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a USDA-ARS, SRRC, Sugarcane Research Unit, 5883 USDA Rd., Houma, LA 70360
b current address: Louisiana State Univ. Agric. Center, Sugar Research Station, 5755 LSU Ag Rd., St. Gabriel, LA 70776
c USDA-ARS, Sugarcane Field Station, 12990 US Hwy. 441 N, Canal Point, FL 33438
* Corresponding author (Thomas.Tew{at}ars.usda.gov).
ABSTRACT
‘HoCP 00-950’ (Reg. No. CV-135, PI 654823) sugarcane (a complex hybrid of Saccharum officinarum L., S. spontaneum L., S. barberi Jeswiet, and S. sinense Roxb. amend. Jeswiet) was selected and evaluated by the USDA-ARS, working cooperatively with the Louisiana State University AgCenter, and the American Sugar Cane League, Inc. It was released to growers in Louisiana in April 2007. In 67 machine-harvested trials on light- and heavy-textured soils from 2004 to 2007 (plant-cane through third-ratoon crop) averaged over nine southern Louisiana locations, HoCP 00-950 produced 5% more sugar and had 6% higher sugar content than the industry standard, ‘HoCP 96-540’. In plant-cane and ratoon-crop maturity tests harvested in 2007, HoCP 00-950 had significantly higher sugar content than HoCP 96-540 across all harvest dates, with 35% higher sugar content at the outset of the harvest season (late September). HoCP 00-950 is resistant to brown rust (Puccinia melanocephala), smut (Ustilago scitaminea), leaf scald (Xanthomonas albilineans), and mosaic diseases. It is susceptible to the sugarcane borer (Diatraea saccharalis) and should not be planted in areas where pesticide use is restricted. The early maturity characteristic of HoCP 00-950 provides growers with a variety that can produce profitable sugar yields early in the milling season without the need to apply a chemical ripener.
Abbreviations: CVB, colonized vascular bundles • LSU, Louisiana State University • SCMV, Sugarcane mosaic virus, SRL, Sugarcane Research Laboratory • SrMV, Sorghum mosaic virus • RSD, ratoon stunting disease • SSR, simple sequence repeat
Based on its pedigree, HoCP 00-950 (Reg. No. CV-135, PI 654823) sugarcane (Saccharum spp.), is a complex hybrid whose genomic makeup consists largely of genes contributed by S. officinarum L. and S. spontaneum L., with minor input from S. barberi Jeswiet and S. sinense Roxb. amend. Jeswiet. Modern sugarcane cultivars such as HoCP 00-950 are allopolyploid (or aneuploid) hybrid derivatives of a few progeny populations developed by crossing S. officinarum x S. spontaneum and backcrossing to the officinarum background to recover the high sucrose content (Roach, 1972; Sreenivasan et al., 1987).
The earliest known maternal ancestor of HoCP 00-950 was ‘Bandjermasin Hitam,’ a S. officinarum accession used by sugarcane breeders on the island of Java (Indonesia) in the early 1900s. Of the 20 commercial sugarcane cultivars released in Louisiana since 1975, only HoCP 00-950 and ‘Ho 95-988’ (Tew et al., 2005a) were maternally derived from Banjermasin Hitam; the other 18 were maternally derived from ‘Black Cheribon’ (S. officinarum). At the time HoCP 00-950 was released, nearly 90% of the area planted to sugarcane in Louisiana was either planted to ‘LCP 85-384’ (Milligan et al., 1994) or one of its progeny, namely, ‘HoCP 96-540’ (Tew et al., 2005b) or ‘L 97-128’ (Gravois et al., 2008). There is a need for increased genetic diversity in Louisiana's sugar industry, and the release of HoCP 00-950 helps address this need.
Methods
Crossing and Early Selection Stages
HoCP 00-950 was selected by scientists from the USDA-ARS Sugarcane Research Laboratory (SRL) at Houma, LA from a cross between HoCP 93-750 and HoCP 92-676. The parents are full-sib progeny of CP 84-722 x LCP 81-30. The cross was made at the USDA-ARS Sugarcane Field Station at Canal Point, FL, in December 1995. The breeding facilities at Canal Point are used to support sugarcane cultivar development programs in Florida (CP), Louisiana (HoCP), and Texas (TCP).
A summary of the steps leading to the release of HoCP 00-950 as a commercial cultivar is displayed in Table 1 . Seed from the cross, HoCP 93-750 x HoCP 92-676, was planted in the SRL greenhouse at Houma, LA, early in January 1996, and seedlings were transplanted to the field at the USDA Research Farm at Schriever, LA, in April 1996 using a spacing interval of 40 cm along 1.8-m-wide raised beds to establish Stage 1 (seedling stage). At Stage 1, the seedlings are cut back in the late fall, and those that survive the winter undergo selection in fall of the following year. In the case of HoCP 00-950, initial selection occurred in 1997. Selection criteria in the early clonal stages included yield components (stalk number, diameter, and height), quality components (Brix only in Stages 1 and 2; sucrose and fiber in Stage 3), resistance or tolerance to natural disease and insect pressures, and general freedom from traits that could adversely affect harvestability, such as proneness to lodge and stalk brittleness. A hand punch and hand refractometer were used to measure Brix in the first two stages. Two stalks were punched, each at approximately 1/3 the distance from ground level to the uppermost visible dewlap of the stalk. About 1 mL of juice was extracted from each stalk, collected in a small reservoir located on the hand punch and then transferred to the hand refractometer. At all early stages of evaluation, commercially important cultivars in the industry were included as standards. For HoCP 00-950, these standards were ‘CP 70-321’ (Fanguy et al., 1979), LCP 85-384, ‘HoCP 85-845’ (Legendre et al., 1994) and ‘LHo 83-153’ (Bischoff et al., 1992).
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To begin Stage 3, locally referred to as second-line trial stage, six stalks were cut at the base, topped to produce a final stalk length of approximately 2 m, and planted in single-row plots 4.0 m in length with a 0.9-m border between plots along the row. Selection in Stage 3 is a 2-yr process. Harvestable stalks (>1.4 m length) were counted and recorded on all clones in the first year (plant-cane crop), and only on the more elite clones in the second year (first-ratoon crop). Clones preselected as the more elite in the first year were sampled and included in increase plots (seedcane source) in the event that they were selected for advancement the following year. Preselection in the first year was based on stalk count, and an overall 1 to 9 visual assessment of yield, harvestability, and evidence of susceptibility to diseases and insects, where 1 = most desirable and 9 = least desirable. Preselected clones were sampled again in the second year.
Sampling was done by hand-cutting 10 stalks at ground level and just below the apical meristem, removing leaf and sheath tissue and then weighing the 10-stalk sample to obtain an estimate of individual stalk weight. The sample was then shredded, and juice was expressed from a 1-kg sample in a core press at 211 kg cm–1 pressure. The remaining "cake" of fibrous residue was weighed then dried at 66°C for 72 h to obtain fiber content. Brix and pol were measured hydrometrically and by polarimetry, respectively in a juice quality laboratory to determine total soluble solids and sucrose content in each sample; from these, together with fiber content, theoretically recoverable sucrose content (kg Mg–1) was estimated as described by Legendre (1992). Cane yield (Mg ha–1) was estimated as the product of stalk population per hectare x individual stalk weight. Sugar yield (Mg ha–1) was estimated as the product of cane yield x sugar content/1000.
Following selection, the permanent cultivar name, HoCP 00-950, was assigned in the first-ratoon crop of Stage 3 in 2000. Both plant-cane and ratoon-crop data were considered before final selection and permanent cultivar name assignment.
Replicated Yield Trials
Replicated on-station nursery trials were conducted at the USDA Research Farm in Schriever, LA, the Louisiana State University (LSU) AgCenter's Sugar Research Station in St. Gabriel, LA, and the LSU AgCenter's Iberia Research Station in Jeanerette, LA. At each location, a randomized complete block design with two replications was used. Plots consisted of single 1.8-m-wide rows that were 4.0 m long with a 0.9-m gap between plots along each row. Data were collected in the plant-cane, first-ratoon, and second-ratoon crops. Data obtained from these trials included stalk population (stalks ha–1), stalk weight (kg), sugar content (Mg ha–1), cane yield (Mg ha–1), and sugar yield (Mg ha–1). The number of harvestable stalks in each plot was determined in early August. As in the second clonal stage, yield estimates were based on 10-stalk hand-cut samples, and the samples were processed using the prebreaker/press method.
The following year, replicated off-station nursery trials were conducted on grower fields at Newton Cane, Inc. in Bunkie, Louisiana; and Westfield Plantation in Paincourtville, Louisiana. Trials were harvested in the plant-cane, first-ratoon, and second-ratoon crops. The plots for these trials were single 1.8-m wide rows that were 6.1 m long with a 1.5-m alley between plots along the rows. Stalk weight, sugar content, and cane and sugar yields were estimated based on stalk counts and 10-stalk hand-cut samples as described earlier.
Initial yield trials, locally referred to as infield tests, were planted in the same year that off-station nursery trials were planted. They were conducted at Sugarland Acres, Inc. in Youngsville, LA, and Blackberry Farms in Vacherie, LA. At this stage and beyond, selected clones are tested along with those from LSU AgCenter's breeding program and evaluated by scientists from USDA-ARS, LSU AgCenter, and the American Sugarcane League. The plots for infield tests were two adjacent 1.8-m-wide rows that were 7.6 m long with a 1.5-m alley between plots. The experimental design for each of these trials was a randomized complete block design with two replications. Cane from each plot was mechanically harvested using combine harvesters and a weigh wagon equipped with electronic load cells to record cane weight. Harvested cane weights from each plot were used to calculate cane yield. Stalk weight, sugar content, and cane and sugar yields were estimated based on a 10-stalk hand-cut sample.
The final yield testing stage of the SRL's sugarcane breeding program, locally referred to as outfield tests, were conducted cooperatively as described above. Forty-five mechanically harvested outfield tests were conducted across nine south Louisiana locations during the 2004 to 2007 (representing plant-cane, first-, second-, and third-ratoon crops) harvest seasons. The outfield test sites are widely dispersed throughout the Louisiana sugarcane industry and are in both light and heavy soil locations (7 silt loam locations; 2 clay locations). The experimental design for each of these tests was a randomized complete block with three replications. Fifteen-stalk samples were collected before harvest to determine stalk weight and for a juice quality analysis. For juice quality analysis, samples were crushed using a small three-roller mill rather than shredded as before. Fiber content is a highly repeatable trait, so to increase throughput and conserve on resources, the roller mill method is used at this stage. Plots were mechanically harvested as in the infield trials. No burning was done before harvest regardless of the stage of advancement.
Disease and Insect Evaluations
The reaction of HoCP 00-950 to the important endemic diseases of sugarcane in Louisiana was determined from observations in performance trials and from artificial inoculated greenhouse and field trials.
Mosaic
In Year 8, young plants of candidate cultivars including HoCP 00-950 were artificially inoculated in the greenhouse as described by Grisham (1994) with Sorghum mosaic virus (SrMV) and Sugarcane mosaic virus (SCMV), the two viruses reported to cause mosaic in the continental United States.
Smut
Beginning in year six of the cultivar evaluation program and continuing until release, HoCP 00-950 was included in inoculated field trials at the USDA Research Farm in Schriever, LA, and the LSU AgCenter's Sugar Research Station in St. Gabriel, LA to test for smut (caused by Ustilago scitaminea H. and P. Sydow) susceptibility. Eighteen stalks (six stalks per replicate) of each cultivar were dipped in a suspension of approximately 5 x 106 smut teliospores mL–1 with >90% germination for 10 min and then planted immediately.
The experimental design for each of these trials was a randomized complete block design with three replications and individual plots consisting of a single row 4.9 m long. Disease ratings were made in mid-June to mid-July during the subsequent plant-cane growing season. Clones were ranked according to the percentage of stalks with whips and assigned a rating of 1 to 9, where 1 = no whip formation and 9 = the group of clones with the highest percentage of stalks with whips, generally >30%. Because the range of percentage stalks with whips that define each rating varies from trial to trial as a result of the environmental effects, 10 commercial cultivars that range from resistant (rating < 3) to susceptible (rating > 7) were included as standards for comparison.
Leaf Scald
The two smut field trials were also used for testing experimental clones for resistance to leaf scald [caused by Xanthomonas albilineans (Ashby) Dowson]. At the USDA research farm, plants were inoculated in April, approximately 1 mo after growth was initiated following winter dormancy when the apical growing point was still below the soil surface. The leaf whorl of all plants in the trial was mowed to a height of about 5 cm and immediately sprayed with a suspension of bacterial cells of X. albilineans (Ashby) Dowson. Bacterial cells were recovered from 7- to 10-d-old cultures grown on Wilbrink agar plates and suspended in distilled water. Bacterial densities were adjusted to approximately 1 x 106 colony-forming units mL–1 using a spectrophotometer.
Plants in the test plots at St. Gabriel were inoculated when they were approximately 3 mo old by hand clipping the leaf whorl of each shoot and spraying the cut surface immediately with a suspension of X. albilineans cells at a similar concentration. Clones of both trials were visually inspected for leaf scald susceptibility in August and October and the percentage of stalks showing acute (systemic) infection was determined for each clone. An average severity rating of 1 to 9 was assigned to each plot, where 1 = no symptoms, 3 = single "white pencil line" symptoms, 5 = multiple white pencil lines per leaf that become necrotic, 7 = significant disease development with younger leaves showing necrotic lines, and 9 = leaf whorl dying and lateral buds germinating. Ratings were based on a comparison with inoculated cultivars with known levels of resistance and susceptibility to leaf scald.
Brown Rust
Performance trials were observed during the spring and summer periods when the conditions for brown rust development from natural infection by Puccinia melanocephala H. and P. Sydow were favorable.
Ratoon Stunting Disease
The effect of ratoon stunting disease (RSD; caused by Leifsonia xyli subsp. xyli Evtsuhenko et al.) on HoCP 00-950 was determined in field experiments as described by Grisham (1991). Infection levels based on the number of colonized vascular bundles (CVB) and effects on yield were determined each fall for two crop cycles (2004–2006 and 2005–2007), each consisting of plant-cane, first-ratoon, and second-ratoon crops.
Sugarcane Borer
HoCP 00-950 was evaluated for its response to the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae). The sugarcane borer is an important pest of sugarcane throughout the Americas and the most important insect pest of sugarcane in the U.S. Procedures for evaluating cultivars for sugarcane borer resistance are those reported by White et al. (2008). Evaluations were conducted in 2004, 2006, and 2007.
Maturity and Freeze Tolerance Tests
Plant-cane and first-ratoon maturity tests were conducted at the USDA Research Farm to assess the maturity profile of released cultivars and near-release clones. In maturity tests, 15-stalk samples (5 per row) were taken monthly from plant-cane tests and biweekly from first-ratoon tests to track the late-season growth as well as accumulation of sucrose. Clones were planted in a randomized complete block design with three replications. Individual plots consisted of three adjacent 1.8-m-wide rows 13.7 m in length with a 1.2-m alley between plots.
Freeze-tolerance trials involving commercial and near-commercial cultivars are established annually at the USDA Research Farm at Schriever. Two cultivars, LCP 85-384, representing good stalk freeze tolerance, and TucCP 77-42 (Mariotti et al., 1991), representing poor stalk freeze tolerance, are included as controls. Following a damaging freeze, changes in juice pol (sucrose), pH, titratable acidity, and deterioration-related products (Legendre et al., 1985) are monitored, usually on a biweekly basis. The cultivars were planted in a randomized complete block design with three replications. Individual plots consisted of four adjacent, 1.8-m-wide rows 13.7-m in length with a 1.5-m alley between plots.
Statistical Analyses
Yield data were analyzed using PROC MIXED (SAS Institute, 2003) with cultivar as the fixed variable and year, location, and replication and their interactions as random variables. Freeze tolerance was also analyzed using PROC MIXED. Least square means were generated for each cultivar and were separated using the PDIFF option (P 
0.05). Ratoon stunting disease data were analyzed using SAS with PROC MIXED with replication as a random variable. Differences between treatment least square means were compared using the PDIFF option at the 0.05 probability level. Entomolological and maturity data were analyzed using PROC GLM (SAS Institute, 2003) and cultivar means were separated using Fisher's Protected LSD (P 0.05).
Replicated Yield Trials
HoCP 00-950 was evaluated in outfield tests that were conducted from 2004 through 2007 (Table 2
). Experimental clones were replanted each year in these tests as long as the experimental clone remained active within the sugarcane breeding program. In 2004, the standard cultivar for comparison in the Outfield Tests, LCP 85-384, was superseded by HoCP 96-540 to reflect the industry's shift away from LCP 85-384 toward HoCP 96-540 largely as a result of LCP 85-384's susceptibility to brown rust disease and decline in yield (Tew et al., 2005b). In the plant-cane, first-, second-, and third-ratoon crops, HoCP 00-950 produced significantly higher sugar yields than LCP 85-384 and sugar yields similar to those of HoCP 96-540. In plant-cane through second-ratoon, the sucrose content of HoCP 00-950 was significantly higher than all cultivars except for ‘L 99-226.’ Yields in the later ratoon crops indicate that HoCP 00-950 is an excellent ratooning cultivar.
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Disease and Insect Reactions
Diseases—Natural Infection
Disease reactions of HoCP 00-950 are shown in Table 3. No visual symptoms of mosaic (SCMV and SrMV), brown rust, smut, or leaf scald were observed among plants of HoCP 00-950 in nurseries or performance trials during evaluation in the varietal development program. Susceptibility of HoCP 00-950 to infection by Sugarcane yellow leaf virus (SCYLV) is unknown. Orange rust [caused by Puccinia kuehnii (W. Krüger) E.J. Butler] first confirmed to be in Florida on 17 July 2007, has not yet been observed in Louisiana. Based on natural infection observations in the crossing area at Canal Point, FL, HoCP 00-950 is moderately resistant to orange rust.
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The dewlaps (collars) of HoCP 00-950 are narrow and squarish with an olive-green color that tends to turn browner with age and exposure to sunlight. The average auricle shape is long lanceolate, often greater than 2 cm long. Unlike LCP 85-384 and L 99-226, the auricles in the upper portion of the canopy do not appear dead or straw colored. HoCP 00-950 exhibits a tan-colored, broad crescent-shaped ligule having a length of 150 mm and a width of 45 mm, with a torn, darker brown edge. Its ligule is broader than that of either LCP 85-384 or HoCP 96-540. HoCP 00-950 exhibits only a slight amount of setaceous hair on the abaxial side of the leaf sheath, compared with the extensive amount observed on LCP 85-384.
The rind color on stalks of HoCP 00-950 is green to yellowish-green, when the stalks are unexposed. Stalks of HoCP 00-950 become light brown colored when exposed to sunlight. A white wax bloom covers the stalks of HoCP 00-950 but is less pronounced than the wax bloom on stalks of LCP 85-384 or HoCP 96-540.
HoCP 00-950 generally has shorter stalks (ground level to the top visible dewlap) than those of HoCP 96-540 at harvest, with the greatest difference (12–16%) being in the plant-cane crop. The average stalk diameter of HoCP 00-950 at midinternode in the plant-cane crop is 21.5 mm, slightly smaller than the diameter of HoCP 96-540 (23.0 mm). HoCP 00-950 exhibits a rather distinctive obconoidal-shaped internode, sufficiently different from the near-cylindrical internodes of most commercial cultivars that this characteristic has proven to be useful for identification purposes. The internodes of HoCP 00-950 occasionally exhibit growth cracks. HoCP 00-950 exhibits an oval but sometimes round bud shape with a central germ pore, unlike LCP 85-384 and HoCP 96-540, both of which have pentagonal buds. The bud diameter of HoCP 00-950 is usually about 5 mm, smaller than that of most commercial cultivars. The buds of HoCP 00-950 rarely extend above the growth ring. HoCP 00-950 does not exhibit a bud groove.
In Louisiana, HoCP 00-950 does not flower. When induced to flower in photoperiod facilities or at lower latitude (e.g., Canal Point, FL), HoCP 00-950 usually reaches anthesis at or near the period that the greatest number of clones are flowering during each crossing season in which it has been used as a parent. The cultivar produces little if any viable pollen and has been consistently rated as male sterile and always used as a female parent in crosses.
The molecular identity of HoCP 00-950 was defined with 21 simple sequence repeat (SSR) markers using a high-throughput procedure (Table 9 ). The primer sequences of these SSR markers can be found in Pan (2006). Based on a previous survey, the total number of SSR fragments/alleles produced by these 21 sugarcane SSR markers from Louisiana commercial clones was 144, and the potential number of SSR fragments/alleles produced per SSR marker varied from 3 to 11 (Pan et al., 2007). The letter A was used to indicate the presence of a fingerprint/allele, while the letter C was used to indicate its absence (fourth row in each section). The overall amplification profile of HoCP 00-950, in terms of As or Cs based on sequential order from 1 through 144 (third row in each section), was represented by CACACAACCCCCCAAAAAACCACCAACC CCCCCCACACCCCCACACACCCCACACCCCCCAAACAAACCCCACCAACCCCCACAACCACCACAAAACCCACAACCACCCCCCCACCCACAAAACAAAAACCACACCAAAAAAAA. This sequence has been used to represent the molecular identity of HoCP 00-950 when comparing with those of other Louisiana commercial clones (Pan et al., 2007).
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Seed cane of HoCP 00-950 will be maintained at the USDA-ARS Southern Regional Research Center's Sugarcane Research Unit, located at Houma, LA, for 5 yr. It is not anticipated that patent protection for HoCP 00-950 will be sought.
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 July 23, 2008.
References
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