Effects of variation in temperature and light intensity at different times on growth and yield of spring wheat

Spring wheat grown in pots outdoors was transferred to growth rooms for various periods to study the effect of increasing the temperature from 14-4 to 20-3 ^oC (Expt 1) or from day/night values of 15-0/15-2 to 20-0/15-2 ^oC (Expt 2) and of increasing the amount of visible radiation in a 16 h day from 424 to 792 J cm^-2 (Expt 1) or 374 to 740 J cm^-2 (Expt 2). There were no interactions between temperature and radiation. In Expt 1 neither the increase in temperature nor extra radiation, applied for 14 days immediately after the appearance of double ridges on the stem apex, or 14 days later, increased grain yield at maturity. Warmth early, but not late, increased dry weight, leaf area and the number of floret primordia immediately after treatment, but these effects had disappeared by anthesis, 30 days later. Dry weight but not leaf area was increased by extra radiation but the effects had disappeared 2 wk after treatment. An increase in temperature imposed for 16 days starting 5 or 21 days after anthesis (Expt 2) increased dry weight of the ear and decreased that of the rest of the plant immediately after treatment, and decreased leaf area at all times. When plants from the two temperatures were put together in the same conditions, ear growth of plants that had been in the warm was slower than that of plants from the cold treatment, so that the difference in ear weight observed after 16 days of treatment reversed and grain yield was decreased by warmth applied in either period; the component of yield decreased by warmth was grain size. Additional radiation in either post-anthesis period increased dry weight of all parts of the plant and had negligible effects on leaf area. Final grain yield was increased by c. 15% because the individual grains were larger. Early treatment also increased grain number slightly. The effects of treatment during the two post-anthesis periods were similar in size, and additive.     

Effects of variation in ear temperature on growth and yield of spring wheat

Wheat plants were kept in a growth room at 15 ^oC from 7 days after an-thesis until maturity and their ears were warmed to 20 or 25 ^oC for various periods. Continuous warming initially increased the growth rate of the ear and decreased that of the stem, but hastened senescence of the ear and decreased final grain yield by decreasing dry weight per grain. Warming the ears increased the movement of ¹⁴C and nitrogen to them from the leaves and stem during the early stages of grain growth but decreased it later. Warming the ears for only the first 10 or 20 days also hastened ear senescence; grain yield decreased progressively with increase in duration of the warm period. All effects were greater at 25 than at 20 ^oC. The effects of changing ear temperature from 15 to 20 ^oC were independent of the temperature of the rest of the plant. Altering the humidity of the air around the ears by 4–7 mb at constant temperature had no effect on ear growth or senescence. Warming all of the plant except the ears from 15 to 20 ^oC increased ear growth slightly during early grain growth and decreased it later, irrespective of ear temperature: stem dry weight, leaf area and net photosynthetic rate of flag leaves and green stems were decreased and dark respiration rate of stems was increased.     

Effects of Radiation and Temperature on Tiller Survival, Grain Number and Grain Yield in Winter Wheat

Effects of the environment on shoot survival were studied inwinter wheat cv. Avalon grown in microplots at a density of247 plants m^–2. The incident radiation and mean temperaturewere altered during one of three periods of between 14 and 29d duration, the first (P1) starting at the end of tiller productionand the last (P3) finishing near the end of the tiller deathphase, about three weeks before anthesis. Plants were giventemperature and radiation treatments in growth rooms in twoexperiments and extra light outdoors in a third experiment:they were at other times grown outdoors. Increasing radiation by between 60 and 100 per cent during P1had negligible effects on shoot number; during P2 it alwaysdelayed tiller death but increased final ear number in onlyone experiment; during P3 it consistently increased ear numberby up to 100 m^–2. Increased radiation always increasedcrop dry weight immediately after treatment but only sometimesdid this increase persist to maturity. Grain dry weight wasincreased by treatment during P3 of one experiment. Increasingthe temperature by 4 C decreased shoot number, usually onlytemporarily, by hastening death of some tillers. Warmer temperaturesdecreased crop growth after, but not during, treatment and decreasedgrain dry weight. Radiation and temperature rarely interacted. Variation in grain yield within and between experiments relatedwell to variation in number of grains m^–2, which in turnrelated to variation in ear dry weight at anthesis. Triticum aestivum L., wheat, radiation, temperature, tillers, grain yield, grain number     

Effects of Age and Environment on Net Assimilation Rate of Barley

To distinguish between the effects of age and environment onnet assimilation rate (E) of barley (var. Brant) grown in theopen in pots at Ottawa, E was measured outdoors (treatment N)and on similar plants transferred to a constant environmentfor the 2 weeks during which E was determined (treatment T).During June and July, E of treatment N decreased by 77 per cent.;for treatment T this fall increased to 90 per cent, of the initialvalue. E and average day and night temperatures were greaterin the constant environment than outdoors in early June, andin July they were greater outdoors. Incident light energy wasalways greater outdoors. Thus, the fall in E with age was partiallymasked outdoors by an increase caused by the improvement inenvironmental conditions during the experiment. Plants grown continuously in the constant environment had lowerE, greater leaf area and dry weight, and ears emerged earlierthan plants of similar age that had been transferred for 2 weeksto the constant environment from outdoors. E of plants growncontinuously in the constant environment decreased with time,both when the pots were moved away from the light panel to maintaina constant light intensity at the base of the youngest leafand when the pots remained stationary so that the plants grewtowards the lights. After ears emerged, E for treatments N and T was measured onplants whose ears were shaded to prevent them photosynthesizing.Photosynthesis in the ear accounted for 19 per cent, of thefinal ear dry weight during the first 2 weeks after emergence,12 per cent, during the 3rd and 4th, and 3 per cent, duringthe 5th and 6th weeks. Shading had no effect on weight of plantparts other than ears and had similar effects outdoors and inthe constant environment.     

Growth, Development, and Yield of Spring Wheat in Artificial Climates

Spring wheat was grown to maturity in three growth rooms providing:(a) 18 h of light at 20° C and 6 h of darkness at 15°C (hot long days, HL); (b) 18 h of light at 15° C and 6h of darkness at 15° C (cold long days, CL); (c) 14 h lightat 20° C and 10 h of darkness at 15° C (hot short days,HS). Plants were moved between environments at spikelet initiationand anthesis, so dividing the growth period into three. Meanlengths in days of these periods in the different environmentswere: Period 1: HL 16, CL 18, HS 25; Period 2: HL 42, CL andHS 61; Period3: HL 53, CL 83, HS 63. The length of periods 2and 3 also depended on previous treatments. Grain dry weight was affected by environmental differences inall periods and effects in successive periods were additive.Compared with HL, CL or HS in period I before initiation increasedgrain yield by 6 per cent by increasing grain number per ear,HS in period 2 between initiation and anthesis decreased itby 24 per cent by decreasing the number of grains per spikeletand the proportion of spikelets that contained grain; CL inperiod 2 increased it by 21 per cent by increasing the numberof ears; CL in period 3 after anthesis increased it by 16 percent because leaves died later; HS in period 3 decreased itby 14 per cent because there was less radiation and hence lessphotosynthesis. Dry weight of shoot and root at maturity wasincreased by CL or HS in periods 1 or 2, and increased by CLand decreased by HS in period 3. The effects on final yieldof treatment during periods 1 and 2 were the consequence ofsimilar effects already produced at anthesis, and shoot androot dry weight changed little during period 3. The effects of environmental differences on grain dry weightcould not be explained by differences in leaf-area durationafter anthesis (D₃), except that CL in period 3 increased bothyield and D₃ but not proportionately, so that, as with HS inthe same period, grain: leaf ratio was decreased. Environmentaldifferences in periods 1 and 2 appeared to affect grain weightby altering the capacity of the ear to accumulate carbohydrates,determined by the number of grains per ear, rather than by alteringthe supply of carbohydrates, determined by D₃. There were some interactions between environments in differentperiods which were usually small compared with the main effects.     

Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Immediately after anthesis ears of spring wheat absorbed lessthan 0.5 mg CO₂, per hour in daylight and later evolved CO₂,in the light and in the dark. The rate of apparent photosynthesisof the combined flag-leaf lamina and sheath and peduncle (collectivelycalled flag leaf) of two spring wheat varieties, Atle and JufyI, was 3–4 mg per hour; the rates of the flag leaf andthe ear of two spring barleys, Plumage Archer and Proctor, wereeach about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergenceand maturity accounted for most of the final grain dry weight.The CO₂, fixed by the wheat ear was equivalent to between 17and 30 per cent of the grain weight, but more than this waslost by respiration, so assimilation in the flag leaf was equivalentto 110–20 per cent of the final grain weight. In barley,photosynthesis in the flag leaf and the net CO₂ uptake by theear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because oftheir greater surface, and flag leaves of wheat photosynthesizedmore than those of barley because they had more surface anda slightly greater rate of photosynthesis per dm².     

Analysis of Growth and Yield of Winter and Spring Wheats

In a field experiment to investigate the physiological causesof variation in yield between autumn- and spring-sown wheatand between old and new varieties, the grain yields of the winterwheats were 3-15 per cent, greater than of the spring ones andthe new varieties Cappelle-Desprez and Jufy I yielded 40-70per cent, more than Squarehead's Master and Atle. Nitrogen fertilizerincreased the yields of Cappelle-Desprez and Jufy I more thanof Atle, and decreased the yield of Squarehead's Master by makingit lodge. Until ear emergence the winter varieties had greater leaf-areaindices (L) and dry weights, but smaller net assimilation rates(E), than the spring varieties. Square-head's Master had greaterL but smaller E, and similar dry weight to Cappelle-Desprez.Jufy I had similar E to Atlc, but greater L and dry weight.Nitrogen increased L and dry weight, but decreased E. All thedifferences in E between varieties and nitrogen treatments couldbe explained by the opposite effects on L, that is to say, thedifferences in E were caused by variation in mutual shadingarising from the differences in L and not by changes in leafphysiology. L of winter wheat reached its maximum at the end of May, butL of spring wheat continued to increase until ear emergence.Afterwards Ldecreased more rapidly for winter than for springwheat, so that eventually spring wheat had the greater L. Thesedifferences in the time changes of L partially compensated forthe shorter growth period of spring wheat, and tended to equalizethe grain yield from winter and spring sowings. After ear emergence total dry weight of winter varieties continuedto be greater than of spring ones, but the difference in dryweight of ears was much smaller because ear: shoot dry-weightratio was greater for the spring varieties. Total dry weight,ear dry weight and ear: shoot ratio were all greater in thenew than in the old varieties. Leaf area duration (D) afterear emergence was slightly greater for the winter than for thespring varieties and similar for old and new. The apparent efficiencyof this leaf area in grain production, measured by the grainleaf ratio (ratio of grain dry weight to D), was similar forwinter and spring varieties but greater for new than for old.This suggests that Cappelle-Desprez and Jufy I have higher grainyields because their ears photosynthesize more than do the earsof Squarehead's Master and Atle. Before ear emergence winter varieties had more shoots than springones, and old varieties more than new. After ear emergence therewere only small differences in numbers of ears; percentage survivalwas greater for spring than for winter and for new than forold varieties. Differences in dry weight between varieties were not causedby differences in nitrogen uptake.     

The Production and Distribution of Dry Matter in Maize after Flowering

An experiment in which different groups of leaf laminae wereremoved, or ears shaded, shortly after silking showed that mostof the dry-matter increase after flowering was produced by upperleaves. The top five, the middle four, and the bottom six laminaeaccounted, respectively, for 26 per cent, 42 per cent, and 32per cent of the leaf area duration (D) of the laminae afterflowering; the estimated contributions of the three groups todry-matter production by the laminae after flowering were about40 per cent, 35–50 per cent, and 5–25 per cent,respectively. The sheaths provided about one-fifth of the totalleaf area and probably contributed about one-fifth, and laminaefour-fifths, of the total dry matter produced after flowering.The contribution from photosynthesis by the ear was negligible,presumably because its surface area was only 2 per cent of thatof the leaves. Leaf efficiency (dry matter produced per unitarea) decreased greatly from the top to the base of the shoot.When laminae were removed, the grain received a larger fractionof the dry matter accumulated after flowering, less dry matterremained in the stem, and the photosynthetic efficiency of theremaining leaves was apparently increased. When alternate laminae were removed at the time of silking (half-defoliation)D was decreased by 40 per cent, and the subsequent productionof dry matter decreased nearly proportionately, so that netassimilation rate (E) was not affected but grain dry weightwas decreased by only 32 per cent. At the final harvest, thegrain of half-defoliated plants constituted 80 per cent of thedry matter accumulated after flowering, compared with 65 percent for intact plants. Stem weight decreased from two weeksafter flowering in half-defoliated plants, but remained nearlyconstant in intact plants. When pollination was prevented andno grains formed, E during the first month after flowering wasunaffected; the dry matter that would have passed into the grainaccumulated in the stem and husks, not in the leaves. The decrease in stem weight caused by defoliation suggests thatpreviously stored dry matter was moved to the grain. That suchmovement is possible was shown by keeping prematurely harvestedshoots in the dark for two weeks with their cut ends in water;the dry weight of the grain increased and that of the stem,laminae, husks, and core decreased. Nevertheless, dry-matterproduction after flowering was more than sufficient for graingrowth, and previous photosynthesis probably contributed littleto the grain.     

The Effect of Shade During Leaf Expansion on Photosynthesis by White Clover Leaves

In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m^–2s^–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m^–2 s^–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m^–2 s^–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m^–2 s^–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance     

Drought resistance of wheat plants inoculated with vesicular-arbuscular mycorrhizae

Summary Drought resistance of wheat (Triticum aestivum L.) as influenced by two vesiculararbuscular mycorrhizal (VAM) fungi,Glomus fasciculatum ¹⁰ andGlomus deserticola ¹⁹, was evaluated. Soil columns 0.15 m diam. by 1.20 m length were used to reduce the influence of limited rooting space. With initial soil water at 0.5 MPa (0.145 kg kg^–1), plants were subjected to low-level water stress throughout the experiment and severe water stress for 24 h at one (55 days after transplanting, Feekes scale 10.1) two (55 and 63 days, Feekes 10.1 and 10.2), or three (55, 63, and 70 days, Feekes 10.1, 10.1, and 10.2) periods. After each stress period, one set of plants was watered and grown to maturity without subsequent water stress. A second set of plants was harvested 1 week after stress.G. fasciculatum-inoculated plants harvested 7 days after stress at 55 days had greater leaf area and leaf, total plant, and root weight than non-VAM plants.G. deserticola-inoculated plants had greater leaf area and leaf weight than non-VAM plants. After stress at 55 and 63 days, leaf area, and leaf and total dry weight were again greater for VAM than for non-VAM plants. However, after stress at 55, 63, and 70 days, differences in aboveground biomass between VAM and non-VAM plants were not significant at P=0.05. Aboveground biomass was not affected by VAM species in plants stressed at 55 or 55 and 63 days, butG. fasciculatum-inoculated plants produced more tillers atter stress at 55 days. When grown to maturity, VAM plants which had undergone three stress periods had twice the biomass and grain yield as non-VAM plants subjected to the same stress. The three stress periods reduced number of heads and kernel numbers of weight of non-VAM plants compared to VAM plants.G. fasciculatum-inoculated plants consistently had increased root weight and rooting depth.Contribution from the Agricultural Research Service, USDA, in cooperation with the Nebr. Agric. Exp. Stn., Univ. Nebr.-Lincoln, Lincoln, Nebr. Published as Paper No. 7571 Journal Series, Nebr. Agric. Exp. Stn.     

Influence of Tops and Roots on Net Assimilation Rate of Sugar-beet and Spinach Beet and Grafts between them

Sugar-beet has a larger storage root and greater net assimilationrate (E) than spinach beet. To determine whether the greaterroot was a result or cause of the greater E, grafts were madebetween tops and roots of sugar-beet and spinach-beet in allfour possible combinations. Grafted plants with sugar-beet roots had greater E and rootdry weight, less leaf area and top dry weight and lower concentrationof sugar in the leaf lamina, than those with spinach-beet roots,irrespective of the type of top. Grafted plants with sugar-beettops had greater E, total and root dry weight, but less leafarea, than those with spinach-beet tops, irrespective of thetype of root. The difference in E between grafted plants withsugar-beet tops and spinach-beet tops was similar to that betweengrafted plants with sugar-beet roots and spinach-beet roots.It increased with time to 60 per cent. Increases in E probably represent increases in rate of photosynthesis.Sugar-beet roots probably increased photosynthesis by providinga better sink for assimilates than spinach-beet roots.     

Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer

Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO₂ respiredduring the whole period of grain growth varied from 163 to 443g m^–2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO₂ lost was respired by the ear. The additionof 180 kg N ha^–1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO₂ lost by the ears.The semi-dwarf varieties lost less CO₂ from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the¹⁴C contents of shoots sampled immediately after a 30 s exposureto ¹⁴CO₂ and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 16–28 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment     

Short and Long Term Fluctuations of the Leaf Mass Per Area of Tomato Plants--Implications for Growth Models

The leaf mass per unit leaf area (LMA) is a key variable inmany growth models, since it is often used to predict leaf areaexpansion from leaf dry weight increase, orvice versa. Influencesof source-sink balance on leaf area, leaf dry weight, LMA, andleaf content in non-structural carbohydrates were investigatedin glasshouse tomato crops. The source-sink balance was manipulatedby artificial shading, CO₂enrichment or fruit removal usingdifferent tomato cultivars. Leaf area was hardly affected bycompetition for assimilates except under extreme conditions.In contrast, leaf dry weight, and consequently LMA, underwentlarge and rapid fluctuations in response to any factor thatchanged source and sink activities. A 60% reduction of photosyntheticallyactive radiation involved a 24% decrease in LMA after 10 d.Carbon dioxide enrichment and fruit removal induced about a45% and 15% increase in LMA, respectively, on plants with twofruiting trusses, but hardly affected LMA of producing plants.No significant cultivar effect could be identified. Changesin starch and soluble sugar content in leaves accounted foronly 29% of diurnal variations in LMA, suggesting regular fluctuationsof other components. We propose that structural LMA varies betweena maximum and a minimum value according to the ratio of assimilatesupply and demand during leaf development. Leaf area is independentof the supply of assimilates when the minimum structural LMAis realised. When the maximum structural LMA is attained, astorage pool of assimilates may accumulate in leaves duringperiods of high supply and low demand. We present a model includingthese hypotheses, which predicts structural and non-structuralLMA variations of plants with different source-sink ratios.Copyright1998 Annals of Botany Company Tomato,Lycopersicon esculentumMill., SLA, SLW, leaf growth, vegetative sink strength, assimilate competition, source-sink ratio, non-structural carbohydrate, models.     

Transport of Recently Assimilated15N Nitrogen to Individual Spikelets in Spring Wheat Grown in Culture Solution

Two cultivars of spring wheat ( Triticum aestivum L.), Sport(high protein) and WL4 (low protein), were grown to maturityin culture solution. Nitrogen in the form of nitrate was addedin daily doses at stepwise-decreasing relative rates to ensurenormal development, and both cultivars received the same totalamount of N during development. At weekly intervals from anthesisto maturity the daily nitrate dose was, for selected groupsof plants, labelled with¹⁵N. After the labelling period theselected plants were harvested and analysed. The cultivar WL4produced more biomass than Sport, as well as more spikeletsand more grains per ear, with a higher mean grain weight, suchthat grain yield of WL4 was 57% greater than Sport. The earsof both cultivars were heterogenous: mean grain weight was highestin middle spikelets, which also contained more grains; the Ncontent followed the pattern of dry weight with more N in themiddle spikelets; but the N concentration was practically thesame in all spikelets (2.15% of d. wt in WL4 and 3.33% in Sport).The distribution of¹⁵N showed that the main stem ear maturedmuch earlier than tiller ears. The results of this nitrogen-labellingexperiment show that, late in development, substantial amountsof recently-absorbed N were immediately assimilated and transportedto the ears. Transport of¹⁵N decreased earlier to the top spikeletsthan to the bottom spikelets. As both cultivars were grown underidentical conditions and both received the same amount of Nit was concluded that the difference in grain N concentrationwas not caused by differences in the capacity of N assimilationand translocation but rather by different rates of accumulationof non-nitrogenous dry matter in the grains. Ear; grain; nitrate; nitrogen transport; Triticum aestivum L.; yield     

Seed Production in Leafless and Conventional Phenotypes of Pisum sativum L. in Relation to Water Availability Within a Controlled Environment

Water requirements in relation to seed production was studiedin near-isogenic lines of leafless (afafstst) and conventional(++++) pea plants (Pisum sativum). The plants were grown toseed maturity in pots in a controlled environment under conditionsof high, medium and low irrigation levels. When each genotypewas irrigated independently and on demand and the soil moisturecontent maintained at 65–80 per cent of full capacitythere was no significant phenotypic difference in water useefficiency (WUE), defined as g d. wt seed per kg H₂O utilized.There existed genotypically-controlled upper and lower limitsto yield between which the total dry weight of seed per plantcan be determined by water availability. There was no significantdifferential effect of genotype or of irrigation treatment onthe number of pods, number of seed, unit seed dry weight andbiological yield per plant. There was significant interactionon stem length, and leaf area at specified nodes. When the wateractually required in relation to the water available was takeninto account, the leafless phenotype consistently utilized 33–38per cent less water and produced a correspondingly lower totaldry weight of seed than the conventional counterpart. Independentlyof regime the total dry weight seed per phenotype remained anear constant proportion of the above-ground biomass. Pisum sativum L., garden pea, leafless peas, seed production, water availability     

Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

The Effects of Silicon on Cucumber Plants Grown in Recirculating Nutrient Solution

Cucumber plants (Cucumis sativus) cv. Corona were grown in recirculatingnutrient solution containing either 10 mg l^–1 SiO₂ (lowSi) which was the level present in the water supply or givenan additional 100 mg l^–1 SiO₂ (high Si). Silicate wasdepleted from the solution when cucumbers were grown, but accumulatedwhen tomatoes were grown. Major effects on cucumber leaves ofadded Si were: increased rigidity of the mature leaves whichhad a rougher texture and were held more horizontally; theywere darker green and senescence was delayed. The mature highSi leaves acquired characteristics of leaves grown in a higherlight intensity, i.e. they had shorter petioles and an increasedfresh weight per unit area, dry weight per unit area, chlorophyllcontent, RuBPcarboxylase activity and soluble protein (all expressedper unit area of interveinal laminar tissue). Addition of Sidid not affect the final leaf area of the mature leaves butroot fresh weight and dry weight were increased. A pronouncedeffect of Si addition was the increased resistance to the powderymildew fungus Sphaerotheca fuliginea. Despite regular applicationsof fungicide, outbreaks of the fungal disease occurred on mostof the mature leaves on the low Si plants, while the high Siplants remained almost completely free of symptoms. The additionof Si could be beneficial to cucumbers grown in areas wherethe local water supply is low in this element, especially whengrown in recirculating solution or in a medium low in Si, e.g.peat. Cucumber, silicon, fungal resistance, powdery mildew, senescence, RuBPcarboxylase     

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     

Physiological Factors Limiting Grain Size in Wheat

The effects on grain size of changing the supply of assimilates,by thinning before anthesis or by shading the plants or by halvingthe ears either early or late in grain growth, were studiedin two glasshouse experiments with Kleiber spring wheat (Triticumaestivum L.), in 1976 and 1977. Late treatments had no effect,presumably because little grain growth occurred thereafter.Thinning the plants before anthesis increased, and shading theplants soon after anthesis decreased grain size. Halving theears soon after anthesis increased the size of the remaininggrains, but grain weight per ear decreased. The effect on grainsize of halving the ear tended to be smaller under conditionsmore favourable for photosynthesis, except when the plants werethinned before anthesis. Shading decreased the total amountof nitrogen per culm and the proportion of total nitrogen recoveredin the ear. Halving increased the retention of nitrogen in thestem of unshaded shoots and had no effect on nitrogen distributionwithin shaded shoots. In 1977 halving the ear increased the rate of dry matter accumulationin the grain throughout the grain filling period, but in 1976the increase in dry weight was faster in the grains of halvedears only during early grain growth. Later the grains in halvedand intact ears increased in dry weight at the same rate, eventhough the supply of photosynthate and the capacity of the grains(as measured by volume) were greater in the halved ears. Theseresults are discussed in relation to the influence on finalgrain weight of assimilate supply and the storage capacity ofthe grain.     

The Dynamics of Leaf Growth and Photosynthetic Capacity in Capsicum frutescens L.

In Capsicum frutescens L. cv. California Wonder the specificleaf weight (dry weight per unit laminar area) at leaf unfoldingis three times higher in the eighth leaf than in the first leafproduced. Intermediate leaves exhibit a trend between the twoThe change in specific leaf weight during laminar expansionis greatest in leaf 1 and least (sometimes zero) in leaf 8.Large changes in specific leaf weight during laminar expansionare associated with a large degree of palisade cell expansion,while leaves showing smaller rates of change have less palisadecell expansion but cell division is more evident. At leaf unfoldingthe fraction I protein content per unit laminar area is higherin upper than in lower leaves. Ribulose diphosphate carboxylaseactivity per unit laminar area and ¹⁴CO₂ fixation per unit laminararea have a similar pattern of development in all leaves andshow no correlation with the changes in specific leaf weight.The peak of activity in all leaves occurs when the laminar areais 10 cm². These results are compared with previous data onlaminar expansion and are seen as in accord with current ideason leaf growth.