Distal Grains Research Articles

Ovary morphology determines ovary-to-grain transition process and final grain weight potential in wheat

The ovary-to-grain transition process is crucial for individual grain weight potential, but the but the physiological regulation of this highly dynamic and complex developmental process remains largely unknown unknown. Here, we performed a high temporal-resolution analysis of the proximal (large) and distal (small) ovaries/grains collected at an interval of 3 days from the booting stage to maturity stage. During grain-filling process, proximal grains always maintained a greater dry matter (0–36 days after anthesis, DAA), water (0–33 DAA), sugar (3–33 DAA), protein (6–36 DAA), and starch (amylose and amylopectin, 18–36 DAA) content, and larger volume (-15–36 DAA) than distal grains, but their partition or concentration did not differ between the proximal and distal grains. This result suggested that the capability of proximal and distal grains to produce water, sugar, protein, and starch within the same volume was similar; thus, grain sink (i.e. volume) was the cause in determinant of grain weight potential. In fact, the proximal ovary had a larger volume and related parameters (length, width and thickness) than the distal ovary before anthesis stage. in addition, the correlation coefficients of length and width with volume are higher than the correlation coefficients of thickness with volume. Clearly, we discovered a dynamic physiological mechanism for high proximal grain weight: the rapid elongation and widening of the proximal ovary improved its size, which passed to the proximal grain a volume advantage in the following ovary-grain transition, which allowed it to took up more sucrose and then converted into more starch and protein, improving dry matter accumulation and increasing proximal grain weight. Our findings provide a precise strategy for breeding and cultivation to increase individual grain weight potential by improving ovary volume.

Effect of micron-scale nonmetallic inclusions on fatigue crack nucleation in a nickel-based superalloy

Micron-level nonmetallic inclusions are likely to be a limiting factor for further improvement in the fatigue resistance of nickel-based superalloys. To investigate the fatigue response of nickel-based superalloys containing micro-inclusions, a dislocation-based crystal plasticity model was employed for numerical simulations, and the local energy storage density criterion was used for damage evolution analysis. The results showed that, as a hard phase, micro-inclusions interfered with the plastic deformation of the matrix, as evidenced by the inhomogeneous slipping of the main slip systems and the activation of new slip systems. Additionally, micro-inclusions induced the accumulation of geometrically necessary dislocations (GNDs) around them. When micro-inclusions appeared on grain boundaries, the above factors changed the energy required for local deformation through potential hardening effects in the model and ultimately affected the evolution of the local energy storage density. When micro-inclusions appeared inside grains, the evolution of local energy storage was often dominated by plastic deformation only. The above mechanism is microstructure sensitive and spatially limited, which leads to the dispersion of lifetimes and negligible effect of micro-inclusions on distal grains.

Awned versus awnless wheat spikes: does it matter?

Awnless and awned wheat is found across the globe. Archeological and historical records show that the wheat spike was predominantly awned across the many millennia following domestication. Thus, ancient farmers did not select against awns at least until the last millennium. Here, we describe the evolution and domestication of wheat awns, quantifying their role in spike photosynthesis and yield under contrasting environments. Awns increase grain weight directly (increasing the size of all grains) or indirectly (increasing the failure of distal grains), but not as a consequence of additional spike photosynthesis. However, a trade-off is produced through decreasing grain number. Thus, favorable effects of awns on yield are not consistently found across environments.

Contribution of Proximal and Distal Grains Within Spikelets in Relation to Yield and Yield Components in the Winter Wheat Production Region of China From 1948 to 2012

Grain number and weight within a spikelet are major yield components which determine the grain yield in wheat. The objective of this study was to explore genetic gains in grain performance within wheat spikelets at the individual grain level and its effect on grain yield and evaluate genetic progress in stem internode length and other yield-related traits. We conducted field experiments across three growing seasons in the western Yellow and Huai Valley of China; incorporating 17 bread wheat cultivars released from 1948 to 2012. Yields were significantly correlated with year of release. Yield gains equated to 3.95 g m−2 yr−1 in response to increases in total grain weight per m2 (GW) in proximal (G1 and G2) and distal (G3 and G4) grains, despite a decline in the proportional contribution of proximal grains to yield and increase in the proportional contribution of distal grains to yield with year of release. Grain number per m2 (GN), thousand-grain weight (TGW), and harvest index (HI) increased with year of release, but plant height decreased. Both grain number per spikelet of proximal and distal grain contributed to the increase in total GN. However, the contribution ratio of GN in proximal grains to total GN declined, and the proportion in distal grains increased. Average single grain weight (SGW) increased linearly at G1, G2, G3, and G4 with year of release and contributed to the increase in TGW. The G3 and G4 grain positions had much lower individual grain weights but increased at a faster rate than G1 and G2. At G1, G2, and G3 grain positions, from bottom to top spikelets, the newly released cultivars had the heaviest grains and the old cultivars had the lightest grains. New cultivars had more spikelets than old cultivars and the number of grains (proximal and distal grains) in the apical spike increased with year of release. The length of five internodes decreased significantly with year of release, more so in the upper than lower internodes, all of which contributed to the decline in plant height. In summary, increasing the number and weight of distal grains could increase grain yield, TGW, and GN.

Carpel size, grain filling, and morphology determine individual grain weight in wheat.

Individual grain weight is a major yield component in wheat. To provide a comprehensive understanding of grain weight determination, the carpel size at anthesis, grain dry matter accumulation, grain water uptake and loss, grain morphological expansion, and final grain weight at different positions within spikelets were investigated in a recombinant inbred line mapping population of bread wheat (Triticum aestivum L.)×spelt (Triticum spelta L.). Carpel size, grain dry matter and water accumulation, and grain dimensions interacted strongly with each other. Furthermore, larger carpels, a faster grain filling rate, earlier and longer grain filling, more grain water, faster grain water absorption and loss rates, and larger grain dimensions were associated with higher grain weight. Frequent quantitative trait locus (QTL) coincidences between these traits were observed, particularly those on chromosomes 2A, 3B, 4A, 5A, 5DL, and 7B, each of which harboured 16-49 QTLs associated with >12 traits. Analysis of the allelic effects of coincident QTLs confirmed their physiological relationships, indicating that the complex but orderly grain filling processes result mainly from pleiotropy or the tight linkages of functionally related genes. After grain filling, distal grains within spikelets were smaller than basal grains, primarily due to later grain filling and a slower initial grain filling rate, followed by synchronous maturation among different grains. Distal grain weight was improved by increased assimilate availability from anthesis. These findings provide deeper insight into grain weight determination in wheat, and the high level of QTL coincidences allows simultaneous improvement of multiple grain filling traits in breeding.

Relationship between fruiting efficiency and grain weight in durum wheat

Future increases in grain number may be achieved through improving fruiting efficiency (FE; grains set per unit spike dry weight at anthesis). In recent experiments it was found a negative relationship between the average weight of the grains and FE. The objective of this paper was to determine whether this negative relationship was constitutive (i.e. the increased FE caused all grains to be smaller) or resulted from the increased proportion of grains of smaller potential size. Four experiments, involving 8 different environmental conditions, were carried out during two consecutive growing seasons (2008–2009 and 2009–2010) in which two durum wheat cultivars contrasting in FE and average grain weight were compared. In these conditions we determined FE and carried out a comprehensive study analysing in detail the weights of each individual grain along each of the spikelets. Averaging all experimental conditions, there was a negative relationship between average grain weight (GW) and fruiting efficiency (FE). Donduro with low FE produced in average heavier grains than Vitron. However, when considering individual grains there were, in general, no differences in GW. Therefore, the negative relationship between average grain weight and FE would not be constitutive, and would mostly represent the increase in the proportion of distal grains within the spikelets or of grains from apical spikelets as a consequence of an increased FE, reducing the average size of the grain but mostly unaffecting the size of particular grains. This provides further and stronger support to the idea of using FE as a criterion to further raise yield potential in wheat breeding programmes.

Source limitations due to leaf rust (caused by Puccinia triticina) during grain filling in wheat

Late foliar diseases (especially leaf rust) reduce assimilate supply during post-anthesis, determining fewer assimilates per grain and thereby inducing grain weight reductions. Although the assimilate reduction hypothesis is the most accepted to explain decreases in grain weight due to late foliar diseases, it has not been clearly established whether those reductions could be completely ascribed to source limitations or whether diminished grain weight could be the consequence of reductions in grain weight potential. The objective of this work was to determine whether grain weight reductions due to leaf rust during grain filling could be associated with source–sink limitations. Two experiments (during 2007 and 2008 growing seasons) including healthy and diseased wheat crops were conducted under field conditions. Source–sink manipulation treatments and grain water content measurements were made to test the source- and sink- limitation hypotheses due to the appearance of late foliar diseases during grain filling. Leaf rust was induced to appear exclusively during grain filling, and in both years, it reduced grain yield and grain weight in both experiments. However, except for distal grains, there were no significant differences between healthy and diseased plots in maximum grain water content, indicating that late foliar diseases did not affect the potential size of the grains. The reserves stored in stems were remobilised to the growing grains in both healthy and diseased crops. However, the reserves remaining at physiological maturity were significantly reduced in diseased crops. Reduction in grain number by trimming the spikes increased the grain weight in diseased but not in healthy crops. Grain weight of trimmed spikes in diseased crops reached similar values to those of healthy crops. These results support the hypothesis that foliar diseases could cause source limitation for grain filling beyond differences in grain weight potential when the crops are severely affected by late foliar diseases such as leaf rust.

Pollination dynamics, grain weight and grain cell number within the inflorescence and spikelet in oat and wheat

Oat (Avena sativa L.) and wheat (Triticum aestivum L.) vary in the structure of their inflores-cences and also in how pollination proceeds within the inflorescence. In both species the grain position in the spikelet determines grain weight potential. Primary grains in oat and proximal grains in wheat weigh more than secondary and distal grains. This variation in grain weight can potentially result from differences in post-pollination cell division in the grain. In this study pollination duration and dynamics were analyzed from head samples collected at two-day intervals, starting from the pollination of the most advanced floret. The number of grain cells was determined for individual grains throughout the inflorescence, starting from the pollination event. When mature, grain position in the spikelet and spike was noted and grain weight assessed. Pollination advance in oat proceeded from the uppermost primary floret towards the basal spikelets in ten to eleven days. Within the spikelet, the primary floret was pollinated on average one day earlier than the secondary floret. In wheat, pollination duration was four to five days, starting from the proximal florets in the mid-section of the inflorescence progressing towards the apical and basal spikelets. Proximal florets were pollinated one to two days earlier than distal florets. Maximum cell number in primary grains exceeded that of secondary grains in two oat cultivars. Similarly, primary grains were heavier than secondary grains. Cell number and single grain weight were correlated in terms of grain position in the spikelet (primary – secondary) and cultivar. Oat cultivar Belinda had a higher single grain weight than Fiia, which was also expressed as larger grain cell number. In wheat, proximal grains had higher maximum cell numbers and were also heavier than distal grains. This grain weight gradient was apparent throughout the inflorescence. Consequently, grain cell number is one of the possible regulators of grain-filling capacity in both cereal crops.

Starch Granule Size Distribution in Grains at Different Positions on the Spike of Wheat (Triticum aestivum L.)

AbstractThe present study was carried out to characterize the effects of soil water status, cultivar and grain position on starch granule size distribution. The starch granule size distribution and protein and starch content were determined from three wheat cultivars with reference to the position of the grain on the spike. The results showed that the contents of A‐, B‐ and C‐type starch granules were affected by soil water, genotype and soil water×genotype interaction. Grain position was significant for A‐ and C‐type starch granules. Genotype×grain position and soil water×genotype×grain position interactions only affected C‐type starch granules. Both basal and distal grains on middle spikelets contained three types of starch granules: smaller C‐type granules with diameters <2.0 μm, medium B‐type granules with diameters 2.0–9.8 μm and large A‐type granules with diameters >9.8 μm at maturity. Both percent volume and percent surface area distribution of starch granules in basal grains showed the typical three populations, and those in distal grains exhibited a two‐peak curve. The volume and surface area percentage of C‐type granules and protein content in basal grains were higher than that in distal grains, but those of A, B‐type granules in basal grains were lower than that in distal grains. Compared with irrigation, the percent volume and surface area of B, C‐type starch granules and protein content in basal and distal grains were significantly increased, and those of A‐type were evidently decreased in rainfed condition.

Grain weight response to increases in number of grains in wheat in a Mediterranean area

This study explored whether the average grain weight of wheat tends to be reduced when grain number is increased due to either competition or, to a consistent increase in the relative proportion of grains of smaller weight potential. Three field experiments considering environmental, genetic and environmental × genetic effects on yield and its main components were analysed during the 2003/2004 growing season in two different locations within the Mediterranean area of Catalonia, Spain. The relationship between grain weight and number of grains per unit land area was analysed for both the average of all grains (AGW) and for grains in specific positions of the main-shoot spikes: proximal (CPg) and distal (CDg) grains of central spikelets, and proximal grains of the near apical (APg) and near basal (BPg) spikelets. The proportional contribution of grains per spike for the different grain positions and the relative contribution of spikes per m 2 made by the main shoot or tillers were also examined. In the three experiments, AGW was reduced when grain number was increased due to genetic and/or environmental factors. However, the slopes of the straight-lines that represented the negative relationship between grain number and grain weight were lower (less negative) and less significant for CPg ( b = −0.20, P > 0.20), CDg ( b = 0.06, P > 0.20) and BPg ( b = −0.21, P > 0.20) than for AGW ( b = −0.40, P < 0.05). The proportional contribution of distal grains and tiller spikes (both with relatively light grains) were directly related to grain number increases. Therefore, as grain number increased there was a higher proportion of grains of low potential weight. Thus, the average grain weight was concomitantly reduced when grain number increased by increasing the proportion of “small grains” in the canopy independently of any competitive relationship between growing grains.

Differential responses of BA injection on yield and specific grain growth in contrasting genotypes of wheat (Triticum aestivum L.)

The effect of exogenous cytokinin (benzyladenine) was investigated on location specific grains in three contrasting wheat genotypes tolerant or susceptible to post anthesis high temperature conditions. Seeds were sown in earthen pots under natural environment in November and January for normal and late sowings, respectively. Grain weight was increased by the application of benzyladenine at anthesis under late sown stress only in those genotypes, which are known, to posses temperature tolerance in developing grains. However, under normal sowing conditions BA application was effective irrespective of genotype response to late sown stress. The effect was most visible in distal spikelets in the spike and distal grains in the spikelet which resulted in higher increment in weight of younger grains (c and d) as compared to older grains (a and b). It has been suggested that the responsiveness of the genotype to BA application under late sown stress is important and may be developed as an indicator to screen wheat genotypes for relative tolerance to late sown stress under irrigated conditions.

Translocation of 14C‐sucrose within the Ear in Durum and Aestivum Wheat Varieties

Excised ears of Triticum durum (HD 4502 and B 449) and T. aestivum (Kalyansona and Kundan) varieties were cultured in 14C‐sucrose, and the uptake and distribution of 14C within the ear was examined. Species‐level differences in the distribution of 14C to spikelets at basal, middle and apical positions in the wheat ear (vertical distribution) were observed. T. aestivum var. Kalyansona and Kundan showed no limitation in vertical translocation of 14C‐sucrose, whereas in T. durum there was a decrease in the distribution of 14C to apical spikelets. Within a spikelet, the distribution of 14C‐sucrose to distal grains was significantly less than that to proximal grains in all the genotypes.

Changes in grain weight as a consequence of de-graining treatments at pre- and post-anthesis in synthetic hexaploid lines of wheat (Triticum durum x T. tauschii)

Grain weight is a trait which has hardly been exploited for raising genetic yield potential of wheat. A clearer understanding of physiological determinants of grain weight potential would be useful in establishing the potential value of this trait in future breeding programs. The objective of this study was to improve understanding of how intra-spikelet competition for assimilates pre- and post-anthesis affect grain weight potential, and to evaluate possible mechanisms determining final grain weight in wheat. Two experiments were carried out under field con-ditions. Proximal or distal grains from the two central spikelets of spikes of three synthetic hexaploid lines were detached at heading or 7 d after anthesis. Synthetic wheats were used since they represent a potential source of genetic variability for grain weight potential. Carpel size at anthesis and grain weight during the grain filling period were measured. The de-graining treatment at heading significantly increased grain weight, especially in distal posi-tions. On the contrary, the de-graining treatment carried out after anthesis caused no increase in final grain weight. The largest response to pre-anthesis de-graining occurred in grain positions with the lowest grain mass. In addition, the effect of de-graining prior to anthesis was associated hyperbolically with weight of carpels at anthesis within each grain position. Therefore, carpel weight at anthesis could be partially associated with the regulation of grain weight potential.

Les minéraux ferrotitanés du littoral sénégalais: Caractérisation et recherche de leur origine

Iron-titanium rich grains (‘ilmenites’ to a various degree of weathering) occuring along the coast line of Senegal and deriving from various parent units are characterized from their size, texture, magnetic and geochemical properties. Both the corresponding data and their multivariate analysis lead to the conclusion that the ‘ilmenite’ grains derive from various sources, mainly local ones, except in the area of Saint-Louis where occur more distal grains from Mauritania. In the North of Cap Vert and in the South of Gambia, the ‘Continental Terminal’ formation represents the main source of the ‘ilmenite’ grains. Along the ‘Petite Côte’, ‘ilmenites’ derive mainly from the Maastrichtian formations of the ‘Massif de Ndiass’. Volcanic formation of the Cap Vert area does not represent a major source, except in the area of the extremity of the peninsula. The old ferricretes do not significantly contribute to the recent accumulation. The ‘ilmenites’ concentration along the beach lineis controlled by the different sedimentary cycles; the nouakchottian transgression beeing probably the most important event. In the Senegalese basin, a significant amount of the ‘ilmenites’ originated from the ‘Continental Terminal’ formation appears to derive from basic metamorphic rocks of the Mauritanide orogen. In the northern part of the basin, ‘ilmenite’ assemblage contains grains suggesting intermediate to acidic magmatic parental rocks. The calc-alkaline igneous complex from the structural units emplaced in the late Paleozoic on the NW margin of the Mauritanide orogen, and the Reguibat uplift, are two possible sources. The ‘ilmenite’ association found in the Maastrichtian formation probably derives from various paleozoic formations but its primary origin can not be deciphered.

Availability and Utilization of Assimilates in Relation to Grain Growth Within the Ear of Wheat

AbstractThe development of grains of different positions in the apical, middle and basal spikelets of wheat var. Kaly‐ansona showed that beyond first two basal grains, the more distal a grain in a spikelet the lower its weight. The distal grains received less assimilates than the proximal grains as revealed from sugar concentration in the grains. The eflficiency of distal grains of kalyansona to synthesize reserves was, however, not inferior than the proximal grains in a spikelet. The depression in grain weight lowards extreme spikelet was lower compared to the depression in weight of individual grams towards a distal position in a spikelet. The study seems to suggest that in order to ensure better grain uniformity while maintaining a higher grain number per ear, the spikelet number per ear should be increased instead of increasing the grain number per spikelet.

Varietal Differences in Grain Filling at the Distal end of Sweet Corn Ear

The bases of varietal differences in the frequency of unfilled grains at the distal end of sweet corn cultivars in relation to : (i) the dry matter production, (ii) partitioning of dry, matter within the ear, and (iii) changes in the florets with emerged silk were investigated.1.Cultivars with delayed silk emergence had the largest total plant dry weight at silking time, the fastest dry matter accumulation rate during grain filling, heaviest ear weight at the harvesting, and the maximaum number of filled grains. A low negative correlation was obtained between the percentage of unfilled grains and dry matter accumulation during grain filling period.2.A positive correlation exists between percentage of the decrease of a single grain weight (SGW) at the distal positions and percentage of the occurrence of unfilled grains on the ear. Ears on cultivars which have significantly lighter SGW at the ear distal end compared to the basal grains had large proportions of unfilled grains.3.A negative correlation exists the percentage of the florets with silk emerging 5 days after the first silk appearance and percentage of the decrease of a SGW at the distal end of the corn ear. The difference in SGW within an ear was small in the cultivars in which silk emerged relatively early, proceeding from the basal to the distal florets.Therefore, the varietal difference in the frequency of unfilled grains are caused, not only by the dry matter accumulation during grain filling, but also by the partitioning of assimilates to the distal grains. Cultivars in which, silk emerged relatively early had : (i) uniform partitioning of dry matter within ear, (ii) greater translocation of assimilate to the distal grains, and (iii) fewer unfilled distal grains.

Individual grain weight responses to genetic reduction in culm length in wheat as affected by source-sink manipulations

This paper describes the effects of Rht alleles in isogenic lines of Maringa spring wheat ( Triticum aestivum L.) on number of grains per spike, average grain weight and weight of individual grains from different positions within the spike. Plants were grown under five environmental conditions in the field (in the 1991, 1992 and 1993 growing seasons, with two sowing dates in the first two years), aiming to determine causes of lower average grain weight commonly observed in semi-dwarf (SD) compared with standard-height (SH) cultivars. The number of grains per spike was significantly greater in SD and dwarf (DD) lines than in the SH line due to differences among lines in number of grains per spikelet. Therefore, the relative contribution of proximal grains was affected negatively by Rht alleles while the contribution of distal grains was affected positively. Average grain weight was reduced with increases in the dose of Rht alleles, and this trait was negatively correlated to number of grains per spike. To understand the possible causes of this negative relationship, individual grains from specific positions within the spike were analysed. Basal grains in central spikelets were heavier than those in near apical and near basal spikelets. Within central spikelets, the ranking of individual grain weights were grains 2 > 1 > 3 > 4, numbered from the most proximal to the most distal positions. Proximal grains (1 and 2) were heaviest in SH, lightest in DD, and intermediate in the SD line. In general, the relative differences between the lines were smaller than that found for the average of all grains of the spike, in particular when grains of different positions within the central spikelets were considered. For all these grains, differences in weight due to Rht alleles were due to differences in rate of grain filling, with the effective duration of grain filling being almost unchanged. An increased source-sink relationship did not significantly modify the weight of any of the analysed grains in SD and SH lines (and just slightly increased rate of grain filling in the DD line). Therefore, the smaller grains in SD and DD lines could hardly have been due to an increased competition for assimilates. Alternatively, SD and DD lines had a greater proportion of grains from distal positions than the SH line, and these grains were always smaller than proximal grains. The reduction in average grain weight produced by Rht alleles therefore was due to a combination of effects on the potential size of each grain and on the contribution of grains from distal positions within the spike, with no effects attributed to an increased competition for assimilates.

Variation of dry matter accumulation at definite positions within wheat ears and levels of indole-3yl acetic acid (IAA)

By sterilization-treatments grain weights in defined positions within the wheat (Triticum aestivum L. cvs. Oskar, Kolibri, Norin 10) ear were varied. Main shoot ears were partitioned into basal, central and apical regions and further into proximal and distal grains. The central region was used for treatments and investigations. Proximal grains were sterilized in order to vary the dry weights of distal grains. Dry matter ac= cumulation and IAA levels were investigated during the grainfilling period. Results from two seasons are presented. In both seasons sterilization treatments accelerated the dry matter accumulation of distal grains in all cultivars, but treatment effects on IAA concentration depended upon interactions between years and cultivars. A parallel variation in grain weights and IAA concentrations occurred only in 1981 in the cultivar Oskar. In 1982, however, IAA concentrations were reduced in all cultivars. The results contradict an assumed causal correlation between dry matter storage and IAA concentration, but they do not exclude a possible role of IAA in regulating grain growth.

Effect of Post-anthesis Drought on Cell Division and Starch Accumulation in Developing Wheat Grains

Wheat plants (Triticum aestivum L., cv. Warigal) were subjected to 20 d of water deficit during the period of endosperm cell division. Drought accentuated the differences in final grain weight between spikelets and between grains within spikelets. The distal grains of top spikelets were most affected by drought. The maximum number of endosperm cells was, respectively, 30 and 40 per cent lower in basal grains and distal grains of draughted plants. In basal grains of middle spikelets, the number of large starch granules per cell was unaffected but the number of small starch granules per cell was 45 per cent lower in grains of draughted plants. The initiation of small starch granules was more affected than cell division because severe water deficit occurred earlier during the former process than the latter. Final dry weight appeared to correlate well with the maximum number of endosperm cells, but depended also on the number of starch granules per cell. Consequently, the amount of dry matter per cell was not constant in both treatments. The concentration of sucrose per endosperm cell was lower only in the droughted distal grains of top spikelets. The supply of sucrose to endosperm cells did not regulate the initiation of small starch granules.

IAA level and dry matter accumulation at different positions within a wheat ear

Dry matter accumulation and IAA level of grains in various positions within the wheat (Triticum aestivum L. cvs Solo and Kolibri) ear were investigated during the grain filling period. Main shoot ears were partitioned into basal, central and apical regions and further into proximal and distal grains. Results from a two‐year experiment with two wheat cultivars of different grain size are presented. The IAA level increased rapidly from about 8 until 20 to 30 days after anthesis, and then decreased dependent upon year and cultivar. The differences in IAA levels, both among spikelets in different regions of the ear (i.e. basal, central and apical) and also among florets within a spikelet (i.e. proximal and distal), were positively correlated with the differences in dry matter accumulation. Although the correlations held true within cultivars in a particular year, differences in dry matter between cvs Solo and Kolibri or differences from year to year were not well correlated with the corresponding changes in IAA levels. Possible interactions between dry matter accumulation and IAA levels are briefly discussed.