Genetic mapping of a mutant gene producing three pistils per floret in common wheat

A common wheat (Triticum aestivum L.) mutation that produces 3 pistils (TP) per floret may result in formation of up to 3 kernels per floret. The TP trait may be important for increasing the number of grains per spike and for improving the yield potential through breeding. This trait is determined by the dominant Pis1 gene. Genetic mapping of Pis1 involved 234 microsatellite markers and bulk segregant analysis of a cross of the TP line with Novosibirskaya 67. The Pis1 gene is located on chromosome 2DL, between markers Xgwm539 and Xgwm349. This result does not agree with a previously published localization of the Pis1 gene on chromosome 5B. The possible importance of TP wheat as an alternative genetic resource is discussed.     

Wheat floret survival as related to pre-anthesis spike growth

Further improvements to wheat yield potential will be essential to meet future food demand. As yield is related to the number of fertile florets and grains, an understanding of the basis of their generation is instrumental to raising yield. Based on (i) a strong positive association between the number of fertile florets or grains and spike dry weight at anthesis; and (ii) the finding that floret death occurs when spikes grow at maximum rate, it was always assumed that floret survival depends on the growth of the spike. However, this assumption was recently questioned, suggesting that assimilates diverted to the spike do not determine the number of florets and grains and that the onset of floret death may instead be a developmental process that is not associated with spike growth. In this study, the relationships between the fate of floret primordia and spike growth from six independent experiments that included different growing conditions (greenhouse/field experiments, growing seasons, photoperiod/shading treatments during the floret primordia phase) and diverse cultivar types (winter/spring, semi-dwarf/standard-height, photoperiod sensitive/insensitive) were re-analysed together. Onset of floret death was associated with the beginning of spike growth at the maximum rate in c. 80% of the cases analysed; and the rate of floret death (the main determinant of floret survival) showed a negative quantitative relationship with spike weight at anthesis. As floret death and survival were shown to be linked to pre-anthesis spike growth, the strategy of focusing on traits associated with pre-anthesis spike growth when breeding to increase wheat yield potential further is valuable.     

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     

Identification of differentially expressed genes in three-pistil mutation in wheat using annealing control primer system

The common wheat line three-pistil (TP) is a valuable mutant for wheat breeding. The TP mutation has normal spike morphology; however, it only produces three pistils per floret. Therefore, it has potential to increase the grain number per spike. In order to determine the underlying molecular mechanism, an annealing control primer system was used to identify the different expressed genes in three-pistil mutation. Using 120 arbitrary ACP primers, we identified three differentially expressed genes in young spikes between two near-isogenic lines (i.e., Chuanmai 28 TP and Chinese Spring TP) and their recurrent parents. We tentatively designated the three differentially expressed genes as DETP-1, DETP-2, and DETP-3. DETP-1 showed similar function with maize cytoplasmic membrane protein, which is involved in cell division in bacteria. DETP-3 is homologous to maize endo-1, 4-beta-glucanase (EGases), which is associated with plant development, cell wall loosening, stem flowering, and root expansion. DETP-2 showed no significant hit with any sequence found in the database and translates unknown protein. These genes would likely play an important role in determining the three pistils trait in wheat.     

Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

Grain number determination in durum wheat as affected by drought stress: An analysis at spike and spikelet level

Yield studies show that increases in grain yield are always accompanied by an increase in grain number and, hence, further increases in yield potential may require additional improvements in grain number. The improvement of modern durum wheat was mainly based on the introduction of semidwarf genes. A 2‐year field drought stress experiment, concerning two different genotype groups (landraces vs modern cultivars), was carried out under a rainout shelter in order (a) to assess the effect of water deficit on floret dynamics and grain number determination, (b) to explore the relationship between plant water status with grain number per spike and its components (i.e., spikelets per spike, fertile florets per spikelet and grain set) and (c) to quantify the importance of several plant traits in determining the final number of grains per spike and fertile florets per spike when the main source of variation is water availability. Compared to control (well irrigated), grain number per spike was reduced, depending on year, genotype and water availability level, by 12.4–58.7% and this reduction was evident almost in all spikelet positions along the spike. Although there were some doubts in the past about the increased sensitivity of semidwarf cultivars to drought stress, they were not confirmed from our results. In most of the cases, the variation in plant water status (by means of water potential index [WPI]) during floret primordia phase (FPP) explained most of the variance in grain number per spike, fertile florets per spikelet, grain set and fertile spikelets per spike. In general, increasing water stress intensity decreased grain number per spike by an average rate of 13.5 and 9.4 grains per 0.2 MPa decrease in WPI, in modern cultivars and landraces, respectively. However, seasonal and genotypic effects were evident by modifying the slopes of the linear regressions between WPI and the studied plant traits. Commonality analysis revealed that the number of fertile florets per spikelet was the best predictor of grain number per spike, indicating that there is still much space for further improvement for this trait in landraces. However, this trait has been clearly improved in modern cultivars, especially at the basal and central spikelets. Although the number of spikelets per spike was the best unique predictor of the number of grains per spike in modern cultivars, grain set presented the highest total effect.     

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.     

The introgression of chromosome 6P specifying for increased numbers of florets and kernels from Agropyron cristatum into wheat

A wheat (Triticum aestivum L.) line 4844 with superior numbers of florets and grains per spike was derived from the cross between Fukohokomugi wheat and Agropyron cristatum (L.) Gaertn. In order to determine the genetic control of floret and kernel number per spike in this line, chromosome addition and substitution lines that were derived from line 4844 were characterized by means of in situ hybridization, microsatellite (SSR), and gliadin analyses. Genomic in situ hybridization analysis with biotinylated P genomic DNA of A. cristatum as a probe demonstrated that the increased number of florets and grains in a spike was associated with the introgression of an A. cristatum chromosome. Fluorescence in situ hybridization, using a repetitive sequence, pAs1, derived from Aegilops squarrosa L., indicated the replacement of chromosome 6D of wheat in the wheat-A. cristatum chromosome substitution lines. This was confirmed by microsatellite analyses with wheat SSR markers specific for chromosome 6D, suggesting that the A. cristatum chromosome was homoeologous to group 6 and was therefore designated as 6P. This conclvsion was further confirmed by amplification using EST-SSR markers and gliadin analysis. The increased number of florets and kernels within a spike of the wheat-A. cristatum hybrids thus was controlled by gene(s) located on A. cristatum chromosome 6P.     

Inheritance of seed dormancy in Tibetan semi-wild wheat accession Q1028

Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao) is one of the Chinese endemic hexaploid wheat genetic resources, distributed only in the Qinghai-Xizang Plateau of China. It has special characters, such as a hulled glume and spike disarticulation. However, seed dormancy, another important character for wheat resistance to pre-harvest sprouting, was rarely reported. Seed dormancy of more than 10 Tibetan semi-wild wheat accessions was evaluated, and their germinations were 0% or near 0% with both treatments of threshed seeds and intact spikes at hard dough stage. Tibetan semi-wild wheat accession Q1028 was investigated for its seed dormant characters by testing the seed germination percentages of intact spikes, seeds with bract powder, normal seeds, seeds with pierced coat, and sectioned embryos. It was observed that embryo dormancy of Q1028 accounted for its seed dormancy. Using threshed seeds and intact spikes at hard dough stage, the inheritance of seed dormancy was carried out using the F1, F2, F3 and F2BC1 populations of the cross between Q1028 and a wheat line 88-1643, susceptible to preharvest sprouting. The germinations of seeds and intact spikes in F1 plants were 1.0% and 0.9%, respectively. It indicated that seed dormancy of Q1028 was inherited as a dominant trait. From the genetic analysis of the F2, F3 and F2BC1 populations it was found that the strong seed dormancy of Q1028 was controlled by two dominant genes.     

Changes in Levels of Endogenous Plant Hormones During Floret Development in Wheat Genotypes of Different Spike Sizes

The levels of endogenous plant hormones regulate floret development and degeneration, and thus grain set in flower crops. This study was undertaken to characterize the changes of endogenous hormone levels during floret development in three wheat (Triticum aestivum L.) genotypes: “97J1" with the highest grain set and fertile florets per spike, “H8679" with the lowest grain set and fertile florets per spike, and a medium, “YM158". The results showed that the peak level of ABA appeared between stamen and pistil differentiation and antherlobe formation of floret development, and the timing delayed with the size of spike (earliest in “H8679” and latest in “97J1”). From antherlobe formation to meiosis, the levels of ABA and GA1+3decreased sharply in the ears of “97J1”, while in the ears of “H8679” there was only a slight decrease in ABA, and even an increase in GA1+3. The ratio of isopentenyladenosine (iPA)/ABA and IAA/ABA in the ears of “97J1” increased sharply from antherlobe formation to meiosis, but changed only slightly in the ears of “H8679”. At antherlobe formation, IAA and GA1+3 levels were higher in the ears of “97J1”, but lower in the ears of “H8679”than in the leaves. At meiosis, ABA, GA1+3 and IAA levels in the “97J1” ears were much lower than in the leaves, but similar in “H8679”. These results indicated that the sharp decreases of ABA and GA1+3 in ears from antherlobe formation to meiosis and the lowest maintenance at meiosis may be favorable for development of fertile florets and enhancement of grain set in wheat.     

Characteristics and inheritance of radiation-induced mutations in barley II. Two short-awned mutations

Two mutations were obtained in a two-rowed, spring-type barley variety, Asahi No. 5. KM 114 was obtained in the X₂ population of X-irradiated dormant seeds (15 Kr) and KM 218 was found in X₂ of gamma-irradiated seeds (15 Kr). KM 114 had very short awns, short plant height, almost normal spike size, and narrow and thinner seeds with pointed tip. The mutant gene is Mendelian recessive. KM 218 plants were normal or slightly taller, had somewhat larger spike, with somewhat longer rachis internodes, medium-long awn, and slightly longer, narrower and thinner kernel than those of the parental variety. At maturity, grains are exposed in many seeds (semi-naked kernels). This mutant also has a conspicuous diagnostic trait; the abnormal development of rachilla into extra florets, some of which set seeds. This mutant gene is also Mendelian recessive. Genes for these two mutants are not allelic and are inherited independently as indicated in F₂ and F₃ analyses. Genes of these two mutations will serve as good marker genes in genetic and linkage studies in barley, because their character expression is consistent and the recessive homozygotes are viable and fertile.     

水稻长颖壳突变体的形态发生、解剖结构观察及其遗传鉴定

长颖壳花器官突变体从野生稻(Oryza ntvara Sharma et Shastry)和栽培稻(Oryza sativa subsp.indica Kato)杂交后代材料中获得.该突变体的内外稃变长、呈叶状,且顶端表现不同程度的开裂;每朵颖花的雄蕊l～10枚不等;雌蕊l～3枚不等;子房上柱头l～5个不等;有的颖花形成雄蕊/雌蕊嵌合体;子房处常附有瘤状物;此突变体结实率为1 8.2%;花粉可育率为62.46%.利用扫描电镜观察了该突变体花器官形态发生过程,并经遗传分析鉴定该突变性状由单隐性基因(暂命名为lh)控制.本文讨论了lh基因和以前鉴定的其他突变体基因之间的关系,通过表型分析推测,突变体基因可能影响花器官数目同时具有拟南芥B类基因的部分功能.     

水分胁迫对耐旱性不同小麦小花化发育和氮磷及激素含量的影响

土壤分水分亏缺导致小麦幼穗内氮、磷、异戊烯基腺嘌呤（ｉＰＡｓ）含量降低,脱落酸（ＡＢＡ）含量升高,影响小花的发育,结实粒数减少。在水分充足的条件下,耐旱性不同的品种穗中氮、氮、ｉＰＡｓ含量和ＡＢＡ含量无显著差异;在水分胁迫条件下,旱地品种幼穗中氮,磷、ｉＰＡｓ含量降低的幅度和ＡＢＡ含量升高的幅度低于水浇地品种,这是耐旱品种在土壤水分亏缺时,较水浇地品种小花发育好、成花率和结实率高,穗粒数稳定的生理     

Phytohormone Levels in the Florets of a Single Wheat Spikelet during Pre-Anthesis Development and Relationships to Grain Set

Lee, B. T., Martin, P. and Bangerth, F. 1988. Phytohormone levelsin the florets of a single wheat spikelet during pre-anthesisdevelopment and relationships to grain set.—J. exp. Bot.39: 927–933. The gradient in grain number found within a single spikeletof wheat (higher grain numbers in proximal positions than indistal positions) was investigated with respect to endogenouslevels of hormones in anthers and carpels. Auxins, abscisicacid and cytokinins were measured using radioimmunoassay. Measurementswere made on both whole ears and floral organs (anthers andcarpels) of a single spikelet during pre-anthesis development.Similar hormonal trends in whole ears compared to those of anthersand carpels were only found for anther abscisic acid and indoleacetic acid levels and carpel zeatin/zeatin riboside levels.In the distal floret positions of the spikelet where fewer orno grains were set, anther abscisic acid levels were higherthan in those of the proximal positions. Key words: Hormones, grain, wheat.     

Developmental Events Associated with the Critical Stage for Sex Determination in Wild-Rice Florets

The developmental events of florets and a critical stage for sex determination in two wild-rice populations (Zizania palustris cv. Franklin and Zizania palustris cv. K-2Pi) have been identified. Formation of bisexual florets precedes the development of both male and female florets. Developmental indicators, established by measuring the length of florets and panicles, indicate that the critical stage for sex determination occurs when floret and panicle lengths are 1-2 mm and 3 cm, respectively. The stage of floret development at which sex determination occurs is the same in the two investigated wild-rice populations. Organ suppression in bisexual florets is an essential step for sex determination during the formation of unisexual florets. Histological examination of suppressed stamens or pistils in unisexual florets of wild-rice indicates that cell death does not occur during sex determination. In addition, the length of anthers and pistils in bisexual florets indicates that floral development in the transition zone is normal when compared with the male florets in the male spikelets and female florets in the female spikelets.     

The effect of genotypes of parental rye lines on the development of quantitative traits in primary octoploid Triticale: spike fertility

The number of seeds and seed setting in the main spike were studied in primary octoploid triticale obtained from crosses between the common wheat cultivar Chinese Spring and 66 inbred rye lines. In some rye lines, the mutations of self-fertility were identified in the S, Z, or T incompatibility loci. The number of seeds was determined under controlled self-pollination of the main spike. In the set of triticale examined, each trait exhibited high variation. Hence, the rye lines were suggested to carry gene alleles both increasing and decreasing these traits in triticale. All the traits studied were significantly influenced by environmental conditions. Ten triticale lines were identified, which had the largest seed setting under self-pollination. Seven out of ten samples with the high number of seeds carried mutations in the T locus and in the three samples, the unidentified self-fertility mutations were present. The triticale lines with mutations in the S and Z loci displayed much lower self-fertility on average. The ways and means of identifying and mapping the rye gene responsible for distinctions between the triticale quantitative traits are discussed.     

小麦-簇毛麦6VS/6AL易位染色体对小麦农艺性状的影响

南京农业大学细胞遗传研究所选育的小麦－簇毛麦6VS/6AL易位系在6VS上携有Pm21基因,用它作抗源已选育出一批高抗白粉病的新品系和新品种。为了研究6VS/6AL易位染色体对普通小麦农艺性状的影响,本研究选用由不同生态类型的推广品种与6VS/6AL易位系经过杂交回交选育的11个高代品系(种)及其轮回亲本和3份涉及6VS/6AL的高代分离品系以及5个F2群体,对产量、株高、穗长、穗粒数、穗粒重和千粒重等农艺性状进行比较分析。结果表明,6VS/6AL易位染色体对后代的小穗数、穗粒数、穗粒重和产量等农艺性状没有表现出明显的影响,对穗长和千粒重表现出一定的正向效应。多数6VS/6AL衍生品系的株高与亲本相比有所增加,但在同一组合的不同品系之间表现出一定的差异,在育种过程中通过选择能够改变增高趋势。6VS/6AL易位系对白粉病免疫,并且遗传稳定,对小麦的抗病育种是很有潜力的抗源亲本。     

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.     

Variation of pollination and resource limitation in a low seed-set tree, Liriodendron chinense (Magnoliaceae)

Pollen limitation and resource limitation have been documented as the major factors responsible for plants commonly producing more ovules than seeds, but few studies have examined pollen deposition directly in natural populations at different sites and times. We investigated the causes of low seed set in four populations of Liriodendron chinense (Magnoliaceae), an insect‐pollinated endangered tree endemic to southern China, over 2–3 years. One pistil potentially produces two ovules. The number of pistils per flower varies among populations, but in three of the four populations the variation in a given population was not significantly different among years. Overall, populations with higher pistil numbers tend to set more seeds per flower, but a positive correlation between pistil numbers and seed production per flower was observed in only one of the four populations. The numbers of pollen grains deposited per stigma varied from 0 to 60. The proportion of pollinated stigmas per flower ranged from 44% to 88% among populations and years. The numbers of pollen grains deposited per stigma and the percentages of pollinated stigmas were significantly different between populations, and two populations showed significant differences between years. A positive correlation between stigmatic pollen load and seed set was sought in ten population‐by‐year combinations but, in a given population, high stigmatic pollen loads did not always result in high seed set. Examination of pollen deposition, pistil and seed production over several sites and years showed that in addition to pollination, other factors such as resource or genetic loads were likely to limit the (lower than 10%) seed set in L. chinense. It appears that small, isolated populations experience severe pollination limitation; one population studied had seed/ovule ratios of 0.84% and 1.88% in 1995 and 1996. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 31–38.     

The Effect of Temperature on Seed Set and Seed Development in Detached Spikelets of Perennial Ryegrass (Lolium perenne L.)

In perennial ryegrass seed yield is low. Pollination, fertilizationand early stages of seed development are critical periods forthe realization of the yield potential. As intact plants aredifficult to handle, we used detached spikelets to study effectsof temperature and genotype on seed set and seed development. Plants of four cultivars were grown in pots. Just prior to flowering,spikelets were detached from the ears and put on water. Afterpollination, various spikelets of each plant were placed atdifferent temperatures (14/14, 17/12 or 20/15°C). Sevendays after pollination the percentage seed set and the lengthof the developing seeds (caryopses) were assessed. Only floretsin the four basal positions were used. For each cultivar an analysis of variance for unbalanced datawas carried out. There were highly significant difference amonggenotypes for seed set and caryopsis length. There was no evidencefor genotypic variation for tolerance to low temperatures. Neithertemperature nor floret position had an effect on seed set. Thecaryopsis length, however, increased with increasing temperatureand basal florets produced longer caryopses than distal florets.The detached spikelets proved to be a useful experimental tool.Copyright1993, 1999 Academic Press Lolium perenne L., perennial ryegrass, seed yield, seed set, detached spikelets culture, temperature, floret position