Urvillei Steud Research Articles

Discovery of natural Paspalum L. (Poaceae) triploid hybrids near sympatric populations of Paspalum urvillei Steud. and species of Paniculata group in northeastern Argentina

Discovery of natural Paspalum L. (Poaceae) triploid hybrids near sympatric populations of Paspalum urvillei Steud. and species of Paniculata group in northeastern Argentina

Understanding the extent of phenotypic variability in accessions of Paspalum urvillei Steud. from the USDA NPGS

The objective of this study was to investigate the phenotypic variability in Paspalum urvillei Steud. related to twelve zootechnical traits to better understand the diversity of 41 accessions from the USDA GRIN platform from seven countries. First, we performed a structure inference based on the phenotypic data, identifying two structure groups, and the majority of Brazilian accessions belonged to the first group. Then, we performed principal component analysis and principal coordinate analysis, making Violin plots for each trait within each structure group. Next, we performed spatial clustering of the accessions and utilized an unweighted pair group method with arithmetic mean clustering. In brief, the Brazilian P. urvillei breeding programs may be successful by importing USDA germplasm resources from the second phenotypic structure group.

Tests of Hexazinone and Tebuthiuron for Control of Exotic Plants in Kauai, Hawaii

Non-native plant species have become serious pests in Hawaii’s delicate island ecosystems. It is necessary to control invasive plants. The herbicides hexazinone and tebuthiuron were evaluated for defoliation efficacy to control several major invasive plants and for non-target effects on native plants at Site I in a rainforest at 1200 m elevation and Site II in a mesic area at 640 m elevation on the island of Kauai, Hawaii. The invasive weed species in the sites included daisy fleabane (Erigeron karvinskianus DC.), faya tree (Myrica faya Ait.), strawberry guava (Psidium cattleyanum Sabine), banana passion fruit (Passiflora mollissima Bailey), vaseygrass (Paspalum urvillei Steud.), and highbush blackberry (Rubus argutus Link. 1822). Native plants included ohia lehua (Metrosideros polymorpha Gaudich.), naupaka (Scaevola cerasifolia Labill.), pilo (Hedyotis mannii), hona (Urera glabra (Hook. & Arn.)), aalii (Dodonaea viscosa Jacq.), and amau (Sadleria sp.). The results showed that broadcast applications of hexazinone granules and tebuthiuron pellets were effective on some of those invasive species. Herbicidal tolerance varied among the native species. For example, D. viscosa showed high tolerance to hexazinone. S. cerasifolia was susceptible to hexazinone, but not to tebuthiuron. The inconsistent defoliation of Sadleria sp. occurred among different applications rates of the two herbicides. M. polymorpha, particularly when it was small, could tolerate hexazinone and tebuthiuron. U. glabra was severely injured by the two herbicides. H. mannii was moderately tolerant to hexazinone, but fairly sensitive to tebuthiuron. The invasive loblolly pine (Pinus taeda L.) was highly tolerant to hexazinone, but was very sensitive to tebuthiuron. M. faya was very sensitive to hexazinone, but very tolerant to tebuthiuron. P. cattleyanum was sensitive to both herbicides. Six and nine months after hexazinone and tebuthiuron treatment, respectively, native plants were transplanted into the Sites to observe injury from residual herbicides. Approximately less than 10% mortality was observed for the out-planted native species three months after planting (MAP), indicating that the native species showed less injury in the early period of transplant. The mortality of the three endangered species Kauai hau kuahiwi (Hibiscadelphis distans), Kauai delissea (Delissea rhytidosperma H.Mann) and kawawaenohu (Alsinidendron lynchnoides), however, increased as the MAP increased. Overall, broadcast treatments of hexazinone and tebuthiuron at rates higher than 1 kg active ingredient per hectare would be problematic. The dissipation half-life values of hexazinone and tebuthiuron in the 1-15 cm layer of soils at the two sites were approximately 7 days and greater than 180 days, respectively.

Effects of the diploidisation process upon the 5S and 35S rDNA sequences in the allopolyploid species of the Dilatata group of Paspalum (Poaceae, Paniceae)

The Dilatata group of Paspalum includes species and biotypes native to temperate South America. Among them, five sexual allotetraploids (x = 10) share the same IIJJ genome formula: P. urvillei Steud, P. dasypleurum Kunze ex Desv., P. dilatatum subsp. flavescens Roseng., B.R. Arrill. & Izag., and two biotypes P. dilatatum Vacaria and P. dilatatum Virasoro. Previous studies suggested P. intermedium Munro ex Morong & Britton and P. juergensii Hack. or related species as their putative progenitors and donors of the I and J genome, respectively, and pointed to a narrow genetic base for their maternal origin. It has not yet been established whether the various members of the Dilatata group are the result of a single or of multiple allopolyploid formations. Here, we aimed to study the evolutionary dynamics of rRNA genes after allopolyploidisation in the Dilatata group of Paspalum and shed some light into the genome restructuring of the tetraploid taxa with the same genome formula. We used double target fluorescence in situ hybridisation of 35S and 5S rDNA probes and sequenced the nrDNA internal transcribed spacer (ITS) region. A variable number of loci at the chromosome ends were observed for the 35S rDNA, from 2 to 6, suggesting gain and loss of sites. For the 5S rDNA, only one centromeric pair of signals was observed, indicating a remarkable loss after polyploidisation. All ITS sequences generated were near identical to the one found for P. intermedium. Although sequences showed a directional homogeneisation towards the putative paternal progenitor in all tetraploid species, the observed differences in the number and loss of rDNA sites suggest independent ongoing diploidisation processes in all taxa and genome restructuring following polyploidy.

Modelling seed retention curves for eight weed species on clothing

AbstractHumans can unintentionally disperse plant propagules (herein referred to as seeds) including weed seeds from clothing when hiking. There is limited experimental or observational information, however, about unintended human‐mediated seed dispersal, particularly from different types of clothing. We experimentally assessed the probability of seed detaching from socks and trousers along a 5 km standardized route for eight common environmental weeds: Bidens pilosa L., Chloris gayana Kunth., Conyza canadensis L., Cynodon dactylon L., Drymaria cordata (L.) Willd. ex Schult., Poa annua L., Paspalum urvillei Steud. and Sporobolus elongatus R.Br. Seed detachment varied among species on both types of clothing, but seeds more easily detached from trousers than socks. When different models were fitted to the data, a three‐parameter generalized exponential model with curves provided the best fit. The curves were leptokurtic, with peak close to the seed source and a long flat tail, which indicates that most seeds dispersed from clothing fall close (within 5 m) to the point of attachment with only a small proportion of seeds dispersed over long distances. Combining attachment and detachment data for the same species, we estimated the actual numbers of seeds potentially dispersed over a hike of 5 km. The study indicates that most seeds are likely to be dispersed at the start of walks, although the actual number of seeds will vary depending on several factors such as the behaviour of the hiker and the amount of weed seeds present at the start of the walk. Those few seeds dispersed much further may, however, be more important in terms of plant invasions. Covering socks with gaiters and avoiding walking through weedy areas such as road edges and car parks before starting walks could minimize the risk of seeds attaching to clothing and hence being dispersed.

Associations between host plant concentrations of selected biochemical nutrients and Mexican rice borer, Eoreuma loftini, infestation

AbstractThe Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an economic pest of sugarcane (Saccharum spp. hybrids) and other graminaceous host crops, and it attacks grassy weeds. Oviposition preference has been known to be for plants with leaves that form folds. This study is the first to associate the nutritional quality of crop and forage plant hosts with Mexican rice borer injury. Three experiments were conducted to determine the levels of selected biochemical nutrients, including free amino acids and sugars, in four grass weeds [barnyardgrass, Echinochloa crus‐galli (L.); broadleaf signalgrass, Urochloa platyphylla (Munro ex C. Wright); johnsongrass, Sorghum halepense (L.) Pers.; and Vasey's grass, Paspalum urvillei Steud.], a forage grass [sudangrass, Sorghum bicolor (L.) Moensch spp. drummondi (Nees ex Steud.) de Wet & Harlan], three crop species [maize, Zea mays L.; sorghum, Sorghum bicolor (L.) Moench; and sugarcane, Saccharum spp.], and a sorghum‐sudangrass forage hybrid (all Poaceae). Of 16 free amino acids detected among plants in the first two experiments, only high accumulations of free histidine in sudangrass and maize were associated with increased infestations by Mexican rice borer larvae. In all three experiments, high levels of fructose were associated with heightened Mexican rice borer infestation. Ramifications of these findings on the potential dispersal of this invasive pest in the USA and possible applications of fructose in baits are discussed.

Morphology and anatomy of the diaspores and seedling of Paspalum (Poaceae, Poales)

The knowledge regarding of the diaspore and post-seminal development of Paspalum L. is important for grassland biodiversity conservation, based on their representativeness and genetic improvement of forage. The morphology of the diaspore and the post-seminal development of Paspalum dilatatum Poir. (rhizomatous), P. mandiocanum Trin. var. subaequiglume Barreto (stoloniferous), P. pumilum Nees. (decumbent caespitose) and P. urvillei Steud. (erect caespitose) was described to distinguish species with different growth forms and to survey the characters useful for taxonomy. P. dilatatum differs by presenting oval diaspores larger than the others, with five prominent nerves and trichomes; P. urvillei presents diaspores with one central nerve that is more developed than the two lateral nerves and trichomes; P. mandiocanum var. subaequiglume presents diaspores with trichomes only in the margin; and P. pumilum differs by presenting glabrous diaspores. The caryopsis involves the seed that presents the differentiated embryo and disposed laterally, an elliptical hilum in all of the studied species and a rostellum in P. dilatatum and P. mandiocanum var. subaequiglume. The post-seminal development is similar in the four species and begins with germination that is marked by the emergence of the coleorhiza, followed by the coleoptile. These characteristics are common to other Poaceae previously studied, indicating a pattern to the family and do not distinguish the growth forms.

First records of Paspalum notatum Flüggé and P. urvillei Steud. (Poaceae) in Korea

While collecting Poaceae weeds at Jeju-do, we found two unrecorded species of the Paspalum, P. notatum Fl<TEX>$\ddot{u}$</TEX>gg<TEX>$\acute{e}$</TEX> and P. urvillei Steud. We provide the descriptions and illustrations of both species. Key to the newly recorded species and related taxa of Korean Paspalum is also presented.

Oviposition and larval development of a stem borer, Eoreuma loftini, on rice and non‐crop grass hosts

AbstractA greenhouse study compared oviposition preference and larval development duration of a stem borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), on rice, Oryza sativa L. cv Cocodrie (Poaceae), and four primary non‐crop hosts of Texas Gulf Coast rice agroecosystems. Rice and two perennials, johnsongrass, Sorghum halepense (L.) Pers., and vaseygrass, Paspalum urvillei Steud. (both Poaceae), were assessed at three phenological stages. Two spring annuals, brome, Bromus spec., and ryegrass, Lolium spec. (both Poaceae), were assessed at two phenological stages. Phenological stages represented the diversity of plant development stages E. loftini may encounter. Plant fresh biomass, dry biomass, and sum of tiller heights were used as measures of plant availability. Accounting for plant availability, rice was preferred over non‐crop hosts, and intermediate and older plants were preferred over young plants. Johnsongrass and vaseygrass were 32–60% as preferred as rice when considering the most preferred phenological stages of each host. Brome and ryegrass received few or no eggs, respectively. Eoreuma loftini larval development (in degree days above developmental threshold temperatures) was fastest on rice and slowest on johnsongrass and vaseygrass. Development duration was only retarded by plant stage on young rice plants. Foliar and stem free amino acid concentrations were determined to help provide insights on the mechanisms of E. loftini oviposition preference and developmental performance.

Feasibility of Using an Alternative Larval Host and Host Plants to Establish &lt;I&gt;Cotesia flavipes&lt;/I&gt; (Hymenoptera: Braconidae) in the Temperate Louisiana Sugarcane Ecosystem

Attempts to establish Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Louisiana sugarcane fields to control the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) have been unsuccessful. Experiments were conducted to investigate the feasibility of using an alternative larval host and host plants to overcome barriers preventing establishment. In addition, we evaluated C. flavipes' ability to search for D. saccharalis in sugarcane without above-ground internodes. Diatraea evanescens Dyar (Lepidoptera: Crambidae) was investigated as an alternative host for C. flavipes. Cotesia flavipes was reared for five generations on D. evanescens without any indication of diminishing fitness as measured by days to parasite pupation and average cocoon mass weight. However, there was a significant reduction in percent parasitism, cocoon mass weight, and percent emergence when C. flavipes parasitized D. evanescens as compared with D. saccharalis, resulting in a 75% reduction in the gross reproductive rate (R(0)). Greenhouse studies indicated little difference in parasitism of D. saccharalis on the weed hosts johnsongrass, Sorghum halepense (L.), and vaseygrass, Paspalum urvillei Steud. However, when planted as refuge plots, we found it difficult to establish infestations of D. saccharalis in either of these hosts, or in two energy sugarcanes. After 3 yr of infesting host plants and releasing parasitoids only one parasitized D. saccharalis larvae was recovered within the johnsongrass refuge. Diatraea evanescens readily established in vaseygrass; however, these larvae appear inaccessible to C. flavipes. In contrast, parasitism of D. saccharalis by C. flavipes infesting young sugarcane was 30%.

Monitoring and First Discovery of the Mexican Rice BorerEoreuma loftini(Lepidoptera: Crambidae) in Louisiana

The Mexican rice borer, Eoreuma loftini (Dyar), is native to Mexico, and has been reported in the Mexican states of Baja California, Colima, Hustecas, Jalisco, Michoacan, Nayarit, Nuevo Leon, Oaxaca, San Luis Potosi, Sinaloa, Sonora, Tamaulipas, Veracruz, and Yucatan (Morill 1925; Van Zwaluwenburg 1926; Riess 1981; Johnson 1984; Rodriguez-del-Bosque et al. 1989; ReayJones et al. 2007). Eoreuma. loftini was originally described by Dyar (1917) as a member of the genus Chilo Zincken from a specimen collected in Arizona, U.S.A. The species was transferred to Eoreuma Ely by Klots (1970). It has been collected from sugarcane (Saccharum officinarum L.), corn (Zea mays L.), rice (Oryza sativa L.), sorghum (Sorghum bicolor (L.) Moench), and lemongrass (Cymbopogon citrates I flexuosus L.) (Johnson 1984). Weedy grasses including johnsongrass (Sorghum halepense (L.) Pers.), vaseygrass (Paspalum urvillei Steud.), Amazon sprangletop (Leptochloa panicoides (J. Presi) Hitchc), and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) also have been reported as hosts (Reagan et al. 2007). It was first reported in the Lower Rio Grande Valley (LRGV) of Texas, U.S.A. during 1959 when a single larva was detected in sugarcane shipped from Mexico (Johnson 1984). By 1980, E. loftini had established itself as a serious pest in the LRGV and populations subsequently spread into the rice production region of Texas along the Gulf Coast (Johnson & van Leerdam 1981, Browning et al. 1989). From 2000 to 2002, female sex pheromone traps captured E. loftini moths in seven new southeast Texas counties (Reagan et al. 2005; Reay-Jones et al. 2007). During 2002, moths were captured within 100 km of sugarcane in east Texas and within 200 km of sugarcane in Louisiana. By 2004, E. loftini was present in over 75% of the Texas rice growing area and had spread into sugarcane plantings in Chambers County, Texas (Reagan et al. 2005, Reay-Jones et al. 2007). In an attempt to slow the spread of E. loftini into Louisiana, in 1999, the Louisiana Department of Agriculture and Forestry (LDAF) entered into a compliance agreement with the Texas Department of Agriculture which placed restrictions on the entry oiE. loftini infested Texas sugarcane into Louisiana for processing. This agreement required that east Texas sugarcane fields be monitored for E. loftini using pheromone traps. The agreement's conditions also stipulated that a positive E. loftini finding in east Texas sugarcane would automatically trigger the establishment of a one-mile-radius quarantine around that field and sugarcane within that quarantined area could not be shipped into Louisiana. All truckloads of sugarcane destined for Louisiana were required to be tagged and certified as E. loftini free (Reagan et al. 2005). In a proactive effort to monitor the natural spread of E. loftini, LDAF initiated deployment of 12 pheromone traps during fall 1999 at selected sugarcane fields and adjacent to sugarcane processing facilities in Louisiana. The number of traps deployed annually increased from 12 to 40 through 2005. During this timeframe, traps also were placed near rice fields. Beginning in 2005, 35 to 40 traps have been deployed annually. Traps remained in the field from planting of rice (Mar) through harvest of sugarcane (DecJan), and until processing facilities finished milling sugarcane. The detection of E. loftini in 2 east Texas pheromone traps adjacent to sugarcane in 2004 (2-IX2004, 20-IX-2004, 2-X-2004) triggered a one-mileradius quarantine (Reagan et al. 2005). By 2005, E. loftini was widespread in east Texas and all sugarcane from that area was prohibited from entry into Louisiana due to the risk of accidental introduction of E. loftini (Reagan et al. 2007). This prohibition helped to slow the spread of E. loftini movement into Louisiana (Reay-Jones et al. 2008). The pheromone trap monitoring program determined that E. loftini was expanding its range 16.5 km/yr through the Texas rice belt toward Louisiana (Reay-Jones et al. 2007). Based on natural movement, Reay-Jones et al. (2007) predicted that E. loftini would establish in Louisiana during 2008. On 12-XII-2008 one E. loftini adult was detected in each of 2 pheromone traps in Calcasieu Parish (Louisiana, U.S.A.) located approximately 8 km from the Texas border. These traps were adjacent to harvested rice fields approximately 8 km apart. C. Carlton confirmed identifications by examination of male genitalia and com-

Grazing Management and Nitrogen Fertilization Effects on Vaseygrass Persistence in Limpograss Pastures

Vaseygrass (Paspalum urvillei Steud.) is a weed in environments where limpograss [Hemarthria altissima (Poir.) Stapf &amp; Hubb.] is a productive pasture grass. The objective of this study was to determine grazing management and N fertilization effects on persistence of vaseygrass in limpograss pastures on a Pomona sand (sandy, siliceous, hyperthermic Ultic Alaquod). Treatments were arranged in a split‐plot experiment; combinations of grazing method (continuous vs. rotational) and stubble height (15 and 30 cm) were the main plots, and N fertilization (50 and 150 kg N ha−1) was assigned to subplots. Continuous stocking for two grazing seasons reduced vaseygrass cover by 15 percentage units (−3 units for rotational) and increased limpograss cover by 6 units (−8 units for rotational). A stubble height × N rate interaction occurred because at the shortest height and lowest N rate the decline in vaseygrass cover (15 units) and increase in limpograss cover (7 units) were most pronounced. After 2 yr of continuous stocking, vaseygrass stem‐base mass was lower than for rotational stocking (12 vs. 23 g plant−1), and stem‐base (0.40 vs. 0.78 g plant−1) and root (0.46 vs. 0.91 g plant−1) content of total nonstructural carbohydrate (TNC) were lower under continuous compared to rotational stocking, respectively. Grazing to a 15‐ vs. 30‐cm stubble height resulted in lower vaseygrass stem‐base mass (12 vs. 23 g plant−1) and TNC content (0.44 vs. 0.73 g plant−1). Continuous stocking reduced vaseygrass plant mass and density while limpograss cover increased, but careful management of stubble height is required to avoid subsequent invasion by other undesirable species.

Seleção de dieta por bovinos em pastagem cultivada em área de várzea

O trabalho foi realizado em uma área de 3,0ha de várzea, situada no Campus da Universidade Federal de Santa Maria, Rio Grande do Sul (Brasil), cultivada com Lolium multiflorum Lam. e Trifolium repens L, onde se destacavam, também, alguns componentes nativos. O objetivo deste trabalho foi acompanhar, de forma paralela às ações de manejo, a dinâmica da composição botânica da dieta selecionada por bovinos em pastejo, sob o efeito de tratamentos (diferentes doses de P e K) e da sazonalidade. O delineamento experimental foi o completamente casualizado com duas repetições. O método de pastejo adotado foi o contínuo, com lotação fixa e carga variável. No inverno, primavera e verão de 1999/2000, foi determinada a composição botânica da dieta pelo método de análise microhistológica de fezes, através da diferenciação da epiderme foliar de L. multiflorum Lam., T. repens L., e dos componentes nativos Paspalum urvillei Steud., Setaria geniculata (Lam.) Beauv. e Echinochloa spp. Os resultados foram comparados através de testes de aleatorização. A composição botânica da dieta não foi afetada pelos tratamentos impostos à pastagem (P=0,87), mas houve efeito das épocas de amostragem sobre a seleção (P=0,03). As espécies da flora nativa, embora prejudicadas pelo manejo imposto, foram selecionadas pelos animais em pastejo, configurando-se num importante recurso forrageiro.

Canopy Height Effects on Vaseygrass and Bermudagrass Spread in Limpograss Pastures

Potential grass weeds in limpograss [Hemarthria altissima (Poir.) Stapf &amp; Hubb.] pastures include vaseygrass (Paspalum urvillei Steud) and common bermudagrass [Cynodon dactylon (L.) Pers.]. Grazing management is critical to controlling spread of these grasses and maintaining productive limpograss swards, but competition dynamics among these species have not been evaluated under grazing. The objective of this experiment was to determine the effect of grazed canopy height (20, 40, and 60 cm) of continuously stocked limpograss pastures on changes in frequency of occurrence and ground cover of limpograss, vaseygrass, and common bermudagrass and plant density of vaseygrass. Experimental units were 0.5‐ha pastures replicated four times in a completely randomized design. During the 2 yr of grazing, vaseygrass density decreased in all pastures, changing most for the 20‐cm canopy height and least for the 60‐cm canopy height (4.4 vs. 0.4 plants m−2). Changes in vaseygrass cover followed the same trend as density. In contrast, bermudagrass cover increased by seven percentage units if pastures were grazed to a 20‐cm height, but the increase was less for 40‐ and 60‐cm swards. These data show that continuous stocking of limpograss pastures decreased vaseygrass plant density, especially when canopy height was low; however, common bermudagrass invasion was favored by grazing to 20 cm, potentially compromising limpograss persistence. It is concluded that grazing continuously stocked limpograss pastures to approximately 40 cm is effective in decreasing existing populations of vaseygrass while minimizing invasion by common bermudagrass.

Cytology and reproductive behavior of hybrids between Paspalum urvillei and two hexaploid P. dilatatum biotypes

Sexual, tetraploid (2n = 4x = 40) vaseygrass (Paspalum urvillei Steud.) was crossed with two apomictic, hexaploid (2n = 6x = 60) dallisgrass (P. dilatatum Poir.) biotypes (Uruguayan and Uruguaiana) to determine their relationships and the reproductive behavior of the hybrids. One vaseygrass × Uruguayan and two vaseygrass × Uruguaiana hybrids were studied and all had 2n = 5x = 50 chromosomes. The mean pairing meiotic association for the vaseygrass × Uruguayan hybrid was 10.18 I and 19.91 II, and for the two vaseygrass × Uruguaiana hybrids was 10.28 I, 19.82 II, 0.006 III, and 0.01 IV. These findings indicate that the parents of both hybrids have two homologous genomes. Because vaseygrass and Uruguayan dallisgrass have the genome formulas IIJJ and IIJJXX, respectively, their hybrid has the formula IIJJX and the two homologous genomes are the I and J genomes. Likewise, chromosome pairing in the vaseygrass × Uruguaiana hybrids demonstrates that both species have two similar genomes, I and J. The Uruguaiana biotype usually has 8–10 univalents per cell and these result from the failure of some members of the third genome to pair. Thus the Uruguaiana biotype has different forms of the X genome, and its genome formula may be designated as IIJJXX2. Cytologically all three hybrids were facultative apomicts but their uniform F2 progeny indicates that only the apomictic embryo sacs are functional. Seed fertility ranged from 10.8 to 16.2%.Key words: Interspecific hybrids, genomes, chromosome pairing, species relationships, dallisgrass, vaseygrass.

Intra‐ and Interspecific Hybridization between Dallisgrass and Vaseygrass

Two sexual tetraploid (2n = 4x = 40) biotypes of dallisgrass (Paspalum dilatatum Poir.) were crossed with vaseygrass (P. urvillei Steud.) (2n = 4x = 40) to investigate their genomic relations and determine the feasibility of gene exchange between these forage grasses. There are some morphological differences between the dallisgrass biotypes. They are referred to as P. dilatatum (F) and P. dilatatum (V) in this study. These biotypes also were crossed to investigate their relations. Cytologically, P. dilatatum (F), P. dilatatum (V), and P. urvillei behaved as allotetraploids, averaging 19.94, 19.97, and 20 bivalents per metaphase I cell, respectively. Crossability between P. dilatatum (F) and P. dilatatum (V) was 19.2%. The intraspecific hybrids had regular meiotic chromosome pairing, averaging 19.94 bivalents per cell. Thus P. dilatatum (V) apparently has the same genomes (II JJ) as the P. dilatatum (F) biotype. Crossability between P. dilatatum (F) and P. urvillei was low (1.2%). Chromosome pairing in the hybrids was regular averaging 19.96 bivalents per cell, indicating that P. dilatatum (F) and P. urvillei share the same genome formula (II JJ). Seed set in the hybrids was low ranging from 1.4 to 2.1%. Crossability between P. dilatatum (V) and P. urvillei was 19.3%. The hybrids exhibited similar meiotic behavior as the previous hybrids averaging 19.88 bivalents per cell. Fertility was investigated for six P. dilatatum (V) ✕ P. urvillei F1 hybrids and seed set ranged from 0.3 to 18.8% among them. Seed set increased in the F2 and backcross progenies. Some backcross plants exhibited similar seed set as the parental species. Findings from this study strongly implies that gene exchange between tetraploid P. dilatatum biotypes and P. urvillei is possible.

琉球列島のサトウキビ畑における雑草の生理・生態 ＩＶ タチスズメノヒエの生育と種子生産に及ぼす土壌水分の影響

タチスズメノヒエの防除に関する基礎的研究の一環として, 本草種を乾土重に対する土壌水分を20%, 32%, 58%及び64%として1/5,000aワグネルポットで栽培し, 土壌水分と生育・種子生産構造との関係を調査した。1. 草丈は土壌水分の高い処理区ほど伸長し, 成熟期に64%区で最高, 20%区で最低となり, 両区間に著しい差が認められた。分けつ数についてもほぼ同様な結果を得た。2. 生長量形質, すなわち地上部乾物重, 地下部乾物重及び全乾物重はいずれも64%区で最高値を, 32%区で最低値を示し, 両区間に著しい差が認められた。3. 種子生産形質, すなわち個体当たり穂数・穂重, 1穂重及び千粒重についても生長量形質と同様な傾向の結果を得た。4. 有効分けつ率は64%区で最高値を示し, 32%区で最低となった。5. 生長量形質と種子生産形質は土壌水分による差異が著しく, 生長量形質では地上部乾物重の可変性が最も高かった。種子生産形質では個体当たり穂数が変異性は最も高く, 千粒重は最低値を示した。6. 本草種は特に多湿地域において生育・繁茂が盛んになり, その除草作業も高い土壌水分のため十分な効果をあげることは期待できないので, 多湿地域におけるサトウキビ栽培に当たってはこの点を十分に考慮する必要がある。

琉球列島のサトウキビ畑における雑草の生理・生態 ＩＩＩ タチスズメノヒエの生育と種子生産に及ぼすしゃ光の影響

遮光処理 (相対照度100%, 80%, 70%, 50%, 30%) がタチスズメノヒエの生育と種子生産に及ぼす影響を検討し, 次の結果を得た。1. 草丈は遮光度が強まるにしたがって増大したが, 分けつ数は減少した。2. 全乾物重と地上部乾物重はいずれも70%区と80%区で大きな値を示したが, これは葉面積と分けつ数の増大が原因と思われた。3. 種子生産形質は千粒重以外はすべて80%区で増大し, その結果種子生産量はこの処理区において最大となった。4. 本草種は弱遮光条件で生育と種子生産が盛んになるので, 防除は作物の被陰が大きくなる以前に行う必要があると思われる。