Rice Spikelet Research Articles

Mechanism of Developmental Stagnancy of Rice Inferior Spikelets at Early Grain-Filling Stage as Revealed by Proteomic Analysis

Rice spikelets display different grain-filling patterns depending on their position on a panicle. The superior spikelets (SS) elongated soon after flowering, whereas the inferior spikelets (IS) hardly elongate and are morphologically stagnant at early grain-filling stage. The developmental stagnancy of IS often leads to slow grain-filling and a low grain weight. To better understand the mechanism of the stagnancy, we took a two-dimensional gel electrophoresis (2-DE)-based proteomic and phosphoproteomic approach to profile the proteins with expression abundance as well as the phosphorylation of SS and IS at the early grain-filling stage. A total of 81 protein spots were found to be significantly different in expression abundance, and 27 protein spots significantly differed in phosphorylation. Bioinformatic analyses implicated that the proteins might be involved in the diverse cellular processes including sugar conversion, starch synthesis, energy pathway, signal transduction, cell growth/division, and protein synthesis and destination. Moreover, using the pull-down assay, we identified 29 14-3-3 binding proteins, and altogether, these 14-3-3 protein was found the important scaffold in the signaling networks of IS development. Our findings provided new proteomic and phosphoproteomic insights on the developmental stagnancy of rice IS that could be highly useful for the improvement of the grain-filling of rice and other cereal crops.

Cooling water before panicle initiation increases chilling-induced male sterility and disables chilling-induced expression of genes encoding OsFKBP65 and heat shock proteins in rice spikelets.

In rice (Oryza sativa L.), chilling-induced male sterility increased when plants experienced low water temperature (Tw , 18 °C for 14 d) before panicle initiation. The number of mature pollen grains after chilling at the booting stage (12 °C for 5 d) was only 45% of total pollen grains in low-Tw plants, whereas it was 71% in normal-Tw plants (Tw not controlled; approximately 23 °C under air temperature of 26 °C/21 °C, day/night). Microarray and quantitative PCR analyses showed that many stress-responsive genes (including OsFKBP65 and genes encoding the large heat shock protein OsHSP90.1, heat-stress transcription factors and many small heat shock proteins) were strongly up-regulated by chilling in normal-Tw spikelets, but were unaffected or even down-regulated by chilling in low-Tw spikelets. OsAPX2 and genes encoding some other antioxidant enzymes were also significantly down-regulated by low Tw in chilled spikelets. The levels of lipid peroxidation products (malondialdehyde equivalents) were significantly increased in low-Tw spikelets by chilling. Ascorbate peroxidase activity in chilled spikelets was significantly lower in low-Tw plants than in normal-Tw plants. Our data suggest that an OsFKBP65-related chilling response, which protects proteins from oxidative damage, is indispensable for chilling tolerance but is lost in low-Tw spikelets.

Abscisic acid and the key enzymes and genes in sucrose-to-starch conversion in rice spikelets in response to soil drying during grain filling.

Abscisic acid mediates the effect of post-anthesis soil drying on grain filling through regulating the activities of key enzymes and expressions of genes involved in sucrose-to-starch conversion in rice spikelets. This study investigated if abscisic acid (ABA) would mediate the effect of post-anthesis soil drying on grain filling through regulating the key enzymes in sucrose-to-starch conversion in rice (Oryza sativa L.) spikelets. Two rice cultivars were field-grown. Three treatments, well-watered (WW), moderate soil drying (MD), and severe soil drying (SD), were imposed from 6 days after full heading until maturity. When compared with those under the WW, grain filling rate, grain weight, and sink activity, in terms of the activities and gene expression levels of sucrose synthase, ADP glucose pyrophosphorylase, starch synthase, and starch branching enzyme, in inferior spikelets were substantially increased under the MD, whereas they were markedly decreased in both superior and inferior spikelets under the SD. The two cultivars showed the same tendencies. Both MD and SD increased ABA content and expression levels of its biosynthesis genes in spikelets, with more increase under the SD than the MD. ABA content was significantly correlated with grain filling rate and sink activities under both WW and MD, while the correlations were not significant under the SD. Application of a low concentration ABA to WW plants imitated the results under the MD, and applying with a high concentration ABA showed the effect of the SD. The results suggest that ABA plays a vital role in grain filling through regulating sink activity and functions in a dose-dependent manner. An elevated ABA level under the MD enhances, whereas a too high level of ABA under the SD decreases, sink activity.

Development of a GFP-expressing Ustilaginoidea virens strain to study fungal invasion and colonization in rice spikelets

The fungal pathogen Ustilaginoidea virens is now widespread in most rice producing areas of the world and attacks the seed spikes of rice, causing sterility, reduced seed weight and accumulation of mycotoxins. The lack of appropriate data relating to the mechanisms of infection leaves a gap within the pathosystem, forcing the search for new methodologies for monitoring the disease. Here, we developed an efficient A. tumefaciens mediated transformation system for rice false smut disease. In addition, infection patterns were explored in rice using the green fluorescent protein gene (gfp) transformed U. virens. ATMT uses both the Hygromycin B resistance (hph) gene and green fluorescent protein as the selection agents. The T-DNA integration into the fungal genome was assessed by PCR. Expression of the gfp gene did not affect the pathogenicity of the U. virens transformants. U. virens pathogenicity was examined on the floral structures using a fluorescence microscope. Fluorescence microscopy allowed in vivo imaging of this pathogen during infection of rice spikelets. These studies will allow us to develop strategies to determine the mechanisms of U. virens–rice interaction in greater detail and to apply functional genomics for the characterization of involved genes at the molecular level either by insertional mutagenesis or gene knock-out.

Phenotypic Characterization, Genetic Analysis and Molecular Mapping of a New Floral Organ Mutant Gene in Rice

A rice floral organ mutant, srs2, derived from a spontaneous mutation, was first discovered in a japonica rice variety GNZ. The mutant displayed various abnormalities in floral organ including longer paleas/lemmas, split spikelets, palea/lemma-like lodicules, two florets of the same rachilla, a decrease in stamen number, and an increase in pistil number. Moreover, the seed-setting rate of the mutant was also reduced to 9.8%. Observations of the floral organ morphogenesis by a scanning electron microscope (SEM) in the mutant indicated that the development of androecium and gynoecia was abnormal and an additional floret and several palea/lemma-like lodicules were usually formed by the irregular development of the floral meristem. Genetic analysis of 4 F2 and 2 BC1F1 populations showed that the mutation was controlled by a single recessive gene, and designated as srs2 (spit rice spikelet 2). Screening of 643 F2 mutant individuals derived from the cross of srs2 × 202R with simple sequence repeat (SSR) markers demonstrated that SRS2 is located between the molecular marker S31 and L75, at a distances of 0.07 and 2 cM, respectively, on chromosome 3. The SRS2 gene was also discussed to be a new floral organ identity gene in rice.

QEMF3, a novel QTL for the early-morning flowering trait from wild rice, Oryza officinalis, to mitigate heat stress damage at flowering in rice, O. sativa

A decline in rice (Oryza sativa L.) production caused by heat stress is one of the biggest concerns resulting from future climate change. Rice spikelets are most susceptible to heat stress at flowering. The early-morning flowering (EMF) trait mitigates heat-induced spikelet sterility at the flowering stage by escaping heat stress during the daytime. We attempted to develop near-isogenic lines (NILs) for EMF in the indica-type genetic background by exploiting the EMF locus from wild rice, O. officinalis (CC genome). A stable quantitative trait locus (QTL) for flower opening time (FOT) was detected on chromosome 3. A QTL was designated as qEMF3 and it shifted FOT by 1.5-2.0 h earlier for cv. Nanjing 11 in temperate Japan and cv. IR64 in the Philippine tropics. NILs for EMF mitigated heat-induced spikelet sterility under elevated temperature conditions completing flower opening before reaching 35°C, a general threshold value leading to spikelet sterility. Quantification of FOT of cultivars popular in the tropics and subtropics did not reveal the EMF trait in any of the cultivars tested, suggesting that qEMF3 has the potential to advance FOT of currently popular cultivars to escape heat stress at flowering under future hotter climates. This is the first report to examine rice with the EMF trait through marker-assisted breeding using wild rice as a genetic resource.

Preparation of Reduced Graphene Oxide–Poly(Safranine T) Film via One-Step Polymerization for Electrochemical Determination of Methyl Jasmonate

In this work, a new reduced graphene oxide–poly(safranine T) (rGO–PST) film was prepared on glassy carbon electrode (GCE) via one-step polymerization using rGO as an electron transfer mediator. The uniform structure of rGO–PST film was exhibited by scanning electron microscopy. Electrochemical characterization indicated that rGO–PST/GCE possessed much larger surface area and faster electron transfer rate constant compared with GCE. Furthermore, the rGO–PST/GCE exhibited strong catalytic ability and sensitive response to the oxidation of methyl jasmonate (MeJA) using derivative linear scan voltammetry. Under optimal working conditions, the oxidation current of MeJA linearly increased with its concentration in the range of 1.0–10 μM and 30–3000 μM after 2-min accumulation, along with a low detection limit of 0.5 μM. As an example of practical application, the rGO–PST/GCE was successfully employed for the determination of MeJA in jasmine essential oil and rice spikelets samples.

Overexpression of the JAZ factors with mutated jas domains causes pleiotropic defects in rice spikelet development

In a determinate meristem, such as a floral meristem, a genetically determined number of organs are produced before the meristem is terminated. In rice, iterative formation of organs during flower development with defects in meristem determinacy, classically called ‘proliferation’, is caused by several mutations and observed in dependence on environmental conditions. Here we report that overexpression of several JAZ proteins, key factors in jasmonate signaling, with mutations in the Jas domains causes an increase in the numbers of organs in florets, aberrant patterns of organ formation and repetitious organ production in spikelets. Our results imply that JAZ factors modulate mechanisms that regulate meristem functions during spikelet development.

High night temperature induces contrasting responses for spikelet fertility, spikelet tissue temperature, flowering characteristics and grain quality in rice.

Climate change is increasing night temperature (NT) more than day temperature (DT) in rice-growing areas. Effects of combinations of NT (24-35°C) from microsporogenesis to anthesis at one or more DT (30 or 35°C) at anthesis on rice spikelet fertility, temperature within spikelets, flowering pattern, grain weight per panicle, amylose content and gel consistency were investigated in contrasting rice cultivars under controlled environments. Cultivars differed in spikelet fertility response to high NT, with higher fertility associated with cooler spikelets (P<0.01). Flowering dynamics were altered by high NT and a novel high temperature tolerance complementary mechanism, shorter flower open duration in cv. N22, was identified. High NT reduced spikelet fertility, grain weight per panicle, amylose content and gel consistency, whereas high DT reduced only gel consistency. Night temperature >27°C was estimated to reduce grain weight. Generally, high NT was more damaging to grain weight and selected grain quality traits than high DT, with little or no interaction between them. The critical tolerance and escape traits identified, i.e. spikelet cooling, relatively high spikelet fertility, earlier start and peak time of anthesis and shorter spikelet anthesis duration can aid plant breeding programs targeting resilience in warmer climates.

Comparative proteomics analysis of superior and inferior spikelets in hybrid rice during grain filling and response of inferior spikelets to drought stress using isobaric tags for relative and absolute quantification

The biological functions of the differentially abundant proteins between superior and inferior spikelet grains were investigated based on the isobaric tags for relative and absolute quantification to further clarify the mechanism of rice grain filling at the proteomic level, as well as the response of inferior spikelets to drought dress (-20kPa or -40kPa). Compared with superior spikelets, inferior ones had lower sink strength due to the lower sink activities (lower abundances of ADP-glucose pyrophosphorylase, granule-bound starch synthase, starch branching enzyme and pullulanase) and smaller sink sizes (lower abundances of structural proteins). The slower and later grain filling resulted from the weaker decomposition and conversion of photoassimilate and the slower cell division. Moderate drought stress (-20kPa) promoted the grain filling of inferior spikelets through regulating the proteins associated with photoassimilate supply and conversion. These proteins may be important targets for rice breeding programs that raise the rice yield under drought condition. The findings offer new insights into rice grain-filling and provide theoretical evidences for better quality control and scientific improvement of super rice in practice. Rice cultivars with large panicles do not always guarantee high yield and grain quality probably due to the slow grain filling and many unfilled grains of inferior spikelets. In general, earlier-flowering superior spikelets, which are usually located on apical primary branches, fill faster and produce larger and heavier grains. In contrast, later-flowering inferior spikelets located on proximal secondary branches are either sterile or fill slowly and poorly, and the differences are more significant in large panicle rice or super rice. The increase of rice yield has been limited by the unsatisfactory grain filling of inferior spikelets, and the inferior spikelets are more prone to environmental factors during grain filling. Thus, we herein investigated the biological functions of differently abundant proteins between superior and inferior spikelet grains by using iTRAQ to unravel the mechanism of rice grain filling and the response of inferior spikelets to drought stress at proteomic level. This study offers new insights into rice grain-filling and provides valuable evidences for better quality control and scientific improvement of super rice in practice.

Data in support of comparative proteomics analysis of superior and inferior spikelets in hybrid rice during grain filling and response of inferior spikelets to drought stress using isobaric tags for relative and absolute quantification

We provide the raw data for protein and peptide identification and quantization of superior and inferior spikelets in hybrid rice during grain filling. The mass spectrometry proteomics data have been deposited to the Proteome Xchange Consortium via the PRIDE partner repository with the dataset identifier PXD001046. Our data presented here is also related to the article “Comparative proteomics analysis of superior and inferior spikelets in hybrid rice during grain filling and response of inferior spikelets to drought stress using isobaric tags for relative and absolute quantification ”in the Journal of Proteomics [1].

Morphogenesis and Molecular Basis on the Unclosed Glumes, a Novel Mutation Related to the Floral Organ of Rice

The development of the rice floral organ directly affects rice yield and quality, and rice spikelet development has always been the hotspot in the field of botanical research. Mutants of the rice floral organ are very important intermediate materials which are used to reveal the genetic mechanism of spikelet development. In the present study, a stable rice mutant named unclosed glumes (ucgl) with a Japonica background, of which the lemma and palea cannot close fully after flowering, was isolated from the population mutagenized by using the ethyl methane sulfonate (EMS) in rice. Results from the genetic analysis indicated that the mutant was controlled by a single recessive gene. The UCGL locus was mapped to a 118-kb region between SSR makers R8UM89 and RM23258 on chromosome 8. There was a C to T substitution at the fifth exon of LOC_Os08g0459600 by sequencing analysis. LOC_Os08g0459600 encodes 12-oxo-phytodienoic acid reductase 7 (OPR7), which is one of the key enzymes in the jasmonic acid (JA) biosynthesis. RT-PCR analysis showed that the UCGL gene could be expressed in all of the tested tissues including roots, stems, leaves, and panicles. Also, the concentration of endogenous JA in the ucgl mutant was reduced in contrast to the wild-type. The expression levels of JA biosynthetic genes including OsLOX and OsAOS were significantly increased in the ucgl mutant plant. The expression of UCGL (OsOPR7) could regulate JA metabolism and affect the closure of glumes in rice. As far as we know, the UCGL is thus a new gene and has not been reported as controlling the closure of rice glumes, thusthe study of it could provide a new insight into the role of JA in rice floral morphological development.

Differentially expressed microRNA cohorts in seed development may contribute to poor grain filling of inferior spikelets in rice.

BackgroundThe inferior spikelets are defined to be those at portions where the grains receive less photosynthetic products during the seed development. The typical inferior spikelets are physically located on the proximal secondary branches in a rice panicle and traditionally characterized by a later flowering time and a slower grain-filling rate, compared to those so-called superior spikelets. Grains produced on the inferior spikelets are consequently under-developed and lighter in weight than those formed on the superior spikelets. MicroRNAs (miRNAs) are recognized as key players in regulating plant development through post-transcriptional gene regulations. We previously presented the evidence that miRNAs may influence grain-filling rate and played a role in determining the grain weight and yield in rice.ResultsIn this study, further analyses of the expressed small RNAs in superior and inferior spikelets were conducted at five distinct developmental stages of grain development. Totally, 457 known miRNAs and 13 novel miRNAs were analyzed, showing a differential expression of 141 known miRNAs between superior and inferior spikelets with higher expression levels of most miRNAs associated with the superior than the inferior spikelets during the early stage of grain filling. Genes targeted by those differentially expressed miRNAs (i.e. miR156, miR164, miR167, miR397, miR1861, and miR1867) were recognized to play roles in multiple developmental and signaling pathways related to plant hormone homeostasis and starch accumulation.ConclusionsOur data established a complicated link between miRNA dynamics and the traditional role of hormones in grain filling and development, providing new insights into the widely accepted concepts of the so-called superior and inferior spikelets in rice production.

First Report of Leaf Blight of Rice Caused by Cochliobolus lunatus in China.

Leaf-streak symptoms were observed on rice (Oryza sativa L.) starting at the booting stage through harvest in Zhejiang Province, China, in 2012. Based on Fuyang County, only 15% of the rice fields were estimated to show these symptoms. However, incidence could be 40 to 80% when the rice got infected. Typical symptoms started as green water-soaked streaks from the tip or edge of leaf blades, similar to bacterial leaf blight caused by Xanthomonas oryzae. Infected leaves turned yellow, then eventually became wilted and dry. No bacterial streaming was observed and no bacteria were isolated. Pieces of infected leaf tissue were surface sterilized using 0.1% (v/v) mercuric chloride, rinsed with sterilized water, then placed on water agar (WA). After 2 or 3 days on WA at 28°C, only fungal growth was observed from surface sterilized tissues. Fungi were isolated, purified by single spore separation process, and subcultured to potato dextrose agar (PDA) plates. Growing on PDA, the surface of the colony was circular, fluffy, and shiny velvety-black, whereas the under surface was dark Prussian blue. Conidiophores were single or fascicled, brown to dark brown, rarely branched, multiseptate, and straight or often geniculate near the apex. Conidia were brown, smooth, fusiform, geniculate or hook-shaped, 17.5 to 28.5 × 8.5 to 14.0 μm, and 3-septate, with the third cell from the base larger and darker than the others. Molecular identification was performed by analysis of the rDNA internal transcribed spacer region (ITS1-5.8S-ITS2). The rDNA-ITS region was amplified with primer pair ITS1 and ITS4 (5), sequenced, and deposited in GenBank (Accession No. KC462186). The sequence of rDNA-ITS (KC462186) showed 100% identity with Cochliobolus lunatus R.R. Nelson & Haasis (JN943422) after BLAST. Based on the results of morphological and molecular analyses, the fungus isolated from infected leaves was identified as C. lunatus (anamorph: Curvularia lunata (Wakk.) Boedijn) (3). Pathogenicity tests were conducted three times by spraying a conidial suspension (1 × 105 spores/ml) with 0.1% (v/v) Tween 20 on 12 healthy rice plants at late tillering stage. The same number of the healthy rice plants sprayed with sterilized water with 0.1% (v/v) Tween 20 were used as control. All plants were kept at 30°C and 75 to 85% relative humidity (RH) under a 12-h light/dark rotation. About 5 to 7 days after inoculation, green water-soaked streaks began to appear on inoculated plants. From 7 to 14 days after inoculation, the lesions developed quickly and the leaves began to wilt. After 14 days, inoculated plants showed symptoms similar to those originally observed in the field, while control plants (sprayed with sterilized water) remained healthy. C. lunatus was re-isolated from all inoculated plants, and re-identified by the same methods (morphological and molecular methods) as described above, thereby satisfying Koch's postulates, and confirming C. lunatus as the cause of the disease. C. lunatus is a pathogen of a wide range of plants and is common in paddy environments. It was reported as one of the causal agents of black kernel of rice (4) and rice spikelet rot disease (SRD) (1,2). The level of incidence observed in the affected fields suggest that this disease could potentially cause major losses under favorable weather conditions if susceptible cultivars are grown. To our knowledge, this is the first report of C. lunatus causing leaf blight of rice in China.

Jasmonic acid regulates spikelet development in rice

The spikelet is the basal unit of inflorescence in grasses, and its formation is crucial for reproductive success and cereal yield. Here, we report a previously unknown role of the plant hormone jasmonic acid (JA) in determining rice (Oryza sativa) spikelet morphogenesis. The extra glume 1 (eg1) and eg2 mutants exhibit altered spikelet morphology with changed floral organ identity and number, as well as defective floral meristem determinacy. We show that EG1 is a plastid-targeted lipase that participates in JA biosynthesis, and EG2/OsJAZ1 is a JA signalling repressor that interacts with a putative JA receptor, OsCOI1b, to trigger OsJAZ1's degradation during spikelet development. OsJAZ1 also interacts with OsMYC2, a transcription factor in the JA signalling pathway, and represses OsMYC2's role in activating OsMADS1, an E-class gene crucial to the spikelet development. This work discovers a key regulatory mechanism of grass spikelet development and suggests that the role of JA in reproduction has diversified during the flowering plant evolution.

A role for TRIANGULAR HULL1 in fine-tuning spikelet morphogenesis in rice.

The lemma and palea, which enclose the pistil, stamens, and lodicules, are the most conspicuous organs in the rice spikelet. We isolated a mutant line (ng6569) in which the lemma and palea were narrower than those of the wild type, and found that the mutant had a defect in TRIANGULAR HULL1 (TH1), which encodes a nuclear protein with an ALOG domain. Detailed morphological analysis indicated that the th1 mutation caused a reduction in the size of tubercles, which are convex structures on the surface of the lemma and palea. This reduction was more pronounced in the apical region of the lemma than in the basal region, resulting in the formation of a beak-like spikelet. By contrast, the number of tubercle rows and their spatial distribution on the lemma were not affected in the th1 mutant. Thus, the TH1 gene seems to be involved in fine-tuning the morphogenesis of the lemma and palea. In situ hybridization analysis revealed that TH1 was highly expressed in the primordia of the lemma and palea, but only weakly expressed in the primordia of the sterile lemma and rudimentary glume. We then examined the effect of th1 mutation on the lemma-like structure formed in the long sterile lemma/glume1 (g1) and extra glume1 (eg1) mutants. The result showed that the th1 mutation strongly affected the morphology of the extra lemma of eg1, but had no significant effect on the transformed lemma of g1.

The pleiotropicSEPALLATA‐like geneOsMADS34reveals that the ‘empty glumes’ of rice (Oryza sativa) spikelets are in fact rudimentary lemmas

The single floret of the rice (Oryza sativa) spikelet is subtended by a pair of enigmatic organs usually termed 'empty glumes' or 'sterile lemmas'. As the identity of these organs remains essentially unknown, we refer to them as 'organs of unknown identity' (OUIs). Here we present a novel mutant of the rice SEPALLATA-like gene OsMADS34 which develops, in addition to disorganized branches and sterile seeds, elongated OUIs. The function and evolution of OsMADS34 were studied. Morphological and molecular markers indicate that the elongated OUIs have adopted lemma identity. Evolutionary analyses show that the ancestral genes of the OsM34 subclade evolved under positive selection, and that three specific motifs occur in the C-terminal region of proteins in the OsM34 subclade. Yeast two-hybrid assays revealed that the C-terminal region of OsMADS34 plays a crucial role in mediating protein interactions. Sequence analyses for the wild rice Oryzagrandiglumis which has elongated OUIs revealed the association of OsMADS34 functionality with OUI identity. Our findings support the hypothesis that OUIs originated from the lemmas of degenerate florets under the negative control of OsMADS34. As OUIs neither are homologues to glumes nor have the identity of lemmas any more, but originated from these organs, we suggest calling them 'rudimentary lemmas'.

A simple model for simulating heat induced sterility in rice as a function of flowering time and transpirational cooling

Rice spikelets become sterile when exposed to high temperatures during flowering. Recent experimental studies have shown that transpirational cooling and flowering time (within the day) are important factors determining sterility. Extrapolation of the results from these experimental studies to other environments requires an integrated approach through incorporating such effects on spikelet fertility in a crop growth model. Here we review existing fertility functions (fertility as a function of panicle temperature) in different studies, and propose a simple new model that incorporates insights on diurnal patterns of temperature and relative humidity, recent studies on the relation between panicle temperature and sterility, and studies on how flowering time depends on environmental conditions. We illustrate the model for a typical arid and typical humid climate. There was a large difference between the existing fertility functions, and simulated fertility was very sensitive to differences in fertility functions, causing differences in simulated fertility of up to 59%. Ignoring transpirational cooling led to overestimation of sterility of 14–73%. Shifting flowering times from 12:00 to 9:00 led to a 7–35% reduction in sterility. Within day flowering duration had only a marginal impact (max 2%). We conclude that any climate change impact simulation is highly dependent on the choice of the fertility function, and identification of causes of differences between reported fertility functions deserves further investigation.

Epiphytic colonization of Ustilaginoidea virens on biotic and abiotic surfaces implies the widespread presence of primary inoculum for rice false smut disease

Ustilaginoidea virens (Uv), the causative agent of rice false smut disease, infects developing rice spikelets at the booting stage, and transforms individual grains of the panicle into smut balls. Epidemics of the disease occur when the rice booting and heading stages coincide with rainy days. Using a green fluorescent protein (GFP)‐labelled Uv isolate that can form false smut balls on rice panicles, it was found that under high humidity and free water conditions the Uv isolate could colonize leaves of plants belonging to various families including the Poaceae (Oryza sativa, Echinochloa crusgalli, Digitaria sanguinalis and Leptochloa chinensis), the Brassicaceae (Arabidopsis thaliana) and the Solanaceae (Nicotiana benthamiana) without symptoms. Over several days, some conidia could germinate on the leaves of these plants and in water on the surface of Parafilm and cellophane, form hyphae and differentiate conidiophores to generate a large number of secondary conidia, while other conidia were able to directly produce secondary conidia. Conversely, in the absence of water some conidia could either bud to form new conidia or were converted into chlamydospores. These data indicate that Uv is one of a few fungal pathogens reported to have epiphytic characteristics. The rapid generation of a large number of spores on biotic and abiotic surfaces greatly increases the inoculum that can infect rice spikelets, resulting in the occurrence of rice false smut disease epidemics. These findings are important in the development of disease control strategies.

High Yield Formation and Its Eco-Physiological Characteristics of Cast-Trans¬planting Rice

Cast-Transplanting rice has a low cost, easy operation, high and stable yield potential advantage, Depth study of the seedings throwing is very important to develop the light and simple cultivation of rice. The purpose of this study is to explore the high yield formation and its eco-physiological characteristics of cast-transplanting rice. Under the rice-wheat cropping systems, conventional japonica cultivar Nanjing 44 and japonica hybrid rice cultivar Yongyou 8 were used to investigate the characteristics of high yield formation including tillering dynamic, LAI, photosynthetic potential, dry matter production and the eco-physiological basis, such as post-root activity, photosynthetic characteristics, material accumulation and translocation, with three cast-transplanting methods of transplanted seedlings (TS), pointed seedlings (PS), and broadcasted seedlings (BS) in contrast with the manually transplanting of seedlings with roots washed beforehand (MTS), which could provide the theoretical and practical basis for the high and stable yield of the cast-transplanting rice. The results showed that the yields of three methods were 21.9%, 18.3%, and 13.2% higher than MTS for Yongyou 8, and 18.3%, 14.1%, and 9.87% higher than MTS for Nanjing 44, respectively. The yields of two cultivars both showed the trend of TS PS BS MTS. Although the filled-grain percentage and 1000-grain weight of cast-transplanting rice were significantly or very significantly lower than those of MTS, the total number of spikelets of cast-transplanting rice was conformably higher than that of MTS at a significant or very significant degree. The increased yield was mainly due to the higher total spikelet number. Compared to MTS, the cast-transplanting rice had more peak seedling tillers, higher or equivalent ratios of productive tillers to total tillers, an enough number of ultimate effective panicles, higher LAI and LAD, and thus a more robust population quality. According to these results, we could give the conclusion of the eco-physiological basis of high and stable yield of cast-transplanting rice. After transplantation, there were earlier tillering, more leaf tillering positions, stronger tillering capability, and higher quality and enough quantity of tillering. At the heading stage, they had suitable plant height, stouter stems and sheaths, efficient leaf configurations, preferable air ventilation and light transmission conditions, higher biomass accumulation, a more coordinated sink-source relationship, and hence a higher yield potential. In the late growth period, the cast-transplanting rice had stronger roots, slower senescence of leaves, more powerful photosynthesis, more coordinated dry matter accumulation and translocation of stem and sheath, higher filling ratios, being more conducive to the higher yield. TS and PS have evident advantages than MTS, and are more favorable in achieving higher yield.