Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

Frost resistance and water status of winter rape leaves as affected by differential shoot/root temperature

Twenty day-old winter rape ( Brassica napus L. var. oleifera L. cv. Jantar) seedlings, grown in nutrient solution, were exposed to different shoot/root temperature (i. e. 20/20, 20/3, 3/20 and 3/3°C) for 2 or 4 weeks. Chilling treatments modified markedly the pattern of plant growth as indicated by changes in dry matter accumulation in individual plant parts (leaves, hypocotyls, roots) and decreased leaf specific area. Growth of roots was less sensitive to low temperature than that of shoots. This was reflected by a decrease in shoot/root biomass ratio. Chilling treatments increased freezing resistance, decreased water content and water potential and modified reducing sugar, soluble protein and phospholipid contents in the leaves. A biphasic character of tissue responses to chilling temperature was observed, the most remarkable changes being registered during the first 7 or 14 days of the treatment. Effects of root or shoot exposure to chilling temperature on ice nucleation temperature, LT₅₀, water potential, accumulation of sugars and phospholipids in leaves were additive. All the observations point to the important role of the root system in plant acclimation to cold. Its impact on water status of leaves is emphasized and some mechanisms of root involvement in acclimation processes are proposed.     

Curd Initiation in the Cauliflower: I. JUVENILITY

Hand, D. J. and Atherton, J. G. 1987. Curd initiation in thecauliflower. I. Juvenility.—J. exp. Bot. 38: 2050–2058. Four cauliflower (Brassica oleracea var. botrytis L.) cultivarswere screened for differences in juvenility, measured as thephase of insensitivity to vernalization. Juvenility persisteduntil the initiation of a critical number of leaves which sharplydefined transition to the sensitive, mature form at 13 to 15leaves in cv. Perfection and at 17 to 19 leaves in cv. WhiteFox. Preliminary investigation showed transition in cv. AlphaCliro to occur between 9 and 18 leaves initiated and in cv.Dole after 19 leaves. Leaf number was a stable marker of theend of juvenility in plants grown under different light conditions,whereas time, leaf area and leaf dry weight were not. Leaf numberwas linearly related to log whole shoot dry weight. The rateof leaf initiation in plants of cv. Perfection growing duringthe juvenile phase was approximately one third that of plantsin the mature phase, when measured on a thermal time base. Chilling mature, vegetative plants at 5 °C for 28 d advancedcurd initiation by up to 35 leaves in cv. Perfection; 27 leavesin cv. White Fox; 27 leaves in cv. Alpha Cliro and 21 leavesin cv. Dok, compared with plants grown continuously at 20 °C. Key words: Cauliflower, vernalization, juvenility     

Effect of paclobutrazol and chilling on leaf membrane lipids in cucumber seedlings

The effects of paclobutrazol on the leaf membrane lipid composition of seedlings of cucumber ( Cucumis sativus L. cv. Victory) subjected to chilling temperatures were assessed. At a non-injurious temperature (12.5°C), there was no difference in the polar lipid fatty acid composition or in the glycolipid, phospholipid or free sterol content of leaves from treated vs untreated seedlings, regardless of whether paclobutrazol was administered 1 or 7 days prior to analysis. In the latter case (7 days pretreatment), there were clear effects of the bioregulator on plant growth and morphology as well as on leaf chlorophyll content. At an injurious chilling temperature (5°C), desaturation of leaf polar lipid fatty acids was markedly reduced in both treated and untreated seedlings. Chilling at 5°C resulted in losses of fresh weight and membrane lipids in leaves of both groups of plants. These losses were either reversible or irreversible, depending upon the duration of chilling and of pretreatment with paclobutrazol. Seedlings pretreated with 10 μg ml⁻¹ paclobutrazol generally sustained less chilling injury than untreated controls, as judged by the extent of wilting, necrosis and desiccation. This correlated with reduced losses of leaf fresh Weight and membrane lipids.     

Determination of the Length of the Vegetative and Pre-floral Stages in the Day-Neutral Plant Helianthus annuus by Chilling Pulses

Helianthus annuus seedlings grown in an 18 h day at 28 ?C wereexposed to one 6 d chilling pulse of 12 ?C, at spaced timesduring the first 21 d from sowing. At 2 d intervals, the terminalbuds of 5 plants were dissected to determine leaf number andto score the vegetative or flowering state of the shoot apex.It was found that, while the rate of leaf initiation was reducedequally by each chilling pulse, pulses commencing on days 9or 12 reduced the total leaf number from 30 to 26, while pulsesapplied earlier had little effect. This variation is interpretedin terms of the time available for leaf production. The apicesof control plants commenced the visible transition to flowering16 d after sowing. Chilling pulses applied from days 3 or 6delayed this transition by about 5 d, whereas later pulses causedonly a 1•5 d delay. In a second experiment, where the chillingwas reduced to 2 d duration, it was again found that chillingdelayed flowering during the first 8 d and was progressivelyless effective when applied later. From this variation in temperaturesensitivity it is proposed that chilling sunflower plants immediatelyafter sowing delays flowering by extending the vegetative phaseof growth and so delaying the attainment of a ‘ripenessto flower’ state that appears to coincide with the expansionof the first pair of leaves. From day 8 onwards processes leadingto flowering that are relatively temperature insensitive apparentlybecome dominant in the apex and result in visible signs of flowering8 d later, although during this transitional stage leaf primordiacontinue to be initiated on the flanks of the apex.     

Growth, photosynthesis and assimilate partitioning in Lolium temulentum exposed to chilling temperatures

Vegetative plants of Lolium temulentum L, grown at 20°C with an 8 h photoperiod were transferred to either 5 or 2°C (8 h photoperiod) at 4th leaf maturity. Measurement of dry weight gain indicated a marked decline in relative growth rate below 5°C, with growth being reduced as much between 5 and 2°C as between 20 and 5°C. This reduction was not associated with increased mortality and was reversible if plants were returned to 20°C. Tissue explants from cold-treated plants retained the ability to extend if returned to 20°C Rates of extension in explants were less temperature sensitive than the relative growth rates observed in intact plants. Measurements of photosynthetic capacity, and of the patterns of accumulation of reserve carbohydrate in plants exposed to different temperatures, suggested that the inhibition of growth caused by chilling is not caused by an inability of the plants to fix sufficient carbon.     

Chilling sensitivity of the frost-tolerant potato Solanum commersonii

Frost tolerance has been reported in the shoots of wild, tuberiferous potato species such as Solanum commersonii when the plants are grown in either field or controlled conditions. However, these plants can survive as underground tubers and avoid unfavorable environmental conditions altogether. As such, leaf growth and photosynthesis at low temperature may not be required for survival of the plants. In order to determine the temperature sensitivity of S. commersonii shoots, we examined leaf growth, development and photosynthesis in plants raised at 20/16°C (day/night). 12/9°C and 5/2°C. S. commersonii leaves grown at 5°C exhibited a marked decrease in leaf area and in total chlorophyll (Chl) content per leaf area when compared with leaves grown at 20°C. Furthermore, leaves grown at 5°C did not exhibit the expected decrease in either water content or susceptibility to low-temperature-induced photoinhibition that normally characterizes cold acclimation in frost-tolerant plants. Measurements of CO₂-saturated O₂ evolution showed that the photosynthetic apparatus of 5°C plants was functional, even though the efficiency of photosystem II photochemistry was reduced by growth at 5°C. A decrease in the resolution of the M-peak in the slow transients for Chl a fluorescence in leaves grown at 12 and 5°C and in all leaves exposed to high light at 5°C indicated that low temperature significantly affected processes on the reducing side of Q_A, the primary quinone electron acceptor in photosystem II. Thus S. commarsonii exhibits the characteristics of a plant that is limited by chilling temperatures. Although S. commersonii can tolerate light frosts, its sensitivity to chilling temperatures may result in shoot dieback in winter in its native habitat. The plants may avoid both chilling and freezing temperatures by overwintering as underground tubers.     

Seasonal growth of tree lupins (Lupinus arboreus) and the effect of defoliation on leaf production

The growth of tree lupins was investigated in two experiments. In the first, two ages of plant, 4-wk-old seedlings and 1-year-old plants, were transplanted into a ryegrass sward in an upland environment. Growth, in terms of leaf production, branching and stem elongation, was measured over two successive growing seasons. Plant dry matter and nutrient contents were determined at the beginning and end of each growing season. In the first summer, the rate of production of new leaves on the main stem of seedling plants averaged 1.8 leaves per wk and main stem length increased from 5 to 67 cm. On older plants, where floral apices had been initiated on main and primary stems, there was a 3–10 fold increase in secondary branch length. In the second season, there was no effect of plant age on rates of leaf appearance or stem extension; dry matter production was higher than in the first season. In the second experiment, the effect of removal of 0%, 50% or 100% of fully expanded leaves on the subsequent growth of 23-wk-old plants was investigated. During the 7-wk growth period, defoliation promoted the rate of production of mature leaves, and area and dry weight of new laminae were slightly higher in defoliated plants. Defoliation did not affect the concentrations of N, P or K in the new laminae, but P and K concentrations in petioles of defoliated plants were significantly higher than those in intact plants. The results from the experiments are discussed in relation to the potential use of tree lupins as nurse species and biomass crops in hill and upland environments of the UK.     

Genotype-specific differences in chilling tolerance of maize in relation to chilling-induced changes in water status and abscisic acid accumulation

Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m⁻² s⁻¹ from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.     

Effects of growth regulators, CCC and B9, on some potato varieties

The effects of CCC and B 9 on the growth habit of potato differed between varieties. CCC diminished stem lengths and dry weight more than Bo because CCC was applied early when shoots emerged from the soil, but B 9 was applied about 3 weeks later when several leaves had formed. In some varieties lateral stem growth was increased by treatment and in others decreased. There was an inverse relation between main stem and lateral stem growth so that varieties with vigorous main stem growth had poor lateral growth and vice-versa. Treatment with the growth-regulators diminished leaf dry weight of main stem leaves less than leaf area, but the degree of magnitudes of the changes depended on the variety. Both regulators lessened net assimilation rate. Net assimilation rate and dry matter per unit area of leaf were inversely related, possibly because accumulation of substances in leaves decreases photosynthesis. Stolon dry weight was positively correlated with main stem leaf area. There was a direct relation between stem length and tuber dry weight, suggesting that tuber initiation occurs at different stem lengths in different varieties. Tubering was earliest in Epicure and latest in King Edward. Epicure had the greatest tuber weight and smallest stem length.     

Increased chilling tolerance and altered carbon metabolism in tomato leaves following application of mechanical stress

We investigated the effects of brushing on the chilling tolerance and metabolism of nonstructural carbohydrates (soluble sugars and starch) in tomato leaves before, during and after a chilling stress. Tomato plants ( Lycopersicon esculentum Mill. cv. Caruso) were cultivated either without mechanical stress application (control plants) or with daily brushing treatments for 15 days (brushed plants), prior to a 7-day chilling treatment (8/5°C day/night). Brushing resulted in shorter plants with a 34% reduction in leaf dry weight per area and a 59% reduction of soluble sugars and starch, on a dry weight basis. The sugar to starch ratio was not affected by brushing. A greater chilling tolerance in the brushed plants was demonstrated by the maintenance of a significantly higher PSII efficiency in brushed plants (42%) compared to that of the control plants (30%) after 7 days of chilling treatment, less visible damage to the leaf tissue, and a more rapid resumption of growth during 3 days of recovery as compared to control plants. During the chilling treatment levels of soluble sugars per leaf dry weight increased 15-fold in the brushed plants and 5-fold in control plants. In the present study we have demonstrated that brushing can increase chilling tolerance in tomato plants. The observed differences in chilling tolerance and concentration of soluble sugars in the leaves may indicate an involvement of soluble sugar levels in acclimation to chilling.     

Patterns of Assimilate Production and Translocation in Muskmelon (Cucumis melo L.) : II. Low Temperature Effects

Muskmelon (Cucumis melo L.) plants were exposed to a 10°C chilling treatment for 72 hours, which induced leaf chilling injury symptoms (wilting, appearance of water-soaked areas, necrosis). Chilling caused an accumulation of starch, sucrose, hexoses (glucose and fructose), and certain amino acids (glutamate, aspartate, and citrulline) in source leaf tissues, but no accumulation of stachyose or other galactosyl-oligosaccharides occurred. Chilling also caused a general increase in sugar (stachyose, raffinose, sucrose) and amino acid content of the phloem sap, although rates of phloem transport were apparently reduced. Pretreatment of the leaves with a 20-milligram per liter abscisic acid (ABA) spray before chilling prevented the appearance of chilling injury symptoms. ABA pretreatment had little or no affect on sugar accumulation in leaf tissues but greatly reduced or eliminated the chilling-induced amino acid accumulation. Higher levels of aspartate and particularly of arginine were found in phloem saps from ABA-pretreated plants. The data indicate that changes in leaf metabolism caused by environmental stresses such as chilling may change the composition of cucurbit phloem sap. This raises the possibility that some of the deleterious effects of stress on sink tissues may, in part, be due to alterations in the nature of the assimilate supply.     

The influence of the parasitic angiosperm Striga gesnerioides on the growth and photosynthesis of its host, Vigna unguiculata

Cowpea plants (Vigna unguiculata) infected with the root hemiparasiticangiosperm Striga gesnerioides accumulated less biomass thanuninfected plants over a growth period of 60 d. The allometricrelationship between shoot and root dry weight was similar inparasitized plants relative to control plants, as was the proportionof dry matter partitioned into leaf, stem and root tissue. However,infected plants failed to make any significant investment ofdry matter in pods. The rate of photosynthesis of the youngestfully expanded leaf of parasitized plants was significantlylower than for control plants. The lower rates of photosynthesiswere not attributable to stomatal limitation, a loss of chlorophyllor to an accumulation of carbohydrate. The depression of photosynthesisin the young leaves was transient. As control leaves aged, photosynthesisdeclined. This also occurred in Striga infected plants, butto a lesser extent resulting in higher rates of photosynthesisin mature leaves when compared to those of uninfected plants.The foliar nitrogen content of parasitized plants was higherthan control plants consistent with the slower rate of photosyntheticdecline of older leaves. The data are discussed with respectto the influence of parasitic weeds on host growth and photosynthesis. Key words: Cowpea, hemiparasite, allometry, nitrogen     

How the roots contribute to the ability of Phaseolus vulgaris L. to cope with chilling-induced water stress

Intact plants and stem-girdled plants of Phaseolus vulgaris grown hydroponically were exposed to 5 degrees C for up to 4 d; stem girdling was used to inhibit the phloem transport from the leaves to the roots. After initial water stress, stomatal closure and an amelioration of root water transport properties allowed the plants to rehydrate and regain turgor. Chilling augmented the concentration of abscisic acid (ABA) content in leaves, roots and xylem sap. In intact plants stomatal closure and leaf ABA accumulation were preceded by a slight alkalinization of xylem sap, but they occurred earlier than any increase in xylem ABA concentration could be detected. Stem girdling did not affect the influence of chilling on plant water relations and leaf ABA content, but it reduced slightly the alkalinization of xylem sap and, principally, prevented the massive ABA accumulation in root tissues and the associated transport in the xylem that was observed in non-girdled plants. When the plants were defoliated just prior to chilling or after 10 h at 5 degrees C, root and xylem sap ABA concentration remained unchanged throughout the whole stress period. When the plants were chilled under conditions preventing the occurrence of leaf water deficit (i.e. at 100% relative humidity), there were no significant variations in endogenous ABA levels. The increase in root hydraulic conductance in chilled plants was a response neither to root ABA accretion, nor to some leaf-borne chemical signal transported downwards in the phloem, nor to low temperature per se, as indicated by the results of the experiments with defoliated or girdled plants and with plants chilled at 100% relative humidity. It was concluded that the root system contributed substantially to the bean's ability to cope with chilling-induced water stress, but not in an ABA-dependent manner.     

Some aspects of respiration and respiration inhibitors in low temperature effects of the cotton plant

Respiration of leaf tissue from cotlon plants in the nine leaf stage was found to be severely reduced at temperatures below 15°C. In another study, young cotton plants were exposed to chilling temperature (2.8°C) for 72 hours and the ability of the plant tissues to recover respiration at normal temperatures (15 and 25°C) was examined at periodic intervals. Chilling exposures of 12 hours injured cotton tissues as indicated by increased respiratiou of leaves and roots at 25°C. Further chilling malerially reduced the capacity of the leaves to re-estahlish normal respiration rales at higher temperatures. Picolinic acid, Dexon and matonate were used to study the influence of respiratory inhibitors on the chill damage of the collon plants. The chemicals were applied six hours before cold exposure aud fhe growth and development of cold injured plants was studied to indicate the effectiveness of the treatments. Tissue weights at the final harvests indicated that picolinic acid and Dexon treated plants recovered better after cold injury than the untreated plauts. The results suggest thai 15°C may be a critical temperaliire for many physiological processes of the cotton plant because the supply of energy needed for plant reactionsis restricted due to inadequate respiration. They also indicate that the disturhances in respiration are among the early effects of chilling colton plants and may be the cause of delayed growth and development of cotton plants subjccled to non-lethal chilling exposures. It is concluded that chemicals like picolinie acid and Dexon may he effective through protection of specific systems rather than a general reduction of respiration.     

Effect of incident radiation integral on cauliflower growth and development after curd initiation

Two field experiments were conducted to assess the response of cauliflower cv. “Nautilus F1” to different radiation integrals after curd initiation by covering the plants with different levels (0, 38, 50 and 68%) of neutral shading materials during the autumn 1998 and summer 2000. Cauliflower growth and development declined with increasing shade levels after curd initiation. Total above ground dry matter increased linearly with accumulated incident radiation integral after curd initiation, however, under lower radiation conditions, the rate of increase per unit incident radiation integral was greater than under higher radiation conditions. Moreover, radiation conversion coefficient declined linearly with increasing incident radiation integrals up to approximately 6.1 MJ m⁻² d⁻¹ and thereafter, declined more slowly with further increase in incident radiation integrals. Therefore, dry matter accumulation was potentially more efficient under lower incident radiation than higher incident radiation levels. Radiation conversion coefficients for plants under low incident radiation levels were greater than under high incident radiation levels. Curd growth also increased linearly with increasing accumulated incident radiation integral with greater mean relative curd dry matter increase per MJ under lower incident radiation conditions than higher incident radiation levels.     

Effects of growth temperature and winter duration on leaf phenology of Erythronium japonicum,a forest spring geophyte

The effects of growth temperature and winter duration on the leaf phenology of Erythronium japonicum were examined in two experiments. Bulbs wintered in the field were cultivated at 10 and 20° C and the bulbs were cultivated at 15° C after chilling treatment at 3° C for 60 and 120 days and without chilling in winter. The plants cultivated at 20° C showed significantly earlier leaf emergence, a more rapid rate of leaf extension and shorter leaf longevity than those cultivated at 10° C. The decrease in the leaf longevity at 20° C resulted from the decreases in the durations of all of the developmental, mature, and senescent phases. The bulbs without chilling treatment did not sprout leaves and those with chilling treatment sprouted leaves. The increase in the length of chilling treatment from 60 to 120 days affected leaf phenology in same manner as the increase in the growth temperature from 10 to 20° C.     

低温胁迫下乌塌菜对外源硅的生理响应

在土培条件下,研究了低温胁迫下不同浓度的硅酸钠对乌塌菜幼苗生长及生理特性的影响。结果表明,低温胁迫抑制了乌塌菜的生长,降低了干物质的积累。外施硅可以显著提高乌塌菜叶片SOD、POD、CAT活性,迅速积累大量的脯氨酸和可溶性蛋白,从而有效缓解低温胁迫对乌塌菜幼苗的影响,尤其是外施0.5mmol·L^-1Na2SiO3处理15d时,乌塌菜干物质积累达到了正常生长植株的86.2%。但随着施用硅浓度的增加,缓解效果则降低。     

Environmental Influences on Panicle Differentiation and Spikelet Number of Pennisetum americanum

Pearl millet (Pennisetum americanum (L.) Leeke) has a juvenilephase after which the time to panicle initiation is reducedby short daylengths. To understand more fully the mechanismunderlying temperature ? daylength interactions on panicle initiationand differentiation, plants were grown (a) at a range of constanttemperatures under a short daylength from sowing until afterpanicle differentiation and (b) at one temperature until 20d after emergence and then at a range of temperatures duringa 10 d exposure to short daylength. Temperature prior to panicle initiation determined the numberof leaves initiated on the main stem and the size of the apicaldome at the start of panicle initiation. The number of leaves,in turn, influenced the duration of the phase from panicle initiationto anthesis: this phase required a constant thermal time whenexpressed as day degrees per leaf. At anthesis, panicle lengthwas positively correlated with the number of leaves on the mainstem (and temperature) prior to panicle initiation. Changingthe temperature only during exposure to inductive daylengthsaffected the rate of growth of the apical dome so that panicledifferentiation began within 10 d at high temperature (30?C)whereas differentiation did not commence in 10 dat 21?C. Paniclesdeveloped normally if differentiation had commenced under inductivedaylengths whereas panicles were abnormal when plants were returnedto long daylengths after panicle initiation but before visibledifferentiation. Relative extension rates of the panicle during differentiationwere correlated positively with temperature. The results areconsistent with the hypothesis that panicle initiation dependson the apex attaining a critical size and that temperature,by determining the number of leaves initiated on the main stem,affects the size of the apical dome and thus the onset of panicleinitiation, the duration of paniclc differentiation and thenumber of spikelets differentiated. Key words: Pennisetum americanum, panicle differentiation, spikelet number     

不同生长阶段遮荫对番茄光合作用、干物质分配与叶N、P、K的影响

对番茄植株做了两种不同程度的遮荫处理,观测了夏季午间遮荫对光合速率,干物质积累量及其在根,茎,叶之间的分配,和叶N,P,K的含量以及经济产量的影响,发现不同时期遮荫影响不同。（1）遮荫增加三个阶段（开花早期,盛花期和开花后期）的气孔导度和胞间CO2浓度,显著降低开花早期中午的净化合速率,但盛花期中度遮荫（40%遮荫）使净光合速率随着时间的增加逐渐上升,在开花后期表现更加明显,平均净光合速率比对照高20%以上,蒸腾速率也增加较多。（2）开花早期和盛花期重度遮荫（如本实验中的75%遮荫）显著降低根,茎的干重,而开花后期中度遮荫的根,茎干重高于对照,但遮荫对叶干重的影响不明显。（3）开花早期和盛花期遮荫不明显影响叶片中N,P,K的含量,但开花后期中度遮荫使N,P,K含量增加,（4）开花早期两种遮荫对果实产量影响较小,但盛花期重度遮荫使产量降低,全部产量中无效部分所占的比例上升,开花后期中度遮荫的总产量和有效产量增加,单果重也增加,这些结果表明,在某些时期中度遮荫可以克服夏天辐射过强,气温过高对番茄的不良影响,对番茄生长,干物质积累和提高产量等有利,在生产上有意义。