observed during diurnal cycles. Leaf extension rate increased linearly with temperature from dawn until midday (phase 1). Leaf extension then increased rapidly, reaching maximum rates in the early evening (approximately 1900h), despite decreasing temperatures during this period (phase 2). Finally, leaf extension rate declined with temperature from evening until dawn (phase 3). This diurnal cycle was described by linear (phase 1) and quadratic (phases 2 and 3 combined) regression models. Although the rate of leaf extension and daily integrals were affected by the water stress and defoliation treatments, the diurnal pattern was consistently observed. Temperature was probably a major factor governing leaf extension rates at night (phase 3), but it appeared unimportant in controlling leaf extension between dawn and midday. The relative importance of physiological and environmental factors controlling leaf extension rate appears to shift during the day in these species under field conditions.     

Physiological Responses of Apple Trees to Supraoptimal Root Temperature

Ungrafted apple rootstocks were grown in sand cultures at constant root temperatures between 20°C to 40°C. Temperatures of 30°C and above reduced root and shoot growth. Serious damage to the leaves occurred at 35°C and above. The O₂ consumption, CO₂ evolution and respiratory quotient (RQ) of the roots showed maximum values at 35°C. Different rootstock cultivars varied greatly in their susceptibility to damage by supraoptimal root temperatures apparently due to anaerobic respiration. The more susceptible ones differed from resistant types in the larger amount of ethanol they accumulated in their roots at supraoptimal root temperature, and the more severe reduction in the malic acid content of the roots at such temperature. Acetaldehyde was also found in roots and leaves at supraoptimal root temperatures, whereas the organic acid content of the leaves tended to decrease. Supraoptimal root temperature also caused a reduction of cytokinins in both roots and leaves accompanied by a reduction in the leaf chlorophyll content. This could be prevented by the application of kinetin or benzyladenine to the leaves. In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C. The leaf water potential increased also with increasing root temperature. Leaf temperature increased with increasing root temperature, irrespective of increasing or decreasing transpiration rates.     

Effects of post-chilling temperature on growth and variegation in Solomon's Seal

Effects of temperature were studied on the current and following season's growth of shoots from chilled rhizomes of Variegated Solomon's Seal. The rate of progress to completed elongation of the aerial shoot in chilled plants increased linearly with increasing temperature up to 28°C (24 h mean). A post‐chilling thermal time of 658 ± 47°Cd (> ‐1.3°C) was required for aerial shoots to become fully extended. Temperatures of 28°C and 33°C accelerated aerial shoot senescence and decreased rhizome and root dry weights, as compared with 18°C and 23°C treatments. Leaf number and variegation were not affected by temperature treatments during current growth season and all plants produced 12–13 leaves with between 7% and 9% leaf area variegated. Leaf variegation, however, was significantly increased in plants that had been grown after chilling at 28°C during the preceding growing season. Proteins of approximately 26, 32 and 62 kDa were present in the green parts of leaves but not in the white parts.     

The influence of temperature on leaf development and growth in potatoes in controlled environments

Three controlled environment experiments were conducted at different temperatures to determine the relation between temperature and leaf development and growth in the potato (cv. Maris Piper). Developmental stages are defined for the appearance and duration of leaf extension in the potato and comparisons made with other temperate zone crops. The rate of leaf appearance was linear over the temperature range (9–25°C) and above 25°C there was no further increase in the rate. The temperature coefficient for the rate of appearance of leaves was 0.032 leaves (degree days)^-1 using a base temperature of 0°C. The duration of extension of an individual leaf decreased with increase in temperature up to 25°C such that the thermal duration was constant at 170 degree days using a base temperature of 0°C for leaf positions 4–10 on the main stem. At higher leaf positions the thermal duration was similar or greater. The advantages and limitations of controlled environment work as a parallel to field experimentation are discussed.     

An analysis of leaf growth in sugar beet.

The responses of leaf appearance and expansion to temperature in sugar beet were measured under controlled conditions, using ruler and auxanometers, to establish a basis for a subsequent analysis of leaf growth in field crops. The studies showed that leaf appearance rate responded linearly to temperature above 1°C, that leaf expansion rate responded likewise above 3°C and that both rates were zero below these base temperatures. Auxanometer measurements of leaf extension showed that daily rates of expansion of leaf area increased linearly with the daily integral of temperature. However, hourly rates of extension in length alternated with those in width during each 24 h cycle in patterns that were not clearly related to hourly changes of temperature or to the day/night sequence.     

Variation in growth attributes of contrasting populations of Trifolium repens

A range of growth attributes was measured in seedlings of 10 Trifolium repens populations, differing in leaf size and origin, grown in three temperature and two glasshouse environments. Growth rates of large leaf types of Mediterranean origin were higher than those of smaller leaf types at 10°C. However, the greater temperature response of the smaller leaf types resulted in higher growth rates for S.100 and S.184 than for a large leaf type from Israel at 20°C. The increase of growth rate with temperature was associated with changes in leaf area ratio and net assimilation rate between 10° and 15°C but only with changes in net assimilation rate between 15° and 20°C. Within each temperature environment, population differences in growth rate were related to differences in net assimilation rate rather than leaf expansion. At low temperature a greater proportion of dry matter was distributed to leaf tissue in large leaf types particularly those of Mediterranean origin but they showed a proportionately smaller increase in allocation to leaves with increasing temperature compared with small leaf types. In the glasshouse environments growth rates in spring were more than double those in the autumn. This difference was associated with net assimilation rates which were about five times greater in the spring environment. However, leaf area ratios in the spring were only half those in the autumn. These differences in leaf area ratio between the glasshouse environments were closely related to differences in specific leaf area but not to differences in distribution of dry matter to leaf tissue which was greater in the spring environment.     

The Effects of Position and Temperature on the Expansion of Leaves of Vicia faba L.

The growth in area of the first eight leaves of broad bean plantswas investigated in growth room experiments. Plants were grownat either 20 or 14 °C or transferred from 20 to 14 °C.Rates of leaf appearance and unfolding increased with temperature.The duration of growth of a leaf increased with leaf numberfor the first five leaves and then remained constant The meangrowth rate declined or remained constant with increasing leafnumber Durations of growth were shorter and growth rates largerat 20 °C than at 14 °C Plants responded immediatelyto the change in temperature Final areas of leaves which expandedafter transfer from 20 to 14 °C were larger than those grownat 20 °C Vicla faba L., broad bean, leaf expansion, temperature responses     

The relative impacts of daytime and night-time warming on photosynthetic capacity in Populus deltoides

In order to investigate the relative impacts of increases in day and night temperature on tree carbon relations, we measured night‐time respiration and daytime photosynthesis of leaves in canopies of 4‐m‐tall cottonwood (Populus deltoides Bartr. ex Marsh) trees experiencing three daytime temperatures (25, 28 or 31 °C) and either (i) a constant nocturnal temperature of 20 °C or (ii) increasing nocturnal temperatures (15, 20 or 25 °C). In the first (day warming only) experiment, rates of night‐time leaf dark respiration (R_dark) remained constant and leaves displayed a modest increase (11%) in light‐saturated photosynthetic capacity (A_max) during the day (1000–1300 h) over the 6 °C range. In the second (dual night and day warming) experiment, R_dark increased by 77% when nocturnal temperatures were increased from 15 °C (0·36 µmol m^?2 s^?1) to 25 °C (0·64 µmol m^?2 s^?1). A_max responded positively to the additional nocturnal warming, and increased by 38 and 64% in the 20/28 and 25/31 °C treatments, respectively, compared with the 15/25 °C treatment. These increases in photosynthetic capacity were associated with strong increases in the maximum carboxylation rate of rubisco (V_cmax) and ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity mediated by maximum electron transport rate (J_max). Leaf soluble sugar and starch concentration, measured at sunrise, declined significantly as nocturnal temperature increased. The nocturnal temperature manipulation resulted in a significant inverse relationship between A_max and pre‐dawn leaf carbohydrate status. Independent measurements of the temperature response of photosynthesis indicated that the optimum temperature (T_opt) acclimated fully to the 6 °C range of temperature imposed in the daytime warming. Our findings are consistent with the hypothesis that elevated night‐time temperature increases photosynthetic capacity during the following light period through a respiratory‐driven reduction in leaf carbohydrate concentration. These responses indicate that predicted increases in night‐time minimum temperatures may have a significant influence on net plant carbon uptake.     

Effects of growth stage and hardening conditions on the association between frost resistance and the expression of the cold-induced protein COR14b in barley

Sowing date, being determinant for growth stage, may play a decisive role in optimising freezing resistance of winter annual plants. In cereal species, in spite of the abundant literature analysing the factors responsible for the acquisition of frost resistance through the cold hardening process, the involvement of the growth stage per se, has been seldom considered, especially at the earlier vegetative phases. In this work the contribution of growth stage in determining resistance to freezing temperature has been analysed in field and growth chamber experiments using winter and spring barley cultivars exposed to different hardening conditions. Field damage was assessed twice during winter on plants sown at three different dates. In the growth chamber experiments several acclimation treatments at 11/7 and/or 3/1 °C (day/night) were simulated. In both field and laboratory experiments the development of cold acclimation was monitored by means of a COR14b specific antibody, since in previous studies the expression of COR14b was found genetically linked to frost resistance. The lowest resistance, found in the youngest plants and in spring cultivars, however, was not always associated with the lowest level of COR14b accumulation. COR14b accumulation correlated with frost resistance at the earlier field sampling date and in plants grown at 11/7 °C. In a following phase of the hardening process (second sampling in field and 4 weeks at 3/1 °C in growth chamber) the accumulation of COR14b was independent of plant stage and genotype, showing no association with freezing resistance. Results suggest that growth stage is crucial for the achievement of maximal resistance in barley, but not for COR14b expression.     

Increased productivity of recombinant tissular plasminogen activator (t-PA) by butyrate and shift of temperature: a cell cycle phases analysis

Directed control of cell metabolism by a modification of the physicochemical conditions (presence of Na-butyrate and modification of the temperature) was used to modulate the productivity of human recombinant tissular plasminogen activator (t-PA) expressed under control of SV40 promoter in Chinese Hamster Ovary (CHO) cell lines. We showed that both by adding Na-butyrate or lowering temperature from 37 °C to 32 °C there is an increase in the amount of t-PA excreted, while cell growth is significantly reduced. The treatments also increased the intracellular amount of t-PA. We measured the distribution of cell cycle phases by cytometry and used a modification of the equations of Kromenaker and Srienc (1991, 1994 a, b) to analyse the intracellular t-PA production rate in the different cell cycle phases. Intracellular t-PA was shown to accumulate in G1 phase in all conditions (at 37 °C, at 32 °C and in presence of butyrate). Moreover, we have shown that the distribution of the time cells treated by butyrate are maintained in the G1cell cycle phase is significantly increased. t-PA produced in the different cell culture conditions tested was analysed by zymogram and western blotting: neither butyrate, neither the shift of temperature changed significantly the overall quality of the protein. The N-glycan patterns of recombinant human t-PA was also analysed with carbohydrate-specific lectins. Butyrate caused a transitory increase in N-linked complex high-mannose oligosaccharides without any effect on the sialic acid content of t-PA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of heat stress in the leaf mitotic cell cycle and chromosomes of four wine-producing grapevine varieties

Grapevine varieties respond differentially to heat stress (HS). HS ultimately reduces the photosynthesis and respiratory performance. However, the HS effects in the leaf nuclei and mitotic cells of grapevine are barely known. This work intends to evaluate the HS effects in the leaf mitotic cell cycle and chromosomes of four wine-producing varieties: Touriga Franca (TF), Touriga Nacional (TN), Rabigato, and Viosinho. In vitro plants with 11 months were used in a stepwise acclimation and recovery (SAR) experimental setup comprising different phases: heat acclimation period (3 h—32 °C), extreme HS (1 h—42 °C), and two recovery periods (3 h—32 °C and 24 h—25 °C), and compared to control plants (maintained in vitro at 25 °C). At the end of each SAR phase, leaves were collected, fixed, and used for cell suspensions and chromosome preparations. Normal and abnormal interphase and mitotic cells were observed, scored, and statistically analyzed in all varieties and treatments (control and SAR phases). Different types of chromosomal anomalies in all mitotic phases, treatments, and varieties were found. In all varieties, the percentage of dividing cells with anomalies (%DCA) after extreme HS increased relative to control. TF and Viosinho were considered the most tolerant to HS. TF showed a gradual MI reduction from heat acclimation to HS and the lowest %DCA after HS and 24 h of recovery. Only Viosinho reached the control values after the long recovery period. Extrapolating these data to the field, we hypothesize that during consecutive hot summer days, the grapevine plants will not have time or capacity to recover from the mitotic anomalies caused by high temperatures.     

Effect of temperature on the dose–response curves for auxin-induced elongation growth in maize coleoptile segments

The dose–response curves for IAA-induced growth in maize coleoptile segments were studied as a function of time and temperature. In addition, the kinetics of growth rate responses at some auxin concentrations and temperatures was also compared. It was found that the dose–response curves for IAA-induced elongation growth were, independently of time and temperature, bell-shaped with an optimal concentration at 10⁻⁵ M IAA. The kinetics of IAA-induced growth rate responses depended on IAA concentration and temperature, and could be separated into two phases (biphasic reaction). The first phase (very rapid) was followed by a long lasting one (second phase), which began about 30 min after auxin addition. For coleoptile segments incubated at 30°C, the amplitudes of the first and second phase were significantly higher, when compared with 25°C, at all IAA concentrations studied. However, when coleoptile segments were incubated at 20°C, the elongation growth of coleoptile segments treated with suboptimal IAA concentrations was diminished, mainly as a result of both phases reduction. In conclusion, we propose that the shape of the dose–response curves for IAA-induced growth in maize coleoptile segments is connected with biphasic kinetic of growth rate response.     

Tree leaf out response to temperature: comparing field observations,remote sensing,and a warming experiment

Leaf out time is a widely used indicator of climate change and represents a critical transition point of annual seasonality in most temperate ecosystems. We compared three sources of data to determine the effect of spring temperature on tree leaf out: field observations, remotely sensed satellite data, and experimental warming. All three methods recorded earlier leaf out with warmer spring temperatures. However, leaf out timing was more than twice as sensitive to temperature in the field study (advancing at a rate of 6.1 days/°C), as under experimental warming (2.1 days/°C), with remote sensing intermediate (3.7 days/°C). Researchers need to be aware of the currently unexplained differences among methodologies when using phenological data to parameterize or benchmark models that represent ecosystem processes. The mechanisms behind these discrepancies must be better understood if we are to confidently predict responses of leaf out timing to future climates.     

The Effects of Light and Temperature on Germination and Growth of Luffa aegyptiaca

The effects of light and temperature on the germination and growth of Luffa aegyptiaca were investigated both in the laboratory and in the field. The seeds germinated in both darkness and light but germination was better in the light. At constant temperatures germination was best at 21°C, while alternating temperatures of 21 and 31°C and 15 and 41°C caused higher germination than the most favourable constant temperature. Constant temperatures of 15 and 31°C and alternating temperatures of 21 and 41°C resulted in very low germination, whereas no germination occurred at 41°C and at alternating temperatures of 31 and 41°C. Soil depth caused only a delay in seed germination, as it did not affect the total germination. High temperature and high light intensity resulted in good seedling growth in terms of dry weight, leaf area and relative growth rate. High temperature and low light intensity caused increased plant height and high shoot weight ratio, both of which manifested in seedling etiolation. They also caused high leaf area ratio. Under low temperatures, irrespective of light intensity, growth was generally poor, but it was significantly poorer under low light intensity, which also caused high root weight ratio. High light intensity was principally responsible for high leaf weight ratio. The results help to explain the abundance of the species in newly cleared areas in Lagos and its environs.     

A model co-ordinating the elongation of all leaves of a sorghum cultivar was applied to both Mediterranean and Sahelian conditions

Sorghum leaf development was analysed at plant level by analysing the time-course of elongation and identifying the beginning and end of the elongation phases of each leaf blade. This was done with destructive and non-destructive measurements in 14 experiments carried out during several growing periods in Southern France and Sahelian Africa. Elongation of each blade was characterized by the succession of a nearly exponential phase and a linear phase. For a given blade and provided that time was expressed in thermal units, initiation, beginning and end of the linear phase, and time-courses of elongation rate were strikingly similar in all experiments, except in environments with a maximum air temperature close to 40 degrees C and a maximum vapour pressure deficit close to 6 kPa. The relative elongation rate during the exponential phase declined with leaf number from 0.08 to 0.02 degrees Cd(-1), while the duration of this phase increased from 140 to 320 degrees Cd. By contrast, the absolute elongation rate during the linear phase was nearly constant from leaf 8 onwards. This phase was shorter than the exponential phase regardless of leaf position, but accounted for the largest part of blade length. A strict pattern of leaf development was observed at the whole plant level, whereby dates of elongation events and leaf and ligule appearance, represented on a thermal time scale, were linearly related to phytomer number. This pattern exhibited a simultaneous elongation cessation of the last-formed leaves and a mismatch between real and apparent (from leaf to ligule appearance) elongation duration.     

Effect of temperature on the sex ratio and life table parameters of the leek-(L1) and tobacco-associated (T) Thrips tabaci lineages (Thysanoptera: Thripidae)

Temperature strongly affects insect biological response. Effects of temperature on the sex ratio, preoviposition, fecundity, egg hatchability rate, and adult longevity of the L1 and T Thrips tabaci lineages were studied under laboratory conditions at three constant temperature levels (15, 23, and 30°C) on cabbage and tobacco leaf discs, respectively. Results showed that temperature affects all the tested life table parameters of L1 and T lineages. The proportion of female's log-linearly increased as temperature increased. Preoviposition period, fecundity, adult longevity, and egg hatchability rate were reduced significantly with increasing temperature. In both lineages, the lowest egg hatchability rates were recorded at 30°C and the highest rates were recorded at 15°C. Mean fecundity of the L1 and T lineages were 107.63 and 84.83 at 23°C, respectively, and mean fecundity of the L1 and T lineages were 19.88 and 70.82 at 15°C, respectively. The lowest mean fecundity was recorded at 15°C and 30°C for the L1 and T lineages, respectively. Mean longevity were 34.22 and 81.82 days at 15°C for L1 and T lineages, respectively. Whereas, the shortest mean longevity (13.63 and 13.91 days) was observed at 30°C for the L1 and T lineages, respectively. Our results demonstrated that 23°C was the optimum temperature for fecundity among the studied temperature levels for the studied population of the L1 and T T. tabaci lineages.     

Base and optimum temperatures vary with genotype and stage of development in wheat

Some assumptions concerning development in wheat (Triticum aestivum, L.) were examined. These are that (i) the rate of development towards anthesis increases linearly with temperature, (ii) the base temperature is 0°C, (iii) the optimum temperature is above the range at which wheat is normally grown, (iv) base and optimum temperatures do not change with development, and (v) the relationships for different cultivars are similar. We tested these assumptions in studies using a naturally lit phytotron with four cultivars and six temperature regimes between 10 and 25°C. Seedlings were vernalized for 50 d and then grown under a photoperiod of 18 h to avoid confounding the responses to vernalization and photoperiod with those to temperature. In cultivars Sunset and Rosella, the rate of development for the full period to anthesis increased linearly between base and optimum temperatures. However, in cultivars Condor and Cappelle Desprez, a linear fit was not statistically acceptable. For these cultivars, the rate of development towards anthesis increased rapidly with increase in temperature from 10 to 19°C, but temperatures higher than 19°C had little or no fürther accelerating effect. When a linear relationship was fitted by ignoring data for temperatures above 19 7deg;C, base temperatures calculated for the full period to anthesis were c. 5.5, 5.5,4.0 and 2.5°C for Sunset, Condor, Rosella and Cappelle Desprez, respectively (i.e. an average value of c. 4 7deg;C). The full period to anthesis was subdivided into three phases for fürther analysis. These were (i) from the beginning of the experiment to terminal spikelet initiation, (ii) from terminal spikelet initiation to heading, and (iii) from heading to anthesis. When these sub-phases were analysed a linear relationship was found to be appropriate for all combinations of cultivar and developmental phase. However, both base and optimum temperatures calculated from the relationships increased as development progressed from (i) to (iii). Averaging across cultivars, base temperatures for the three phases were -1.9, %1.2 and %8.1°C, respectively, while optimum temperatures were <22, 25 and >25°C, respectively. Cultivars differed substantially in all these parameters. The progressive increase in optimum temperature with phasic development was apparently the main reason why linear fits for the three sub-phases became a curvilinear fit for the full phase to anthesis.     

Photosynthetic pigments,morphology and leaf gas exchange during ex vitro acclimatization of micropropagated CAM Doritaenopsis plantlets under relative humidity and air temperature

The effect of relative humidity (RH) and temperature on CO₂ assimilation (An), stomatal conductance (Sc), transpiration rate (Tr), chlorophyll content, fresh and dry weight, leaf length, leaf area, leaf width, formation of new root and survival rate have been assayed in Doritaenopsis in growth chamber after 1 month of acclimatization. Reduced growth was observed at below and above 25 °C whereas it was increased with increasing humidity. Relative water content (RWC) was decreased at 50% and 70% humidity after second day of transfer and recovered completely with the progression of acclimatization. RWC also reduced at high temperature but recovered slowly and a gradual decrease of RWC was observed at 15 °C. A visual symptom of severe leaf tip burn was observed at 50–70% humidity and at 35 °C during acclimatization. At 15 °C and 50% humidity sudden decrease of photosynthetic efficiency (F_v/F_m) was observed, which could not recover in temperature treated plantlets during acclimatization period. Chlorophyll content increased with increasing humidity and at 15 and 35 °C chlorophyll content was decreased compared to 25 °C. Chlorophyll a/b ratio was unchanged while total chlorophyll/carotenoids ratio was increased from low to high temperature. Exposure of plantlets to high temperature led to a noticeable decrease in An, Sc and Tr, and at 15 °C they were more decreased whereas significant differences were not observed in the parameters tested under humidity after 25 days of acclimatization. During daytime at 15 °C, increase in An, Sc and Tr indicates the plantlets adaptability in the new environment. The peroxidase activity remained unaffected in all humidity stress whereas low temperature increased the peroxidase activity compared to high temperature. These finding suggests that photosynthetic properties was greatly affected by air temperature conditions with a reduction of An, Sc and Tr at 15 and 35 °C compared to humidity stress that played a greater role in limiting photosynthesis.     

Effects of Leaf Age, Inoculum Dose and Freezing on Development of Chocolate Spot (Botrytis fabae) Lesions on Field Bean (Vicia faba) Leaves

Botrytis fabae spore suspensions containing c. 1, 10, 10², 10³, 10⁴, 10⁵, or 10⁶ spores/ml were used to inoculate 5, 17 or 30-day-old field bean leaves. The percentages of the leaf areas covered by, chocolate spot lesions and the percentages of the leaf areas bearing conidiophores were assessed 1, 6, 12, 14, and 19 days after inoculation. The percentage of the area covered by lesions and the percentage of the area bearing conidiophores (logit-transformed) increased linearly with increasing spore concentration (log₁₀-transformed). The proportions of leaf areas covered by lesions and bearing conidiophores were both greater on 17 and 30-day-old leaves than on 5-day-old leaves. The rate of lesion growth increased with both increasing inoculum dose and increasing leaf age. Generally there was no interaction between the effects of leaf age and the effects of inoculum dose on either lesion growth or sporulation. Two days after inoculation with suspensions of either 10⁴ or 10⁶ spores/ml, 7-day-old leaves grown at 15°C were transferred to –16°C or 2.5°C or kept at 15°C for 4 days. Two days later more spores had been produced on leaves which had been frozen (–16°C) than on, leaves kept at 2.5°C.