Perennial Wild Rice Research Articles

Taxonomic Studies in Genus <I>Oryza</I> L. II. some Nomenclature Confusions

Wild rices of Asia have been variously referred to by different workers as Oryza perennis, O. fatua, Oerufipogon, O. sativa var. fatua, O. saliva L. f. spontanea, O. balunga, O. formosana etc. Validity of each of these names and their application to the taxa are discussed and it is concluded that (i) the name O. perennis is to be discarded, (ii) valid name for perennial wild rice of Asia is O. rufipogon and (iii) annual wild rice of Asia lacks a valid name.

Genome-wide and pan-genomic analysis reveals rich variants of NBS-LRR genes in a newly developed wild rice line from Oryza alta Swallen.

Oryza alta Swallen is an allotetraploid perennial wild rice and contains CCDD genome, which may harbor favorable genes for the enrichment of genetic resource. A new wild rice line, Huaye 5, was developed from Oryza alta Swallen in our lab. Whole genome re-sequencing and pan-genomic analysis were employed to analyze its genomic variations and novel genes. More than ten million genomic variations were detected when compared with Asian cultivar. Among the variational genes, 724, 197 and 710 genes coded protein kinase, synthetase and transcription factor, respectively. A total of 353, 131 and 135 variational genes were associated with morphological trait, physiological trait, resistance or tolerance, respectively. A total of 62 were NBS-LRR genes were detected, in which 11 NBS-LRR genes expressed in sheath and mature stem, and 26 expressed in young and mature roots expressed. The pan-genome sequences of wild rice species with CCDD genome were constructed by integrating 8 Oryza alta (OA), 2 Oryza grandiglumis (OG) and 18 Oryza latifolia (OL) accessions. A total of 28 non-reference NBS-LRR genes were revealed, and 7 of which were mainly expressed in mature roots. This research demonstrated rich DNA variation in the Oryza alta Swallen that may provide a new germplasm for rice resistance breeding.

Gene Flow Between the Wild Rice Species (Oryza longistaminata) and Two Varieties of Cultivated Rice (Oryza sativa) in Kilombero District, Tanzania

The direction and rate of gene flow between the perennial wild rice species, O. longistaminata and cultivated rice, O. sativa was investigated using nine Microsatellite (SSR) markers. The study involved characterization of parental lines of two cultivated rice varieties and O. longistaminata and their F1 progenies. Presence of crop-specific alleles in the wild species or vice-versa was used as an indicator of occurrence of gene flow between the two species. The study revealed that gene flow between O. longistaminata and each of the two varieties of O. sativa occurs naturally. The direction of gene flow was mainly from the cultivated to wild species. The rate (frequency) of gene flow was higher from cultivated (O. sativa) to wild rice (O. longistaminata) than from O. longistaminata to O. sativa and varied with cultivated rice variety. Higher rate of gene flow from cultivated to wild species could be due to floral structure and out-crossing nature of the wild species (O. longistaminata). Gene flow between O. longistaminata and O. sativa is likely to change genetic integrity of natural populations of the two species in areas where they occur sympatrically. However, isolation by distance can help to control gene flow between these species.

Endophytic bacterial communities in wild rice (Oryza officinalis) and their plant growth-promoting effects on perennial rice.

Endophytic bacterial microbiomes of plants contribute to the physiological health of the host and its adaptive evolution and stress tolerance. Wild rice possesses enriched endophytic bacteria diversity, which is a potential resource for sustainable agriculture. Oryza officinalis is a unique perennial wild rice species in China with rich genetic resources. However, endophytic bacterial communities of this species and their plant growth-promoting (PGP) traits remain largely unknown. In this study, endophytic bacteria in the root, stem, and leaf tissues of O. officinalis were characterized using 16S rRNA gene Illumina sequencing. Culturable bacterial endophytes were also isolated from O. officinalis tissues and characterized for their PGP traits. The microbiome analysis showed a more complex structure and powerful function of the endophytic bacterial community in roots compared with those in other tissue compartments. Each compartment had its specific endophytic bacterial biomarkers, including Desulfomonile and Ruminiclostridium for roots; Lactobacillus, Acinetobacter, Cutibacterium and Dechloromonas for stems; and Stenotrophomonas, Chryseobacterium, Achromobacter and Methylobacterium for leaves. A total of 96 endophytic bacterial strains with PGP traits of phosphate solubilization, potassium release, nitrogen fixation, 1-aminocyclopropane-1-carboxylate (ACC) deaminase secretion, and siderophore or indole-3-acetic acid (IAA) production were isolated from O. officinalis. Among them, 11 strains identified as Enterobacter mori, E. ludwigii, E. cloacae, Bacillus amyloliquefaciens, B. siamensis, Pseudomonas rhodesiae and Kosakonia oryzae were selected for inoculation of perennial rice based on their IAA production traits. These strains showed promising PGP effects on perennial rice seedlings. They promoted plants to form a strong root system, stimulate biomass accumulation, and increase chlorophyll content and nitrogen uptake, which could fulfil the ecologically sustainable cultivation model of perennial rice. These results provide insights into the bacterial endosphere of O. officinalis and its application potential in perennial rice. There is the prospect of mining beneficial endophytic bacteria from wild rice species, which could rewild the microbiome of cultivated rice varieties and promote their growth.

QTL Mapping of a Novel Genomic Region Associated with High Out-Crossing Rate Derived from Oryza longistaminata and Development of New CMS Lines in Rice, O. sativa L.

High seed cost due to poor seed yield severely limits the adoption of hybrid rice by farmers. Increasing the out-crossing rate is one of the key strategies to increase hybrid seed production. Out-crossing rate is highly influenced by the size of female floral traits, which capture pollen grains from male donor plants. In the current study, we identified 14 QTLs derived from the perennial wild rice Oryza longistaminata by composite interval mapping for five key floral traits: stigma length (five), style length (three), stigma breadth (two), stigma area (one), and pistil length (three). QTL analysis and correlation studies revealed that these stigma traits were positively correlated and pleiotropic to the stigma length trait. We selected the major-effect QTL qSTGL8.0 conferring long stigma phenotype for further fine mapping and marker-assisted selection. The qSTGL8.0 (~ 3.9 Mb) was fine mapped using newly developed internal markers and was narrowed down to ~ 2.9 Mb size (RM7356–RM256 markers). Further, the flanking markers were validated in a segregating population and in progenies from different genetic backgrounds. The markers PA08-03 and PA08-18 showed the highest co-segregation with the stigma traits. The qSTGL8.0 was introgressed into two cytoplasmic male sterile (CMS) lines, IR58025A and IR68897A, by foreground, background, and trait selection approaches. The qSTGL8.0 introgression lines in CMS backgrounds showed a significantly higher seed setting rate (2.5–3.0-fold) than the original CMS lines in test crosses with their corresponding maintainer lines. The newly identified QTLs especially qSTGL8.0, will be quite useful for increasing out-crossing rate and this will contribute to increase seed production and decrease seed cost.

Comparison of wild rice (Oryza longistaminata) tissues identifies rhizome-specific bacterial and archaeal endophytic microbiomes communities and network structures.

Compared with root-associated habitats, little is known about the role of microbiota inside other rice organs, especially the rhizome of perennial wild rice, and this information may be of importance for agriculture. Oryza longistaminata is perennial wild rice with various agronomically valuable traits, including large biomass on poor soils, high nitrogen use efficiency, and resistance to insect pests and disease. Here, we compared the endophytic bacterial and archaeal communities and network structures of the rhizome to other compartments of O. longistaminata using 16S rRNA gene sequencing. Diverse microbiota and significant variation in community structure were identified among different compartments of O. longistaminata. The rhizome microbial community showed low taxonomic and phylogenetic diversity as well as the lowest network complexity among four compartments. Rhizomes exhibited less phylogenetic clustering than roots and leaves, but similar phylogenetic clustering with stems. Streptococcus, Bacillus, and Methylobacteriaceae were the major genera in the rhizome. ASVs belonging to the Enhydrobacter, YS2, and Roseburia are specifically present in the rhizome. The relative abundance of Methylobacteriaceae in the rhizome and stem was significantly higher than that in leaf and root. Noteworthy type II methanotrophs were observed across all compartments, including the dominant Methylobacteriaceae, which potentially benefits the host by facilitating CH4-dependent N2 fixation under nitrogen nutrient-poor conditions. Our data offers a robust knowledge of host and microbiome interactions across various compartments and lends guidelines to the investigation of adaptation mechanisms of O. longistaminata in nutrient-poor environments for biofertilizer development in agriculture.

Assessment of Genetic Diversity of the Wild Rice (Oryza longistaminata) Populations in Tanzania Using Microsatellite Markers

The genetic diversity of 132 samples of the perennial wild rice (Oryza longistaminata) populations from selected districts (Bagamoyo, Kibaha, Kilombero and Mbarali) in Tanzania was evaluated using twenty eight microsatellite markers. Genomic DNA was extracted using standard protocols. Polymerase Chain Reaction (PCR) was carried out in a total reaction volume of 10 μL, using Touchdown protocol. It was found that all 28 microsatellite markers generated polymorphic patterns, with average Polymorphic Information Content (PIC) value of 0.631. Moreover, a total of 243 alleles were detected by the 28 markers, with average of 8.68 alleles per marker. The percentages of genetic variations among and within populations were 10% and 90%, respectively, implying that there was more gene flow among populations than within populations. Furthermore, the O. longistaminata population from Kilombero had highest genetic diversity followed by population from Mbarali, while the lowest genetic diversity was recorded in the population from Kibaha. Generally the populations from Kilombero, Mbarali and Bagamoyo were found to have relatively high genetic diversity, hence have potential to be used in rice breeding. In situ conservation of this species is recommended, and it can be achieved by conserving all areas which harbour populations with high levels of genetic diversity.
 Keywords: Genetic diversity; Microsatellites; SSR Markers; Oryza longistaminata; Wild rice;

Molecular and Morphological Divergence of Australian Wild Rice.

Two types of perennial wild rice, Australian Oryza rufipogon and a new taxon Jpn2 have been observed in Australia in addition to the annual species Oryza meridionalis. Jpn2 is distinct owing to its larger spikelet size but shares O. meridionalis-like morphological features including a high density of bristle cells on the awn surface. All the morphological traits resemble O. meridionalis except for the larger spikelet size. Because Jpn2 has distinct cytoplasmic genomes, including the chloroplast (cp), cp insertion/deletion/simple sequence repeats were designed to establish marker systems to distinguish wild rice in Australia in different natural populations. It was shown that the new taxon is distinct from Asian O. rufipogon but instead resembles O. meridionalis. In addition, higher diversity was detected in north-eastern Australia. Reproductive barriers among species and Jpn2 tested by cross-hybridization suggested a unique biological relationship of Jpn2 with other species. Insertions of retrotransposable elements in the Jpn2 genome were extracted from raw reads generated using next-generation sequencing. Jpn2 tended to share insertions with other O. meridionalis accessions and with Australian O. rufipogon accessions in particular cases, but not Asian O. rufipogon except for two insertions. One insertion was restricted to Jpn2 in Australia and shared with some O. rufipogon in Thailand.

Cellular and proteomic events associated with the localized formation of smut-gall during Zizania latifolia–Ustilago esculenta interaction

The perennial wild rice Zizania latifolia is confined in the swampy habitat and wetland of the Indo-Burma biodiversity hotspot of India and infection by the biotrophic fungus Ustilago esculenta is hallmarked by swellings that develop to form localized smut-gall at the topmost internodal region. The cellular and proteomic events involved in the non-systemic colonization of Z. latifolia by U. esculenta leading to smut-gall formation is poorly understood. Proteins were extracted from the smut-gall region at the topmost internodal region below the apical meristematic tissue from the infected and uninfected parts of Z. latifolia. By combining transmission electron microscopy (TEM) and fluorescent microscopy (FM), we showed that U. esculenta hyphal morphological transitions and movement occurred both intercellularly and intracellularly while sporulation occurred intracellularly in selective cells. Following proteome profiling using two dimensional SDS-PAGE at different phenological phases of smut-gall development and U. esculenta infection, differentially expressed proteins bands and their relative abundance were detected and subjected to liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. Importantly, the fungus explores at least 7 metabolic pathways and 5 major biological processes to subdue the host defense and thrive successfully on Z. latifolia. The fungus U. esculenta produces proteases and energy acquisition proteins those enhance it's defensive and survival mode in the host. The identified differentially regulated proteins shed-light into why inflorescence is being replaced by bulbous smut-gall at late stages of the disease, as well as the development of resistance in some Z. latifolia plants against U. esculenta infection.

Diverse genetic variation in maternal lineages with high heterogeneity among in situ-conserved wild rice (Oryza rufipogon Griff.) developed in Thailand.

Wild rice, Oryza rufipogon, is a genetic resource that can be used to improve cultivated rice, but its populations are now decreasing in terms of both size and number. Extensive research on wild rice has been conducted in Thailand, where two in situ conservation sites have been preserved in natural areas where perennial wild rice predominates. The genetic structure of wild rice populations was investigated by examining both the chloroplast and nucleus genomes at sites of in situ conservation site in Thailand. One accession from an in situ-conserved site was re-sequenced against the chloroplast genome of O. sativa cv. ‘Nipponbare’ to develop chloroplast insertion/deletion (cpINDEL) markers. These cpINDEL markers revealed unique maternal lineages in the in situ-conserved populations upon comparison with other Asian wild rice accessions. Diverse genetic variation was also detected with SSR markers throughout the genome. Three populations differed from each other and also within single populations. The sub-populations within an in situ-conserved population showed a complex population structure due to their multiple maternal lineages and relatively higher number of haplotypes when they maintained a relatively large population size. Such a heterogeneous population would serve as a unique gene pool for rice breeding.

English

The Zizania latifolia Griseb. Turcz. ex Stapf., a perennial wetland wild rice species get infected by a basidiomycetous fungus Ustilago esculenta Henn that produces gall. Here we report the morphogenesis behaviour of this plant during gall transformation. The identity of Z. latifolia and U. esculenta were confirmed by comparing microsatellite and Internal Transcribed Spacer region of nuclear ribosomal DNA sequence with the public database. U. esculenta infection transforms the Z. latifolia into two distinct morphotypes such as gall forming and non-gall forming. The non-gall bearing morphotype exhibited pinkish microporous lamellar discs (15-20 numbers) filled with mycelia in the internodal spaces. Whereas the gall bearing morphotype fuses 3-4 nodes into compact spindle shaped hypertrophic tissue measuring 2.5 cm diameter x 8-10 cm length tapering at the tip end where dark brown coloured teliospores are deposited in linear sori. In vitro culture of lamellar discs and teliospores in Potato Sucrose Agar medium initially develops white colony 2.6- 4.0 cm diameter later turned into yellowish brown after 7 -10 days and subsequent sporulation within 8-12 days. Spherical sporangium of 28 µm diameter developed on long sporangiophore 7 µm diameter filled with large number of spores 1-1.5 µm in diameters. The unsuccessful sporulation of Ustilago even after infection failed to develop gall in the host plants behave normal life cycle and are not consumed. The spore along with hypertrophic soft tissue is consumed as vegetable in the oriental countries. Key words: Manchurian wild rice, teliospore, microsatellite.

Investigation on the biotrophic interaction of Ustilago esculenta on Zizania latifolia found in the Indo-Burma biodiversity hotspot

Ustilago esculenta is a uniquely flavored biotrophic smut fungus that forms a smut gall on the top internodal region of Zizania latifolia, a perennial wild rice found in the Indo-Burma biodiversity hotspot. The smut gall is an edible vegetable locally called “kambong” in Manipur, India. The life cycle of the fungus was studied in vitro and its biotrophism was observed during different stages of the plant growth starting from the bud stage to decaying stage using light, fluorescent and electron microscopy. The size of the smut gall and the number of internodes below the apical smut gall varied significantly (P < 0.05). Examination of various parts of infected plants using culture methods, microscopy and polymerase chain reaction revealed that Ustilago esculenta colonized Zizania latifolia in a non-systemic manner. Spores and fragmented hyphae of U. esculenta were present in the rhizome of infected plant throughout the year, but shoot interiors were without any fungal structures from April until September. The smut region of infected plants in early September to December were heavily sporulated with fragmented hyphae, while the nodal regions of infected plants had no spores and fragmented hyphae. Hyphae and spores were also absent in the internodes and membranes aboveground up to smut region of infected plants but were present in the old rhizomes.

A systems-wide comparison of red rice (Oryza longistaminata) tissues identifies rhizome specific genes and proteins that are targets for cultivated rice improvement.

BackgroundThe rhizome, the original stem of land plants, enables species to invade new territory and is a critical component of perenniality, especially in grasses. Red rice (Oryza longistaminata) is a perennial wild rice species with many valuable traits that could be used to improve cultivated rice cultivars, including rhizomatousness, disease resistance and drought tolerance. Despite these features, little is known about the molecular mechanisms that contribute to rhizome growth, development and function in this plant.ResultsWe used an integrated approach to compare the transcriptome, proteome and metabolome of the rhizome to other tissues of red rice. 116 Gb of transcriptome sequence was obtained from various tissues and used to identify rhizome-specific and preferentially expressed genes, including transcription factors and hormone metabolism and stress response-related genes. Proteomics and metabolomics approaches identified 41 proteins and more than 100 primary metabolites and plant hormones with rhizome preferential accumulation. Of particular interest was the identification of a large number of gene transcripts from Magnaportha oryzae, the fungus that causes rice blast disease in cultivated rice, even though the red rice plants showed no sign of disease.ConclusionsA significant set of genes, proteins and metabolites appear to be specifically or preferentially expressed in the rhizome of O. longistaminata. The presence of M. oryzae gene transcripts at a high level in apparently healthy plants suggests that red rice is resistant to this pathogen, and may be able to provide genes to cultivated rice that will enable resistance to rice blast disease.

Population structural analysis of an &lt;i&gt;in-situ&lt;/i&gt; conservation site for wild rice in Laos

An in-situ conservation site in Laos for a mixture of annual and perennial wild rice, LV27, which is a single swamp with an observation pier has been developed. In order to develop a strategy for evaluation of natural resources, systematic leaf sampling has been conducted and their genetic characteristics measured with 16 SSR loci. In order to determine population structure, a small number of individuals localized together were regarded as sub-populations belonging to a single mother population. Annual individuals were clustered at particular peripheral areas of the pond. Perennial individuals were close by and growing within deeper pond water. Scores of observed heterozygosity (Ho) were not significantly different between annual and perennial sub-populations, but relatively lower in annual ones. Genetic distance among annual and perennial sub-populations in close juxtaposition at peripheral sites showed that annuals were clustered against perennials. In addition, comparison of perennial sub-populations peripheral areas and inside the swamp, found they clustered together and were some distance from annual ones. When the genetic components were compared in detail, private alleles were frequently found in annual plants, suggesting there might be restriction of gene flow between annual and perennial types. Partitions of deep water perennial sub-populations identified private alleles in particular areas, suggesting there were some areas with unique polymorphisms. Combining peripheral perennial sub-populations led to the disappearance of most private alleles which implied there is frequent gene flow among perennial sub-populations. This in-situ conservation site allowed us to observe the succession of populations and also to research detailed population structure of a typical wild population and this found wild rice genetic structure in this single swamp is complex. The data obtained will provide valuable insight about how to evaluate wild populations genetically and how to deal with such populations as field collections.

Analysis of ESTs from a Normalized cDNA Library of the Rhizome Tip of Oryza longistaminata

Oryza longistaminata, a perennial wild rice species with an AA genome, is characterized by the presence of rhizomatous stems. The rhizomatous trait in rice was previously shown to be quantitatively controlled by many genes, but the molecular mechanism related to rhizome development is still unknown. In the present study, expressed sequence tags (ESTs) generated from rhizome tips of O. longistaminata were collected and analyzed. A total of 10,283 complimentary deoxyribunucleic acid clones were randomly sequenced, which generated 10,136 raw sequences, and finally, 4,419 unisequences with diverse functional categories were generated. These unisequences were mapped onto the Oryza sativa genome, which revealed that 4,285 (96.97%) and 4,151 (93.94%) of the unisequences were alignable to the japonica and indica genomic sequences, respectively, with >80% sequence identity. Additionally, 41 unisequences showed four typical types of alternative splicing patterns. More than 600 simple sequence repeats were identified in these unisequences. A subset of unisequences were physically colocalized onto rhizome-related quantitative trait locus intervals in rice and sorghum, and one gene, OLRR1, was further confirmed to be enriched in the rhizome tip and young leaf by real-time polymerase chain reaction and in situ hybridization. Unisequences reported in this study provide valuable data for molecular dissection of the rhizomatous growth habit in O. longistaminata.

Identification of rhizome-specific genes by genome-wide differential expression analysis in Oryza longistaminata.

BackgroundRhizomatousness is a key component of perenniality of many grasses that contribute to competitiveness and invasiveness of many noxious grass weeds, but can potentially be used to develop perennial cereal crops for sustainable farmers in hilly areas of tropical Asia. Oryza longistaminata, a perennial wild rice with strong rhizomes, has been used as the model species for genetic and molecular dissection of rhizome development and in breeding efforts to transfer rhizome-related traits into annual rice species. In this study, an effort was taken to get insights into the genes and molecular mechanisms underlying the rhizomatous trait in O. longistaminata by comparative analysis of the genome-wide tissue-specific gene expression patterns of five different tissues of O. longistaminata using the Affymetrix GeneChip Rice Genome Array.ResultsA total of 2,566 tissue-specific genes were identified in five different tissues of O. longistaminata, including 58 and 61 unique genes that were specifically expressed in the rhizome tips (RT) and internodes (RI), respectively. In addition, 162 genes were up-regulated and 261 genes were down-regulated in RT compared to the shoot tips. Six distinct cis-regulatory elements (CGACG, GCCGCC, GAGAC, AACGG, CATGCA, and TAAAG) were found to be significantly more abundant in the promoter regions of genes differentially expressed in RT than in the promoter regions of genes uniformly expressed in all other tissues. Many of the RT and/or RI specifically or differentially expressed genes were located in the QTL regions associated with rhizome expression, rhizome abundance and rhizome growth-related traits in O. longistaminata and thus are good candidate genes for these QTLs.ConclusionThe initiation and development of the rhizomatous trait in O. longistaminata are controlled by very complex gene networks involving several plant hormones and regulatory genes, different members of gene families showing tissue specificity and their regulated pathways. Auxin/IAA appears to act as a negative regulator in rhizome development, while GA acts as the activator in rhizome development. Co-localization of the genes specifically expressed in rhizome tips and rhizome internodes with the QTLs for rhizome traits identified a large set of candidate genes for rhizome initiation and development in rice for further confirmation.

Molecular Analysis of Utility of a Retrotransposon, p-SINE1-r2 in the Asian Wild Rice and Weedy Rice Populations

The distribution of a retrotransposon, p-SINE1-r2 located at the waxy locus was analyzed by the PCR assay in the perennial wild rice (Oryza rufipogon) which inhabited in four isolated and six disturbed populations and in the weedy rice population. The level of clonality of the wild rice species was determined in populations subject to level of water supply and another disturbance. The results showed that all four isolated populations carried the genotype (-/-) and (-/+), while three genotypes (-/-), (-/+) and (+/+) was found on the six populations which grown near by rice fields. This finding was strongly supported the idea that the original wild rice populations of O. rufipogon exhibited prominent genotype (-/-) and (-/+) and mainly propagated by vegetative reproduction and the allele (+) which found in the wild rice plant with the genotype (+/+) may originated from gene flow from cultivated rice to wild rice. Weedy rice accessions used in this study showed the three genotypes based on this DNA locus. The distribution of this DNA locus in wild rice and weedy rice populations were deviated from the Hardy-Weinberg equilibrium. The perennial wild rice populations were annually under season drought (March to May of the year in Thailand, Laos and Cambodia), they tended to have small size clones with relatively high clonal diversity (i.e., number of genotypes), except for the population from Cambodia, which carried only the genotype (-/+). Although DNA maker used to detect genetic variation at population levels is too small, but this locus is very sensitive enough to be a useful indicator for genetic variation at the population level.

Ultrastructure of Oryza glumaepatula, a wild rice species endemic of tropical America.

Orv'za gluniaepatula is a perennial wild rice species, endemic to tropical America, previously known as the Latin American race of Orrza rufipogon. In Costa Rica, it is found in the northern region of the country, mainly in the wetland of the Medio Queso River, Los Chiles, Alajuela. It is diploid, of AA type genome and because of its genetic relatedness to cultivated rice it is included in the O. saliva complex. We describe the ultrastructure of leaf blade, spikelet, ligule and auricles. Special emphasis is given to those traits of major taxonomic value for O. glumaepatula and to those characters that distinguish this species from O. rufipogon and O. sativa. O. glumaepatula has a leaf blade covered with tombstone-shaped, oblong and spheroid epicuticular wax papillae. It has diamond-shaped stomata surrounded by spherical papillae, rows of zipper-like silica cells, bulky prickle trichomes of ca. 40 microm in length and small hirsute trichomes of ca. 32 tpm in length. The central vein is covered with large, globular papillae of ca. 146 microm in length, a characteristic that distinguishes this species from O. rufipogon and O. sativa. The border of the leaf blade exhibits a row of even-sized bulky prickle trichomes of ca. 42.5 microm in length. Auricles have attenuated trichomes of ca. 5.5 mm in length on the edges and small bicellular trichomes of 120 microm in length on the surface. The ligule has a large number of short attenuated trichomes on its surface of 100 microm in length. These latter two traits have important taxonomic value since they were found in O. glumaepatula but not found in O. sativa or in O. rufipogon. The spikelet has the typical morphology of the Oryza genus. Fertile lemmas have abundant spines, a trait shared with O. rufipogon but not with O. sativa. The sterile lemmas are wing-shaped with serrated borders, a characteristic that distinguishes this species from O. rufipogon and O. sativa. All the ultrastructure characters observed in O. glumaepatula from Costa Rica are also common to the specimens from Brazil.

Variations of Floral Traits in Asian Cultivated Rice (Oryza sativa L.) and its Wild Relatives (O. rufipogon Griff.)

To clarify the inter- and intraspecific variations of floral traits in rice, we investigated eleven traits related to pistil, stamen and glume using 128 Asian cultivated rice (Oryza sativa L.) accessions including 72 Indica and 56 Japonica type accessions, and 53 wild rice (O. rufipogon Griff.) accessions including 32 perennial and 21 annual ecotype accessions. We examined the results from three specific levels: intraspecific variation between perennial and annual ecotypes of wild rice, interspecific variation between cultivated rice and wild rice, and intraspecific variation between Indica and Japonica type cultivars. The annual wild rice accessions exhibited a shorter stigma and anther than the perennial wild rice ones. The cultivated rice accessions showed a lower stigma exsertion, shorter stigma, shorter anther, and thicker and wider lemma and palea than the wild rice accessions. These floral traits of cultivated rice are considered to play an important role in selfing and high seed production. None of the floral traits showed distinct differences between the Indica and Japonica type accessions in cultivated rice, although the Indica type accessions tended to display a slenderer stigma and glume than the Japonica type accessions. It is suggested that the varietal differentiation into the Indica and Japonica types is not likely to be related to genetic variations of floral traits. We clarified the differences in floral traits between annual and perennial ecotypes of wild rice, between cultivated rice and wild rice, and between the Indica and Japonica type cultivars, and discussed the relationship between genetic variations of floral traits and domestication and varietal differentiation in rice.

Pollen competition between cultivated and wild rice species (Oryza sativaandO. rufipogon)

Summary Post‐pollination competition is reported here in cultivated rice (Oryza sativa) and a perennial wild rice (O. rufipogon) to investigate the occurrence of crop‐to‐wild gene flow. Wild and cultivated rice (variety Minghui‐63) were grown in a common garden in Hunan province, China, and crop‐specific genetic markers were used to detect hybridization following hand‐pollinations. Using 11 sequential pollination treatments, the effects of the relative timing of pollination on the success of foreign pollen was investigated. Foreign pollen from the crop resulted in lower pollen germination, fewer pollen tubes per style, and a significant reduction of seed set, demonstrating a disadvantage of foreign pollen even in the absence of pollen competition. When 1 : 1 pollen mixtures were applied, only 2% of the resulting seeds were hybrids, revealing a much stronger disadvantage of foreign pollen when competing with conspecific pollen. Testing the effects of the relative timing of pollination on the success of foreign pollen suggested that conspecific pollen is often more successful than foreign pollen. Nonetheless, hybridization is possible following the deposition of pollen mixtures, especially when foreign pollen arrives earlier than conspecific pollen. Pollen competition between wild and cultivated rice could slow the rate of crop‐to‐wild gene flow, but even if pollen competition was ubiquitous it would not prevent gene flow from the crop.