Paspalum Species Research Articles

Cytoembryology of Paspalum chaseanum and Sexual Diploid Biotypes of Two Apomictic Paspalum Species

This study was undertaken to determine the cytology, method of reproduction, and flowering behaviour of three Paspalum species. Paspalum plicatulum has long been considered a segmental allotetraploid that reproduces by obligate apomixis with the type being apospory followed by pseudogamy. Paspalum simplex is an apomictic autotetraploid species, while P. chaseanum is a rare species for which no information regarding cytology and reproduction is available. This investigation concerns diploid cytotypes (2n = 2x = 20) of P. plicatulum and P. simplex that were recently collected in subtropical South America. In addition, two accessions of P. chaseanum were also recorded and both had 2n = 2x = 20 chromosomes. Meiosis showed regular bivalent chromosome pairing. Embryological observations indicated that the three species reproduce sexually at the diploid level. Pollen–pistil interaction following self-pollination suggested the presence of a self-incompatibility system responsible for allogamy. The results indicate that P. plicatulum and P. simplex complexes consist of diploid sexual allogamous cytotypes in addition to the known tetraploid apomictic cytotypes. Diploid strains constitute a source of sexuality for plant improvement. Chromosome doubling will likely produce sexual tetraploids to be used as females in crosses with natural apomictic tetraploid biotypes. Since diploid self-incompatible sexual Paspalum plants usually have apomictic tetraploid co-specific counterparts, the self-incompatible diploid P. chaseanum described in this study warrants further exploration for its apomictic counterpart.

Resistance of Paspalum spp. to Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) Larvae

ABSTRACT Development of improved grass cultivars has provided the southern half of the United States with some of its most important pasture grasses. Resistance to larvae of the fall armyworm, Spodoptera frugiperda (J. E. Smith), has been found in several grasses, including bermudagrass (Cynodon spp.), centipedegrass [Ere-mochola ophiuroides (Munro) Hack.], and zoysiagrass (Zoysia spp.). Eighty-one Paspalum spp. were investigated for resistance to larvae of the fall armyworm. Very high levels of antibiosis were discovered in ‘PI 404468’ (Paspalum modestum) and ‘PI 442872’ (Paspalum scrobiculatum). Fall armyworm larvae that were fed P. modestum (‘PI 404468’) or R scrobiculatum (‘PI 442872’) were significantly smaller at 9 d (16 and 13 mg, respectively) than larvae that were fed other species of Paspalum, and larvae reared on diet containing these two grass genotypes failed to develop to pupation.

Cytogenetics and Reproduction of Paspalum dasypleurum and Its Hybrids with P. urvillei and P. dilatatum Ssp. Flavescens

Paspalum dasypleurum has the southernmost distribution of the Paspalum species in South America. It is a sexual, self-fertile tetraploid with 40 chromosomes that pair as 20 bivalents at meiosis. This is the first report concerning its cytology and reproductive behavior. Morphologically, this species belongs to the Dilatata group and was crossed with two other tetraploid taxa of the same group: Paspalum urvillei (Vaseygrass) and Paspalum dilatatum ssp. flavescens (yellow-anthered Dallisgrass), both with the genome formula II JJ. Crossability between P dilatatum ssp. flavescens (female) and P. dasypleurum (male) was 0.8%, and their hybrids showed regular meiotic behavior with 20 bivalents. All hybrids were male-sterile, but approximately 8% of the spikelets set seed after backcrossing with pollen from either parent. Crossability between P. dasypleurum (female) and P. urvillei (male) was 53.9%, and their hybrids had regular meiotic behavior with 20 bivalent at diakinesis and metaphase I. All hybrids had indehiscent anthers, and none produced seed when selfed. Backcrosses to P. dasypleurum set a mean of 4.8% seed, and 18.6% (mean of five F1 plants) to P. urvillei. The regular meiotic chromosome pairing in P. dilatatum ssp. flavescens x P. dasypleurum and P. dasypleurum x P. urvillei hybrids indicated that P. dasypleurum has the I and the J genomes that were previously described for tetraploid biotypes of P dilatatum and for P. urvillei. The ability of the hybrids to produce seed following backcrossing suggests that gene exchange through hybridization may be a feasible method for plant improvement among these species.

Paspalum niquelandiae (Poaceae: Paniceae), a New Species from the Serpentine Outcrops of Central Brazil

Paspalum niquelandiae Filgueiras, a new species of Poaceae from the serpentine outcrops of Niquelindia, a municipality in the Brazilian state of Goils, is described, illustrated, and compared with Paspalum soboliferum Chase, P. humboldtianum Flugge, and P. inconstans Chase. The conservational importance of a serpentine endemic grass flora in central Brazil is briefly discussed. Recent fieldwork carried out in the municipality of Niquelandia, in the Brazilian state of Goias, where serpentine soils have been reported (Brooks et al., 1990), resulted in the description of several new taxa in the Poaceae (Davidse & Filgueiras, 1993; Filgueiras et al., 1993; Filgueiras & Davidse, 1994). A new species of Paspalum L. from the same area is herein described, illustrated, and compared to similar species. Paspalum niquelandiae Filgueiras, sp. nov. TYPE: Brazil. Goils: Municipio de Niquelindia, ca. 14?18'S-48023'W, morro pedregoso, ca. 2 km Leste da localidade de Macedo, planta crescendo entre pedras, pr6ximo a pequena floresta de galeria, ocasional na Area, 19 maio 1993, T. S. Filgueiras & F. C. de A. Oliveira 2461 (holotype, IBGE; isotypes, F, G, ICN, K, MEXU, MG, MO, R, SI, SP, US). Figure 1. Paspalo sobolifero Chase spiculis ellipticis subtiliter pilosis, gluma superiore marginibus ciliatis simile, sed culmis non ramosis, ligula 0.2-0.3 mm longa, laminis 2045 cm longis et 8-22 mm latis, communi rhachidi 9-15 cm longa, gluma superiore ciliis densis, numerosis, coroniformibus abunde differt. Coarse, caespitose perennial. Rhizomes well developed, knotty, covered with cataphylls. Culms 120185 cm tall, erect, unbranched in the vegetative portion, with 5-8 elongated internodes; internodes hollow, stramineous, glabrous; nodes dark, glabrous. Prophyll not seen. Leaves mostly cauline; sheaths strongly striate, glabrescent to pilose in the lower half, becoming papillose-hispid upward, the margins free, both ciliate or one glabrous toward the base; auricles absent; ligule a minute, brown, glabrous membrane, v-shaped, 0.2-0.3 mm long; cilia at the ligular area 5-8 mm long, colorless; blades 20-45 cm long, 8-22 mm wide, flat, lanceolate, glabrescent to papillose-hispid, acuminate apically, the midrib projecting abaxially, the margins serrate-denticulate to ciliate; uppermost blade reduced, minute. Inflorescence of unilateral, ascending racemes, divergent in maturity; peduncle well exserted, 12-22 cm long, glabrous; common rachis 9-15 cm long, glabrous, cylindrical at the base, becoming 3-4-angulate upward, the margins denticulate, the internode at the base of each raceme with a tuft of colorless hairs 2-2.5 mm long; racemes 8-30, 2.5-8.5 cm long; rachis 1-1.5 mm wide, zig-zag, flat abaxially, with a central ridge adaxially, arcuate in maturity, bearing spikelets to the tip, the margins ciliate or denticulate, or both. Pedicels of unequal length, 0.10.3 mm long, scabrid, the apex discoid. Spikelets paired, each pair alternate on each side of the rachis, pedicelled, 2.3-3.3 mm long, 1-1.2 mm wide, broadly elliptic-lanceolate in outline, pale to purplish, dorsally compressed, abaxial, awnless, with 2 florets, disarticulating below the glume and falling as a unit; lower glume absent; upper glume slightly to strongly convex on the back, 2.3-3.3 mm long, 3-nerved, glabrous to finely appressed pubescent, the margins densely ciliate-pectinate; the cilia colorless, 0.3-0.7 mm long, with bulbous bases, the apex apiculate; lower floret sterile, consisting only of a lower lemma; lower lemma 2.2-2.9 mm long, narrower than the upper glume, 3-nerved, navicular, hyaline, with a depressed area at the base, the surface glabrous to short-pubescent, the apex glabrous to slightly ciliate; lower palea absent; upper floret 2.2-2.7 mm long, bisexual, slightly chartaceous, pale; upper lemma obscurely 5-nerved, navicular, glabrous, the surface finely papillose-striate, the apex acute; germination flap evident; upper palea 2.1-2.2 mm long, acuminate, glabrous, slightly chartaceous, the surface finely papillose-striate; lodicules 2, fleshy, conduplicate, 0.1-0.2 mm long; stamens 3; anthers 1.22 mm long, laterally exserted; ovary 0.5-0.8 mm long, glabrous; styles 2, separate, 1.5-1.8 mm long; stigmas 2, plumose, yellow or purplish. Caryopsis 1.8-1.9 mm long, 0.9-1 mm wide, light-colored, NovoN 5: 30-33. 1995. This content downloaded from 157.55.39.58 on Fri, 24 Jun 2016 06:19:47 UTC All use subject to http://about.jstor.org/terms Volume 5, Number 1 Filgueiras 31 1995 Paspalum niquelandiae

A New Species of Paspalum (Gramineae) from Bolivia

Summary. A new species, Paspalum reticulinerve Renvoize, is described from Bolivia and compared with 6 other related species of section Pectinata Chase ex Rodriguez. The genus Paspalum with 330 species, the majority of them in the New World, is the fourth largest in the Gramineae, after Poa (500), Panicum (470) and Festuca (450). Paspalum species are readily recognized by their typically ovate, orbicular or elliptic, strongly plano-convex 2-flowered spikelets arranged in 2 or 4 dense rows on one side of a broad or narrow rachis. The new species described here is somewhat atypical and belongs to Section Pectinata Chase ex Rodriquez in which the spikelets are strongly dorsiventrally flattened, imbricate, and lanceolate in shape, and the upper glume is usually winged and cordate. The new species differs from all the other related species most obviously in its ciliate rachis. P. reticulinerve Renvoize sp. nov. P. aspidioti Trin. affinis sed planta omnis villosa, laminis angustioribus, racemis exsertis, rachidi ciliata, spiculis brevioribus differt. Typus: Bolivia, Solomon 17003 (holotypus LPB; isotypi K, MO). Gramen perenne, caespitosum, villosum; culmis erectis 120 cm altis. Foliorum basalium vaginae papyraceae; laminae lineares 20-30 cm x 3-5 mm planae attenuatae, basi rectae. Racemi 2(-3) terminales exserti conjugati 9 cm longi; rhaches lunares, 1 mm latae, ciliatae. Spiculae solitariae late lanceolatae, 4 -55 mm longae, dorsiventraliter compressae bifariae imbricatae. Gluma superna lemmatem infera longior et latior, foliaceo-alata, alae reticulato-venosae acutae cordatae 5-nerviae, margines apicalibus ciliolati. Lemma infera coriacea granulatopapillosa, 3 -5 mm longa, alata, alis reticulato-venosis, basi plicatis marginibus apicalibus ciliolatis. Anthoecium hermaphroditum ellipticum 3 mm longum. Caespitose, villous perennial with erect culms 120 cm high. Basal leaf-sheaths papery; blades linear, 20-30 cm x 3-5 mm, straight at the base, flat, tapering at the apex. Racemes 2(-3), exserted, conjugate, 9 cm long; rachis crescentic, 1 mm wide, ciliate. Spikelets usually solitary, occasionally paired imbricate, arranged in two rows, broadly lanceolate, 4"-5-5 mm long, dorsi-ventrally compressed. Upper glume longer and broader than the lower lemma, foliaceously winged, the wings reticulately nerved, cordate, 5-nerved, acute, the margins ciliolate near the apex. Lower lemma coriaceous, granular-papillose, 3-5 mm long, winged, the wings reticulately nerved, plicate at the base, the margins ciliolate towards the apex. Upper floret hermaphrodite, elliptic, 3 mm long. Fig. 1A-G.

Humid tropical leguminous tree and pasture grass responsiveness to vesicular-arbuscular mycorrhizal infection

Phosphorus is the major nutrient limiting plant growth in a Costa Rican silvopastoral system located on an acid, high P-retaining, volcanic soil. We investigated plant responsiveness to vesicular-arbuscular mycorrhizal (VAM) inoculation using the leguminous tree species Erythrina berteroana Urban, and the two dominant grass species Paspalum conjugatum Berg and Homolepsis aturensis Chase of this silvopastoral system. We grew grass seedlings in the greenhouse for 15 weeks in a methyl bromide-sterilized study soil to which either mixed-species VAM inoculum (Theobroma cacao feeder roots) or autoclave-sterilized cacao roots (non-inoculated control) were added. E. berteroana was grown from both seedlings and vegetative stakes (40 cm long) for 30 and 19 weeks, respectively. Upon harvest, we measured above and below ground biomass, N and P content, root∶shoot ratio, legume nodulation, and VAM infection levels. The total above-ground and root biomass of mycorrhizae-inoculated P. conjugatum seedlings were 2.5 and 2.8 times greater than those of noninoculated seedlings. In contrast, VAM-inoculated seedlings of H. aturensis produced 8.4 and 5.9 times more total above-ground and root mass than noninoculated seedlings. Mycorrhizae-inoculated E. berteroana seedlings produced 10.6 times greater shoot biomass for inoculated versus noninoculated seedlings, while E. berteroana vegetative stakes exhibited a negative growth response to VAM inoculation (an approximately 16% decrease in shoot biomass for VAM-inoculated cuttings). The difference in responsiveness between Erythrina growth forms is hypothesized to reflect the cost-benefit relationship between plant host and fungal symbiont for energy and nutrient reserves.

Post-Zygotic Seed Abortion in Sexual Diploid × Apomictic Tetraploid Intraspecific Paspalum Crosses

In many species of Paspalum, diploid (2x) cytotypes are usually outbreeders due to a self incompatibility system, while tetraploid (4x) conspecific counterparts are pseudogamous self-fertile apomicts. Intraspecific crossability between 2x female and 4x male cytotypes was investigated using classical methods of crossing in P. almum, P. brunneum, P. rufum, P. intermedium and P. quadrifarium. Expected triploid BII hybrids were obtained in P. intermedium (crossability: 0.004%) and in P. brunneum (crossability: 0.015%). In P. rufum, only tetraploid BIII hybrids were achieved with a crossability of 0.025% Looking for a better performance, in vitro ovary rescue was attempted 5 days after pollination in intraspecific 2x × 4x crosses of P. almum, P. quadrifarium, P. intermedium and P. rufum. The method was useful to recover some triploid BII hybrids in P. almum (success rate: 0.49%) and in P. rufum (0.59%), but failed in P. intermedium and P. quadrifarium. Pollen tube growth was usually inhibited at the stigma or style levels after self-pollination in 2x plants, confirming that diploids are self-incompatible. Pollen of 4x cytotypes germinated and penetrated the pistils of diploid conspecific cytotypes. This indicated that no incompatibility system exists in these species to keep the 2x cytotypes from hybridising with 4x conspecific cytotypes as pollen donors. However, after pollination of 2x cytotypes with pollen of 4x counterparts, most ovules showed embryo and endosperm development, but a few days later, endosperms collapsed and embryos stopped their development. As a result of these processes, sexual self-incompatible 2x cytotypes of Paspalum species produced very few triploid hybrids when pollinated with pollen of their apomictic 4x counterparts. Thus, the low diploid-tetraploid crossability was due to the existence of a post-zygotic abortive system and not caused by pre-fertilisation barriers.

Biomass and primary-production of herbaceous plant communities in the Amazon floodplain

The increase in biomass of different aquatic and terrestrial herbaceous plant communities was measured during various growth periods in the Amazon floodplain near Manaus. Maximum biomass varied from 4–11.2 t ha−1 dry weight in mixed annual terrestrial communities to 6–23 t ha−1 in aquatic annual species (Paspalum repens, Oryza perennis, Luziola spruceana and Hymenachne amplexicaulis) and 15.6–57.6 t ha−1 in communities of the perennial species Paspalum fasciculatum. Cumulative biomass of 3 successively growing annual species reached 30 t ha−1 a−1. Net primary production is considerably higher than maximum biomass. Paspalum fasciculatum reached 70 t during a growth period of 8 months. If one considers for annual species a monthly loss of 10–25% of the biomass, then net primary production in areas with three successive macrophyte communities and a cumulative maximum biomass of 30 t ha−1 is estimated to reach up to 50 t ha−1 a−1. Annual P/B ratio may reach about 3.

Two New Species of Paspalum (Poaceae: Paniceae) from Venezuela and Colombia

Morphological characters support the description of two new species of Paspalum: P. atabapense, from Depto. Atabapo, Venezuela, in group Alterniflora; and P. tillettii, from Comisaria del Guainia, Colombia, and Territorio Federal Amazonas, Venezuela, in an unspecified taxonomic group but clearly related to P. schultesii Swallen. Preparatory to completing an account of the genus Paspalum for the Flora of the Venezuelan Guayana, two new species are described and illustrated. Paspalum L., with more than 350 species, is one of the largest genera of grasses. It is confined primarily to the New World, although a few species occur in Africa, Asia, and Oceania. Several species are pantropical or nearly so, and two weedy species have now become widely naturalized as weeds in the tropics. A few have been widely distributed as forage grasses and have subsequently become naturalized in new areas. The most useful taxonomic treatment of this genus remains the monograph of the North American species (including Mesoamerica) by Chase (1929). Paspalum atabapense Davidse & Zuloaga, sp. nov. TYPE: Venezuela. Amazonas: Depto. Atabapo, SE bank of the middle part of Caio Yagua at Cucurital de Yagua, 3036'N, 66?34'W, 120 m, 8 May 1979, G. Davidse, 0. Huber & S. S. Tillett 17414 (holotype, MO; isotypes, IAN, SI, US, VEN). Figure 1. Gramen perenne caespitosum; culmi 45-75 cm alti. Folia basalia; ligulae 0.5-1.2 mm longae, glabrae; laminae 6-18.5 cm x 0.3-0.4 mm, filiformes. Racemus 1, 39.5 cm longus; rhachis 0.4-0.5 mm lata, exalata vel interdum anguste alata basin versus. Spiculae 2.6-3.6 x 1.0-1.3 mm, ellipticae anguste, singulares, pubescentes; gluma inferna absens; gluma supera 0.3-0.7 mm spicula brevior. Flosculus superus 2.6-3.5 x 1.0-1.3 mm, stramineus. Antherae 1.5-1.9 mm longae. Caespitose, perennial herbs. Culms 45-75 cm long, erect, unbranched above the base, with 2-3 nodes above the base; internodes cylindric, glabrous; nodes dark, glabrous or pilose. Leaves basal. Sheaths striate, rounded, densely pilose toward the base with appressed, whitish hairs, to sparsely pilose toward the apex, the margins glabrous. Ligules 0.5-1.2 mm long, membranous, glabrous, erose. Blades 6-18.5 cm long, 0.3-0.4 mm wide, filiform, involute, the adaxial surface scabrous, prominently ridged, the abaxial surface glabrous, the apex permanently involute, somewhat pungent. Inflorescences terminal, long-exserted; peduncle 4-17 cm long, cylindric, glabrous; raceme 1, 3.0-9.5 cm long, slightly arching, densely pilose at its base; rachis 0.4-0.5 mm wide, puberulent to glabrous, concavo-convex, unwinged or sometimes with partially developed wings 0.1-0.2 mm wide near a portion of the base, terminating in a spikelet; pedicels 0.1-0.3 mm long, densely short-pilose. Spikelets 2.6-3.6 mm long, 1.0-1.3 mm wide, solitary, plano-convex, narrowly elliptic, pilose. Lower glume always absent. Upper glume 2.4-3.0 mm long, 0.3-0.7 mm shorter than the upper floret, acute, 3-nerved. Lower floret sterile. Lower lemma as long as the spikelet, 3-nerved, glabrous to puberulent in the middle portion, pilose toward the margins. Lower palea usually absent, rarely developed and then to 5/6 as long as the lower lemma. Upper floret 2.6-3.5 mm long, 1.0-1.3 mm wide, as long as the spikelet, bisexual, narrowly elliptic, stramineous, chartaceous, smooth, papillose, the papillae regularly distributed; lemma 3-nerved, short-pilose, with prickle hairs at the apex. Stamens 3; anthers 1.5-1.9 mm long, purple. Styles 2, separate; stigmas about as long as the styles, plumose. Caryopsis (1.2-)1.4-1.5 mm long, 0.9-1.0 mm wide, obovate in outline; hilum punctiform; embryo ca. 2/5 as long as the caryopsis. Paratypes. VENEZUELA. AMAZONAS: Depto. Atabapo, area between the W base of Cerro Yapacana and the headwaters of Caio Cotua, 3?38'N, 66?52'W, 6 May 1979, Davidse, Huber & Tillett 17251 (K, MO, SI, US, VEN); Depto. Atabapo, sabanas y bosques ribereios en los alrededores de Canarip6, en la margen izquierda (Sur) del bajo Rio Ventuari, a unos 20 km al E de la confluencia NOVON 2: 193-197. 1992. This content downloaded from 157.55.39.209 on Sat, 14 May 2016 04:53:24 UTC All use subject to http://about.jstor.org/terms

Cytology of Sexual and Apomictic Paspalum Species.

The cytology, reproductive behavior and fertility of seven different Paspalum species were studied to determine how they might be used in an interspecific hybridization program. Paspalum palustre Mez and P. bertonii Hack. were diploids with 2n=2x=20 chromosomes. Paspalum dedeccae Quarin; P. denticulatum Trin., and one P. distichum L. accession were tetraploids with 2n=4x=40 chromosomes. Another P. distichum accession, P. inaequivalve Raddi, and P. ramboi Barreto were hexaploids with 60 chromosomes. Meiosis was regular with primarily bivalent pairing in P. palustre, P. bertonii, tetraploid P. distichum, P. inaequivalve and P. ramboi. Paspalum dedeccae, two P. denticulatum accessions, and hexaploid P. distichum were meiotically irregular with univalent, bivalent and multivalent (primarily quadrivalent) associations at metaphase I. Megasporogenesis and embryo sac development in P. palustre, P. bertonii, and P. inaequivalve indicated sexual reproduction. Paspalum palustre and P. bertonii were self-incompatible and did not produce self-pollinated seed but P. inaequivalve was self-compatible. Paspalum dedeccae, P. denticulatum, P. distichum, and P. ramboi all reproduced by aposporous apomixis.

Evaluation of Paspalum germplasm for variation in leaf wax and heat tolerance

The genus Paspalum contains a number of important forage grasses, including P. dilatatum Poir. (dallisgrass) and P. notatum Flugge (bahiagrass). Even though many Paspalum species are adapted to moist, humid areas, they frequently are subjected to extended periods of drought stress which reduces forage productivity. This study was initiated to determine the range of variation for different indicators of drought tolerance in several Paspalum species. Fifteen species representing a broad cross section of germplasm were grown in a replicated field nursery and sampled for leaf epicuticular wax content on four dates over three years. Wax was extracted with chloroform and quantified by the dichromate oxidation technique. Heat tolerance (solute leakage technique) was also determined by calculating the ratio of the conductivity of the external bathing solution of leaves following a heat treatment to the conductivity of the bathing solution after leaves were boiled. Wax values of the entries ranged from 5.7 to 0.88 mg/dm2. Both relative rankings and absolute wax values were very consistent across all sampling dates. The accessions of Paspalum nicorae Parodi and P. quandrifarum Lam. were consistently high in wax content, while the accessions of P. commune Lillo and P. unispicatum (Scribn. et Merr.) Nash were consistently low. The heat tolerance testing demonstrated that the accession of P. notatum var. saurae Parodi was the most heat tolerant of the entries. Results from this investigation demonstrate the wide range of diversity that exists for both epicuticular wax and heat tolerance within the genus Paspalum.

Interspecific Hybrids between Five Paspalum Species

Interspecific crosses were made among Paspalum intermedium Munro, P. haumanii Parodi, P. brunneum Mez, P quadrifarium Lam., and P. rufum Nees, species with both sexual diploid (2n = 20) and apomictic tetraploid cytotypes. Eight different interspecific hybrid progenies involving diploid species were recovered from crosses using P. intermedium or P. haumanii as the female parent. When P. rufum was the female parent in crosses with the other four species, only the hybrid with P. intermedium as pollen donor was recovered. Paspalum brunneum as female parent gave hybrid progenies only with P. rufum. All hybrids had 2n = 20 chromosomes, and the degree of meiotic pairing was high in most of them. Excepting P. haumanii x P. brunneum, all other hybrids had some pollen mother cells (PMC) with 10 II. Paspalum haumanii x P. brunneum had the least number of bivalents (mean = 4.7, maximum = 7 II). Almost complete pairing was observed in P. intermedium x P. haumanii and P. quadrifarium x P. brunneum, with a mean of 9.86 and 9.9 bivalents/PMC, respectively. The high degree of meiotic pairing in the hybrids is consistent with morphological and ecological affinities of the species as well as their geographical distribution. The data indicate that the genome of each of these species evolved from an ancestral common basic genome, and each of them may be a particular form of the I genome previously assigned to P intermedium. The low rate of crossability among these five species and the high sterility of the hybrids are important barriers preventing introgression.

Cytogenetics and Reproductive Behavior of Different Chromosome Races in Six Paspalum Species

Etude cytologique et potentiel d'utilisation dans un programme d'hybridation d'accessions de P. quadrifolium, P. brunneum, P. haumanii, P. rufum et P. maculosum

Phylogenetic Relationships among Paspalum Species with Different Base Chromosome Numbers

The genus Paspalum has two base chromosome numbers: x = 6 and x = 10. One P. jurgensii (2n = 20) x P. hexastachyum (2n = 12) hybrid had 2n = 16 and a mean meiotic chromosome pairing of 12.78I and 1.61II. Five hybrids were obtained from the P. intermedium (2n = 20) x P. hexastachyum; two hybrids had 2n = 16; the other three, 2n = 26. The mean meiotic chromosome association in the 2n = 16 hybrids was 9.08I and 3.46II and in the 2n = 26 hybrids, 6.07I and 9.96II. The 2n = 26 hybrids may have originated from the fertilization of an unreduced egg of P. intermedium. The crosses of P. dilatatum (2n = 40) x P. hexastachyum produced five hybrids with 2n = 26, with a mean meiotic association of 22.2I and 1.9II. Except for pairing between the P. intermedium chromosomes in the 2n = 26 P. intermedium x P. hexastachyum hybrids, the bivalents in all of the above hybrids were loosely synapsed and did not demonstrate strong homologies. Two hybrids were recovered from P. dilatatum x autotetraploid P. almum (2n = 24). One hybrid had 2n = 32, with 11.13I and 10.44II of which 6II were from autosyndetic pairing of the P. almum chromosomes, and the remaining bivalents, from intra- or intergenomic pairing of the P. dilatatum chromosomes. This study indicates that the x = 6 and x = 10 species are not closely related.

Cytomorphological studies of three species of Paspalum Linn. from South India.

Cytological studies have been made on three species of Paspalum, two of which were collected from natural populations while P. scrobiculatum is a cultivated species. P. commersonii consists of forms with diverse morphological varieties, occurring either as mesophyte or hydrophyte. P. scrobiculatum and P. orbiculare show regular meiosis with n=20 and 2n=40. In contrast, in P. commersonii which has a somatic number of 2n=60 meiosis is very irregular with total asynapsis of chromosomes. This species is probably of hybrid origin and apomictic. The results of the present cytological studies clearly indicate that variations in morphological characters and habit shown by these species are correlated with cytological distinctness. Therefore these three taxa deserve separate specific rank as suggested by Bor (1960).

Pollen germination, pollen tube growth and fertilization following self and interspecific pollination of Paspalum species

Crossability between most Paspalum species is very low. This study was undertaken to identify the impediments to hybridization. Accessions of P. intermediumMunro. ex Morong, P. jurgensiiHackel and P. dilatatumPoir were self-pollinated and crossed with one anther. Paspalum intermedium is essentially self-sterile but P. jurgensii and P. dilatatum are highly self-fertile. Following pollination, pollen germination and tube growth were studied by observing the pollinated pistils with fluorescent microscopy. Examination of self-pollinated pistils revealed that the pollen germinated shortly after contacting the stigmas. Germination was over 80% for the P. intermedium and P. dilatatum accessions but only 57% for P. jurgensii. Pollen tubes grew to the micropyle within 45 minutes after pollination in P. dilatatum and 1 hour and 15 minutes in P. jurgensii. However, in the P. intermedium accessions most tubes did not grow beyond the stigma and very few penetrated the style and ovary. Apparently stylar-incompatibility is the reason for the low selfed seed set. In the cross-pollinations, pollen germinated shortly after pollination and germination ranged from 57 to 88% for the different crosses. In all crosses the pollen tubes grew to the micropyle within 30 minutes to 2 hours after pollination indicating that a cross-incompatibility system is not the cause for low crossability among these species. By examining embryo sacs from P. intermedium × P. dilatatum, its reciprocal and P. intermedium × P. urvillei crosses, it was determined that gametes failed to unite in some crosses and this is a major reason for low crossability.

Photosynthesis, water use and growth of a C4 grass stand at high CO2 concentration

Leaf photosynthesis rate of the C4 species Paspalum plicatulum Michx was virtually CO2-saturated at normal atmospheric CO2 concentration but transpiration decreased as CO2 was increased above normal concentrations thereby increasing transpiration efficiency. To test whether this leaf response led growth to be CO2-sensitive when water supply was restricted, plants were grown in sealed pots of soil as miniature swards. Water was supplied either daily to maintain a constant water table, or at three growth restricting levels on a 5-day drying cycle. Plants were either in a cabinet with normal air (340 μmol (CO2) mol(-1) (air)) or with 250 μmol mol(-1) enrichment. Harvesting was by several cycles of defoliation.With abundant water supply high CO2 concentration did not cause increased growth, but it did not cause an increase in growth over a wide range of growth-limiting water supplies either. Only when water supply was less than 30-50% of the amount used by the stand with a water-table was there evidence that dry weight growth was enhanced by high CO2. In addition, with successive regrowth, the enhancing effect under a regime of minimal water allocations, became attenuated. Examination of leaf gas exchange, growth and water use data showed that in the long term stomatal conductance responses were of little significance in matching plant water use to low water allocation; regulation of leaf area was the mechanism through which consumption matched supply. Since high CO2 effects operate principally via stomatal conductance in C4 species, we postulate that for this species higher CO2 concentrations expected globally in future will not have much effect on long term growth.

Genetic studies in diploid and tetraploid Paspalum species

Genetic studies in diploid and tetraploid Paspalum species

Environmental Influences on Fiber Component Concentrations of Warm‐season Perennial Grasses1

AbstractEvaluation and management of warm‐season perennial grasses are complicated by seasonal fluctuations in forage quality. Field studies have indicated that a significant proportion of this seasonal variation is due to environmental conditions. Due to confounding effects under field conditions the variation cannot be directly attributed to specific environmental factors. In this study, Coastal and common bermudagrass [Cynodon dactylon (L.) Pers.], Pensacola bahiagrass (Paspalum notatum Flugge), and dallisgrass (Paspalum dilatatum Poir.) were grown in an artificial medium under 4 day/night temperatures (35/24, 32/31, 29/18, 26/15 C), 4 photon flux densities (1,050, 840, 630, 420 µE m−2 sec−1 PAR) and two soil moisture levels (high and low) in growth cabinets to evaluate the relative influence of each factor on fiber component concentrations. Grasses were harvested at 14 and 21 days and analyzed for neutral‐detergent fiber (NDF), acid‐detergent fiber (ADF), cellulose (CEL), hemicellulose (HEM), permanganate lignin (LIG), and silica (SIL) concentrations. multiple regression analysis was used to obtain reduced prediction equations for evaluating responses of all measured variables to temperature (T) and photon flux density (L) at each soil moisture level. Prediction equations for fiber component concentrations of each grass included T effects at both soil moisture levels but did not consistently include L effects. Coefficients of determination (R2 values) for the prediction equations indicated that T and L effects on fiber component concentrations varied with the fiber component, grass, and soil moisture level.Concentration of NDF increased in the Cynodon species and decreased in the Paspalum species as T increased. In all grasses, predicted concentrations of ADF, CEL, LIG, and SIL increased with increasing T at both soil moisture levels, while HEM concentrations decreased. In all grasses L effects consistently influenced ADF, LIG, and SIL concentrations at both soil moisture levels and CEL concentrations at the low moisture level. Concentrations of ADF, CEL, and SIL decreased slightly, while LIG concentrations increased with increasing L. Although T effects consistently had greater influence in this study, both T and L and their interaction effects significantly influenced predicted fiber component concentrations. The data emphasize the importance of considering environmental influences when evaluating forage quality differences of warm‐season perennial grasses.

Genome Relations among Four Diploid Paspalum Species

Paspalum intermedium Munro ex Morong, P. notatum Flugge, P. pumilum Nees, and P. vaginatum Swartz, all 2n = 2x = 20, were crossed to investigate their cytogenetic relationships. All of the hybrids had 2n = 2x = 20 and irregular meiosis. Three P. intermedium x P. notalum hybrids had a mean chromosome association of 18.43 univalents and 0.78 bivalents per cell, indicating that the two species are not closely related. Eight P. notatum x P. vaginatum hybrids had a mean chromosome association of 18.83 univalents and 0.59 bivalents per cell, indicating that the genomes of these two species are different. Seven P. pumilum x P. vaginatum hybrids and two reciprocal hybrids had a mean of 19.46 univalents and 0.27 bivalents per cell and 19.48 univalents and 0.25 bivalents, respectively, indicating that these two species have different genomes. Paspalum intermedium and P. vaginatum have the genome formulas II and DD. The genomic formula NN is proposed for the diploid form of P. notatum. Since P. pumilum and P. notatum are in the same taxonomic group, P. pumilum may also have the formula NN. None of the hybrids produced fertile seed.