Sucrose Accumulation and Harvest Schedule Recommendations for CP Sugarcane Cultivars

Sugarcane (Saccharum spp.) is harvested during a 5-month period (October to March) in the Everglades Agricultural Area (EAA) of south Florida. The genetic and temporal variability of sugarcane sucrose concentration is well established, but sucrose accumulation curves have not been reported for the Canal Point (CP) clones used in Florida since 1977. The objective of this study was to compare sucrose accumulation for recently released clones and provide harvest schedule recommendations based on this information. Thirteen CP clones were sampled at 2-week intervals throughout 4 consecutive harvest seasons. Based on seasonal changes in cultivar ranking in sugar per ton, recommended harvest scheduling relative to October 14 (time = 0 days) are: early-season (0 to 50 days) for cultivars CP 70-1133, CP 80-1743, and CP 88-1762; mid-season (50 to 100 days) for cultivars CP 78-1628 and CP 84-1198; and late-season (100 to 150 days) for cultivars CP 72-1210, CP 72-2086, CP 80-1827, CP 85-1382, CP 88-1508, and CP 89-2377. Sucrose accumulation in cultivar CP 89-2143 was greatest across all harvest periods and should be grown by Florida producers interested in improving the sucrose concentration of their crop. Introduction Given present milling capacity in south Florida, a full 5 months (October to March) are required to process the 450,000 acres planted to sugarcane (Saccharum spp.). Sugarcane is grown in 4 counties (Glades, Hendry, Martin, and Palm Beach) in Florida, with the majority of the production area extending in a 30-mile wide arc from the south and east of Lake Okeechobee (Fig. 1). Some sugarcane must be harvested before achieving physiological maturity to sustain early-season (October to November) milling operations. “Early-maturing” cultivars are preferentially harvested during this time, recognizing that they may not have reached their peak sucrose content, but may have higher sucrose content than other later-maturing cultivars at the onset of mill operations (7). Fig. 1. Map of the sugarcane production area (green) in Florida. Crop Management 2 April 2004 Previous research has focused on the interaction of cultivar × date of sampling to produce sucrose content “maturity curves” in South Africa (1), Louisiana (3,4,9), and Mauritius (6). While the genetic variability of sugarcane sucrose accumulation rate has been well established, maturity curves for recently-released CP sugarcane clones bred at Canal Point, FL have not been reported since 1977 (7,8). CP clones account for greater than 70% of Florida sugarcane acreage, and are also economically important (11) in many countries including Argentina (25% of total acreage), Belize (16%), El Salvador (50%), Guatemala (65%), Honduras (47%), Mexico (15%), Morocco (54%), Nicaragua (75%), Senegal (9%), and Venezuela (9%). Although most sugarcane growers in Florida are now planting a diverse selection of newer cultivars, lack of maturity curves for these clones makes it difficult to make informed harvest scheduling decisions. The objective of this study was to use repeated sampling over time to compare sucrose accumulation characteristics among commercial CP cultivars in Florida, and to use this information to provide harvest scheduling recommendations for growers. Sampling CP Clones During Four Harvest Seasons The data for this analysis were collected from a series of experiments conducted at 5 locations (University of Florida Everglades Research and Education Center, Hundley, Lakeview, Sundance, and Hillsboro farms) in the Everglades Agricultural Area of south Florida. Soil types included a Torry muck (euic, hyperthermic Typic Haplosaprist) for the Lakeview location and Lauderhill muck (euic, hyperthermic Lithic Haplosaprist) for the remaining 4 sites. Harvest data were collected from October to March during 4 consecutive seasons (1998-1999 to 2001-2002). All experiments were planted in a randomized block design with 3 or 4 replications with cultivar as the main treatment. Plots were 35 ft long and 5 rows wide with 5-ft row spacing. Fivestalk harvest samples were collected from each plot at approximately 2-week intervals, commencing on October 14 of each season and ending by March 27 the following year. Each harvest sample was topped in the field, and the millable fresh stalk weight, Brix, and pol measured in the laboratory (data not presented). The fresh weight, Brix, and pol measurements were used (7) to calculate sugar per ton (SPT in lb/ton) of cane biomass for each cultivar and sampling date. A quadratic regression was performed in SAS (5) to generate regression relationships for SPT (Y-axis) versus harvest date (X-axis). For this discussion, harvest dates within any given season represent the number of days after October 14. Biweekly means and standard errors were calculated for each cultivar and sampling date. Intercept, linear, and quadratic coefficients describing SPT trends over time were analyzed with the GLM procedure in SAS to determine statistically significant differences (LSD values) between cultivars. Regression lines generated were used to describe SPT at 25 (early-season, November 8); 75 (midseason, December 28); and 125 (late-season, February 16) days after onset of harvest for each cultivar. Cultivars were selected for this study based on either their economic importance as documented in the most recent sugarcane census (2) or recent release date. The first two digits in the cultivar name represent the year the clone was named, usually 7 to 10 years prior to cultivar release. Table 1 provides a brief description of the cultivars included in this study. Cultivars are ordered by release date in tables and figures throughout this article. Cultivars are separated into 3 figures by year of introduction for ease in identifying individual clone sucrose accumulation patterns, but statistical comparisons were done between all clones included in this study. Crop Management 2 April 2004 Table 1. Florida sugarcane acreage and description of the CP clones included in this study. a Source: (2). b Source: (12). Sucrose Accumulation Curves All regression coefficients describing sucrose accumulation maturity curves for each cultivar were significant at the P < 0.001 level (Table 2). “Early sugar” is an important characteristic that influences grower adoption of commercial germplasm. The intercept term (α) represents clonal SPT on October 14 at the onset of the harvest season. Cultivars CP 80-1743, CP 88-1762, and CP 89-2143 were notable for their large intercept terms, which were significantly greater than 10, 8, and 11 cultivars, respectively, indicating that these clones would be good choices for October harvest in the EAA. In contrast, CP 88-1834 and CP 89-2377 had significantly lower intercepts than 11 of 12 cultivars, and thus would be poor choices for early harvest. Regression equations were also used to calculate optimal harvest dates based on maximum SPT for each cultivar (Table 2). These dates ranged from January 26 (CP 80-1743 and CP 88-1762) to February 22 (CP 85-1382). Maximum SPT ranged from 267 lb/ton (CP 88-1834) CP clone 2001a acreage (% of total) Descriptionb and photo (click for larger view) 70-1133 2.8 Former widely-grown cultivar, slowly being phased out of industry due to low sugar content. 72-1210 < 1 Former widely-grown cultivar phased out due to susceptibility to rust, yellow leaf virus, and ratoon stunting disease. 72-2086 13.8 Widely adapted to S. Florida. Poor early growth but good post-freeze characteristics. 78-1628 11.5 Most widely-grown cultivar on mineral soils in Florida. 80-1743 25.1 Vigorous tillering characteristics and welladapted to mechanical harvest. Most widely-grown cultivar on muck soils (and overall) in Florida. 80-1827 5.1 Source of mechanically cut seed cane. Good postfreeze characteristics. 84-1198 4.8 Large stalk weight, easily uprooted. 85-1382 < 1 Poor ratooning ability. Preferred host of West Indian Cane Weevil. 88-1508 < 1 Very erect cultivar, low sugar content. 88-1762 6.2 Large stalk weight, high plant population, subject to lodging. 88-1834 < 1 Susceptible to pineapple disease.