Interactions Among Number of Spikelets, Number of Grains and Grain Weight in the Spikes of Wheat (Triticum aestivum L.)

In a field experiment, comprising four spring wheat cultivars,the frequency and final weight of the grains developing fromeach individual floret were determined in intact spikes andin spikes of which up to nine spikelets had been removed. Theextent of damage caused by the cutting procedure was estimated. Characteristic distributions of the frequencies and weightsof the individual grains were found for each cultivar. Removalof spikelets resulted, in most cases, in a small increase inthe number of grains and in a considerable increase in the weightof the grains of the remaining spikelets. These increases compensatedonly partially, and differently in the different cultivars,for the loss of the removed spikelets. Defoliation at the timeof earing caused a subsequent reduction in grain yield of intactspikes but no reduction in the yield of spikes from which ninespikelets had been removed. The removal of the upper floretsin each spikelet resulted in a certain increase in the weightof the two basal grains. It is concluded that an increase in the number of spikeletsper spike may reduce grain weight but will nevertheless contributeto yield. The number of grains per spikelet is cultivar dependentbut not causally associated with grain weight. Grain set indistal florets is expected to add rather small grains to thespike's yield. Under conditions of limited supplies it may causea reduction in the weight of the basal grains. Any increasein grain weight is anticipated to contribute to grain yieldand is not liable to affect spikelets per spike or grains perspikelet. Wheat cultivars, Triticum aestivum, growth of inflorescence, grain yield, spikelet number     

Effects of exogenous hormones on floret development and grain setin wheat

At specific stages during floret development, solutions of IAA,GA₃, zeatin and ABA were injected into the leaf sheath around theyoung spike of wheat (Triticum aestivum L.) to study theregulating effects of exogenous hormones on floret development. Zeatin promotedfloret development and significantly increased the number of fertile florets aswell as grain set, especially at the stage of anther-lobe formation. Zeatinalsoincreased the sugar concentrations in spikes at anthesis. In contrast, IAA,GA₃ and ABA inhibited floret development, with different patternsforeach of the hormones. IAA inhibited the development of the whole spike and allflorets in the spikelets such that grain loss occurred in all positions in thespikelets. GA₃ increased the number of fertile florets per spike,butdecreased grain set of the third floret in each spikelet, especially whenapplied at terminal spikelet formation. ABA inhibited floret development, anddecreased the number of fertile florets and grain set at almost all developmentstages, except at anther-lobe formation. The inhibitory effect of ABA wasmainlyon the first and third florets in each spikelet.     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

A genetic playground for enhancing grain number in cereals

Improving the yield stability of cereal crops with a view to bolstering global food security is an important priority. The components of final grain number per plant at harvest are determined by fertile spikes per plant, number of fertile spikelets per spike and number of grains per spikelet. In this review article, we focus on the genetic factors of floral development and inflorescence architecture known to influence grain number and provide a broad overview of genes and genetic pathways that potentially can be manipulated to increase the yield of cereal crops, in particular wheat (Triticum aestivum) and barley (Hordeum vulgare). In addition, we discuss the outcome of multidisciplinary genomics knowledge to identify potential gene targets to develop conceptual ideotypes to meet the future demand.     

Branching Shoots and Spikes from Lateral Meristems in Bread Wheat

Wheat grain yield consists of three components: spikes per plant, grains per spike (i.e. head or ear), and grain weight; and the grains per spike can be dissected into two subcomponents: spikelets per spike and grains per spikelet. An increase in any of these components will directly contribute to grain yield. Wheat morphology biology tells that a wheat plant has no lateral meristem that forms any branching shoot or spike. In this study, we report two novel shoot and spike traits that were produced from lateral meristems in bread wheat. One is supernumerary shoot that was developed from an axillary bud at the axil of leaves on the elongated internodes of the main stem. The other is supernumerary spike that was generated from a spikelet meristem on a spike. In addition, supernumerary spikelets were generated on the same rachis node of the spike in the plant that had supernumerary shoot and spikes. All of these supernumerary shoots/spikes/spikelets found in the super wheat plants produced normal fertility and seeds, displaying huge yield potential in bread wheat.     

Changes in duration of developmental phases of durum wheat caused by breeding in Spain and Italy during the 20th century and its impact on yield

Background and Aims

Although the apical development of wheat has been widely described, studies analysing how genetic breeding over the 20th century influenced the developmental phases and its consequences on yield generation are lacking, especially for durum wheat under field conditions in Mediterranean environments. The aims of this study were to analyse the effects of breeding in Spain and Italy on crop development during the last century, to determine whether or not breeding significantly altered the developmental phases between sowing and maturity, and to evaluate the importance of each phase in determining the number of grains per spike of durum wheat (Triticum durum) cultivars representing the germplasm grown throughout the 20th century in Spain and Italy.

Methods

Eight field experiments were carried out during 4 years in two contrasting latitudes (Lleida and Granada, Spain). Plant material consisted of 24 durum wheat cultivars (12 Italian and 12 Spanish) grown throughout the 20th century in Spain and Italy.

Key Results

In Spanish materials, breeding reduced the duration of the period from sowing to anthesis, placing the grain-filling period in better conditions. In those cultivars, the sub-phase sowing–terminal spikelet formation was reduced while the duration of the period from booting to anthesis was increased. The number of grains per spike increased by 23 % from old to modern cultivars, by changes in the number of grains per spikelet in both Spanish and Italian cultivars. Floral abortion from booting to anthesis diminished by 24 % from old to modern cultivars, and grain setting increased by 13 %.

Conclusions

The results suggest that breeding reduced not only plant height, but also the time to anthesis. By extending the duration of the phase from booting to anthesis, which was associated with an increase in spike dry weight and grains per spike, it suggests that future increases in spike fertility could be achieved by enlarging that phase.     

Development and Floret Survival in Wheat Ears With Supernumerary Spikelets

In the supernumerary spikelet wheat, AUS159I0, the supernumeraryspikelet primordia appeared just after the ear reached the terminalspikelet stage. Appearance of the primordia of the multiplesessile spikelets preceded that of indeterminate rachilla spikelets.Supernumerary spikelets had a lower number of potentially fertileflorets per spikelet than normal (non-supernumerary) spikeletsin the ear and thus a smaller number of grains per spikelet.Mean weight per grain in the supernumerary spikelet wheat waslower than in the cultivar, Meering, without supernumerary spikelets.Total grain number in the supernumerary spikelet ear was greaterthan in the normal ear despite the lower spikelet fertilityin the former. Within the supernumerary spikelet ear the multiplesessile spikelets had a higher number of grains per spikeletand mean weight per grain than the indeterminate rachilla spikelets.It appears possible to improve the productivity of the supernumeraryspikelet ear by breeding for reduced expression of the indeterminaterachilla spikelets. Wheat, ear development, floret survival, supernumerary spikelets, grain number     

Inheritance of five quantitative characters of bread wheat

Summary Heritability estimates of five characters of the wheat plant were studied in five crosses involving six cultivars of bread wheat. Parents, F₁, F₂ and backcrosses to both parents were used in the estimation of the genetic parameters.Heritability was low for number of fertile spikes/plant, moderate for number of spikelets/spike, number of kernels/spike, 1000-kernel weight and moderately high for number of kernels/spike. Evidence for mainly nonadditive gene effects were observed in the expression of number of fertile spikes and 1000-kernel weight. Although nonadditives contributed to a lesser degree to the gene action, additives seemed to be the most important genetic expression regulating number of spikelets/spike, number of kernels/spike, and number of kernels/spikelet. Except for number of fertile spikes/plant, selection in F₂-populations seems to be promising.     

Soluble Carbohydrates and Floret Fertility in Wheat in Relation to Population Density Stress

Wheat, variety Sonalika, was grown at different densities inboth field and pots during the winter seasons 1983–84and 1984–85. Grain yield pattern of the spikelets of themain shoot inflorescence was similar in both the field and pots,the spikelets in the middle part of the ear contributed mostand yield per spikelet decreased progressively towards the apexand the base. Increased population density decreased yield ofgrain, primarily by decreasing spikelet number and the fertilityof florets. High population density accelerated growth of thespike for some time during the pre-anthesis period and the solublecarbohydrate concentration was also higher under these conditions.During both anthesis and post-anthesis, the soluble carbohydrateconcentration and the growth of the spike declined much fasterin the high-density population. High density also decreasedthe floret fertility and growth in dry weight in all the spikelets,but it was more severe on the basal spikelets, resulting incomplete sterility of the florets at these nodes. The solublecarbohydrate concentration of these slow-growing, sterile, basalspikelets was found to be higher in comparison to that of fertilespikelets in the middle and top positions within the ear. Soluble carbohydrates, spike, spikelet, fertility, grain number     

西藏小麦资源在都江堰试种的表现及评价

对125份来源于西藏的小麦地方品种进行农艺性状分析和评价。结果显示,西藏小麦植株高度总体偏高,少数适中。分蘖数多数在10个以下,少数偏多。穗长、小穗数的单位长度着生的小穗数存在明显差异,存在一些密穗类型和多小穗类型。多数小麦品种穗粒数不少,但千粒重明显偏低。性状相关分析表明,随着分集数增多、穗长增长、小穗数增多,株高有增加的趋势,而株高的增加又导致了千粒重的降低。小穗数多其穗长通常比较长。中时西藏小麦资源进行了评价、利用方式进行了探讨、在都江堰与西藏表现差异的原因进行了分析。     

Deciphering the environmental impact on spike architectural traits for grain yield consolidation in bread wheat (T. aestivum L.)

The realization of grain yield in wheat is decided by source-sink balance under prevailing environmental conditions. Management conditions like changing the sowing time influence the source-sink capacity through modification in agronomic traits. Therefore, this experiment was conducted to decipher the influence of spike architectural traits (SATs) on grain yield and to open avenues for further grain yield enhancement. Comparatively early sowing over timely sowing gives the advantage of realizing higher grain yield with a positive relationship with SATs namely spike length, spikelets per spike, individual spike weight, individual grain weight, number of grains per spikelet, grain length, and grain width of upper and lower spike portion. Confirmatory factorial analysis revealed that spike length, spikelets per spike, individual spike weight, grains per spikelet were having a significant effect in deciding grain yield in early sown. The presence of a significant effect of genotype by environment interaction over grain yield and SATs allows the exploitation of available genotypic and environmental variability for further yield enhancement. GGE analysis on transformed and standardized grain yield-trait (GY-trait) combinations was used in the selection of genotypes having high GY-trait combinations for both sowing times. In early sowing, WG 11 was the best for high GY with high individual spike weight; grain length and grain width at lower and upper parts of the spike; and shorter days to 50% flowering. Genotypes exclusively having the high GY-trait combination along with low values of remaining GY-trait combinations were also selected with genotype focused GGE approach.     

Varietal response in wheat to water supply in the field, and male sterility caused by a period of drought in a glasshouse experiment

Field experiments in 1961 and 1962 with four winter wheat varieties (Professeur Marchal, Cappelle-Desprez, Hybrid 46 and Holdfast) compared three water regimes: irrigation to prevent the soil water deficit exceeding 2 in.; shielding from rain; and normal rainfall. The experiments were done on soils selected for their liability to drought. Grain yield was decreased by water deficit; the effects differed between varieties, but the varietal differences were not consistent in the 2 years. In glasshouse experiments, plants of Cappell-Desprez were subjected to drought for 3–4 days during ear development and subsequently watered normally. When this treatment preceded pollen meiosis by a few days many of the lower florets of each spikelet were male-sterile but female-fertile. Also there was often proliferation, within the spikelet, of normally fertile florets above the male-sterile ones, showing that the number of florets formed may increase until a late stage in ear development. The results of the field experiment suggested that grain yield was restricted by the capacity of the grains as sinks for photosynthates. If so, a genetic improvement in grain yield could be obtained by breeding for an increase in number of florets per spikelet.     

Yield response of a common spring wheat cultivar to inoculation withAzospirillum brasilense at various levels of nitrogen fertilization

Summary The yield response of a common spring wheat cultivar,Triticum aestivum, to inoculation withAzospirillum brasilense was studied at four levels of N fertilization. Plant yield increased due to the inoculation treatment only at medium and high levels of N fertilization, with a maximum yield increase of about 8.0 per cent at the highest level (approximately 1.0 g of pure N per plant). Yield increase was mostly due to an increase in the number of grains per spike, and at the highest level of fertilization, also due to a higher number of spikes per plant. At all N levels, the inoculation caused an increase of 0.5–1.4 per cent in the number of fertile spikelets per main spike.Grain protein percentage was unaffected by the inoculation, though significantly increase due to the fertilization treatments.The occurrence of maximum yield response at the highest N level, the response by early-determined yield components, i.e. spikelet number, and the unaffected grain protein content are in accord with the suggestion that the contribution ofAzospirillum brasilense to wheat yield is not through N₂-fixation.     

Autophagy regulated by day length determines the number of fertile florets in wheat

SUMMARY: The wheat spikelet meristem differentiates into up to 12 floret primordia, but many of them fail to reach the fertile floret stage at anthesis. We combined microarray, biochemical and anatomical studies to investigate floret development in wheat plants grown in the field under short or long days (short days extended with low-fluence light) after all the spikelets had already differentiated. Long days accelerated spike and floret development and greening, and the expression of genes involved in photosynthesis, photoprotection and carbohydrate metabolism. These changes started while the spike was in the light-depleted environment created by the surrounding leaf sheaths. Cell division ceased in the tissues of distal florets, which interrupted their normal developmental progression and initiated autophagy, thus decreasing the number of fertile florets at anthesis. A massive decrease in the expression of genes involved in cell proliferation, a decrease in soluble carbohydrate levels, and an increase in the expression of genes involved in programmed cell death accompanied anatomical signs of cell death, and these effects were stronger under long days. We propose a model in which developmentally generated sugar starvation triggers floret autophagy, and long days intensify these processes due to the increased carbohydrate consumption caused by the accelerated plant development.     

Genetic insight into yield-associated traits of wheat grown in multiple rain-fed environments

Background

Grain yield is a key economic driver of successful wheat production. Due to its complex nature, little is known regarding its genetic control. The goal of this study was to identify important quantitative trait loci (QTL) directly and indirectly affecting grain yield using doubled haploid lines derived from a cross between Hanxuan 10 and Lumai 14.

Methodology/Principal Findings

Ten yield-associated traits, including yield per plant (YP), number of spikes per plant (NSP), number of grains per spike (NGS), one-thousand grain weight (TGW), total number of spikelets per spike (TNSS), number of sterile spikelets per spike (NSSS), proportion of fertile spikelets per spike (PFSS), spike length (SL), density of spikelets per spike (DSS) and plant height (PH), were assessed across 14 (for YP) to 23 (for TGW) year × location × water regime environments in China. Then, the genetic effects were partitioned into additive main effects (a), epistatic main effects (aa) and their environment interaction effects (ae and aae) by using composite interval mapping in a mixed linear model.

Conclusions/Significance

Twelve (YP) to 33 (PH) QTLs were identified on all 21 chromosomes except 6D. QTLs were more frequently observed on chromosomes 1B, 2B, 2D, 5A and 6B, and were concentrated in a few regions on individual chromosomes, exemplified by three striking yield-related QTL clusters on chromosomes 2B, 1B and 4B that explained the correlations between YP and other traits. The additive main-effect QTLs contributed more phenotypic variation than the epistasis and environmental interaction. Consistent with agronomic analyses, a group of progeny derived by selecting TGW and NGS, with higher grain yield, had an increased frequency of QTL for high YP, NGS, TGW, TNSS, PFSS, SL, PH and fewer NSSS, when compared to low yielding progeny. This indicated that it is feasible by marker-assisted selection to facilitate wheat production.     

A Study of Floret Development in Wheat (Triticum aestivum L.)

Plants of wheat (Triticum aestlvum L.) cv. Aotea were grownat high or low nitrogen levels and in a natural photoperiodor continuous light. Starting 17–21 days from the double-ridgestage, eight plants from each treatment were sampled every 3days until anthesis, and the two basal, the sixth, and the terminalspikelets were sectioned longitudinally. A developmental scorewas assigned to each floret and rates of development calculated.Continuous light hastened development but reduced the numberof spikelets per ear, while high nitrogen delayed developmentbut increased spikelet numbers. The number of florets initiatedin each spikelet varied within narrow limits, but grain settingdepended strongly on spikelet position and on treatment. Althoughflorets were initiated in acropetal succession, the rate ofdevelopment tended to increase up to floret 4 but then declinedmarkedly. As a result grain setting was confined to basal floretpositions, although the two basal spikelets developed so slowlythat they contributed relatively little to grain yield. Distalflorets degenerated almost simultaneously at or before ear emergence,but those in intermediate positions continued to develop untilafter fertilization in the lower florets. It is argued thatthe spikelet is an integrated system in which correlative mechanismsplay a part throughout the development of the florets.     

The Effect of High Temperature at Different Stages of Ripening on Grain Set, Grain Weight and Grain Dimensions in the Semi-dwarf Wheat 'Banks'

Grain number in the wheat cultivar Banks was reduced by up to11 % with a rise in temperature from 21/16 °C to 30/25 °Cover a 10-d period immediately following first anthesis in general,the upper ‘d’ and ‘c’ florets were moreaffected by high temperature than the basal ‘a’and ‘b’ florets within a spikelet and florets fromthe upper spikelets were more sensitive than those lower onthe ear Grain weight and grain length at maturity were most affectedby a 10 d period of high temperature commencing 7–10 dafter anthesis However, if dry-matter accumulation between thestart of a treatment and grain maturity was used as a base forcomparison, the response was more uniform throughout development,with a peak in sensitivity 25 d after anthesis Although grainposition within an ear did not have a large effect on the responseto temperature, grains from the basal spikelets were more sensitivethan those from the apex, and the upper floret grains of a spikeletwere more sensitive to high temperature than those at the base There is a need to obtain, for a range of cultivars, more comprehensivedata on the effect of the timing and degree of temperature stressfollowing anthesis, for use in interpreting the response torising temperatures late in the development of the crop in thefield Triticum aestivum L, wheat, temperature, grain development     

大穗多花种质B46的选育及细胞遗传学鉴定

利用普通小麦(Triticum aestivum L.)7182与华山新麦草(Psathyrostachys huashanica)杂交、回交和自交,经多代选育出能够稳定遗传的大穗多花种质B46.对B46进行形态学观察及其细胞学检测与GISH鉴定.结果表明,B46形态学特征表现大穗多花特性,穗长12 cm左右,小穗达23个,小穗粒数平均6个;其根尖细胞染色体计数为2n=44;根尖原位杂交(GISH)及减数分裂中期Ⅰ染色体的基因组原位杂交(GISH)显示,B46附加1对来自于华山新麦草的同源染色体.由此可以确定B46为小麦-华山新麦草的二体异附加系,其综合农艺性状优于小麦亲本7182,可作为培育高产小麦品种的优良种质材料.     

The Effects of Floret Sterilization on Grain Number and Grain Weight in Wheat Ears

This paper describes the effects of sterilizing certain floretson the development of others within the ears of wheat, cultivarMaris Ranger. Sterilization of all the florets in spikelets2, 4, 6, and 8 (numbered from the base of the ear upwards) ledto more grain setting and greater grain growth in the untreatedspikelets. These compensatory increases were insufficient toprevent a depression in the yield of grain per ear. Sterilizationof more than one of the basal florets of spikelet 8 led to amore frequent setting of the grain in the distal florets onthat spikelet and to the centrally positioned grain becomingheavier. The physiological basis for the inhibitory influences of theolder and developing grain on the unfertilized florets and youngergrain is discussed.     

Effect of awns and drought on the supply of photosynthate and its distribution within wheat ears

The presence of awns doubled the net photosynthetic rate of wheat ears and also increased the proportion of ¹⁴CO₂ assimilated by the ear that moved to the grain. The effect of water supply on photosynthesis and movement of assimilates was greater for leaves than ears, so that drought increased the proportion of assimilate contributed by ear photosynthesis to grain filling from 13% to 24% in the awnless ears, and from 34% to 43% in the awned ears. ¹⁴C assimilated by the ears was most important to the economy of the upper spikelets and to the distal florets in each spikelet, whereas flag leaf assimilate went mainly to the spikelets in the lower half of the ear, and to the proximal florets. Awns increased grain yield in the dry but not in the irrigated treatment, despite the large contribution of awned ears to grain filling. Either the supply of assimilate did not limit grain yield when water supply was not limiting, or there were compensating disadvantages to awns. However, they did not seem to have any adverse effect on the development of the upper florets, nor did they reduce grain number per ear.