contribution of stem dry matter to grain yield in wheat cultivars

Aust. J. Plant Physiol., 1991, 18, 53-64

Contribution of Stem Dry Matter to Grain Yield in Wheat Cultivars

P. C. pheloungA and K. H. M. siddiqueB

A Crop and Pasture Sciences, School of Agriculture, University of Western Australia, Nedlands, W.A. 6009, Australia.

Division of Plant Industries, Western Australian Department of Agriculture, Baron-Hay Court, South Perth, W.A. 6151, Australia.

Abstract

Field experiments were conducted in the eastern wheat belt of Western Australia in a dry year with and without irrigation (1987) and in a wet year (1988), comparing three cultivars of wheat differing in height and yield potential. The aim of the study was to determine the contribution of remobilisable stem dry matter to grain dry matter under different water regimes in old and modern wheats.

Stem non-structural carbohydrate was labelled with 14c 1 day after anthesis and the activity and weight of this pool and the grain was measured at 2, 18 and 58 days after anthesis. Gutha and Kulin, modern tall and semi-dwarf cultivars respectively, yielded higher than Gamenya, a tall older cultivar in all conditions, but the percentage reduction in yield under water stress was greater for the modern cultivars (41, 34 and 23%). In the grain of Gamenya, the increase in I4c activity after the initial labelling was highest under water stress. Generally, loss of 14c activity from the non-structural stem dry matter was less than the increase in grain activity under water stress but similar to or greater than grain activity increase under well watered conditions. Averaged over environments and cultivars, non-structural dry matter stored in the stem contributed at least 20% of the grain dry matter.

Introduction

Grain yield in wheat is a composite of assimilate produced over the life of the plant. This may be partitioned into three components: dry matter produced after anthesis and translocated directly to the grain, dry matter produced before anthesis and remobilised to the grain during grain filling and dry matter produced after anthesis but stored temporarily in vegetative organs before being remobilised to the grain. The principal location of non- structural dry matter (NSDM), which may be remobilised at a later time, is in the stem of wheat. Sucrose and low molecular weight fructans are the main components of stem NSDM (Jude1 and Mengel 1982; Blacklow et al. 1984).

The importance of NSDM as a source of grain dry matter has been the subject of conjecture for some time. Dry matter formed prior to anthesis has been estimated to contribute 3-30% of the grain dry matter at maturity (Stoy 1963; Rawson and Evans 1971; Gallagher et al. 1976; Austin et al. 1977; Bidinger et al. 1977). There have been very few attempts to quantify the role of stem NSDM produced after anthesis in grain filling. In well watered wheat, most of the stem NSDM accumulates in the first 3 weeks after anthesis (Blacklow et al. 1984). In a recent study by Blacklow and Pheloung (unpublished data), the calculated contribution of post-anthesis stem NSDM to grain dry matter was 10-2570.

The improvement in grain yield in modern cultivars is largely a consequence of increased harvest index and hence more efficient use of the dry matter resources for grain filling (Evans and Dunstone 1970; Austin et al. 1980; Perry and D'Antuono 1989; Siddique et al. 1989b). Higher harvest index could be due to greater use of NSDM for grain filling or more

0310-7841/91/010053$05.00

P . C . Pheloung and K. H. M. Siddique

storage of NSDM before anthesis and soon after anthesis, when grain demand is low. Alternatively, if stems are physically smaller, there may be less storage capacity and greater sensitivity to environmental stress in modern cultivars.

Water stress during grain filling is one factor which may result in an increase in the contribution of stored dry matter to grain filling relative to current assimilate. Under such conditions the relative contribution of dry matter produced prior to anthesis may increase substantially (Gallagher et a/. 1976; Johnson and Moss 1976; Bidinger et al. 1977) but it is not clear if the stored dry matter makes a larger contribution in absolute terms. No information is available on the influence of water stress on the contribution of post-anthesis stem NSDM.

The work reported here was part of a project aimed at identifying morphological and physiological characters associated with high grain yield of modern Australian wheats (Kirby et al. 1989; Loss et al. 1989; Siddique et al. 1989a, 1989b, 1990a, 1990b). In this study, our aim was to estimate the contribution of stem NSDM to grain yield in old and modern wheats under dry and well watered conditions. Accumulation and remobilisation of stem NSDM from anthesis to maturity were investigated by using a 14c labelling technique in three cultivars, a recently released semi-dwarf wheat and a tall wheat and an older, tall wheat.

Materials and Methods

Agronomy

Two experiments, in 1987 and 1988, were done at Merredin in the eastern wheat belt of Western Australia (31°29'S.,1180E., alt. 315 m) as part of studies reported earlier (Siddique et al. 1989a, 19900, 1990b).

Ten and nine cultivars of wheat (Triticum aestivum L.) were used in the 1987 and 1988 experiments respectively. The cultivars chosen represented a chronological sequence of economically significant wheats released between the 1860s and the present day. A randomised complete block design was used with cultivars randomised within four replications. The plots were sown on 27 May 1987 and 24 May 1988 at a seed rate of 50 kg ha- ' using a 12 row cone seeder. Plot size was 2.16 m wide (12 rows, 18 cm apart), 40 m long and the seeding depth was 3-4 cm. Details of site, soil, weather, treatments and cultural practices were given in Siddique et al. (1989b, 19900). In 1987, 10 m at one end of the plots was trickle irrigated in all replications. The irrigation commenced on 25 August at ear emergence of early maturing cultivars and continued until maturity at frequent intervals to prevent plant moisture stress.

The three wheat cultivars Gamenya (tall, most widely grown wheat cultivar in Western Australia between 1960 and 1980), Gutha (tall, released 1982) and Kulin (semi-dwarf, released 1986) were selected for 14c studies in 1987. Similar anthesis dates was a criterion for the selection of these cultivars. In 1988 there was no irrigation treatment and two wheat cultivars, Gamenya and Kulin, were selected for 14c studies.

Application of [14~]urea

Anthesis was from 7 September until 14 September in 1987 (Siddique et al. 1989b) and 5 September until 12 September in 1988 (Siddique et al. 1990~) . Plant mainstems, selected for uniformity at mid- anthesis (anthers present in middle third or ear), were assigned to treatments during this time. On the following day (1 day after anthesis) between 6 and 7 a.m., 3 mL vials containing 0 . 5 mL [I4c]urea (170 kBq/mL, 5.23 ng/mL) were attached to the plants below the flag leaf. The tip of the flag leaf was cut under distilled water, placed in the vial and sealed with a styrofoam plug. After 8 h in sunshine each vial was removed by cutting the leaf along the vial rim and the leaf tips were rinsed with distilled water. We assume that urease activity in the leaf releases C 0 2 from urea which is subsequently assimilated or lost to the atmosphere during gas exchange. Analysis of I4c activity in stem extracts showed that most of the I4c translocated from the leaf to the stem was associated with carbohydrates (Blacklow and Pheloung, unpublished data). It had been shown that solution absorbed from the vials through the immersed tips remained in the leaf lamina and any label found in the grain was through assimilation and translocation in the phloem (Blacklow 1982).

Stem Dry Matter and Grain Yield in Wheat

Sampling

A t 1, 17 and 57 days after I4C application (2, 18 and 58 days after anthesis), two plants were sampled in 1987 and three plants in 1988 from each replication (8 and 12 plants per cultivar in 1987 and 1988) and immediately divided into flag leaf, peduncle, penultimate internode, third internode (nodes included) and ear, and placed in plastic sealed vials. The vials were packed in dry ice for transport to the laboratory where the frozen samples were freeze-dried and stored. The dry ears were partitioned into grain and non-grain fractions. All samples were oven dried (80°C for 24 h), weighed for total dry matter (TDM) and immediately ground in the vials using a reciprocating ball mill (Barton 1966). At 23 and 37 days after anthesis in the 1987 experiment, 1 m2 samples were taken from the non-irrigated plots and oven dried (Siddique et al. 1989b). Five mainstems (not labelled with [14C]urea) were subsampled from the Gamenya, Gutha and Kulin samples. Dry matter in the grain and internodes from these samples was measured.

Extraction of stem NSDM

Subsamples (100 mg) of ground stem sections were placed in 50 mL extraction tubes with 10 mL of 70% ethanol and incubated, with periodic agitation, for 2 h at 80°C in a water bath. The extracts were removed using a pasteur pipette and the residue re-extracted with 2 further lots of 70% ethanol. It was shown that subsequent water extracts of the ethanol insoluble residue yielded less than 0.5% of the total anthrone-positive material in the extract (Blacklow et al. 1984). The final volume of the combined extracts was determined gravimetrically and the extracts stored at 5OC. The residue was dried and weighed to determine ethanol insoluble dry matter (EID) and ethanol soluble dry matter (ESD) by difference.

The sample time at 18 days after anthesis was selected for maximum stem ESD based on the results of earlier studies on a winter wheat (Blacklow et a/. 1984) and a spring wheat (Blacklow and Pheloung, unpublished data). These results showed that stem ESD reached a plateau about 14 days after anthesis and remained at this level for about 7-14 days before declining rapidly. The maximum stem ESD measured was partitioned into components formed before and after anthesis as shown in Fig. 1. Stem ESD remaining at maturity was low in soluble carbohydrate (Blacklow et al. 1984) and not included in either partition.

anthesis maturity

Fig. 1. Method used to partition remobilised stem NSDM into pre-anthesis and post-anthesis fractions. Stem ESD is assumed to be equivalent to stem NSDM.

Pre-anthesis ESD = ESDss - ESD2. Post-anthesis ESD = ESDls - ESD2.

Time after anthesis (d)

Analyses

I4c uptake and assimilation

Total uptake of 14c was estimated from the loss of 14c activity from the vials. The weight of the solution remaining in the vial, to which 0 . 5 mL water was added and mixed thoroughly, was measured and 50 pL subsampled for measurement of 14c activity by liquid scintillation. The portion of the flag leaf remaining in the vial was digested in Soluene (Packard) and the activity measured added to the activity measured in the vial solution.

14c activity in plant parts

Subsamples of ground plant material (10-15 mg) and the residues from internode extraction were transferred to 5 mL plastic scintillation vials and suspended in 3 mL of a scintillation cocktail con-

P. C. Pheloung and K. H. M. Siddique

taining 5.5 g/L PPO, 0 . 1 g/L POPOP and 40 g/L of a thixotropic gel (Cab-0-Sil, Packard) in toluene. Activity in the samples was measured in an Isocap liquid scintillation counter with sample quenching corrected using the channels ratio method. After quench correction, counting efficiency was consistently found to be 66 k 4% based on a comparison with the activity measured on a subset of the samples by a combustion method (Bucholtz and Hess 1983). The gel suspension method was highly reproductible and the overall counting efficiency similar for different plant parts. Subsamples of the internode ethanol extracts (50 pL) were suspended in a scintillation cocktail containing toluene PPO POPOP, C40 wetting agent (Sigma Chemicals) and water (4 : 2 : 1).

Differences in leaf size and water potential could contribute to large variations in the amount of 14c taken up. In order to remove this source of variation, the data were transformed to percentages of the plant activity at each sample time or to percentages of the activity lost from the uptake vial, prior to calculating the replicate means.

Results

Dry Matter

Crop yield

Biomass, grain yield and harvest index at crop maturity are shown in Table 1. Rainfall was poor in 1987, particularly during ear initiation and anthesis (Siddique et al. 1989b) but good throughout the season in 1988 (Siddique et al. 1990~) . In the absence of irrigation, the 1987 grain yields and harvest index were low and cultivar differences were not significant. In 1988 and with irrigation in 1987, plant biomass was about 60% greater in all cultivars compared with the unirrigated (1987) treatment. The harvest index of Kulin showed the greatest improvement with irrigation and the increase in grain yield was greatest for this cultivar. Grain weight per ear, calculated from the data of (Siddique et al. 19890, 1990a), is shown with data from plant samples used in the experiments presented here (Table 1 ) . Because these samples were mainstems only, the grain yields are greater but the direction and magnitude of the trends are similar. In all conditions, but particularly when water is not limiting, Kulin ranked highest in grain yield and Gamenya lowest.

Table 1. Grain yield, biomass and harvest index From Siddique et al. 1989b and 1990a

Treatment Cultivar Biomass Ear No. HI Grain yield

(g m-2) (m - 2, (g m -2) (g ear - ')

Dry Gamenya 478 217 0.35 168 0.774* 1 . 1 8 7 ~ Gutha 527 22 1 0.36 189 0.855 1.454 Kulin 512 208 0.37 189 0.909 1,818

1987

Irrigated Gamenya 892 253 0.39 349 1.379 1.535 Gutha 843 221 0.41 358 1.620 2,451 Kulin 808 180 0 .49 392 2.178 2.749

1.s.d. ( P = 0 , 0 5 ) n.s. 53 0.06 42 - 0.226

1988

Gamenya 765 224 0.32 242 1.080 1.666 Kulin 734 237 0.41 301 1.270 2.081

1.s.d. (P=0.05) n.s. n.s. 0.03 57 - 0.337

* These values calculated as g r r 2 / e a r s m - 2 from data of Siddique et al. (19896 and 1990~) . Values are for mainstem only. Mean of 8 plants (1987) or 12 plants (1988).


Dry matter changes during grain filling The change in stem weight and grain weight during grain filling is shown in Fig. 2a.

Under well watered conditions, stem TDM above the third node increased during the first 15 days after anthesis before decreasing to or below the level at anthesis. No early increase in TDM occurred during the dry conditions of 1987.

Changes in the stem ESD are shown in Fig. 2b. The changes in stem TDM were closely matched by corresponding changes in the ESD. In irrigated Gemenya for example, the increase and standard error of 4 replications in TDM and ESD was 207 + 74 and 163 i: 38 mg/stem respectively in the 3-18 day interval and the decrease was 301 i: 100 and 338 i: 42 mg/stem respectively in the 18-58 day interval.

3.0 - - L

1987 Dry 1987 Irrigated 1988 -(a)

- 2.5 - - T

Time after anthesis (days)

Fig. 2. Dry matter of grain and stem above the third node (a) and ethanol soluble dry matter of stem above the third node (b) in Gamenya (H), Gutha (m) and Kulin (A) during grain filling. Open symbols are grain dry matter; closed symbols are stem dry matter. Vertical bars represent 1.s.d. (P = 0.05). In (a), the upper bars refer to grain dry matter and lower bars refer to stem dry matter.

In Fig. 3, ESD lost from the stem was partitioned into pre-anthesis and post-anthesis fractions (Fig. 1). Within a cultivar, the loss of ESD produced before anthesis was similar under all water regimes. This fraction was 50 to 70% greater in Kulin than in Gamenya or Gutha. Under well watered conditions, stem ESD was produced after anthesis and accounted for up to 50% of the total ESD lost from the stem. The change in grain dry matter is shown in Fig. 3 for comparison to the stem ESD changes.

In Table 2, the loss of pre- and post-anthesis stem ESD is expressed as a percentage of the total grain dry matter a t maturity. In dry conditions, pre-anthesis stem ESD loss was

P . C. Pheloung and K. H. M. Siddique

a larger proportion of-the grain dry matter than in well watered conditions. A loss of stem ESD produced after anthesis occurred only in the well watered treatments and consequently, the overall loss, as a percentage of grain dry matter, was similar for water regimes and

Kulin Gutha

Grain

ESD

Fig. 3. Dry matter change in the stem ESD and grain during grain filling. The pre-anthesis and post- anthesis components are derived as shown in Fig. 1 . In the grain, the hatched portion of the bar depicts the increase in dry matter from 2 to 18 days after anthesis and the remainder of the bar depicts the increase from 18 to 58 days after anthesis.

Table 2. Loss of pre- and post-anthesis stem ESD as a percentage of grain weight

Environment ESD Loss of ESD (%) partition Gamenya Gutha Kulin

1987

Dry Pre 22 18 25 Post 0 0 0 Total 22 18 25

1.s.d. (P= 0.05) 4.5

1987 Irrigated Pre 1 1 12 13

Post 1 1 10 9 Total 22 22 22

1.s.d. (P=0.05) 5.5

1988

Pre 15 - 2 1 Post 22 - 10 Total 3 7 - 3 1

1.s.d. (P=0.05) 14.7


Uptake and Partitioning of 14c

Uptake and distribution One day after application, total I4c activity initially recovered from the plant was

50-60s of the activity lost from the application vial. The activity was greater under dry conditions (Fig. 4) initially, presumably because the leaf water potential was lower. Greater than 95% of the plant activity was located in the ear, flag leaf and stem above the third internode. Loss of plant activity from 18-58 days after anthesis was less than 20% of the activity at day 18 (Fig. 4). One day after application of 14c, ESD was uniformly distributed in the upper three internodes but I4c was located predominantly above the third internode (Fig. 5).

1987 Dry

b C 1987 Irrgated


Fig. 4. Total activity in the mainstem above the third node for Gamenya (m), Gutha (A) and Kulin (a) during grain filling. L.s.d.s (P = 0.05, for com- parisons of sample time or cultivar) are shown as vertical bars for each of the environmental conditions.

Changes in 14C partitioning In Fig. 6, the percentage distribution of 14c in the grain, stem ESD and stem EID and

the remainder of plant is shown. Grain activity increases substantially in all cultivars and treatments relative to other organs. In the 1987 dry treatment the pattern of change in the distribution was similar in all cultivars with grain activity reaching a maximum of 70% of the total at maturity. In the well watered conditions of 1987 and 1988, relative grain activity at maturity ranged from 28% in Gamenya to 58% for Kulin. More than half of the redistribution of activity to the grain occurred after the 18 day sample time in the well watered treatments. The relative activity in the stem EID increased from 2 to 18 days after anthesis, particularly in the well watered treatments but remained constant thereafter.

In Fig. 7, the changes in I4c activity in the grain and stem ESD, as a percentage of activity taken up by the plant, are shown for the 2-18 and 18-58 day intervals. In the dry conditions of 1987, the increase in grain activity was considerably greater for Gamenya due to a greater increase in the 18-58 day interval. Under moist conditions, by contrast, the increase in Gemenya grain activity was similar to or less than that of the other cultivars.

Loss of 14c activity from the stem ESD was consistently greatest in Gamenya under all conditions (Fig. 7). Loss of stem ESD activity was similar to or greater than the corresponding increase in grain activity under moist conditions but significantly less than the increase in grain activity in the dry treatment (Fig. 7). The trend was most pronounced for Gamenya, which implies a large increase in the proportion of stem ESD recovered by the grain in this cultivar in dry conditions.


r Gamenya Kulin

87 D 87 1 88

Discussion

G u t h a

Fig. 5. Distribution of dry matter (a) and "C activity (b) in the ethanol soluble fraction of the peduncle (hatched), penultimate internode (closed) and third internode (open) 1 day after labelling (2 days after anthesis).

Yield ranking of the cultivars in this study is consistent with results presented by Siddique et al. (1989a). In that paper, the authors showed that grain yield was related to the ear- stem ratio at anthesis and suggested that the yield potential was determined during ear development, prior to anthesis. Realisation of the yield potential is nevertheless dependent on environmental conditions before and after anthesis. Reduced photosynthesis resulting from a water deficit will reduce the size of the source that the grain can draw on. During a season of adequate rainfall in 1988 and under irrigation in 1987, photosynthesis exceeded grain filling requirements during the early grain filling phase and stem NSDM continued to accumulate after anthesis. With a moisture stress during heading and flowering in the 1987 season, this accumulation did not occur. As a result, any stored stem NSDM contributing t o grain yield in the unirrigated 1987 treatment was produced prior to anthesis.

Moisture stress during heading and flowering in the 1987 season resulted in a greater yield reduction, relative to the irrigated treatments, for Gutha and Kulin than for Gamenya (41%, 34% and 23% respectively). Under good conditions, Gutha and Kulin may utilise a larger fraction of photosynthate produced after anthesis in grain filling than Gamenya. When photosynthesis is limited by water stress, Gamenya may consequently have a larger, otherwise unexploited, reserve of dry matter for grain filling. This cannot be shown from measurements of stem dry matter loss, however, since in all cases, including unirrigated


- 2 1 8 5 ' 8 87 Dry

Gamenya

2 18 58 87 lrrig

Fig. 6. I4c activity expressed as a percentage of the total activity of the plant mainstem above the third node during grain filling for the grain (closed), stem ESD (cross- hatched), stem EID (hatched) and remainder of plant (open).


Gamenya, stem ESD decreased to a low level at maturity. To test the hypothesis, it is necessary to establish what proportion of the accumulated stem dry matter is recovered in the grain.

A large fraction of 14c activity assimilated at anthesis was retained in other plant organs for up to 18 days before moving into the grain (Fig. 6). Earlier studies have demonstrated a significant contribution of pre-anthesis assimilated 14c (Stoy 1963; Gallagher et al. 1976; Bidinger et al. 1977). Austin et al. (1976) estimated that, of the photosynthate produced soon after anthesis, 50% was retained for 10 days or more in stems or leaves before being translocated to the grain. More recently, Kiyomoto and Gent (1989) and Gent and Kiyomoto (1989) presented data on the movement of 14c assimilated at anthesis to the grain consistent with the results presented here. The mature grain of the semi-dwarf, Kulin, had a higher proportion of the total plant activity than the tall cultivars, Gamenya and Gutha. Gent and Kiyomoto (1989) obtained a similar result with tall and semi-dwarf cultivars.

From Fig. 6 it is evident that, of the dry matter assimilated within a few days of anthesis, the grain contains the greatest fraction at maturity under dry conditions. Gamenya displays the greatest extremes in this regard with the smallest fraction of 14C activity in the

P. C. Pheloung and K. H. M. Siddique

Fig. 7. Change in 14c activity in the stem ESD above the third node and grain during the interval 2-18 days after anthesis (open) and 18-58 days after anthesis (closed). L.s.d.s (P = 0.05) are shown as vertical bars for each of the environmental conditions.

Gam Kul Gut Gam Kul Gut

1 9 8 7 Dry 1 9 8 7 I r r iga ted

Gam Kul

1 9 8 8

mature grain under moist conditions and the largest fraction under dry conditions. Gallagher et al. (1975) discussed the role of photosynthate produced before anthesis in stabilising mean grain weight and Blacklow and Incoll (1981) emphasised the importance of stem NSDM produced after anthesis for this purpose. In this study, Gemenya appeared to function in this manner, utilising stem NSDM only as required to maintain grain weight but the same flexibility was not apparent for Gutha and Kulin.

Since activity decreases in all plant parts except the grain and no activity was detectable below the third internode, 14c activity lost from the stem either moves into the grain or is respired. Comparison of the loss of stem NSDM activity and corresponding increase in grain activity indicated that generally, the grain recovered less of the lost stem activity in the well watered treatments (Fig. 7). This effect of treatment was most pronounced in the case of Gamenya.

In previous studies, little or no attempt has been made to convert retranslocated 14c activity into dry matter. The difficulty arises from the probable large variations in specific activity of 14c labelled dry matter located in the various regions of the plant. A small transfer of dry matter from the flag leaf to the grain is likely to result in an increase in grain activity comparable to a much larger transfer from the stem NSDM. Nevertheless an estimate of the actual movement of stem NSDM to the grain may be made for the latter interval of this experiment (18-58 days after anthesis).

The stem sugar pool is subject to turnover and previous studies in this laboratory (Blacklow and Pheloung, unpublished data) have shown that photosynthate labelled with 14c at anthesis was uniformly distributed through the stem NSDM as sucrose and fructans within 14 days. Subsequently, changes in stem NSDM activity will reflect bulk dry matter changes which can be related to changes in grain activity and dry matter. Most of the stem activity was in the stem above the second node (Fig. 5b) so the estimate would be predominantly of NSDM from this region.

In Table 3, the contribution of stem NSDM to the grain was calculated as the change in grain activity over the 18-58 day interval divided by the stem NSDM specific activity (Bq per mg) above the second node at 18 days after anthesis. If the grain activity change exceeded the loss of stem activity then the loss of stem NSDM activity was substituted for


the increase in grain activity in the calculation. The underlying assumption is that, by virtue of proximity, the stem NSDM will supply grain demand before remobilised leaf dry matter is utilised. The specific activity of the non-grain parts of the ear was low and total activity did not change greatly (data not shown). The resulting estimate is comparable to the measured stem dry matter loss and lends strong support to the hypothesis that the stem is an important source of grain dry matter during the late grain filling stage. The calculated estimate, as a proportion of the measured stem NSDM loss, was greater in the dry conditions of 1987 than in the irrigated 1987 treatment or the 1988 season. In each treatment the proportion was highest for Kulin.

We conclude that more of the stem NSDM is utilised for grain filling under dry conditions and the higher yielding semi-dwarf, Kulin, may utilise more of the stem NSDM than Gamenya in all the treatments. In terms of grain yield, the contribution of dry matter from stem reserves during the latter half of grain filling can range from 0.4 to 1.3 t/ha (interpolated from Tables 1 and 3), a significant fraction of the total grain yield. Other studies have shown that selection pressure leading to yield improvement is, in part, a consequence of greater partitioning of photosynthate to the ear rather than other structural components of the plant (Siddique et al. 1989a). Results reported here indicate that high- yielding modern cultivars utilise remobilisable photosynthate, produced before and after anthesis, more efficiently for grain filling.

Table 3. Calculated contribution of the peduncle and pentultimate internode ESD to grain dry matter in the interval 18-58 days after anthesis A, calculated contribution: (change in grain activity) x (stem ESD/stem activity at 18 days after anthesis); B, loss of stem ESD; C, change in grain DM; D, calculated contribution as a percentage of stem ESD loss: A/B x 100

-

Environment Cultivar A (mg) B (mg) C (mg) D (%)

Dry Gamenya Gutha Kulin

Irrigated Gamenya Gutha Kulin

Gamenya Kulin

Acknowledgments

We thank Mr T. Parr and Ms L. Laughlin for their excellent technical assistance during this study. We also thank Mr N. Venn for setting up the irrigation system in 1987. The Wheat Research Council and the Wheat Research Committee of Western Australia provided finanacial support for this study. We are indebted to Dr W. M. Blacklow for the calculation of dry matter contributions from changes in activity and for his general comments on the manuscript. We also thank Mr M. W. Perry and Dr N. C. Turner for their encouragement and comments on the manuscript.

References Austin, R. B., Edrich, J . A., Ford, M. A., and Blackwell, R. D. (1977). The fate of dry matter,

carbohydrates and 14c lost from the leaves and stems of wheat during grain filling. Annals of Botany 41, 1309-21.


Austin, R. B., Bingham, J., Blackwell, R. D., Evans, L. T., Ford, M. A., Morgan, C. L., and Taylor, M. (1980). Genetic improvements in winter wheat yields since 1900 and associated physiological changes. Journal of Agricultural Science, Cambridge 94, 675-89.

Barton, G. E. (1966). A grinding technique for small radioactive grass samples. Laboratory Practice 15, 1255-8.

Bidinger, F., Muscrave, R. B., and Fisher, R. A. (1977). Contribution of stored preanthesis assimilate to grain yield in wheat and barley. Nature 270, 431-3.

Blacklow, W. M., and Incoll, L. D. (1981). Nitrogen stress of winter wheat changed the determinants of yield and the distribution of nitrogen and total dry matter during grain filling. Australian Journal of Plant Physiology 8, 191-200.

Blacklow, W. M. (1982). "N moved to the grain of winter wheat when applied as nitrate to senescing flag leaves. Australian Journal of Plant Physiology 9 , 641-6.

Blacklow, W. M., Darbyshire, B., and Pheloung, P. (1984). Fructans polyrnerised and depolymerised in the internodes of winter wheat as grain filling progressed. Plant Science Letters 36, 213-18.

Bucholtz, D. L., and Hess, F. D. (1983). An inexpensive combustion apparatus for preparation of radioactive samples. Weed Science 31, 159-62.

Evans, L. T., and Dunstone, R. L. (1970). Some physiological aspects of evolution in wheat. Australian Journal of Biological Science 23, 725-41.

Gallagher, J . N., Biscoe, P . V., and Scott, R. K. (1975). Barley and its environment. V. Stability of grain weight. Journal of Applied Ecology 12, 319-36.

Gallagher, J. N., Biscoe, P . V., and Hunter, B. (1976). Effects of drought on grain growth. Nature 264, 541-2.

Gent, M. P. N., and Kiyomoto, R. K. (1989). Assimilation and distribution of photosynthate in winter wheat cultivars differing in harvest index. Crop Science 29, 120-5.

Johnson, R. R., and Moss, D. N. (1976). Effect of water stress on 14c02 fixation and translocation in wheat during grain filling. Crop Science 16, 697-701.

Judel, G. K., and Mengel, K. (1982). Effect of shading on nonstructural carbohydrates and their turnover in culms and leaves during the grain filling period of spring wheat. Crop Science 22, 958-62.

Kirby, E. J. M., Siddique, K. H. M., Perry, M. W., Kaesehagen, D., and Stern, W. R. (1989). Variation in spikelet initiation and ear development of old and modern Australian wheat varieties. Field Crops Research 20, 113-28.

Kiyomoto, R. K., and Gent, M. P. N. (1989). Photosynthetic assimilation of 14c02 and fate of 14c-

labelled photosynthate in winter wheat (Triticum aestivum) near-isolines differing in alleles at the rhtl and rht2 reduced height loci. Annals of Applied Botany 114, 141-8.

Loss, S. P., Kirby, E. J. M., Siddique, K. H. M., and Perry, M. W. (1989). Grain growth and development of old and modern Australian wheats. Field Crops Research 21, 131-46.

Perry, M. W., and D'Antuono, M. F. (1989). Genotypic change in Australian wheat varieties. Grain yield and analysis of genotype adaptation in Western Australia. Australian Journal of Agricultural Research 40, 457-72.

Rawson, H. M., and Evans, L. T. (1971). The contribution of stem reserves to grain development in a range of wheat cultivars of different height. Australian Journal of Agricultural Research 22, 851-63.

Siddique, K. H. M., Kirby, E. J. M., and Perry, M. W. (1989~). Ear : stem ratio in old and modern wheat varieties; relationship with improvement in number of grains per ear and yield. Field Crops Research 21, 59-78.

Siddique, K. H. M., Belford, R. K., Perry, M. W., and Tennant, D. (1989b). Growth development and light interception of old and modern wheat varieties in a Mediterranean-type environment. Australian Journal of Agricultural Research 40, 473-87.

Siddique, K. H. M., Belford, R. K., and Tennant, D. (1990~). Root : shoot ratios of old and modern, tall and semi-dwarf wheats in a Mediterranean environment. Plant and Soil 121, 89-98.

Siddique, K. H. M., Tennant, D., Perry, M. W., and Belford, R. K. (1990b). Water use and water use efficiency of old and modern wheat cultivars in a Mediterranean-type environment. Australian Journal of Agricultural Research 41, 431-47.

Stoy, V. (1963). The translocation of c14-labelled photosynthetic products from the leaf to the ear in wheat. Physiologia Plantarurn 16, 85 1-66.

Manuscript received 26 April 1990, accepted 24 September 1990

contribution of stem dry matter to grain yield in wheat cultivars

Documents