Duration Of Grain Research Articles

Kernel water relations and duration of grain filling in maize temperate hybrids

Kernel water relations play a key role in controlling the duration of grain filling. This duration is controlled by the relationship between kernel water and biomass development, as it determines the timing kernels reach a critical percent moisture content (MC, measured on a fresh weight basis) at which biomass accumulation stops. The time in which this critical percent MC is attained can be affected by the timing kernel net water uptake stops (i.e. maximum water content is reached), or by the relationship between water loss and biomass deposition after maximum water content is attained. Which of the two mechanisms could be behind genotypic differences in maize ( Zea mays L.) grain-filling duration was unknown. We also studied the relationship between kernel water and volume development, as it was unknown in this species. Thirteen commercial hybrids were evaluated under different growing environments, and weight, water content and volume of their kernels were measured throughout grain filling. There were no differences among hybrids in their kernel percent MC at physiological maturity ( p > 0.05), showing that hybrid differences in grain-filling duration (from 1117 to 1470 °C day) were related to variations in the accumulated thermal time from flowering to this critical percent MC. There were no differences in the accumulated thermal time from silking to kernel maximum water content, and this stage was always reached at the same kernel percent MC (ca. 540 g kg −1). Differences in grain-filling duration were explained by the pattern of percent MC decline after maximum water content was reached. This percent MC decline was dependent upon the relationship between water loss and biomass deposition; the higher the water loss rate and the higher the kernel growth rate the shorter the duration ( r 2 = 0.60; p < 0.001). Maximum kernel volume was achieved after maximum water content, and close to physiological maturity. Hybrids differed ( p < 0.05) in the kernel volume generated after maximum water content, and this was also related to the relationship between biomass and water development late in grain filling. Results showed the importance of understanding and predicting percent MC development throughout grain filling, as there were no differences between hybrids and environments in their kernel percent MC at specific developmental stages (i.e. maximum water content or physiological maturity). Our results highlighted the importance of the relationship between water loss and biomass deposition during late kernel development in the duration of maize grain filling.

Source/sink ratio and the relationship between maximum water content, maximum volume, and final dry weight of maize kernels

Final kernel weight (KW) is closely related to maximum kernel volume (KV) and maximum kernel water content (KWC). It is not clear, however, how changes in the reproductive sink capacity, assimilate availability during grain filling and physical restriction to kernel expansion affect the relationship between KW and KWC or between KW and KV. Three experiments were conducted at Balcarce, Argentina and Ames, USA. Defoliation, thinning, plant density, restricted pollination and volume restriction treatments were imposed to manipulate KV, sink and source capacity. KW varied from 111 to 436 mg across all hybrid–treatments combinations and was related to the source/sink ratio during grain filling ( r 2 = 0.85). Treatment variation in KW was related primarily to changes in kernel growth rate, except for the complete defoliated treatment, which also shortened the duration of grain filling. KW was correlated with maximum KWC ( r 2 = 0.77, p < 0.001) and with maximum KV ( r 2 = 0.91, p < 0.001). The developmental patterns for KW, KWC and KV during grain filling were not affected by the source/sink manipulations, except for severe defoliation. In the latter case, maximum KWC was not a good estimate of final KW. KV, however, was sensitive to reductions in carbohydrate supply during grain filling and was closely correlated to KW. Physical restriction to kernel expansion reduced kernel weight 13% relative to its control ( p < 0.01). But restricting kernel expansion did not alter the general relationships between KW and KWC or between KW and KV, because kernel density was not affected.

Plasticity of sorghum kernel weight to increased assimilate availability

Understanding source or sink limitations on crop yield is critical for the rational design of agricultural practices as well as breeding strategies. In the present article, we studied sorghum [ Sorghum bicolor (L.) Moench] source–sink yield limitations during grain filling, and tested the hypothesis that the time in which kernel maximum water content is reached during grain filling defines a temporal limit for the crop to profit from source increases. Earlier studies have never tested increasing assimilate availability per kernel in different developmental stages. We conducted a field experiment increasing assimilate availability per kernel at anthesis and 15 days after anthesis in commercial hybrids. The anthesis treatment was aimed to increase assimilates per kernel from early grain filling, and the 15 days after anthesis treatment from the stage kernel maximum water content was achieved. Both treatments removed 50% of the kernels from one side of the panicle. Kernel dry weight (KW), kernel water content and kernel volume were measured in apical and basal positions of the panicle throughout grain filling. Increased assimilate availability always yielded a higher KW (∼34% increase). This KW increase was consistent across the two kernel developmental stages when the treatment was imposed, the panicle position and hybrid. Achieving maximum water content did not prevent kernels from increasing their weight when assimilates were subsequently increased. Final KW was closely related to maximum kernel volume ( r 2 = 0.72; n = 42; p < 0.0001). Increased assimilate availability per kernel promoted changes in both kernel growth rate and duration of grain filling. We applied a quantitative approach for determining the magnitude of sorghum KW changes in response to assimilate availability changes during grain filling. This allowed us to compare our data to previously published articles, and to determine any general response pattern across environments. The analysis supported our observation that sorghum KW is highly responsive to increased assimilates, and indicated that increased assimilate availability during filling always increased sorghum KW. As such, growth of sorghum kernels is predominately source limited; breeding and management practices aimed to increase assimilate availability per kernel will be likely to enhance sorghum yield. Results show that the crop has the capacity to profit from source increases even after the initial grain-filling stages have occurred.

Grain weight responses to post-anthesis spikelet-trimming in an old and a modern wheat under Mediterranean conditions

Average grain weight is a major yield component contributing to its variation, especially in Mediterranean regions where grain weight is frequently exposed to terminal stresses affecting grain growth. Most of the literature agrees that wheat grain growth is hardly limited by the source. However, no source–sink ratios studies seem to have been conducted in the Mediterranean region to determine to what degree wheat grain growth is actually limited by the source in these particular regions. We conducted two field experiments in Catalonia (north-eastern Spain), where an old cultivar (Anza) and a more recently released one (Soissons) were sown in a range of different nitrogen and water availabilities and sowing dates. This was to analyse the degree of source limitation for grain growth. Sink size was modified by removing half of the spikelets c. 10 days after anthesis, virtually doubling the availability of assimilates per grain effectively growing. Trimming the spikes did not produce significant changes in grain growth rate or duration of grain filling. Consequently, grain weight did not respond noticeably to the reduction in sink demand and any eventual response has been far from representing a strong competition among grains during grain filling.

Grain filling parameters and yield components in wheat

Grain yield of wheat (Triticum aestivum L.) is influenced by number of grains per unit area and grain weight, which is result of grain filling duration and rate. The aim of the study was to investigate the relationships between grain filling parameters in 4 wheat genotypes of different earliness and yield components. Nonlinear regression estimated and observed parameters were analyzed. Rang of estimated parameters corresponds to rang of observed parameters. Stepwise MANOVA indicated that the final grain dry weight, rate and duration of grain filling were important parameters in differentiating among cultivars grain filling curves. The yield was positively correlated with number of grains/m2, grain weight and grain filling rate, and negatively correlated with grain filling duration. Correlation between grain weight and rate of grain filling was positive. Grain filling duration was negatively correlated with grain filling rate and number of grains/m2. The highest yield on three year average had medium late Mironovska 808, by the highest grain weight and grain filling rate and optimal number of grains/2 and grain filling duration.

Source–sink relations and kernel weight differences in maize temperate hybrids

Maize ( Zea mays L.) kernel weight (KW) response to changes in assimilate availability per kernel during grain filling suggests that plants establish an early kernel sink potential that place them to grow close to a saturating assimilate availability condition during late grain-filling, meaning source limitations are common only early in kernel development. As maize reproductive efficiency in kernel set is not constant across different plant growth rates (PGR) around flowering, we used PGR per kernel during this period as an indicator of source availability per kernel. We tested whether PGR per kernel during flowering or during the effective grain-filling period were correlated to genotypic and environmental differences in final KW. Plant growth rate during both periods, KW, kernel growth rate during the effective grain-filling period, total duration of grain filling and kernel number per plant were measured in 12 commercial genotypes differing in KW sown at two sites under full irrigation. As expected from the curvilinear response relating kernel number per plant and PGR around flowering, increased PGRs resulted in higher PGR per kernel around this period ( r 2 = 0.86; p < 0.001). Differences in final KW due to genotypes or environments were significantly explained by the PGR per kernel around flowering ( r 2 = 0.40; p < 0.001), and not by the PGR per kernel during the effective grain-filling period. Genotypes differed in kernel growth rate ( p < 0.001) and grain-filling duration ( p < 0.001). The former was well explained by PGR per kernel around flowering ( r 2 = 0.66; p < 0.001), but showed no relationship with the PGR per kernel during the effective grain-filling period. Grain-filling duration was partially explained ( r 2 = 0.27; p < 0.01) by the ratio between PGR per kernel during the effective grain-filling period and kernel growth rate, but differences in duration were negligible compared to those observed in the ratio (∼41% versus ∼130%, respectively). Together, these results support the importance of source availability per kernel during early grain filling on the determination of maize potential sink capacity and final KW. Early resource availability per kernel was accurately estimated as PGR per kernel around the period of kernel number determination, which helped explain genotypic and environmental differences in maize final KW as well as in kernel growth rate.

Sorghum Kernel Weight

The influence of genotype and panicle position on sorghum [Sorghum bicolor (L.) Moench] kernel growth is poorly understood. In the present study, sorghum kernel weight (KW) differences during grain filling were analyzed by kernel water relationships previously described in other crops. Eight commercial genotypes differing in KW were used, and KW, water content, kernel volume, kernel moisture content, and kernel density were measured in two positions within the panicle (apical and basal) throughout the grain‐filling period. At physiological maturity (PM), KW ranged from 16.5 to 25.1 mg kernel−1, and a significant (p &lt; 0.05) genotype × position interaction was detected. Independently of final KW, apical kernels always exhibited a higher rate (p &lt; 0.001) and a shorter duration of grain filling (p &lt; 0.001) than basal kernels. Maximum water content was related to kernel growth rate but not to final KW. Basal kernels reached maximum kernel volume after attaining maximum water content, with dry matter accumulation affecting kernel volume determination. Kernel density increased with a similar pattern regardless of genotype or panicle position when related to the kernel moisture decline, but at PM, basal kernels were always more dense than apical ones. Differences in the kernel desiccation pattern and in the critical moisture content for biomass accumulation helped explain differences in the grain‐filling duration between positions. A general kernel growth curve based on kernel moisture content was impossible to obtain because of the differences in kernel growth patterns within the panicle.

Effects of drought stress on growth and yield of barley

Barley (Hordeum vulgare) grown in Mediterranean regions undergoes drought stress during the grain-filling period. A greenhouse experiment was conducted to study the effect of drought stress on grain growth and yield of barley. Plants were exposed to three drought treatments at the beginning of grain filling: (1) well-watered at 100% field capacity, (2) mild drought stress at 60% field capacity, and (3) severe drought stress at 20% field capacity until grain maturity. Grain moisture content and dry weight were determined for grains harvested at 3, 10, 17, 23 and 31 days after the beginning of grain filling. Grain dry weight for severe drought stress plants reached a maximum value earlier than grains from mild drought stress and well-watered plants, indicating that grains from severe drought stress plants had a higher growth rate than those of mild drought stress and well-watered plants. Drought-stressed plants had shorter duration of grain filling than well-watered plants. Drought stress treatments reduced grain yield by reducing the number of tillers, spikes and grains per plant and individual grain weight. In conclusion, postanthesis drought stress was detrimental to grain yield regardless of the stress severity.

EFFECT OF HEAT STRESS ON SOME AGRONOMIC TRAITS OF BREAD WHEAT (TRITICUM AESTIVUM, L) GENOTYPES UNDER UPPER EGYPT CONDITIONS

Combined analysis of variance for all studied traits in twelve breadwheat genotypes showed highly significant differences among lines andsowing dates, as well as, the lines x sowing date interaction whichshowed significant and highly significant for all traits except grain yield.Delaying the sowing date to 20 December reduced grain yield, 1000kernel weight, accumulated growing degree days (GDD), and duration ofgrain filling period by 30.0, 6.2, 10.3, and 11.4%, respectively whencompared to normal sowing date (20 December), while the rate of grainfilling period was increased by 7% when compared to the optimumsowing date (25 November).Susceptibility index “s” for grain yield showed that lines 1, 2, 3, 7, 9and 10 were the most tolerant lines to high temperature, meanwhile theother lines were the more susceptible. Line number 5 recorded thehighest grain yield, longest duration with medium rate of grain fillingunder late sowing date. These results indicated that the tolerant lines mayhave genes controlling tolerance to heat stress. Hence, they could be useas parents in breeding programs in Upper Egypt.

Morphological and Agronomical Diversity Patterns in the Spanish Barley Core Collection

Seven thousand years of barley cultivation under the environmental hardships typical of the Mediterranean climate have generated genetic singularity of the Spanish barleys, consistently reported in the literature. From the Spanish National Collection of 2289 accessions, a core subset with 159 landraces and 16 old varieties was constituted. Twenty-seven characters were evaluated for the core collection, to define the structure of the diversity. Several evaluation trials were carried out in 1999-2000, whereas yield trials were performed in earlier years. Phenotypic diversity was large for most of the characters studied. Comparisons of genetic diversity between the core and the original collections suggested that the core is a good representation of the existing diversity in the BNG. Comparisons with results of studies on Spanish materials from other collections seem to indicate that the Spanish diversity is not well represented in some world collections. Principal component analyses for quantitative and qualitative characters revealed a clear distinction between two- and six-row cultivars, and also between landraces and commercial varieties. Geographical origins of the landraces were correlated with grain yield, heading date, duration of grain filling period, and growth class. In relation to diseases, altitude played an important role on the resistance to powdery mildew and brown rust. For brown rust, all the resistant landraces came from low altitudes. These geographical gradients seemed consistent with prior knowledge about barley adaptation, and would confirm the agreement between passport data and true adaptive origin of these landraces from a geographical point of view.

Observed duration and average and maximum grain filling rates in wheat genotypes of different earliness

Grain yields of wheat (Triticum aestivitm L) are influenced partly by final grain dry weight, which is largely determined by the rate and duration of the grain filling process. A study was undertaken to compare the observed final grain dry weight of five groups of wheat genotypes differing in earliness (extra early, medium early, medium late, late and a control group of high yielding NS cultivars) with the observed duration and average and maximum rates of grain filling in two different environments. Correlation coefficients were used to determine which grain filling parameter had more influence on final grain dry weight, in an environment common for our country (2002), final grain dry weight was strongly positively correlated with the average and maximum rates and strongly negatively correlated with the duration of grain filling. The medium late and control groups had the highest final grain dry weights. Correlations between final grain dry weight and the duration and average rate of grain filling were positive in an unfavorable environment (2001). The NS cultivars and extra early genotypes had the highest final grain dry-weights. The rate and duration of grain filling are usually negatively correlated. The influence of grain filling parameters on final grain dry weight is not the same in different environments, so the ability of the genotype to compensate for the low grain filling rate with grain fill prolongation in unfavorable environments might be more important. The observed average grain filling rate is probably more important as a parameter for describing these processes than the maximum one.

Optimising harvest timing by predicting dry matter content of whole-crop cereals for silage

Abstract Timing of harvest is the single most important factor affecting the yield and quality of whole-crop cereals used for conserved feed. Changes in dry matter content (%DM) and relationships to herbage quality and maturation are presented for experiments conducted over three seasons beginning in 2001/ 2002. Changes in crop characteristics such as ear moisture, ear fresh weight, ear dry weight and leaf fraction were monitored to determine whether growers could use crop-based measurements in place of whole-crop % DM content to assist withdecision making close to harvest. A preliminary model defined the rate of crop maturation for a range of currently grown cultivars. Linear patterns of dry down occurred with only small variation in drying rate for the duration of grain filling. A model with specific inputs for cultivar, date of awn tip appearance (GS49), and developmental response to thermal time formed the basis of a decision support tool that enables growers and contractors to predict optimum harvest timing for whole-crop cereals. Keywords: silage maturity, supplements, forage, herbage quality

Ion distribution in wheat cultivars in response to salinity stress

In a pot experiment, 30 cultivars of wheat ( Triticum aestivum L.) were evaluated in terms of their leaf and grain K/Na ratios and their ion selectivity responses to NaCl salinity. A completely randomized block design with factorial treatments in three replications was employed. Tap water, both with and without NaCl, producing a soil extract EC of 16 ds m −1 was used as the salinity treatment, beginning at the stem elongating stage. Significant correlations observed between grain dry matter (DM) and some ionic traits indicate that, beside the adverse effects of the higher leaf Na concentration on grain DM, the processes involved in the rate and/or duration of grain filling may be more efficient in terms of salt tolerance where grain yield is concerned. This may allow for the reproductive phase of growth to be salt tolerant independently of the vegetative one. Cultivar Inia-66 could serve as an example of this, showing higher rates of salt tolerance through the more suitable DM partitioning pattern. Mean comparisons made between the cultivars showed that the salt tolerant Roshan cultivar and, 10 other following cultivars, had the highest rates of absolute salt tolerance. This cultivar had the lowest leaf Na concentration, the highest K versus Na selectivity in ion transport from the soil to the grains, and also the highest grain K/Na ratios. It produced grain DM 7.5 times higher than the salt sensitive Ghods cultivar that had the lowest grain DM. The former 11 cultivars could therefore be considered as the most completely salt tolerant cultivars. In the cultivar Kharchia, salinity did not reduce the grain K/Na ratio and ion selectivity, but its grain filling period and HI were reduced under saline conditions.

Analysis of effects in wheat of high temperature on grain filling attributes estimated from mathematical models of grain filling

Compared with growth at 20/15°C (day/night), exposure of wheat (Triticum aestivum L.) plants to moderately high temperature (30/25°C) significantly decreased grain weight through shortening the duration of grain filling, combined with small (or no) positive increases in the rate of grain filling. Several mathematical models of grain filling were assessed for their suitability as means of analysing these effects of temperature. The ordinary logistic model was found to be the most appropriate model and was used for the analysis of grain filling responses in four cultivars differing in their responses. Genotypic variation in response to temperature was observed for both rate and duration of grain filling, but the variation for the duration of grain filling among cultivars was small at the higher temperature. Significant correlation was found between single grain weight with the rate, but not with the duration, of grain filling at high temperature, which indicated an important role for synthetic processes involved in grain filling in the temperature sensitivity of wheat cultivars. As they are independent traits, both rate and duration are required selection criteria for the improvement of heat tolerance. Responses of one attribute estimated from the logistic model, the inflection point of the course of grain filling, may give insight into a temperature response that is distinguishable from that associated with the duration of grain filling. The inflection point appears to be worth including as a criterion in selecting for high temperature tolerance in wheat.

Simulating growth, development, and yield of tillering pearl millet. III. Biomass accumulation and partitioning

Pearl millet landraces from Rajasthan, India, yield significantly less than improved cultivars under optimum growing conditions, but not under stressed conditions. To successfully develop a simulation model for pearl millet, capable of capturing such genotype×environment (G×E) interactions for grain yield, we need to understand the causes of the observed yield interaction. The aim of this paper is to quantify the key parameters that determine the accumulation and partitioning of biomass: the light extinction coefficient, radiation use efficiency (RUE), pattern of dry matter allocation to the leaf blades, the determination of grain number, and the rate and duration of dry matter accumulation into individual grains. We used data on improved cultivars and landraces, obtained from both published and unpublished sources collected at ICRISAT, Patancheru, India. Where possible, the effects of cultivar and axis (main shoot vs. tillers) on these parameters were analysed, as previous research suggested that G×E interactions for grain yield are associated with differences in tillering habit. Our results indicated there were no cultivar differences in extinction coefficient, RUE, and biomass partitioning before anthesis, and differences between axes in biomass partitioning were negligible. This indicates there was no basis for cultivar differences in the potential grain yield. Landraces, however, produced consistently less grain yield for a given rate of dry matter accumulation at anthesis than did improved cultivars. This was caused by a combination of low grain number and small grain size. The latter was predominantly due to a lower grain growth rate, as genotypic differences in the duration of grain filling were relatively small. Main shoot and tillers also had a similar duration of grain filling. The low grain yield of the landraces was associated with profuse nodal tillering, supporting the hypothesis that grain yield was below the potential yield that could be supported by assimilate availability. We hypothesise this is a survival strategy, which enhances the prospects to escape the effects of stress around anthesis.

Investigating the physiological bases of predictable and unpredictable genotype by environment interactions using three-mode pattern analysis

Understanding of the underlying physiology of the genotype-specific responses to predictable and unpredictable environmental variation would improve the efficiency of selection within a complex target population of environments. Three-mode principal component analysis (PCA) can be used for interpreting the complex three-way (genotypes, environments, attributes) trial datasets from which this understanding should emerge. The efficiency of this method largely depends on the right combination between the biological and statistical models used, especially on the attributes selected to describe the genotypic responses and the centring of the three-way input data. In this study, we assessed the scope of yield determination models and double-centring of input data for generating some physiological understanding of the genotype×environment (G×E) interactions observed in a sunflower genotype–environment system and for developing ideotype-based breeding strategies. Double-centring of the three-way arrays permitted the separation of predictable and unpredictable G×E interactions. This, in combination with the use of models that explain the physiological bases of yield variation among genotypes, has served to identify three relevant sources of genotypic variation for use in a breeding program, namely: (i) attributes that can be selected to achieve specific adaptation to the target environment by emphasising predictable interactions (e.g. duration of grain filling, a trait associated with canopy stay green); (ii) attributes that allow the unpredictable G×E interactions to be accommodated, improving the linkage between managed-environments and target production environments (e.g. grain set); and (iii) genotypes of similar response pattern for yield but contrasting relative behaviour for the primary and secondary yield determinants. Breeding projects involving crosses between these genotypes could generate better opportunities for yield improvements for individual mega-environments.

Effects of Planting Date, Genotype, and Their Interactions on Sunflower Yield

Sunflower (Helianthus annuus L.) yields are strongly reduced when normal sowing dates are delayed. The objectives of this study were to investigate the physiological bases of the sowing date (S), genotype (G), and G x S interaction effects on sunflower yield, and to contribute to the formulation of ideotype-based selection strategies for improving yield at late plantings. Nine hybrids differentially adapted to northern and central Argentina were evaluated during two seasons in October (normal) and December (late) planting dates at Venado Tuerto, Argentina. Yield was defined as the product of total biomass and harvest index. Sowing date accounted for most of the yield variation. The G × S interaction, in turn, accounted for a portion of the total variability three times higher than the contribution of G. Both S and G x S interaction effects on yield mostly involved the variation of attributes and processes expressed postanthesis. Biomass differences between planting dates were the dominant determinant of the S effect on yield. The genotype-specific responses for harvest index were the dominant determinant of the G x S interaction, and were mostly associated with changes in the rate of harvest index increase. Variations in biomass and harvest index were strongly associated with the amount of intercepted radiation during grain filling which, in turn, was associated to duration of grain filling and green leaf area. Canopy stay green proved to be associated with adaptation to late planting dates. This indirect selection criterion appears to be a more reliable attribute for use in breeding for adaptation to late plantings than some other genotype characteristics linked to yield.

Effects of Planting Date, Genotype, and Their Interactions on Sunflower Yield

Sunflower (Helianthus annuus L.) yields are strongly reduced by late sowing dates. The objectives of this study were to investigate the physiological bases of the sowing date (S), genotype (G), and genotype × sowing date (G × S) interaction effects on sunflower yield and contribute to development of ideotype-based selection strategies for improving yield at late plantings. Nine differentially adapted hybrids were evaluated during two seasons at normal and late planting dates at Venado Tuerto, Argentina, by means of the framework that defines oil yield as the product of grain number and weight and oil concentration. Sowing date was the major source of variation for oil yield. The G × S interaction, in turn, accounted for a portion of the total variability four times higher than the contribution of G. The S and G × S interaction effects on grain number were mostly determined by grain set in the central portion of the capitulum. Duration of grain filling was the main determinant of the S and G × S interaction effects on grain weight and grain oil concentration. Variation in grain oil concentration between sowing dates was largely due to changes in kernel oil proportion, rather than changes in kernel percentage. Relative changes in rate of grain filling and kernel percentage also contributed to the observed G × S interactions for grain weight and oil concentration, respectively. Although some degree of compensation among oil yield components underlie the observed G × S interactions, it was found that seed set in the central portion of the head can be used as an indicator of adaptation to late planting dates.

The effects of fungicides on rate and duration of grain filling in winter wheat in relation to maintenance of flag leaf green area

Three field experiments were conducted on sandy-loam soils comparing the effects of triazole, strobilurin and oxazolidinedione fungicides applied at flag leaf emergence and again at ear emergence to wheat between 1998 and 2000. Cultivars Hereward and Consort were included in all 3 years, Cockpit in 1999 and 2000 and Charger in 1999. Foliar disease, green area of the flag leaf, grain weight and moisture content were assessed weekly during grain filling and senescence. Grain yield, 1000 grain weight (TGW) and specific weights were measured at harvest maturity. Septoria tritici was the dominant disease in all cultivars except Cockpit, where Puccinia striiformis caused most damage. Consort was more affected than Hereward by S. tritici in all years. Effects of fungicides on disease control were usually reflected in green flag leaf area duration (GFLAD), with large gains in Consort and Cockpit. In 2000, however, fungicides increased GFLAD of Hereward and Consort by similar amounts. Apical grains had smaller water content than medially placed grains. Maximum water content was positively influenced by fungicides where significant disease was controlled before maximum grain weight had been attained. Grain weight in Hereward was less affected than other cultivars by fungicides in both positions. Grain filling rates varied between cultivar and ear position by inconsistent and small amounts, but large and significant gains from fungicide treatment were made in grain filling periods. These varied from 0·16 days per day GFLAD in Hereward to 0·69 days per day GFLAD in Consort in apical grains in 2000. Gains in GFLAD were associated with increased yield, TGW and specific weight, but these relationships varied with cultivar. Increases in GFLAD by fungicide in Hereward in 2000 occurred much later relative to grain filling and thus after the time of maximum grain water content, resulting in smaller gains in filling duration, yield, TGW and specific weight than that seen in Consort. There was no evidence of differing relationships between GFLAD and yield for the different fungicide groups used in these experiments.

Inter‐relationships Amongst Grain Characteristics, Grain‐Filling Parameters and Rice (Oryza sativa L.) Milling Quality

Resistance to breakage is a desirable trait of the rice kernel. Many factors, such as the genetics of the cultivar, the plant growth environment and the conditions of the milling process, will affect kernel breakage. Although many papers have discussed the factors that may affect and improve rice milling quality, few have related the grain‐filling process to head rice, the unbroken polished kernels obtained after milling. The objectives of this paper were: (i) to characterize the interrelationships amongst grain filling and grain structural characteristics; (ii) to determine whether the grain‐filling process and grain characteristics affect head rice, and (iii) to suggest a pathway through which grain characteristics can influence head rice recovery. An analysis of the interrelationships amongst all grain characteristics suggested that variables of grain structure (size, volume and per cent hull) have a decisive influence on the grain‐filling process (rate and duration of grain filling). The grain‐filling process will affect final grain traits such as weight and density, which in turn will have a direct impact on head rice. In addition, non‐uniformity, whether expressed in terms of variable grain size and shape or grain filling and maturity, has a detrimental effect on rice milling quality. The implication of these findings is that rice breeders need to pay more attention to selecting plant types that have a high degree of uniformity of grain characteristics on the panicle, and to those traits (such as greater grain size, weight and density) that have a positive impact on yield and milling quality.