| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
a USDA-ARS, Crop Germplasm Research Unit, 430 Heep Center, Texas A&M Univ., College Station, TX 77843-2474
b School of Plant, Environmental and Soil Sciences, Louisiana State Univ., Baton Rouge, LA, current address: USDA-ARS, Grazinglands Research Lab., 7207 W. Cheyenne St., El Reno, OK 73036
c Dep. of Soil & Crop Sciences, Texas A&M Univ., College Station, TX 77843-2474
* Corresponding author (Byron.Burson{at}ars.usda.gov).
ABSTRACT
‘Sabine’ dallisgrass (Paspalum dilatatum Poir.) (Reg. No. CV-2, PI 655527) was released by the USDA-ARS, Louisiana State University Agricultural Center, and Texas AgriLife Research on 2 Sept. 2008. Sabine is phenotypically and cytologically different from common dallisgrass because it is a different P. dilatatum biotype, called the Uruguayan biotype. Sabine is a single plant selection from an off-type plant that originated from the facultative apomictic accession PI 404826. It was selected because it usually produced more forage and was consistently more persistent under defoliation than common dallisgrass in multiyear forage evaluation plots in Louisiana and Texas. Its forage nutritive value is equivalent to that of common dallisgrass. Since common is the only dallisgrass biotype grown for forage throughout the southern United States, Sabine was released to provide livestock producers in the southeastern United States with a new, more productive, and more persistent dallisgrass option.
Abbreviations: CP, crude protein • DM, dry matter • IVTD, in vitro true digestibility • LSU, Louisiana State University • NDF, neutral detergent fiber
Common dallisgrass, Paspalum dilatatum Poir., is purported native to southern Brazil, Uruguay, and eastern Argentina (Evers and Burson, 2004). It was introduced into the United States before 1840 (Chase, 1929) and became naturalized throughout most of the southeastern United States, where it is now an important component of many permanent pastures, especially those growing on loam and clay soils. It initiates growth earlier in the spring and usually persists longer into the fall than most warm-season perennial grasses, which extends the grazing season (Holt, 1956; Davies and Forde, 1991). Unlike most warm-season perennial grasses, common dallisgrass has excellent forage nutritive value when properly managed (Henderson and Robinson, 1982); however, it has several traits that limit its use. Its forage yield is often less than that of other warm-season forage grasses, and there is a need for more productive cultivars.
Because common dallisgrass is an obligate apomict (Bashaw and Holt, 1958), efforts to improve it using conventional breeding methods have not been successful (Evers and Burson, 2004). The grass is a pentaploid (2n = 5x = 50) with irregular meiosis (Bashaw and Forbes, 1958), which also has negatively impacted efforts to improve the species through wide hybridization. Even though common dallisgrass is the most prevalent and widely distributed biotype, several other P. dilatatum biotypes exist in South America, and they differ morphologically and cytologically from common (Burson et al., 1991; Evers and Burson, 2004). Several of these biotypes and common dallisgrass were evaluated in multiyear replicated forage tests in Texas and Louisiana to determine their comparative forage yields. It was determined that several accessions of a biotype from Uruguay, known as the Uruguayan biotype, usually produced more forage than common dallisgrass and the other biotypes tested (Burson et al., 1991; Venuto et al., 2003). Almost all accessions of the Uruguayan biotype persisted much better under defoliation than common and most of the other biotypes, especially when grown on wet or moist soils for extended periods (Venuto et al., 2003). This was unexpected because common has the reputation of being adapted to heavy moist soils (Evers and Burson, 2004). Because most accessions of the Uruguayan biotype outperformed common dallisgrass, our objectives were to identify the most productive and persistent accession and release it as a new dallisgrass cultivar.
Materials and Methods
Germplasm
Sabine dallisgrass (Reg. No. CV-2, PI 655527) indirectly originated from PI 404826. Accession PI 404826 differed from the other accessions of the Uruguayan biotype in that it had yellow-colored anthers and produced a low frequency (<5%) of off-type progeny (Millot, 1977). Cytological studies and progeny testing confirmed that PI 404826 is a facultative apomict with a low level of sexuality (Burson et al., 1991). Except for PI 404826, all other accessions of this biotype had purple-colored anthers, and their progeny were uniform and resembled the maternal parent. The designation 554 was assigned to the seed collected from a purple-anthered progeny of PI 404826. These seed were germinated and 20 seedlings were transplanted into a space-planted nursery. Once the plants grew to maturity, they were evaluated for variability and uniformity. All plants were uniform and appeared identical to the off-type plant from which the seed were collected, indicating apomictic reproduction. Cytological and histological studies of several 554 plants revealed that all were hexaploid with 60 chromosomes that associated as 30 bivalents during meiosis and reproduced by aposporous apomixis (Burson et al., 1991). When several thousand plants were grown in a seed increase field, however, a very low frequency of less-vigorous plants were observed, indicating that 554 is a facultative apomict with a very low level of sexual reproduction.
Forage Production and Quality and Plant Persistence
Replicated forage clipping trials, consisting of 11 dallisgrass accessions (nine of the Uruguayan biotype and two of common dallisgrass), were established at Louisiana State University (LSU) Agriculture Center's Ben Hur Farm in Baton Rouge, LA, on a Sharkey clay (very fine, smectitic, thermic Chromic Epiaquerts), at LSU Agriculture Center's Iberia Research Station near Jeanerette, LA, on a Baldwin silty clay loam (fine, smectitic, hyperthermic chromic Vertic Epiaqualfs), and at the Texas AgriLife Research (formerly Texas Agricultural Experiment Station) Plantation near College Station, TX, on a Weswood silt loam (fine-silty, mixed, superactive, thermic Udifluventic Haplustepts).
All plots were established by transplanting 12 seedlings of each entry into a single row at a distance of 0.3 m between each plant with a 1-m spacing between rows. The plots were planted in a randomized complete block design with four replications. All plots were fertilized with 150 kg N ha–1 applied in two split applications each year. Phosphorous and potassium were applied with the first N application according to soil test analyses at the beginning of the study and each subsequent year as needed. The plots were harvested with a mechanical harvester three to five times each year at a stubble height of 8 cm. The harvested forage was weighed in the field, and subsamples from each entry were collected and oven dried at 60°C to determine percentage dry matter (DM) and subsequent dry forage yield. These samples were then ground with a Wiley mill equipped with a 1-mm screen and analyzed for crude protein (CP), neutral detergent fiber (NDF), and in vitro true digestibility (IVTD). For details regarding how these nutritive components were analyzed, see Venuto et al. (2003). Plant counts were made at the end of the establishment year (1995) and again 3 yr later to determine relative persistence of each accession.
The plots at the Iberia Research Station were harvested twice during the 1996 growing season (data not reported) and were last fertilized in April 1997. Thereafter, the plots were abandoned except for an occasional mowing for maintenance purposes. On 11 Mar. 1999, they were evaluated for plant persistence.
Pasture Study and Grazing Persistence
To compare the performance and persistence of the two biotypes under grazing, six of the higher-yielding and more-persistent Uruguayan accessions and a commercial source of common dallisgrass were evaluated at the LSU Agricultural Center's Iberia Research Station on a Baldwin silty clay loam. The plots were planted in an unimproved 1.62-ha pasture consisting of annual ryegrass (Lolium multiflorum Lam.), broadleaf signalgrass [Urochloa platyphylla (Munro ex C. Wright) R.D. Webster], common bermudagrass [Cynodon dactylon (L.) Pers.], carpetgrass [Axonopus fissifolius (Raddi) Kuhlm.], common dallisgrass, jungle ricegrass [Echinochloa colona (L.) Link], smooth crabgrass [Digitaria ischaemum (Schreb. ex Schweigg.) Schreb. ex Muhl.], smutgrass [Sporobolus indicusi (L.) R. Br. var. indicus], yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.], and miscellaneous dicotyledonous species. The experimental design was a randomized complete block with six replications. Each entry was hand-transplanted into a plot consisting of 50 transplants in five rows with 10 plants per row at a spacing of 45 cm within and between rows. The soil in each plot was not disturbed except for digging small holes about 8 cm in diameter and 8 cm deep to plant the transplants. A 1.8-m border of the unimproved pasture was left between the plots within each replication, and a 2.8-m border was left between replications. The plots were fertilized with 168 kg N ha–1 applied in two split applications each year, and 30 kg P ha–1 and 100 kg K ha–1 were added with the first application of N each spring.
The plots were established on 27 Mar. 1998, and grazing was initiated on 6 May 1999. During 1999 and 2000, the plots were grazed only four times each year because of drought. Duration of grazing was 4 d for each grazing period. Stocking density was adjusted throughout the grazing season based on forage availability and averaged 13.6 500-kg Angus cows ha–1. Before grazing, one dallisgrass plant in each plot and a 30- by 30-cm pasture area adjacent to each plot were hand-clipped to a height of 10 cm and forage mass was determined. Grazing was initiated when inflorescences were observed on the Uruguayan biotypes and terminated when plots were grazed to a height of 10 to 15 cm. Immediately after grazing, all plots were mowed to a uniform height of 10 cm to minimize differential residual effects of grazing, especially those that might be associated with palatability. Surviving plants in each plot were counted at the end of the establishment year (12 Nov. 1998) and each growing season (8 Dec. 1999 and 28 Nov. 2000). During the 2001 season, the plots were stocked continuously with an average of 2.5 500-kg cows ha–1. Grazing was initiated in May, and the animals were removed in October. On 14 November, the surviving plants of the original transplants in each plot were counted.
All data were analyzed with PROC MIXED (SAS Institute, 2003). For the clipping study, entry was considered a fixed effect. Year, location, and block within location were considered random effects. For comparisons made among biotypes, biotype was considered a fixed effect. For the grazing study, entry was considered a fixed effect and year and block were considered random effects. All tests of significance were made at the 0.05 probability level unless otherwise stated.
Results and Discussion
Sabine dallisgrass was jointly released by the USDA-ARS, LSU Agricultural Center, and Texas AgriLife Research on 2 Sept. 2008 to provide livestock producers in the southern United States a more productive and persistent alternative to common dallisgrass. Sabine was evaluated under the experimental designation 554. This is the first dallisgrass cultivar released in the United States since 1951 when the Louisiana Agricultural Experiment Station released two common dallisgrass cultivars (Owen, 1951). Sabine is morphologically and genetically different from common dallisgrass because it is a different P. dilatatum biotype.
Clipping Studies
Differences in dry matter yield were observed for location, year, location x year, entry, and entry x location (Table 1
). During 1996 and subsequent years, all entries produced more forage at College Station, TX, than Baton Rouge, LA. At Baton Rouge, all Uruguayan accessions, except for PI 404831, produced significantly more DM than both common dallisgrass entries. At College Station, both common dallisgrass entries produced essentially twice as much forage (P < 0.01) than at Baton Rouge, and there were no significant differences between the common entries and the Uruguayan accessions, except for PI 404831 (Table 1). PI 404831 was less vigorous and morphologically different from the other Uruguayan accessions and it consistently produced less forage than the other accessions (Table 1). During the second and third years of clipping, greater yield differences were apparent between locations. In 1997, the amount of forage produced by the Uruguayan accessions (except PI 404831) at Baton Rouge decreased approximately 50% from what was produced in 1996 and continued to decrease in 1998 (Table 1). An even greater yield decline was observed for both common dallisgrass entries between 1996 and 1997 (Table 1).
|
When the mean amount of forage produced over all 3 yr is considered, all entries of both biotypes produced significantly more forage (P < 0.01) at College Station than at Baton Rouge (Table 1). At Baton Rouge, the 3-yr means for all Uruguayan accessions (except PI 404831) and the common entries were 7.9 and 3.5 Mg ha–1, respectively. At College Station, the Uruguayan and common means were 14.8 and 13.6 Mg ha–1, respectively. Sabine did not produce significantly more forage than the other Uruguayan accessions (except for PI 404831 and PI 404812 in 1996 at Baton Rouge), but its yield was always in the upper one-third of the Uruguayan accessions or was the greatest (Table 1). Therefore, across locations and years, Sabine was consistently among the most productive Uruguayan accessions tested in the clipping studies (Table 1) and was never significantly below the top entry. At Baton Rouge, Sabine significantly outyielded both common entries over the course of this study, except for PI 404841 in 1998. Although the mean yields of the common entries, compared with the Uruguayan entries (except for PI 404831), at College Station were not significantly different, the yields for Sabine were consistently higher than the means of the common entries for all 3 yr.
Nutritive Characteristics
Significant differences were not observed for IVTD among all Uruguayan and common entries at either location. However, some minor variations for CP and NDF were observed among entries at both locations. At Baton Rouge, except a difference between the common entry PI 404841 and the Uruguayan accessions PI 404820 and PI 404831, none of the remaining Uruguayan accessions including Sabine differed from both common entries (Table 2
). Larger variation existed among the Uruguayan accessions for NDF, and Sabine had significantly higher NDF content than the common entries. At College Station, only the commercial common dallisgrass entry and PI 404831 differed significantly for CP (Table 2). Variability for NDF at College Station was somewhat less than that observed at Baton Rouge. However, unlike at Baton Rouge, Sabine differed only from the commercial common entry (Table 2). Overall, CP and NDF of Sabine were slightly less than the mean of the common entries but forage digestibility was not different.
|
|
Pasture Study and Grazing Persistence
Forage biomass production, as estimated from clipped samples before grazing, was different for entry, year, and grazing period. All Uruguayan accessions were superior to common dallisgrass with DM yield per plant averaging 156 g for common compared to a mean of 232 g for the six Uruguayan accessions. Yields declined with each grazing period, but there was no grazing period x entry interaction. Common dallisgrass had lower NDF values than any of the Uruguayan accessions, but there were no differences in CP and IVTD (data not shown). The relative palatability of these dallisgrass biotypes was not specifically evaluated, but field observations indicated there were no gross animal preferences among entries during the grazing periods, and all plots were grazed at about the same intensity.
Data in Table 4 clearly show that when grazed, all Uruguayan accessions persisted better than common dallisgrass. Survival at the end of the establishment year (1998) did not differ statistically among entries (Table 4). After the first grazing season (1999), stand densities of all entries numerically decreased, but the greatest reduction was in the common dallisgrass plots. The mean stand density (94%) of the six Uruguayan entries was significantly higher (P < 0.01) than that of common dallisgrass (64%), and each Uruguayan accession was significantly higher than common. Following the second grazing season (2000), stand density of the Uruguayan accessions declined to a mean of 90%, whereas common decreased to 53%. Once again, the stand densities of all six Uruguayan entries were significantly superior to common. Of the six Uruguayan accessions, Sabine was the most persistent for both years (Table 4). Even though entry PI 404812 was the least persistent of the Uruguayan accessions, it persisted much better (P < 0.01) than common.
|
Other Characteristics
Sabine dallisgrass is more robust and grows more upright than does common. Its leaves are bluish-green in color with some purple coloring at the tips of the blades. Because of the bluish color, its leaves normally appear darker than those of common. Besides the differences in their overall plant size and leaf color, the inflorescences of common and Sabine are distinctly different. Inflorescences of Sabine have more racemes (8–15) than common (3–5). The racemes of common dallisgrass usually are attached to the opposite sides of the central axis of the inflorescence, essentially in one plane, whereas those of Sabine are attached to the central axis in a spiraled arrangement.
The chromosome number and meiotic behavior of Sabine and common differ. Sabine is a hexaploid with 60 chromosomes that pair essentially as 30 bivalents during meiosis I (Burson et al., 1991), and common is a pentaploid with 50 chromosomes that associate as 20 bivalents and 10 univalents at metaphase I of meiosis (Bashaw and Forbes, 1958). Both biotypes reproduce by aposporous apomixis (Bashaw and Holt, 1958; Burson et al., 1991). However, Sabine is a facultative apomict with a very low level of sexuality, and common is an obligate apomict.
Seed production studies comparing Sabine with common have not been conducted, but seed set of individual plants averaged 52% for Sabine and only 21% for common (Burson et al., 1991; Burson and Tischler, 1993). This difference is probably a result of the viability of their pollen, which are products of their meiotic behavior. Pollen stainability of common was 23% (Burson and Tischler, 1993); whereas, Sabine was 84% (Burson et al., 1991). Even though both reproduce by apomixis, pollen viability can influence seed set because both are pseudogamous and require that the polar nuclei in the female gametophyte be fertilized for the endosperm to develop.
The only major disease that affects dallisgrass is ergot, Claviceps paspali Stevens & Hall, and Sabine appears to be as susceptible to the causal organism as common dallisgrass. However, if proper pasture management practices are used, potential problems from ergot can be reduced or eliminated. Besides ergot, no other diseases or insect problems were observed at any location during the forage evaluation trials.
Sabine has the same amount of cold hardiness as common dallisgrass, and it may be slightly more cold tolerant (Burson et al., 1991). Because the cultivar persisted in central Arkansas and northern Mississippi for four years, its area of adaptation may extend to northern Arkansas and southern Tennessee.
Availability
Three classes of seed (Breeder, Foundation, and Certified) are recognized for Sabine dallisgrass. Breeder seed will be produced and maintained by the USDA–ARS, Southern Plains Agricultural Research Center at College Station, TX. Foundation seed will be maintained and distributed by the Texas Foundation Seed Service, Texas AgriLife Research, at Vernon, TX. Seed of Sabine dallisgrass was deposited in the National Plant Germplasm System.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication November 10, 2008.
References
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
