Agronomy Department, Shandong Agricultural University, Taian, Shandong Province, China

Allocation of Photosynthates and Grain Growth of Two Wheat Cultivars with

Different Potential Grain Growth in Response to Pre- and Post-anthesis Shading

Z. Wang, Y. Yin, M. He, Y. Zhang, S. Lu, Q. Li and S. Shi

Authors’ address: Prof. Dr Z. Wang (corresponding author; e-mail: zlwang@sdau.edu.cn), Prof. Y. Yin, M. He, Y. Zhang,

S. Lu, Q. Li and S. Shi, Agronomy Department, Shandong Agricultural University, Taian, Shandong Province 271018, China

With 2 figures and 6 tables

Received December 3, 2002; accepted February 5, 2003

Abstract

Grain yield in wheat is dependent on photosynthateproduction and allocation. Light intensity is one of themain factors affecting photosynthate production andallocation, and grain yield. This study was conducted todetermine whether cultivars varying in grain number perspike and grain weight respond differently to pre-anthesisshading (PRE) and post-anthesis shading (POST), and tocharacterize the responses in production and allocation ofphotosynthate, yield and yield components, and spiketraits. Both PRE and POST caused a decrease in bothdry matter (DM) accumulation and allocation to grain.Cultivar Lumai 22, which has a large spike and largegrains, was more sensitive to either PRE or POST. PREreduced photosynthate production and partitioning to thespike in Lumai 22 at anthesis. In contrast, PRE had littleinfluence on these parameters in the small-spike, small-grain cultivar Yannong 15. POST reduced the partition-ing to the grain, especially in Lumai 22, for whichmarked reductions in biomass and grain yield were foundfor both the PRE and POST treatments. Changes in yieldcomponents attributable to shading varied with cultivars.The number of spikes m)2 was not affected by eitherPRE or POST. Lumai 22 was more seriously affected byshading than Yannong 15 in terms of grain number perspike and weight per grain. The decreases in grainnumber or weight per spikelet in both the PRE andPOST treatments took place mainly in the upper andbasal spikelets, especially in Lumai 22. We concludedthat the adaptability of the small-spike, small-graincultivar Yannong 15 to either PRE or POST was muchgreater than that of the large-spike, large-grain cultivarLumai 22 in terms of many characteristics closely relatedto grain yield. Hence, we suggest that, in areas where lowlight intensity often occurs, the small-spike, small-graincultivar would be more likely to produce high, stablegrain yields.

Key words: dry matter accumulation — photosynt-hate partitioning — shading effect — spike traits —Triticum aestivum L. — yield

Introduction

Grain yield in wheat is dependent on photosynt-hate production and allocation. Factors such aslight intensity affect photosynthesis and photosynt-hate allocation and influence grain yield in anumber of ways. In eastern China, includingShandong, Jiangsu, Anhui and part of Henan,low light intensity as a result of cloudy or rainydays often occurs during the growth period frombooting until grain filling. This has a large effect ongrain yield and yield components (Jin 1996).

Various authors have demonstrated that pre-anthesis shading primarily reduces spike density,spikelet number and grain number per spike; post-anthesis shading mainly reduces grain weight, andthen grain number (Willey and Holliday 1971,Kemp and Whingwiri 1980, Fischer 1975, 1985,McMaster et al. 1987, Savin and Slafer 1991).Many studies have suggested that changes in grainnumber per spike and per m2 are closely associatedwith changes in biomass allocated to spikes duringspike development. Shading before anthesis signi-ficantly reduces both the number of grains perspike or per m2 and grain yield (Fischer andStockman 1980, Fischer 1985, Grabau et al. 1990,Jedel and Hunt 1990, Savin and Slafer 1991, Slaferet al. 1994). As shading effects on the number ofgrains are to a large extent linked to effects on drymatter accumulation and allocation to the spike atanthesis, differences must exist between cultivarswith different potential grain number or grainweight responses. However, this aspect has notbeen studied in detail.

The dry matter in winter wheat grains is mainlyderived from both reserve photosynthate in thesheath and stem stored prior to anthesis and

J. Agronomy & Crop Science 189, 280—285 (2003)� 2003 Blackwell Verlag, BerlinISSN 0931-2250

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current photosynthate produced after anthesis(Evans et al. 1975). Yu (1990) and Jin (1996)suggested that 2 ⁄3 to 3 ⁄4 of dry matter in winterwheat grains originates from photosynthate pro-duced after anthesis. Ravi and Ghildiyal (2001)found that genotypic differences existed betweenlarge-grain and small-grain cultivars in 14C-sucroseuptake and 14C-sucrose conversion to insolublecomponents. Shading after anthesis lowers photo-synthate production, leading to decreases in grainweight (McMaster et al. 1987, Jedel and Hunt1990, Slafer et al. 1994). Little information isavailable concerning the responses of cultivarsvarying markedly in potential grain number orgrain weight to post-anthesis shading, in terms ofphotosynthetic production and allocation, grainyield, and yield components.

The objectives of the study were: (1) to determinewhether large-spike, large-grain and small-spike,small-grain cultivars respond differently to pre- andpost-anthesis shading, and (2) to characterize theirresponses to pre- and post-anthesis shading interms of the production and allocation of photo-synthates, yield and yield components, and spikemorphology. The results reported here contributeto criteria for selection of suitable cultivarsfor higher grain yield of winter wheat in easternChina.

Materials and Methods

Plant material

The field experiments were conducted in two seasonsfrom October 1995 to June 1996 and from October 1996to June 1997 at the Experimental Station of Shan-dong Agricultural University, Taian, China (36�11¢ N,117�08¢ E). The soil was a sandy loam that containedorganic matter at 1.35 % and available nitrogen (N),phosphorus (P) and potassium (K) at 103.5, 38.5 and85.5 mg kg)1, respectively. Maize (Zea mays L.) was theprevious crop. Pre-sowing fertilizer was applied at the rateof 6 kg m)2 farmyard manure, 20 g m)2 urea, 13 g m)2

calcium superphosphate and 10 g m)2 potassium sulphate.The N fertilizer was topdressed in twice, each time at therate of 10 g m)2 urea at the initiation of elongation andat the boot stage (when the flag leaf expanded), respect-ively.

Two typical cultivars of winter wheat currently used inlocal production were chosen for this study. CultivarLumai 22 has large spikes (50–55 grains per spike), largegrains (48–54 mg per grain), and usually a spike weight of2.5–2.9 g. Cultivar Yannong 15 has small spikes (28–33grains per spike), small grains (36–39 mg per grain), andusually a spike weight of 1.1–1.3 g.

Shading treatments for each cultivar consisted of acontrol with full light intensity (CONT), a pre-anthesisshading treatment (PRE) and a post-anthesis shadingtreatment (POST). Shades were made from muslin suspen-ded 0.2 m above the crop canopy. They reduced the lightintensity to about 65 % of full light intensity. TreatmentPRE was imposed for a 22-day period (approximately thebooting period) prior to anthesis. The treatment POST wasimposed for a 22-day period after anthesis. The treatmentswere arranged in a randomized complete block design withthree replications. The plot size was 4 m by 12 rows (0.20 mbetween rows). Seeds were sown on 3 October 1995 and 5October 1996 in each plot. At the three-leaf stage, plotswere thinned to a density of 155 plants m)2.

Dry matter accumulation and allocation

At anthesis, 50 culms were harvested from each plot bycutting the stems at soil level, which were used forestimating dry matter from each plot to determine the drymatter accumulation before anthesis. At maturity, 50 culmswere harvested from each plot to determine the dry matteraccumulation from anthesis until maturity. The sample of50 culms was separated into grain and vegetative parts todetermine dry matter allocation between grain (reproduc-tive part) and vegetative parts and to calculate the harvestindex as the fraction of grain in the total above-ground drymatter (biomass) at maturity.

Radioactive labelling and radioactivity determination

At both the initial stage of anthesis and the mid-grain fillingstage, flag leaves of selected plants in each treatment werepulse-labelled with 14CO2. Each flag leaf was placed into achamber of transparent polyethylene film filled with 10 cm3

of 14CO2, which was generated by acidifying Na14CO3

solution with excess of 50 % lactic acid and whoseradioactivity was 925 KBq dm)3. The enclosed flag leaveswere allowed to assimilate for 30 min (10:00 h local time)under natural light, and then the chambers were removed.The labelled plants were harvested 3 days after labellingand separated into subsamples: spike, stem, sheath andblade (sampling at anthesis) or grains, chaff, stem, sheathand blade (sampling at grain filling). Each subsample wassubjected to a temperature of 105 �C, dried in an oven at80 �C to constant weight and ground into powder. Fromeach subsample, 50 mg was used for the analysis of 14C.The radioactivity of each subsample was determined by theliquid scintillation method, and calculated per unit drymatter of organ. The percentage of radioactivity in eachplant part was then determined.

Yield and spike characteristics

Five 1-m-long rows were harvested to determine grain yieldper unit area. The spike characteristics, including grainsetting and grain size in each spikelet position on the rachis,

Effect of Shading on Wheat 281

were investigated in order to ascertain pre- and post-anthesis shading effects on yield components.

Statistical analysis

The results obtained for the different shading treatmentswithin each cultivar were analysed using one-way analysisof variance. The treatment means were compared usingleast significant differences at the the 0.05 level of probab-ility.

Results and Discussion

Dry matter (DM) accumulation and allocation

PRE led to a significant decrease in DM accumu-lation at anthesis in both cultivars (Table 1). Thetwo cultivars differed, however, in the response ofDM allocation to PRE. The decrease of DMaccumulation attributable to PRE in Lumai 22 was10.1–12.4 % more than that in Yannong 15,indicating that the two cultivars were significantly

Table 2: Dry matter accumulation in two cultivars of winter wheat from anthesis to maturity

Cultivar

DM accumulation in g culm)1 (% of control)

1995–1996 1996–1997

CONT PRE POST CONT PRE POST

Lumai 22 2.541 a (100) 2.259 b (88.9) 2.073 c (81.6) 2.475 a (100) 2.229 b (90.1) 2.071 c (83.7)Yannong 15 1.297a (100) 1.324 a (102.1) 1.229 b (94.8) 1.157 a (100) 1.150 a (99.4) 1.061 b (91.7)

Means within a cultivar followed by a different letter are significantly different at P ¼ 0.05.

Table 3: Dry matter allocation in various plant parts at maturity for two cultivars of winter wheat underthree treatments

Season Cultivar Treatment

DM allocation

Grain Vegetative parts Total

mg culm)1 % mg culm)1 % mg culm)1 %

1995–1996 Lumai 22 CONT 2507 a 100 3171 a 100 5678 a 100PRE 2103 b 83.9 2844 b 89.7 4947 c 87.1POST 2128 b 84.9 3082 a 97.2 5210 b 91.8

Yannong 15 CONT 1362 a 100 1850 a 100 3212 a 100PRE 1366 a 100.3 1837 a 99.3 3203 a 99.7POST 1287 b 94.5 1857 a 100.1 3144 a 97.9

1996–1997 Lumai 22 CONT 2576 a 100 3357 a 100 5933 a 100PRE 2165 b 84.0 3088 b 92.0 5253 b 88.5POST 2057 c 79.9 3354 a 99.9 5411 b 91.2

Yannong 15 CONT 1243 a 100 1718 a 100 2961 a 100PRE 1189 b 95.7 1719 a 100.0 2908 a 98.2POST 1142 b 91.9 1709 a 99.5 2851 b 96.3

Means within a cultivar followed by a different letter are significantly different at P ¼ 0.05.

Table 1: Dry matter accumulation in two cultivars of winter wheat at anthesis

Cultivar

DM accumulation in g culm)1 (% of control)

1995–1996 1996–1997

CONT PRE CONT PRE

Lumai 22 3.137 a (100) 2.688 b (85.7) 3.458 a (100) 3.023 b (87.4)Yannong 15 1.915 a (100) 1.879 a (98.1) 1.804 a (100) 1.758 a (97.5)

Means within a cultivar followed by a different letter are significantly different at P ¼ 0.05.

282 Wang et al.

different in their adaptability to PRE. DM accu-mulation from anthesis until maturity is a veryimportant index related to grain yield in wheat(Evans et al. 1975). Although the wheat stand ofLumai 22 in the PRE treatment was not shadedafter anthesis, DM accumulation from anthesisuntil maturity still decreased by about 10 %, ascompared with the control. However, a similarresult was not obtained for Yannong 15. POSTreduced DM accumulation from anthesis untilmaturity by 16.3–18.4 % in Lumai 22 and by5.2–8.3 % in Yannong 15 (Table 2).

DM allocation between the grain (reproductivepart) and vegetative parts of the wheat plant isshown in Table 3. It was found that DM allocationin the grain was affected to a greater extent byeither PRE or POST than that in the vegetativeparts, especially in Lumai 22. As compared withthe control, 16.0–16.1 % and 15.1–20.1 % decrea-ses of DM allocation in grains of Lumai 22occurred in PRE and POST treatments, respect-ively.

From the above results, it could be concludedthat, of the two cultivars, Lumai 22 was moresensitive to either PRE or POST than Yannong 15in terms of both total DM and DM allocation ingrains; as regards DM allocation in the vegetativeparts and in grains, the latter was more affected byeither PRE or POST, regardless of cultivar.

Photosynthate partitioning

At anthesis, a large proportion of photosynthateswas partitioned into the stem and sheath, andabout 11.4–20.4 % into the spike in the controltreatment (Table 4). The effect of PRE on parti-tioning of photosynthates varied markedly betweencultivars. PRE reduced partitioning of photosynt-hates to the spike in Lumai 22, while it had a littleeffect in Yannong 15.

The grain was the main importer of the photo-synthates produced during grain filling, and acertain proportion of photosynthates was alsopartitioned to the stem and sheath (Table 5). The

Table 4: Effects of pre-anthesis shading on photosynthate partitioning into various parts of wheat plantsat anthesis

Season Cultivar Treatment

Photosynthate partitioning (%)

Spike Stem Sheath Blade

1995–96 Lumai 22 CONT 15.2 39.8 26.9 18.1PRE 10.8 35.9 27.6 25.7

Yannong 15 CONT 20.4 38.1 26.2 15.3PRE 17.8 40.3 24.7 17.2

1996–97 Lumai 22 CONT 11.4 44.3 23.2 21.1PRE 8.3 38.5 24.9 28.3

Yannong 15 CONT 18.9 38.8 22.7 19.6PRE 18.1 34.3 23.9 23.7

Table 5: Effects of pre- and post-anthesis shading on photosynthate partitioning into various parts ofwheat plants at mid-grain filling

Season Cultivar Treatment

Photosynthate partitioning (%)

Grain Chaff Stem Sheath Blade

1995–1996 Lumai 22 CONT 32.8 3.2 25.6 23.3 15.1PRE 41.7 4.8 21.7 17.8 14.0POST 25.1 3.5 28.7 23.5 19.2

Yannong 15 CONT 35.7 4.3 22.3 19.6 18.1PRE 39.8 3.3 19.7 22.5 14.7POST 32.5 4.7 20.4 20.7 21.7

1996–1997 Lumai 22 CONT 36.2 4.6 25.7 20.4 13.1PRE 46.7 5.9 20.4 12.8 14.2POST 28.9 5.1 31.6 21.7 12.7

Yannong 15 CONT 40.4 3.7 20.9 19.6 15.4PRE 48.3 4.3 15.7 16.9 14.8POST 35.4 4.7 23.4 22.7 13.8

Effect of Shading on Wheat 283

photosynthate partitioning to the grain wasenhanced by PRE, and was 4.1–10.5 % higher thanthat of control in both Lumai 22 and Yannong 15 inthe two seasons. The effect of POST on photosynt-hate partitioning was opposite to that of PRE. Thepartitioning to the grain was markedly reduced byPOST, especially in Lumai 22.

Yield and yield components

The biomass of wheat was reduced significantly byeither PRE or POST in Lumai 22. However, therewas no significant change of biomass attributableto either PRE or POST in Yannong 15 (Table 6).

Either PRE or POST caused a marked reductionin the grain yield of Lumai 22, the magnitude ofwhich was larger than that of the reduction inbiomass (Table 6). In Yannong 15, shading wasalso found to decrease grain yield, but the extentof the decrease was much less than that inLumai 22.

The change in yield components attributable toshading varied with cultivar. In Lumai 22, PREmarkedly reduced grain number per spike andslightly reduced grain weight. No significant effectof PRE on either grain number per spike or grainweight was found in Yannong 15 (Table 6). POSThad no significant effect on grain number per spikein the two cultivars. As for grain weight, decreasesof 11.2–15.6 % in Lumai 22 and 7.0–7.1 % inYannong 15 were found in the POST treatment ascompared with the control (Table 6).

Neither PRE nor POST had an effect on spikenumber per unit area (Table 6).

Grain number per spikelet (GNPS)

The response of GNPS to either PRE or POSTvaried with cultivar (Fig. 1). The GNPS of Yan-nong 15 was not obviously affected by either PREor POST, indicating that Yannong 15 had greateradaptability in GNPS to shading than Lumai 22.Shading markedly reduced the GNPS of Lumai 22,mainly in the upper and basal spikelets. The effectof PRE on GNPS was much greater than that ofPOST.

Grain weight per spikelet (GWPS)

In Lumai 22, GWPS in the upper and basalpositions on the spike were markedly reduced byboth PRE and POST, especially by the latter(Fig. 2), which resulted mainly from the decrease of T

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284 Wang et al.

GNPS induced by shading. A similar effect inYannong 15 was also observed, but its magnitudewas much smaller than that in Lumai 22.

Conclusions

These results suggest that the adaptability of thesmall-spike, small-grain cultivar Yannong 15 toeither pre- or post-anthesis shading is much greaterthan that of the large-spike, large-grain cultivarLumai 22 in terms of many characteristics closelyrelated to grain yield. Hence, we suggest that, inareas where low light intensity often occurs, thesmall-spike, small-grain cultivar would be morelikely to produce high, stable grain yields.

Acknowledgements

This study was funded in part by a grant from theNational Natural Science Foundation of China. The

authors are grateful to Prof. Yu Songlie, academician ofthe China Academy of Engineering, for his suggestions.We also appreciate helpful comments from the anony-mous reviewers.

References

Evans, L. T., I. F. Wardlaw, and R. A. Fischer, 1975:Wheat. In: L. T. Evans (ed.), Crop Physiology,pp. 101—149. Cambridge University Press, London.

Fischer, R. A., 1975: Yield potential in dwarf springwheat and the effect of shading. Crop Sci. 15,

607—613.Fischer, R. A., 1985: Number of kernels in wheat crops

and the influence of solar radiation and temperature.J. Agric. Sci. 105, 447—461.

Fischer, R. A., and Y. M. Stockman, 1980: Kernelnumber per spike in wheat (Triticum aestivum L.):responses to preanthesis shading. Aust. J. PlantPhysiol. 7, 169—180.

Grabau, L. J., D. A. Van Sanford, and Q. W. Meng,1990: Reproductive characteristics of winter wheatcultivars subjected to postanthesis shading. Crop Sci.30, 771—774.

Jedel, P. E., and L. A. Hunt, 1990: Shading and thinningeffects on multi- and standard-floret winter wheat.Crop Sci. 30, 128—133.

Jin Shanbao, 1996: Wheat in China. China AgriculturePress, Beijing.

Kemp, D. R., and E. E. Whingwiri, 1980: Effect of tillerremoval and shading on spikelet development andyield components of the main shoot of wheat and onthe sugar concentration of the ear and flag leaf. Aust.J. Plant Physiol. 7, 501—510.

McMaster, G. S., J. A. Morgan, and W. O. Willis, 1987:Effects of shading on winter wheat yield, spikecharacteristics, and carbohydrate allocation. CropSci. 27, 967—973.

Ravi, I., and M. C. Ghildiyal, 2001: Translocation of14C-sucrose within the ear in durum and aestivumwheat varieties. J. Agron. Crop Sci. 186, 9—13.

Savin, R., and G. A. Slafer, 1991: Shading effects on theyield of Argentinean wheat cultivars. J. Agric. Sci.116, 1—7.

Slafer, G. A., D. F. Calderini, D. J. Miralles, and M. F.Dreccer, 1994: Preanthesis shading effects on thenumber of grains of three bread wheat cultivars ofdifferent potential number of grains. Field Crops Res.26, 31—39.

Yu Songlie, 1990: Wheat in Shandong. China Agricul-tural Press, Beijing.

Willey, R. W., and R. Holliday, 1971: Plant population,shading and thinning studies in wheat. J. Agric. Sci.77, 453—461.

0

50

100

150

200

250

1 3 5 7 9 11

Spikelet position

13 15 17 19 21 23

Gra

in w

eigh

t per

spi

kele

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g)

CONT

PRE

POST

CONT

PRE

POST

Fig. 2: Grain weight per spikelet for two cultivars ofwinter wheat under three treatments (1996–1997). Opensymbols represent cv. Lumai 22, and closed symbolsrepresent cv. Yannong 15

01 3 5 7 9 11

Spikelet position

13 15 17 19 21 23

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Fig. 1: Grain number per spikelet for two cultivars ofwinter wheat under three treatments (1996–1997). Opensymbols represent cv. Lumai 22, and closed symbolsrepresent cv. Yannong 15

Effect of Shading on Wheat 285