Published in Crop Sci. 43:1996-1998 (2003).
© 2003 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
CROP BREEDING, GENETICS & CYTOLOGY
Early Plant Selection Effects on Crown Traits in Pensacola Bahiagrass with Selection Cycle
A. R. Blount*,a,
R. N. Gatesb,
P. L. Pfahlerc and
K. H. Quesenberryc
a North Florida Research and Education Center, Univ. of Florida, Quincy, FL 32351
b Crop Genetics and Breeding Research Unit, USDA-ARS, P.O. Box 748, Coastal Plain Exp. Stn., Tifton, GA 31794-0748
c Agronomy Dep., P.O. Box 110500, Univ. of Florida, Gainesville, FL 32311-0500
* Corresponding author (ablount{at}mail.ifas.ufl.edu).
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ABSTRACT
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A positive relationship between crown traits of greenhouse-grown plants and crown development in the field would allow for the efficient evaluation of large populations of bahiagrass (Paspalum notatum Flügge) for rapid stand establishment. The objective of this study was to determine if young plants exhibiting greater crown vigor (expressed as rapid crown area growth and profuse tillering) in the greenhouse would result in larger, more vigorous plants when grown in the field. Fifty young bahiagrass plants, from each of four cycles (C0, C4, C9, and C23) resulting from recurrent restricted phenotypic selection (RRPS), were evaluated in the greenhouse for plant vigor, crown width, crown wet weight, and tiller number. Plants were transplanted to the field and crown area was determined at 6 and 15 mo after establishment. Crown vigor of greenhouse plants was greatest for C4 and C9 plants. Vigor ratings for C9 plants were smaller (P < 0.05) than C4 in Exp. 2, but larger than C0 and C23. Crown area, crown wet weight, and tillering of the greenhouse plants favored plants from C4 populations. Greenhouse plants of C23 generally had smaller crowns and less tillering. Crown area of individual plants from greenhouse plants, for all cycles, was positively correlated with crown area in the field after 6 mo following transplanting (r = 0.74 to 0.87 for Exp. 1 and 0.75 to 0.93 for Exp. 2). At 15 mo after transplanting to the field, bahiagrass crowns had filled the area between spaced plants. Selecting young superior bahiagrass plants in the greenhouse should aid breeders in developing germplasm that could hasten field establishment.
Abbreviations: C0, Cycle 0 • C4, Cycle 4 • C9, Cycle 9 • C23, Cycle 23 • RRPS, recurrent restricted phenotypic selection
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INTRODUCTION
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PENSACOLA BAHIAGRASS (P. notatum Flügge var. saure Parodi) occupies >2.5 million ha in Florida and the southern Gulf Coast (Burton et al., 1997). It is valued as a pasture grass because of its adaptation to the soils and climate of the southern Coastal Plain of the USA. The grass is also widely used in crop rotation (Stephens and Marchant, 1960) and has been grown to reduce plant-parasitic nematode populations in various cropping systems (Rodriguez-Kabana et al., 1993, 1994). ‘Tifton 9’ (Burton, 1989), which has been a successful cultivar in the southeastern USA, is one of the few bahiagrass cultivars developed through traditional plant breeding.
Burton (1974)(1982) developed and used a RRPS method to improve bahiagrass for low heritability traits such as forage yield. In 1982, this procedure involved selecting the largest young plants in the greenhouse for transplanting to the field to improve the system of the RRPS for increasing forage yield. Significant changes in forage yield and plant morphology of space-planted Pensacola bahiagrass were reported from a study by Werner and Burton (1991) in which 16 cycles of RRPS resulted in improvements in forage yield with successive cycles, but reduced the crown diameter. Werner and Burton (1991) suggested that selection for increased plant weight might be positively correlated with selection of plants with greater culm numbers. There have been limited published reports of enhancing plant vigor by selecting young plants for vigorous phenotypes to hasten bahiagrass improvement (Burton, 1982; Werner and Burton, 1991; Gates and Burton, 1998). Gates and Burton (1998) noted a significant improvement of seedling emergence in Cycle 18, when compared with Tifton 9 and Pensacola bahiagrass. They attributed improved emergence to selection for more vigorous germination of greenhouse-grown plants that were used for field evaluation.
Several studies at the North Florida Research and Education Center at Quincy, FL, suggest that improvement in the speed in which crown area is achieved in field-grown spaced plants could be enhanced by selection for crown traits in young bahiagrass plants grown in the greenhouse (2001, unpublished data). In greenhouse-germinated bahiagrass, crown size was found to be a highly variable trait observed in several RRPS selection cycles. Developing a greenhouse procedure to screen large populations of young plants for superior crown development should aid breeders in developing bahiagrass germplasm that will hasten field establishment. The objective of this study was to determine if young plants exhibiting greater crown vigor (expressed as rapid crown area growth and profuse tillering) in the greenhouse would result in larger, more vigorous plants in the field.
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MATERIALS AND METHODS
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Experiment 1
Seeds from each of four RRPS cycles of C0 bahiagrass, (Pensacola originating from Wide Gene Population), C4, C9 (Tifton 9), and C23 were obtained from G.W. Burton, Coastal Plain Exp. Station, Tifton, GA. Fifty seeds from each of the four selection cycles described above were sown into 50- x 50-mm containers of sterile Metro Mix 200 potting soil (Scotts-Sierra, Marysville, OH) on 19 Feb. 1999 and arranged in a randomized complete block design in a greenhouse at the North Florida Research and Education Center (31° N lat). Plants were grown at an average 28°C, fertilized monthly with 0.1 g per plant Osmocote 14-14-14 (N–P2O5–K20; Scotts-Sierra), and watered daily.
On 22 June 1999, when plants were about four months of age, they were washed free of soil and fibrous roots were removed. Plants were visually rated on a 1-to-5 scale for vigor based on a selection index where 1 = a small crown width and low tillering (smallest 20% of plants), to 5 = a large crown width and vigorous tillering (largest 20% of plants). Top growth (leaves) above a height of 5 mm from the crown was removed, crown width was measured (total mm across the widest part of the crown and branches), crown wet weight was recorded (g wet weight), and tillers were counted. Individual plants were then placed in containers and allowed to reestablish their roots and leaves.
On 24 June 1999, a 0.5-ha field on Norfolk sandy loam soil (fine-loamy, kaolinitic, thermic Typic Kandiudults) was broadcast-fumigated with methyl bromide at a rate of 39.2 g m-2 (98% methyl bromide: 2% chloropicrin [nitrotrichloromethane] by volume). On 14 July 1999, plants were transplanted to the fumigated field arranged in a randomized complete block design with 50 replications. Each block consisted of one plant from each of the four cycles. Plants were planted on a square grid, on 0.6-m centers. Crown area of the field-grown plants was measured on 20 Jan. 2000 at 6 mo after transplanting, and remeasured 6 Oct. 2000, 15 mo after transplanting. Crown growth was determined with a grid system devised from a 500-mm2 plastic frame, arranged with cross-section squares of 100 mm2. The number of squares the crown occupied provided a quick method to measure the crown area of an individual plant and was reported as m2 per plant.
Experiment 2
Experiment 2 was a repetition of Exp. 1 with different dates of planting, transplanting, and measurements. The seeds were planted in the greenhouse on 14 Feb. 2000 by the same planting procedures, location, and fertilization as outlined in Exp. 1.
On 20 July 2000, 50 plants from each selection cycle were washed free of soil, and fibrous roots were removed. Data were recorded and plants were allowed to reestablish in containers as previously described in Exp. 1.
Plants from Exp. 2 were transplanted to the same field adjacent to Exp. 1 on 22 Aug. 2000. The experimental design was a randomized complete block design with 50 replications. Crown area of the field-grown plants was determined on 25 Jan. 2001 (6 mo after transplanting) and 10 Oct. 2001 (15 mo after transplanting) with the grid system described in Exp. 1.
Experiment x population (cycles) interactions were found in the overall ANOVA. Therefore, results are reported separately for Exp. 1 and 2. Analysis of variance and correlation coefficients of greenhouse and field data were calculated with SAS GLM (SAS Institute, 1987) and Statistix 7 (Analytical Software, 2000) at P = 0.05. Least significant difference at the 0.05 level of probability was used for comparisons among means.
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RESULTS AND DISCUSSION
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Phenotypic crown vigor ratings made among plants in the greenhouse representing the four RRPS bahiagrass selection cycles indicated that maximum crown vigor occurred in both C4 and C9 in Exp. 1, although C9 was less (P < 0.05) than C4 in Exp. 2 (Table 1). For greenhouse data in both experiments, C4 plants appeared to be more uniform for the number of tillers on individual plants and have greater crown width and weight compared with individual plants from the other cycles. Greenhouse data from both experiments indicated a slight decline in crown vigor was evident between C4 and C9, although ratings in Exp. 1 between these two cycles were not different (P > 0.05). Visual ratings of C0 plants were not as great as those of C4 in Exp. 1, and those of C4 and C9 in Exp. 2. In both experiments, C23 lacked appreciable tillering, had lower crown width and weight, and ranked lowest for crown vigor compared with the other cycles.
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Table 1. Tiller number, crown area, crown wet weight, and visual vigor rating for greenhouse-grown recurrent restricted phenotypic selection (RRPS) bahiagrass cycles in Exp. 1 and 2.
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Crown width, crown wet weight, and tillering were greatest for C4 in both experiments (Table 1). While plants of C9 tillered well, had superior crown wet weight, and crown width in Exp. 1, this was not the case in Exp. 2. Plants of C9 had less tillering, smaller crown width, and lower crown wet weight (P < 0.05) than plants of C4, and were not different (P > 0.05) from C0 for the same traits. Plants of C23 had lower crown wet weight and width, and had fewer tillers than plants in other cycles.
These morphological changes in the plant were similar to those reported by Werner and Burton (1991) based on their field observations. Werner and Burton (1991) reported morphological changes occurred toward more upright, taller plants with advancing selection cycles. Werner and Burton (1991) attributed these changes to the RRPS breeding method used to select increased forage production of space-plant populations which favored upright (smaller crown diameter) over prostrate plant growth habit. Burton's improved RRPS procedure, used to develop Tifton 9, included selecting the largest greenhouse-grown seedlings to advance to the field in the next selection cycle (Burton, 1982; G.W. Burton, 1999, personal communication). Werner and Burton (1991) suggested that plant breeding improvement in plant weight could be made by selecting for increased number of culms on a plant; however, they concluded that visual selection would be less time-consuming and would not eliminate large plants with fewer culms. Utilizing visual selection for culm number as a main selection criteria to improved forage yield, the morphology of the plants comprising each cycle was altered toward a more upright growth habit with a smaller basal diameter by Cycle 16 (Werner and Burton, 1991).
A crown area measurement of C4 plants in the field at 6 mo was greater (P < 0.05) than those of C0 and C9, while C23 had the smallest (P < 0.05) crowns (Table 2). Experiment 1 plants measured at 15 mo indicated that C0 plants had rapidly covered the ground and were larger plants than C9 or C23, but not greater (P > 0.05) than C4. In Exp. 1, C23 plants at 15 mo had the smallest crowns. Crown measurements in Exp. 2 at 6 mo were similar to the results obtained in Exp. 1, although C0 and C4 did not differ. At 15 mo, C0 plants in Exp. 2 were larger than those of C4, followed by C9 and C23.
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Table 2. Crown area of recurrent restricted phenotypic selection (RRPS) bahiagrass cycles of field-grown plants in Exp. 1 and 2.
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Crown widths obtained in Exp. 1 from C0, C4, C9, and C23 plants, taken in the greenhouse were highly positively correlated with crown area at 6 mo after transplanting in the field (Table 3). However, the crown width of plants measured in the greenhouse did not correlate (P > 0.05) with crown area of plants 15 mo after transplanting. Similar results were found for comparisons of Exp. 2 greenhouse plants with crown area at 6 mo and 15 mo in the field.
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Table 3. Correlation coefficients for crown vigor rating in the greenhouse and crown area in the field at two dates following transplanting for recurrent restricted phenotypic selection (RRPS) bahiagrass cycles from Exp. 1 and 2.
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Although positive correlations only were identified in field-grown plants 6 mo after transplanting to the field, the lack of positive correlation at 15 mo resulted from the plants having outgrown the grid used in this study. At 15 mo following transplanting to the field, the individual plants were difficult to separate from one another. Positive correlation of selected crown traits in greenhouse-grown bahiagrass plants with crown area in the field may provide breeders with a rapid screening tool to improve establishment of bahiagrass pastures.
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ACKNOWLEDGMENTS
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The authors wish to thank Dr. G.W. Burton for bahiagrass RRPS C0, C4, C9, and C23 used in this study and his comments on methods of greenhouse selection for rapid advancement of polycrossed plants.
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NOTES
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Florida Agric. Exp. Stn. Journal Series No. R-08744.
Received for publication April 16, 2002.
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REFERENCES
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- Analytical Software. 2000. Statistix 7 for Windows. Version 7. Analytical Software, Tallahassee, FL.
- Burton, G.W. 1974. Recurrent restricted phenotypic selection increases forage yields of Pensacola bahiagrass. Crop Sci. 14:831–835.[Abstract/Free Full Text]
- Burton, G.W. 1982. Improved recurrent restricted phenotypic selection increases bahiagrass forage yields. Crop Sci. 22:1058–1061.[Abstract/Free Full Text]
- Burton, G.W. 1989. Registration of ‘Tifton 9’ Pensacola Bahiagrass. Crop Sci. 29:1326.[Free Full Text]
- Burton, G.W., R.N. Gates, and G.J. Gascho. 1997. Response of Pensacola bahiagrass to rates and ratios of nitrogen, phosphorus, and potassium fertilizers. Proc.—Soil Crop Sci. Soc. Fla. 56:31–35.
- Gates, R.N., and G.W. Burton. 1998. Seed yield and seed quality response of Pensacola and improved bahiagrasses to fertilization. Agron. J. 90:607–611.[Abstract/Free Full Text]
- Rodriguez-Kabana, R., N. Kokalisburelle, D.G. Robertson, P.S. King, and L.W. Wells. 1994. Rotations with Coastal bermudagrass, cotton, and bahiagrass for management of Meloidogyne arenaria and southern blight in peanut. J. Nematol. 26:665–668.
- Rodriguez-Kabana, R., D.G. Robertson, and J. Bannon. 1993. Bahiagrass–cotton rotations and the management of Meloidogyne incognita and Hoplolaimus galeatus. Nematropica 23:141–147.
- SAS Institute. 1987. SAS/STAT guide for personal computers. Version 6. SAS Inst., Cary, NC.
- Stephens, J.L., and W.H. Marchant. 1960. Bahiagrass for pastures. Bull. N.S. 67. Georgia Agric. Exp. Stn., Athens, GA.
- Werner, B.K., and G.W. Burton. 1991. Recurrent restricted phenotypic selection for yield alters morphology and yield of Pensacola bahiagrass. Crop Sci. 31:48–50.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
