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a USDA-ARS Sugarcane Field Station, 12990 US Hwy. 441 N., Canal Point, FL 33438
b Florida Sugar Cane League, Inc., P.O. Box 1208, Clewiston, FL 33440
c United States Sugar Corp. 111 Ponce de Leon Ave., Clewiston, FL 33440
d Univ. of Florida, Everglades Research and Education Center, 3200 East Palm Beach Road, Belle Glade, FL 33430
e current address: Seminis Vegetable Seeds, Inc., P.O. Box 249, Felda, FL 33930. Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA, the University of Florida, or the Florida Sugar Cane League, Inc
* Corresponding author (Barry.Glaz{at}ars.usda.gov).
ABSTRACT
Research to develop ‘CPCL 97-2730’ (Reg. No. CV-137, PI 655943) sugarcane (a complex hybrid of Saccharum spp.) was initiated by the United States Sugar Corporation (USSC) and completed cooperatively by the USDA–ARS, the University of Florida, and the Florida Sugar Cane League, Inc. CPCL 97-2730 was released to growers in Florida in December 2008. CPCL 97-2730 was selected from a cross of USSC proprietary genotypes CL 75-0853 x CL 88-4730 made at Clewiston, FL, in December 1996. The female parent, CL 75-0853, had high commercial recoverable sucrose (CRS) but because of low cane yields was not used extensively by USSC. The male parent, CL 88-4730, is a high-yielding genotype that USSC is evaluating in commercial fields with sand and muck soils for possible extended use. CPCL 97-2730 was released because of its acceptable yields of cane and CRS on sand soils and its resistance to smut (caused by Ustilago scitaminea Syd. & P. Syd.), brown rust (caused by Puccinia melanocephala Syd. & P. Syd.), orange rust [caused by P. kuehnii (Kruger) E. Butler], leaf scald [caused by Xanthomonas albilineans (Ashby) Dowson], and sugarcane mosaic virus strain E.
Abbreviations: CP, Canal Point • CP program, Canal Point sugarcane cultivar breeding and selection program • CRS, commercial recoverable sucrose • EI, economic index • USSC, United States Sugar Corporation
CPCL 97-2730' (Reg. No. CV-137, PI 655943) is a sugarcane (a complex hybrid of Saccharum spp.) derivative of a long-term recurrent selection program conducted by the United States Sugar Corporation (USSC). Final selection for release was made through cooperative research of the USDA–ARS, the University of Florida, and the Florida Sugar Cane League, Inc., collectively referred to as the Canal Point (CP) sugarcane cultivar breeding and selection program (CP program) because its base of operations is at Canal Point, FL. It was released in Florida in December 2008. Modern sugarcane cultivars, such as CPCL 97-2730, are allopolyploid (with aneuploidy) hybrids, and in the mainland United States, they can be traced back to 17 founder clones (Deren, 1995). These founders were used in S. officinarum x S. spontaneum crosses and the F1 hybrids were backcrossed to the S. officinarum background to recover high sucrose content (Roach, 1972; Sreenivasan et al., 1987). Modern sugarcane cultivars represent advanced generations of long-term breeding that began with these backcrosses.
CPCL 97-2730 was released because of its high yields of cane and commercial recoverable sucrose (CRS) on sand soils and its resistance to smut (caused by Ustilago scitaminea Syd. & P. Syd.), brown rust (caused by Puccinia melanocephala Syd. & P. Syd.), orange rust [caused by P. kuehnii (Kruger) E. Butler], leaf scald [caused by Xanthomonas albilineans (Ashby) Dowson], and sugarcane mosaic virus strain E (mosaic) in Florida. Edmé et al. (2005) reported that the CP program was responsible for significant sugarcane yield gains on muck soils in Florida over a 33-yr period but that there were no sugarcane yield gains for sand soils. It is hoped that CPCL 97-2730 will help improve yields on sand soils.
While in the USSC program, the name of CPCL 97-2730 was CL 97-2730 because it was the 2730th selection from 72,865 genotypes planted in 1997 (CL 97) from true seeds. The CP was added to the name in 2004 to indicate that USSC donated CL 97-2730 to the USDA–ARS and that the CP program would continue testing of CPCL 97-2730 for possible release. CPCL 97-2730 was selected from the cross of USSC proprietary genotypes CL 75-0853 x CL 88-4730 made at Clewiston, FL, in December 1996. Evaluations of commercial plantings of the female parent, CL 75-0853, by USSC indicated that it had high CRS but its cane yields were not acceptable for commercial production in Florida. The male parent, CL 88-4730, is currently under extensive evaluation in USSC commercial fields. Yields of cane and sucrose are high, but USSC is concerned about moderate levels of brown rust infections on CL 88-4730. The male parent of CL 75-0853 was cultivar CL 54-378 (Weetman and Bourne, 1971), which peaked at 11.6% of Florida's sugarcane acreage in 1983 (Glaz and Donovan, 1984). The male parent of CL 88-4730 was CL 78-1600, which was a proprietary genotype planted moderately in commercial fields by USSC until it became susceptible to brown rust. Cultivar CP 72-1210 (Miller et al., 1981), a great-great grandparent of CPCL 97-2730, was the most widely planted sugarcane cultivar in Florida from 1985 through 1991, and it peaked at 61% of Florida's sugarcane acreage in 1987 (Coale and Glaz, 1988). Growers discontinued planting CP 72-1210 because it became susceptible to brown rust.
METHODS
Early Selection Stages
Evaluations on CPCL 97-2730 were made in the USSC breeding and selection program until the final selection stage of this program, when it was donated to the USDA–ARS, (Table 1
). One of 220 crosses made by USSC in the 1996–1997 crossing season at Clewiston, FL, was CL 75-0853 x CL 88-4730. The F1 seed was planted in flats in a greenhouse early in 1997, and CPCL 97-2730 was one of 72,865 genotypes transplanted to the field in June 1997 on a Terra Ceia muck soil (euic, hyperthermic Typic Haplosaprist) at Ritta Plantation of USSC (Ritta), just east of Clewiston. From this stage on, the USSC program propagated genotypes clonally.
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CPCL 97-2730 was one of 1324 genotypes advanced from the unreplicated to the replicated A-Plot stage at Ritta in October 2000. Selection was based on the Brix, determined by a hand refractometer, of juice that was extracted from the stalk by a hand-punch, subjectively assigned cane yield rating in September 2000, and freedom from diseases (especially brown rust, smut, leaf scald, and mosaic), and insects [spider mites (Oligonychus grypus), yellow sugarcane aphids (Sipha flava), and lace bugs (Leptodictya tabida)]. Disease and insect resistance was based on natural infection. Row and plot spacing in the replicated A-Plots was similar to those of unreplicated A-Plots except that plot rows were 3.0 m in the replicated A-Plots. Genotypes were replicated two times. Three reference cultivars were ‘CP78-1628’ (Tai et al., 1991) and proprietary USSC cultivars CL 77-0797 and CL 84-3152. The three reference cultivars were replicated an average of 19 times. CL 77-0797 was the primary reference cultivar for cane and sucrose yields. Visual ratings were made on growth type. Generally, highly recumbent or uprooted genotypes, genotypes with protruding buds, and genotypes with many broken stalks were not selected.
Stalks were counted in the replicated A-Plots in August 2001. In October 2001, 10-stalk samples were collected from each plot and weighed. Cane yield was calculated as the product of stalk weight by stalk number.
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All stalks were then milled to extract juice and determine CRS, measured as grams of sucrose per kilogram cane, using a modified version of the calculations described by Legendre (1992). The modifications used USSC sugar recovery efficiencies assuming a 10% fiber for all genotypes. Theoretical economic index (EI; profitability) was calculated based on a procedure that estimated the profitability of a cultivar using the cane yield, sucrose content, and costs of harvesting, hauling, and milling the cane (Deren et al., 1995). Costs identified by USSC were used in EI calculations for the replicated A-Plots.
The major selection criteria in the replicated A-Plots were EI, sucrose yield, cane yield, sucrose content, stalk number, and resistance to brown rust, smut, mosaic, and leaf scald. Sucrose yield was calculated as
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Yield Trials in Commercial Fields
From the first-ratoon of the replicated A-Plots, 89 genotypes were advanced to the Screen Test in November 2002. The 89 genotypes from the replicated A-Plots and six reference cultivars (USSC proprietary cultivars CL 77-0797 and CL 89-5189, CP 73-1547 [Miller et al., 1982], CP 78-1628, CP 84-1198 [Glaz et al., 1994], and CP 89-2143 [Glaz et al., 2000]) were planted in yield trials in commercial fields at three USSC farms, Townsite (Margate sand soil [siliceous, hyperthermic Mollic Psammaquent]), Bourne (Pahokee muck soil [euic, hyperthermic Lithic Haplosaprist]), and Ritta (Terra Ceia muck soil). All three trials had two replications of each genotype planted in randomized complete block designs in plots with three rows 10.5 m long. Plots were separated by 4.5-m alleys at both ends of each experiment. Data were collected in the plant-cane (October 2003 and February 2004) and first-ratoon (October 2004) crops (although the decision to advance CPCL 97-2730 was made on the plant-cane data only). Cane yield was estimated by taking the average of two estimates. One estimate was determined by multiplying stalk number by stalk weight after counting stalks and estimating stalk weight by weighing a 10-stalk sample. The second estimate was determined by weighing the sugarcane stalks in all three rows. Commercial recoverable sucrose was estimated from 10-stalk samples at the beginning of each harvest season (October) and later (January–February). Based on its cane yield and CRS, as well as its resistance to brown rust, leaf scald, mosaic, and smut, CPCL 97-2730 was among 18 genotypes advanced from the Screen Test to Stage 4 in December 2003.
The 18 Stage-4 genotypes, including CPCL 97-2730, were planted in yield trials within commercial fields of USSC at Townsite (Margate sand soil) and Benbow (Margate–Oldsham [fine, smectitic, calcareous, frigid cumulic Vertic Endoaquoll] sand soil) in December 2003. Reference cultivars were CP 78-1628 and CP 89-2143. Although most genotypes were replicated three times at each location, there were only two replications of CPCL 97-2730 at Townsite. Genotypes in each trial were planted in a randomized complete block design in plots four rows wide and 10.5 m long. Alleys of 4.5 m separated plots. After these tests were planted, CPCL 97-2730 was donated to the USDA–ARS, and personnel in the CP program conducted all experiments from this point.
Samples of 10 stalks were milled to extract juice and determine theoretical recoverable sucrose, which was calculated as described by Legendre (1992). Percentage fiber of CPCL 97-2730 was estimated from two five-stalk samples collected in February 2007. Leaves were stripped from these stalks, which were then cut into three approximately even sections (bottom, middle, and top stalk sections). Two randomly selected bottom, middle, and top sections were processed through a Jeffco cutter-grinder (Jeffries Brothers, Ltd., Brisbane Queensland, Australia). About 75 g of material (fresh bagasse) processed through the cutter-grinder were collected and weighed. These fresh bagasse samples were then placed in cloth bags and washed twice in a washing machine to remove soluble solids. Samples were then dried at 63°C until their weights no longer dropped. The fiber percentage of a genotype was calculated as
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Samples of CP 89-2143 were also processed when fiber samples of CPCL 97-2730 were processed, and the fiber percentage of CPCL 97-2730 was corrected to the historic fiber percentage of CP 89-2143. For example, the reported fiber percentage of CP 89-2143 is 9.85%. If its estimated fiber was 10.00% on the day when the fiber of CPCL 97-2730 was estimated, then the estimated fiber percentage of CPCL 97-2730 was corrected by multiplying it by 0.985.
Ten-stalk samples were collected in October 2004 from the plant-cane trial at Townsite and in October 2005 from the first-ratoon trial at Benbow. These samples were used to estimate CRS at the beginning of Florida's sugarcane harvest season. Commercial recoverable sucrose was also estimated from a second set of 10-stalk samples collected each year from both locations in January 2005 (plant-cane crop), January 2006 (first-ratoon crop), and October and December 2006 (second-ratoon crop). To estimate CRS, all values of theoretical recoverable sucrose were multiplied by 0.86 to approximate CRS. Similarly, Legendre (1992) reported the calculation of a liquidation factor (ranging from 0.83 to 0.90) that was used by commercial mills in Louisiana to convert theoretical recoverable sucrose to CRS.
Stalk weight was estimated from the same 10-stalk samples that were used to estimate CRS. Stalks were counted in the two interior rows of each plot in July 2004 (plant cane), August and September 2005 (first ratoon), and September 2006 (second ratoon). Cane tonnage was estimated by the product of stalk weight by stalk number.
Characterization by Microsatellite Genotyping
Six pairs of microsatellite primers (Table 2
) developed through the International Consortium for Sugarcane Biotechnology (Cordeiro et al., 2003) were used to generate a genetic fingerprint for CPCL 97-2730. This was compared with those of cultivars CP 72-2086 (Miller et al., 1984), CP 78-1628, CP 80-1743 (Deren et al., 1991), CP 88-1762 (Tai et al., 1997), and CP 89-2143. These five major commercial cultivars occupied 86% of the sugarcane acreage in Florida in 2007 (Glaz, 2008).
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CHARACTERISTICS
Field Performance
CPCL 97-2730 was tested on sand soils in six harvests at two trial locations in Florida during 2004–2005 (two plant-cane harvests), 2005–2006 (two first-ratoon harvests), and 2006–2007 (two second-ratoon harvests). CPCL 97-2730 had higher stalk weights than CP 78-1628 in both ratoon crops, and the two cultivars had similar stalk weights in the plant-cane crop (Table 3
). The stalk weight of CPCL 97-2730 was higher than that of CP 89-2143 in the second-ratoon crop; otherwise, the two cultivars had similar stalk weights. Fiber content of CPCL 97-2730 was 9.52%.
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CPCL 97-2730 was the first genotype donated to USDA–ARS at Canal Point by USSC that was released for commercial production in Florida. It was at an advanced testing stage when it was donated so it was decided to continue that testing rather than incorporate it into the trials routinely conducted by the CP program. However, advancement decisions and the release recommendation were made according to CP program protocols. That is, these decisions were made by a committee of sugarcane farmers and public and private scientists. Members of this committee recommended release of CPCL 97-2730 in June 2008 due to its acceptable yields of cane and sucrose on sand soils, its resistance to brown and orange rust, and its resistance or tolerance to other major sugarcane diseases found in Florida.
Agronomic, Botanical, and Molecular Descriptions
Plants described here were characterized on 28 July 2008 at 252 d after planting in a field at USSC–Townsite, FL (Table 4
). The CPCL 97-2730, CP 72-2086, and CP 89-2143 stalks characterized and compared were from inner rows unexposed to direct sunlight unless otherwise noted. Colors were determined from Munsell Color Charts for Plant Tissues, and botanical descriptions were based on terminology of Artschwager and Brandes (1958). However, color and other phenotypic expressions may vary in sugarcane cultivars without any change in the genotype with differences in growth, environment, and cultural conditions.
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The mean stalk height (ground level to top visible dewlap, dewlaps form the hinge of the blade joint in sugarcane) of 10 CPCL 97-2730 stalks was 230 cm compared with stalk heights of 175 cm for CP 72-2086 and 169 cm for CP 89-2143 (Table 4). The mean internode length of five CPCL 97-2730 stalks at the fifth internode from the ground was 19.2 cm compared with 15.5 cm for CP 72-2086 and 13.8 cm for CP 89-2143. Stalk diameter was measured at the middle of the second (low) and fifth (middle) internodes from the ground as well as at the middle of the hardened internode closest to the top visible dewlap (upper) on five stalks. The mean low, middle, and upper stalk diameters of CPCL 97-2730 were 27.7, 25.3, and 21.4 mm, respectively. These compared with CP 72-2086 low, middle, and upper diameters of 32.5, 29.5, and 27.7 mm, respectively; and CP 89-2143 diameters of 26.8, 30.1, and 32.0 mm, respectively.
CPCL 97-2730 exhibited a cylindrical shaped internode and a growth ring with a mean width of 2.7 mm at the fifth internode from the ground. The root band of CPCL 97-2730 was 7.9 mm wide and had primordia with diameters ranging from 1.9 to 2.6 mm. The root band had a light wax layer. When present, bud furrows on stalks of CPCL 97-2730 extended about half the length of the internode. CP 72-2086 internodes occasionally had shallow bud furrows and CP 89-2143 internodes infrequently exhibited indistinct bud furrows. The buds of CPCL 97-2730, CP 72-2086, and CP 89-2143 were yellow (5 Y 8/4). Buds of CPCL 97-2730 and CP 72-2086 extended to the growth ring. Buds of all three cultivars were raised above the surface of the root band and exhibited shapes described by Artschwager and Brandes (1958) as round with central germ pore at the fifth internode from the ground. The mean bud length and width of the fifth bud from the bottom from five stalks of CPCL 97-2730 were both 7.2 mm. The mean widths of CP 72-2086 and CP 89-2143 buds were 6.4 and 6.0 mm, respectively; and the mean lengths of CP 72-2086 and CP 89-2143 buds were 6.0 and 6.1 mm, respectively. None of these cultivars exhibited pubescence on the buds.
The canopy of CPCL 97-2730 was curved compared with the erect canopies with drooping tips of CP 72-2086 and CP 89-2143. The mean leaf blade lengths and widths of CPCL 97-2730, CP 72-2086, and CP 89-2143 at the top visible dewlaps were 147 and 3.9 cm, 153 and 4.6 cm, and 156 and 4.0 cm, respectively. Leaf sheaths of CPCL 97-2730 did not adhere tightly to the stalk, and their center regions had heavy pubescence. Leaf sheaths were yellow-green (5 GY 7/2). CPCL 97-2730, CP 72-2086, and CP 89-2143 leaves exhibited raised midribs on their abaxial sides. The mean midrib width of CPCL 97-2730 at the widest part of the leaf at the top visible dewlap was 5.4 mm on the adaxial side. These compared with midrib widths of 6.1 mm on CP 72-2086 and 6.7 mm on CP 89-2143. The midrib of CPCL 97-2730 was green yellow (5 GY 5/4) on the abaxial side. On the adaxial side, the midrib of CPCL 97-2730 was white.
After scraping off their light wax covering, dewlaps on the upper leaves of mature plants were green-yellow (2.5 GY 8/4), and their shape was squarish subcrescent, using the terminology of Artschwager and Brandes (1958). Dewlap shape of CP 72-2086 was deltoid, and dewlaps of CP 89-2143 had a double crescent deltoid shape. CPCL 97-2730 had auricles only on one side of the leaf sheath, and their shape was long lanceolate. The auricles of CP 72-2086 were deltoid but were not always present on both sides of the leaf sheath, and auricles of CP 89-2143 were deltoid and present only on one side. Mean auricle lengths, measured four nodes below the top visible dewlap for CPCL 97-2730, CP 72-2086, and CP 89-2143 were 19.2, 15.5, and 13.8 mm, respectively. The linear crescent ligule shape of CPCL 97-2730 compared with the crescent with lozenge shape of CP 72-2086 ligules and broad crescent ligules of CP 89-2143.
The six microsatellite primer pairs amplified 36 fragments, ranging from 105 to 257 bp, in CPCL 97-2730 (Table 2). The number of fragments amplified by each primer pair ranged from 4 to 9. Of the 36 fragments amplified, 23 were polymorphic and 13 were monomorphic. CPCL 97-2730 shared 22 fragments with CP 78-1628, 25 with CP 72-2086, 21 with CP 89-2143, 27 with CP 80-1743, and 29 with CP 88-1762. Fragments unique to CPCL 97-2730 among the genotypes examined were identified in the fingerprints obtained using primer pairs SMC334BS, SMC1493CL, mSSCIR14, and mSSCIR53.
Disease Reactions
Screening of CPCL 97-2730 was conducted by inoculation testing and/or monitoring for natural infection to smut, leaf scald, brown rust, mosaic, and Sugarcane yellow leaf virus (Table 5
).
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Genotypes in the routine CP selection program are inoculated with eye spot [caused by Bipolaris sacchari (E.J. Butler) Shoemaker] in Stage 2. Since CPCL 97-2730 did not pass through this selection stage, its reaction to an eye spot inoculation is unknown. However, eye spot is not a commercial problem on sugarcane in Florida. During its 3 yr in Stage 4, no smut sori due to natural infection were observed on CPCL 97-2730. Two sori were observed on CP 78-1628 during this period. Smut susceptibility of CP 78-1628 is at the upper limit of acceptability for commercial production in Florida. Based on this limited information, CPCL 97-2730 was considered resistant to smut at the time of its release.
Greenhouse inoculations on CPCL 97-2730 were conducted with leaf scald in 2005 and mosaic in 2005 and 2006. Number of infected CPCL 97-2730 plants with leaf scald and mosaic were compared with number of infected plants of CP 72-2086. CP 72-2086 is resistant to leaf scald and is at the upper infection level for mosaic that is acceptable for commercial production in Florida. In the leaf scald inoculation test, 5.7% of CPCL 97-2730 plants were infected with leaf scald compared with 18.1% for CP 72-2086. In both years, no plants of CPCL 97-2730 were infected with mosaic compared with 18.1 and 70.3% for CP 72-2086 in 2005 and 2006, respectively. Throughout its final stage yield testing, no plants of CPCL 97-2730 were identified that were naturally infected with mosaic, and only four plants were found infected with leaf scald. Based on these inoculation tests and natural infection evaluations, CPCL 97-2730 was considered to have sufficient resistance to leaf scald and mosaic for commercial production in Florida. No information is available on the reaction of CPCL 97-2730 to ratoon stunt (caused by Clavibacter xyli subsp. xyli Davis et al.).
Availability
In its initial year of release, seed cane of CPCL 97-2730 will be available from the Florida Sugar Cane League, Inc., for commercial planting in Florida. It is not anticipated that patent protection for CPCL 97-2730 will be sought. Small quantities of seed cane for research purposes may be obtained at the USDA–ARS Sugarcane Field Station, Canal Point, FL, where CPCL 97-2730 will be maintained for at least five years from the date of this publication.
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 January 27, 2009.
References
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