QTLs of cold tolerance-related traits at the booting stage for NIL-RILs in rice revealed by SSR

QTLs for cold tolerance-related traits at the booting stage using balanced population for 1525 recombinant inbred lines of near-isogenic lines (viz.NIL-RILs for BC5F3 and BC₅F₄ and BC₅F₅) over 3 years and two locations by backcrossing the strongly cold-tolerant landrace (Kunmingxiaobaigu) and a cold-sensitive cultivar (Towada) was analyzed. In this study, 676 microsatellite markers were employed to identify QTLs conferring cold tolerance at booting stage. Single marker analysis revealed that 12 markers associated with cold tolerance on chromosome 1, 4 and 5. Using a LOD significance threshold of 3.0,compositive interval mapping based on a mixed linear model revealed eight QTLs for 10 cold tolerance-related traits on chromosomes 1, 4, and 5. They were tentatively designatedqCTB-1-1, qCTB-4-1, qCTB-4-2, qCTB-4-3, qCTB-4-4, qCTB-4-5, qCTB-4-6, andqCTB-5-1. The marker intervals of them were narrowed to 0.3-6.8 cM. Genetic distances between the peaks of the QTL and nearest markers varied from 0 to 0.04 cM. We were noticed in some traits associated cold tolerance, such asqCTB-1-1 for 5 traits (plant height, panicle exsertion, spike length, blighted grains per spike and spikelet fertility),qCTB-4-1 for 8 traits (plant height, node length under spike, leaf length, leaf width, spike length, full grains per spike, total grains per spike and spikelet fertility),qCTB-4-2 for 3 traits (spike length, full grains per spike and spikelet fertility),qCTB-5-1 for 5 traits (plant height, panicle exsertion, blighted grains per spike, full grains per spike and spikelet fertility). The variance explained by a single QTL ranged from 0.80 to 16.80%. Three QTLs (qCTB-1-1, qCTB-4-1, qCTB-4-2) were detected in two or more trials. Our study sets a foundation for cloning cold-tolerance genes and provides opportunities to understand the mechanism of cold tolerance at the booting stage.     

QTLs influencing panicle size detected in two reciprocal introgressive line (IL) populations in rice (Oryza sativa L.)

Two sets of reciprocal introgression line (IL) populations, i.e., ILs with Lemont as recurrent parent (IL_LT) and ILs with Teqing as recurrent parent (IL_TQ), were developed and evaluated for traits representing panicle size, including primary branch number (PBN), secondary branch number (SBN), and spikelet number per panicle (SNP). Together with the regression to recurrent parent by advanced backcross, transgressive segregations were observed for all traits. Correlation and regression analysis showed that SBN had much higher contribution to SNP than PBN. It was confirmed by the QTL analysis that many common loci were detected between SBN and SNP, in comparison with single common locus between PBN and SNP. One and three main effect QTLs (M-QTLs) were detected for PBN in IL_LT and IL_TQ, respectively. Six M-QTLs per trait per populations were associated with SBN and SNP. Less number and lower contribution of epistasis were detected in IL populations in comparison with mapping result from F ₂ or RI population. There were only four QTLs in fourteen loci (near 30%) commonly detected in both reciprocal IL populations implying the large impact of genetic background on QTLs expression. H. W. Mei and J. L. Xu contributed equally to this work.     

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.     

Mapping quantitative trait loci for heat tolerance at the booting stage using chromosomal segment substitution lines in rice

High temperature stress is a major obstacle in rice productivity. Considerable progress has been made on studying heat tolerance (HT) at different stages. However, the genetic basis of HT at the booting stage is poorly understood. In this study, we analyzed the morphological features of a heat-sensitive japonica cultivar Sasanishiki under natural high temperature stress at the booting stage. The anthers became smaller and the number, and fertility, of pollen grains were decreased significantly. As a result, there was a dramatic reduction in spikelet fertility. In contrast, the indica cultivar Habataki showed high HT and normal spikelet fertility under high temperature stress. Additonally, a set of chromosome segment substitution lines, derived from Sasanishiki and Habataki, were evaluated for HT related quantitative trait loci (QTLs) across two environments in the natural field. A total of 12 QTLs associated with HT were detected, of which, 5 were identified in two environments, and 7 in one environment. Furthermore, one of the major-effect QTLs (qHTB3-3) detected on the long arm of chromosome 3, was confirmed using overlapping substituted lines. qHTB3-3 was finally mapped between the two markers RM3525 and 3-M95, approximately 2.8 Mb apart. These findings and further gene cloning of qHTB3-3 will help us better understand the molecular control of HT in rice, and may contribute to the development of high HT rice varieties.     

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.     

Characterization and mapping of a Prbs gene controlling spike development in Hordeum vulgare L.

The barley mutant, poly-row-and-branched spike (prbs) showed altered inflorescence morphology: complete conversion of the rudimentary lateral spikelets in two-rowed barley into fully developed fertile spikelets similar to the six-rowed phenotype, and additional spikelets in the middle of spike. Moreover, branched spikes emerged in progeny from a cross between the mutant and a six-rowed barley cultivar. Morphological observation of the development of immature spikes of the mutant and descendants with branched spikes showed that the Prbs gene is involved in spikelet development in the triple-mound stage. In mutant prbs, new meristems initiated at the flanks of lateral spikelets and middle spikelet meristems were converted to branch meristems, developing branched spikes. These observations suggested that the Prbs gene plays a crucial role in spikelet initiation and identity maintenance. The Prbs gene may be an important modifier in inflorescence differentiation from a panicle into a spike. The branched spikes emerging in hybrids from a cross between the mutant and six-rowed barley cultivar were not conferred by the gene vrs1 or Int-c, which decide spike morphology in six-rowed barley. These results imply that although six-row genes vrs1 and Int-c and prbs have similar effects on lateral spikelet development, they have different functions in branched spikes. The Prbs gene was mapped to chromosome 3H between SSR marker Bmag0023 and marker Cbic60 at a genetic distance of 3.3 and 5.4 centimorgans (cM), respectively.     

Behaviour of photosynthetic products associated with growth and grain production in the rice plant

Summary A study of the behaviour of the photosynthetic products assimilated at different growth stages was conducted in the field and in the greenhouse using C¹⁴ tracer.In general, the assimilated carbon is translocated to and accumulates in the growing organs. The carbon assimilated at the maximum tiller number stage is distributed mostly to the lower leaves. The carbon assimilated at the booting stage is distributed mostly to the spikelet, certain leaf sheaths and culms. The carbon accumulated in the form of carbohydrates in the leaf sheaths and the culm before flowering is retranslocated to the panicle after flowering. However, because of the consumption by respiration, the efficiency of this type of carbohydrate in grain production is not very high. The carbon assimilated after flowering accumulated mostly and efficiently in the brown rice.The release of the assimilated carbon as CO₂ is most intense immediately after assimilation. Thirty-five to 60 per cent of the assimilated carbon is consumed through respiration under the conditions of this experiment. As the carbon, which is in the form of sugars, rapidly changes to other forms, and also is consumed by respiration, the consumption declines rapidly. The retention percentage of assimilated carbon decreases as mutual shading increases.The large proportion of carbon released through respiration indicates the importance of studies on the significance of respiration in relation to growth.A portion of the thesis for the Master of Science degree submitted by Mr. Shen Lian to the Graduate School, University of the Philippines, College of Agriculture.     

Development of near-isogenic lines with different alleles of Piz locus and analysis of their breeding effect under Yangdao 6 background

Rice blast is one of the most destructive diseases of rice. The most effective way of managing this disease is to develop resistant cultivars by introducing resistance genes into elite rice recipients. In this study, the near-isogenic lines (NILs) of six resistance alleles of the Piz locus (Pizt, Pi2, Pigm, Pi40, Pi9 and Piz) were constructed with Yangdao 6 as genetic background. Seedling inoculation tests showed that most of the NILs, namely NIL-Pi2, NIL-Pigm, NIL-Pi9, NIL-Pizt and NIL-Pi40, exhibited good resistance to blast with resistance frequencies (RFs) of over 82.50 %, execpt NIL-Piz which showed lower resistance with a RF of only 36.13 %. Furthermore, the improved-resistance NILs exhibited high similarity of their resistance spectra, with overlapping degrees of resistance spectrum (OD) of more than 75.83 %. However, the RF of panicle blast for all NILs decreased significantly compared with seedling blast in an artificial inoculation test. Although NIL-Pigm showed a higher panicle blast RF of 80 %, other NILs with outstanding performance in seedling blast resistance, namely NIL-Pizt, NIL-Pi2, NIL-Pi9 and NIL-Pi40, exhibited middle or low RFs of panicle blast with values from 56.67 to 33.30 %. Natural induction in a disease nursery showed a consistent trend in artificial inoculation results at seedling and heading stages. While NIL-Pigm was found to exhibit good resistance to leaf blast and panicle blast, NIL-Pi9 and NIL-Pizt were further demonstrated to show excellent resistance in Suichuan, Jiangxi province and Enshi, Hubei province, respectively, because of the race–region specificity. Agronomic traits of NILs were also investigated in order to evaluate the linkage drag effect of different alleles of the Piz locus. The resistance effects of the different alleles of the Piz locus under identical genetic background against seedling blast and panicle blast was first reported in this study, and the above results are expected to provide a theoretical support for the rational utilization of broad-spectrum resistance genes in breeding practice.     

Identification and characterization of OsEBS,a gene involved in enhanced plant biomass and spikelet number in rice

Common wild rice (Oryza rufipogon Griff.) is an important genetic reservoir for rice improvement. We investigated a quantitative trait locus (QTL), qGP5‐1, which is related to plant height, leaf size and panicle architecture, using a set of introgression lines of O. rufipogon in the background of the Indica cultivar Guichao2 (Oryza sativa L.). We cloned and characterized qGP5‐1 and confirmed that the newly identified gene OsEBS (enhancing biomass and spikelet number) increased plant height, leaf size and spikelet number per panicle, leading to an increase in total grain yield per plant. Our results showed that the increased size of vegetative organs in OsEBS‐expressed plants was enormously caused by increasing cell number. Sequence alignment showed that OsEBS protein contains a region with high similarity to the N‐terminal conserved ATPase domain of Hsp70, but it lacks the C‐terminal regions of the peptide‐binding domain and the C‐terminal lid. More results indicated that OsEBS gene did not have typical characteristics of Hsp70 in this study. Furthermore, Arabidopsis (Arabidopsis thaliana) transformed with OsEBS showed a similar phenotype to OsEBS‐transgenic rice, indicating a conserved function of OsEBS among plant species. Together, we report the cloning and characterization of OsEBS, a new QTL that controls rice biomass and spikelet number, through map‐based cloning, and it may have utility in improving grain yield in rice.     

Identification of a novel homolog for a calmodulin-binding protein that is upregulated in alloplasmic wheat showing pistillody

Intracellular signaling pathways between the mitochondria and the nucleus are important in both normal and abnormal development in plants. The homeotic transformation of stamens into pistil-like structures (a phenomenon termed pistillody) in cytoplasmic substitution (alloplasmic) lines of bread wheat (Triticum aestivum) has been suggested to be induced by mitochondrial retrograde signaling, one of the forms of intracellular communication. We showed previously that the mitochondrial gene orf260 could alter the expression of nuclear class B MADS-box genes to induce pistillody. To elucidate the interactions between orf260 and nuclear homeotic genes, we performed a microarray analysis to compare gene expression patterns in the young spikes of a pistillody line and a normal line. We identified five genes that showed higher expression levels in the pistillody line. Quantitative expression analysis using real-time PCR indicated that among these five genes, Wheat Calmodulin-Binding Protein 1 (WCBP1) was significantly upregulated in young spikes of the pistillody line. The amino acid sequence of WCBP1 was predicted from the full-length cDNA sequence and found to encode a novel plant calmodulin-binding protein. RT-PCR analysis indicated that WCBP1 was preferentially expressed in young spikes at an early stage and decreased during spike maturation, indicating that it was associated with spikelet/floret development. Furthermore, in situ hybridization analysis suggested that WCBP1 was highly expressed in the pistil-like stamens at early to late developmental stages. These results indicate that WCBP1 plays a role in formation and development of pistil-like stamens induced by mitochondrial retrograde signaling.     

Chromosomal Localization of Genes Conferring Desirable Agronomic Traits from Wheat-Agropyron cristatum Disomic Addition Line 5113

Creation of wheat-alien disomic addition lines and localization of desirable genes on alien chromosomes are important for utilization of these genes in genetic improvement of common wheat. In this study, wheat-Agropyron cristatum derivative line 5113 was characterized by genomic in situ hybridization (GISH) and specific-locus amplified fragment sequencing (SLAF-seq), and was demonstrated to be a novel wheat-A. cristatum disomic 6P addition line. Compared with its parent Fukuhokomugi (Fukuho), 5113 displayed multiple elite agronomic traits, including higher uppermost internode/plant height ratio, larger flag leaf, longer spike length, elevated grain number per spike and spikelet number per spike, more kernel number in the middle spikelet, more fertile tiller number per plant, and enhanced resistance to powdery mildew and leaf rust. Genes conferring these elite traits were localized on the A. cristatum 6P chromosome by using SLAF-seq markers and biparental populations (F₁, BC₁F₁ and BC₁F₂ populations) produced from the crosses between Fukuho and 5113. Taken together, chromosomal localization of these desirable genes will facilitate transferring of high-yield and high-resistance genes from A. cristatum into common wheat, and serve as the foundation for the utilization of 5113 in wheat breeding.     

Photosynthesis and growth of winter wheat in response to waterlogging at different growth stages

A study on photosynthetic and yield effects of waterlogging of winter wheat at four stages of growth was conducted in specially designed experimental tanks during the 2007–2008 and 2008–2009 seasons. Compared with the control, waterlogging treatments at tillering and jointing-booting stages reduced photosynthetic rate (P _N) and transpiration (E) significantly, it also decreased average leaf water-use efficiency (WUE, defined as the ratio of P _N to E) by 3.3% and 3.4% in both years. All parameters returned quickly to the control level after soil was drained. Damage to the photosynthetic apparatus during waterlogging resulted in a lower F_v/F_m ratio, especially at the first two stages. A strong reduction in root length, root mass, root/shoot ratio, total dry mass, and leaf area index were observed. The responses from vegetative plants at tillering and jointing-booting stages were greater than in generative plants at onset of flowering and at milky stages. The number of panicles per hectare at tillering stage and the spikelet per panicle at the stages of jointing-booting and at onset of flowering were also significantly reduced by waterlogging, giving 8.2–11.3% decrease of the grain yield relative to the control in both years. No significant difference in yield components and a grain yield was observed between the control and treatments applied at milky stages. These responses, modulated by the environmental conditions prevailing during and after waterlogging, included negative effects on the growth, photosynthetic apparatus, and the grain yield in winter wheat, but the effect was strongly stage-dependent.     

云南不同类型一季稻产量形成及其与气象因子的关系

利用云南省14个不同海拔农业气象观测站1994-2010年水稻大田发育期和产量观测资料,研究水稻产量形成及气象因子对低产水稻产量构成因素的影响;根据14个站点水稻产量构成因素的系统聚类分析结果和水稻类型,将水稻分为低产粳型、低产籼型、高产粳型和高产籼型4个类型.对这4类水稻产量构成因素的分析结果表明,单位面积颖花量与产量呈极显著正相关,低产粳型水稻产量主要受结实率和颖花量影响,其他3类颖花量对产量影响较大.低产粳型水稻主要受低温的影响,孕穗期低温降低颖花量和有效穗数,孕穗期和抽穗开花期低温增加空壳率,以平均气温、平均最高气温和冷积温的影响较大;乳熟前期较低的平均气温增加秕谷率,同时降低千粒重.低产籼型水稻产量构成因素受多种气象因子的综合影响明显;分蘖期和拔节期一定程度的增温不利于增加低产籼型水稻有效穗数,而分蘖期较多的日照时数和较大的平均气温日较差有利于有效穗数的增加,分蘖期和拔节期气温和日照时数与每穗粒数的关系呈“抛物线型”;低产籼型水稻空壳率一定程度上受抽穗开花期低温的影响,而乳熟前期高温少雨不仅增加秕谷率,还导致千粒重明显下降.     

Canopy and Seasonal Profiles of Nitrate Reductase in Soybeans (Glycine max L. Merr.)

Nitrate reductase activity of soybeans (Glycine max L. Merr.) was evaluated in soil plots and outdoor hydroponic gravel culture systems throughout the growing season. Nitrate reductase profiles within the plant canopy were also established. Mean activity per gram fresh weight per hour of the entire plant canopy was highest in the seedling stage while total activity (activity per gram fresh weight per hour times the total leaf weight) reached a maximum when plants were in the full bloom to midpod fill stage. Nitrate reductase activity per gram fresh weight per hour was highest in the uppermost leaf just prior to full expansion and declined with leaf position lower in the canopy. Total nitrate reductase activity per leaf was also highest in the upper-most fully expanded leaf during early growth stages. Maximum total activity shifted to leaf positions lower in the plant canopy with later growth stages.     

Growth and gas exchange response to water shortage of a maize crop on different soil types

The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early leaf senescence. Canopy and leaf gas exchanges, measured by eddy correlation technique and by a portable photosynthetic system, respectively, were affected by water stress and a greater reduction in net photosynthetic rate (A _N) and stomatal conductance (g _s) was observed on SS. Chlorophyll and carotenoids content was not affected by water shortage in either condition. Results support two main conclusions: (1) leaf photosynthetic capacity was unaffected by water stress, and (2) maize effectively endured water shortage during the vegetative growth stage.     

德国鸢尾‘常春黄’花芽分化的形态观察及两种代谢产物的动态变化

鸢尾是世界著名观赏花卉,为研究其花芽分化期的形态和生理指标变化情况,我们以德国鸢尾两季花品种‘常春黄’（Iris germanica cv. Lovely Again）为材料,运用扫描电镜（SEM）观察了德国鸢尾‘常春黄’的花芽分化过程。结果表明：整个形态分化过程可分为6个阶段：花序原基分化期、外轮花被分化期、雄蕊分化期、内轮花被分化期、雌蕊分化期、髯毛形成期。结合上述形态分化过程,分别取其二次花花芽分化时期的顶芽、根茎和叶片部位,以蒽酮比色法测定可溶性糖,以考马斯亮蓝G-250法测定蛋白质含量。结果表明：可溶性糖在花序原基分化的初始阶段含量最高,且在3个部位的含量大小关系始终是：根茎﹥叶片﹥顶芽;蛋白质含量呈先上升后下降的趋势,蛋白质含量的峰值出现于花序伸展初期。     

不同时期开沟施氮对水稻物质生产及产量的影响

通过田间试验 ,研究了水稻不同生育时期开沟深施氮肥对水稻叶片、叶鞘和茎秆干重以及生物产量和籽粒产量的影响 .结果表明 ,孕穗期开沟深施氮肥处理比分蘖期开沟、穗分化始期开沟和不开沟处理的水稻叶片干重保持最大值 (2 .9g/穴 )时间长 ,叶面积指数达到最大值 (LAI =8.9)后保持缓慢下降 ;叶鞘干重 (2 .7g/穴 )变化小 ;处理以后茎秆干重 (4.3g/穴 )稳步增加 .孕穗期开沟施肥处理的水稻生物产量(0 .73g·d-1/穴 )递增速度快 ,籽粒产量 (10 4 34kg·hm-2 )高 .与不开沟施肥相比 ,孕穗期开沟施氮对产量增加作用最大 ,为水稻开沟深施氮肥的最佳时期 ;其次为穗分化始期 ,分蘖期开沟施氮效果较差 ,但仍有一定的增产作用 .     

Genetic Overlap in the Quantitative Resistance of Rice at the Seedling and Adult Stages to <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis>

The genetic components responsible for the qualitative and quantitative resistance of rice to three Chinese races (C2, C4, and C5) of Xanthomonas oryzae pv. oryzae (Xoo) were investigated at the seedling and adult stages in two successive years in set of Lemont/Teqing cross introgression lines (ILs) in a Teqing background, to create a complete linkage map using 160 well-distributed SSR markers. Teqing was resistant to C2 and C4, but moderately susceptible to C5, whereas Lemont was susceptible to all three races. Highly significant correlations were detected among the resistance to different races at different developmental stages. A major gene (Xa4), 14 main-effect QTLs (M-QTLs), and 18 epistatic QTLs were identified in the two developmental stages over 2 years, and were largely responsible for the segregation of resistance in the ILs. In 2007, the Lemont alleles at all loci in the seedling stage, except QBbr10 to C4, increased lesion length (LL) or decreased resistance. The Teqing allele at the Xa4 locus acted as a resistance gene against C2 and C4, but acted as a M-QTL when its resistance was overcome by the virulent race C5. M-QTLs showed a degree of race specificity and had a cumulative effect on resistance. Most M-QTLs (94%) consistently expressed resistance to the same race at the seedling and adult stages, indicating that a high degree of genetic overlap exists between Xoo resistance at both developmental stages in rice. Among the digenic interactions, most co-introgressed Lemont alleles at the two epistatic loci lead to significantly smaller LL with all three races, compared to other types of interacting alleles at both development stages. The results indicate that a high level of resistance may be achieved by the cumulative effect of multiple M-QTLs, including the residual effects of “defeated” major resistance genes and the epistatic effects of co-introgression from diverse susceptible varieties.     

Sugars,antioxidant enzymes and IAA mediate salicylic acid to prevent rice spikelet degeneration caused by heat stress

Salicylic acid (SA) can alleviate damage to rice plants induced by heat stress, but its role in preventing spikelet degeneration under high-temperature stress has not been documented. Rice plants pretreated with SA (0–50 mmol L^?1) were subjected to heat stress at 40?°C at the pollen mother cell meiosis stage for 10 days. The results indicated that there were no significant differences in grain yields and yield components among rice plants that were exogenously sprayed with SA (0–50 mmol L^?1) under natural conditions. Under heat stress, the grain yield, spikelet number per panicle and setting rate in response to SA treatments were higher than under the control (0 mmol L^?1 SA or NON-SA) treatment, especially with 1 and 10 mmol L^?1 SA. A higher grain yield, spikelet number per panicle and setting rate were recorded in these two SA treatments compared with the NON-SA treatment. During this process, soluble sugars, proline, phytohormones including ABA, GA₃, BRs, IAA, ZR and JA, and antioxidant enzymes, such as superoxide dismutase, peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), were induced by SA. Moreover, soluble sugars, IAA, POD and APX in the spikelets with SA treatments were not only higher than with the NON-SA treatment but the changing patterns were also similar to that of the spikelet number per panicle under natural conditions and heat stress. Therefore, our results suggest that sugars, antioxidant enzymes and IAA might mediate SA to prevent spikelet degeneration caused by heat stress.     

Comparative analysis of photosynthetic characteristics and productivity in F2 hybrids of winter rye

Diversity of photosynthetic characteristics determined by plant genotypes provides the grounds for the increase in potential crop productivity by means of producing plant forms whose photosynthetic apparatus (PSA) has optimal size and functional efficiency. Parental forms of winter rye (Secale cereale L.) and their interline and intravarietal reciprocal F₂ hybrids were compared in terms of photosynthetic pigment (PSP) content, characteristics of chlorophyll a (Chl) fluorescence, some morphological traits, and grain productivity. At the booting and anthesis stages, significant divergence in chlorophyllous pigment content and Chl a fluorescence parameters was observed for winter rye inbred lines, rye varieties, and hybrids. The hybrids were revealed whose elevated grain productivity correlated with high PSP content and the highest photosystem II (PSII) activity. Analysis of correlations in reciprocal F₂ hybrids at booting and anthesis stages of rye development showed that accumulation of PSII is related to stem-forming capacity and to the flag leaf surface area. In reciprocal hybrids, the correlations between morphological traits, grain productivity, plastid pigments, and photochemical activity were subject to variations. The relationships between PSA parameters and grain productivity in winter rye F₂ hybrids varied depending on the developmental stage as well as on crossing combination; this relation was largely determined by the choice of pairs for hybridization, by direction of crosses, and by genetic features of parental forms.