The Everglades Agricultural Area (EAA) is a 700,000 acre agricultural region south of Lake Okeechobee in Florida. Sugarcane is grown on approximately 375,000 acres in the EAA (VanWeelden et al. 2019). Sugarcane (Saccharum spp.) is harvested at different locations throughout the EAA, and growers must factor in the effect of sugarcane genotype (G) and environment (E) on potential yield performance when scheduling their harvests. "Environment" is defined to include the effects of soil type, climate, and management factors at different locations. The vast majority of research addressing the effects of environment on sugarcane yields has focused on G x E interaction effects. Although numerous studies have reported significant G x E interactions and recommended sugarcane selection in differing environments (Arceneaux and Hebert 1943; Glaz et al. 1985; Milligan et al. 1990; Bull et al. 1992; Mirzawan et al. 1994; Bissessur et al. 2000), other studies have concluded that the number of locations in sugarcane breeding programs could be reduced (Gravois and Milligan, 1992; Milligan 1994; Jackson and McRae 1998; De Sousa-Vieira and Milligan 1999).
While G x E interactions have been studied primarily as a tool to help breeders make informed decisions regarding the design of sugarcane breeding programs, less information has been published in the scientific literature on G x E interactions and their impact on yield performance within recently released commercial sugarcane cultivars. Improving our understanding of the significance of environment, genotype, and G x E interaction in recently released cultivars would help growers make confident cultivar-selection choices for their growing environments and would also help breeders verify the success of their sugarcane breeding program. In addition, since breeding programs often lack the resources to allow replanting of the same cultivars in the same environment (Brown and Glaz 2001), multi-site data sets in which environment, crop age, and year are not confounded are often limited or simply not available.
The following discussion reports the results of a series of experiments (Gilbert et al. 2006) that were designed to compare and contrast relative sugarcane cultivar performance at different locations throughout the EAA.
The data for this analysis were collected from a series of experiments conducted in the EAA of south Florida at five locations (Figure 1), including the UF/IFAS Everglades Research and Education Center (UF/IFAS EREC), Hundley Farm (HU), Lakeview Farm (LV), Sundance Farm (SU), and Hillsboro Farm (HB). The sites represented diversities in soil depth and expected minimum temperatures that occur during freezes throughout the sugarcane production region on organic soils. Soil types included a Torry muck (euic, hyperthermic Typic Haplosaprist) for the Lakeview location and Lauderhill muck (euic, hyperthermic Lithic Haplosaprist) for the remaining four sites (Rice et al. 2005). Harvest data were collected from October to March during four consecutive seasons (1998/1999 to 2001/2002).
Cultivars were selected for this study based on either their recent release date or their economic importance as documented in the most recent sugarcane variety census at the time of study (Glaz 2006). The first two digits in the cultivar name represent the year the clone was named, usually 7–10 years prior to cultivar release. A brief description of the cultivars included in this study can be found at https://edis.ifas.ufl.edu/sc069. Cultivars are ordered by release date in tables and figures throughout this article. For more information on this study, please see Gilbert et al. (2004) and Gilbert et al. (2006).
Using combined data from all study sites, Table 1 presents the overall cultivar ranking for sucrose concentration (lb. sucrose/ton; SPT), cane yield (tons cane/acre; TCA), and sucrose yield (tons sucrose/acre; TSA) for each cultivar. Ranking was based on yield, from highest (1) to lowest (13). 'CP89-2143' was notable for the highest rank in SPT, TCA, and TSA. According to latest variety census (VanWeelden et al. 2016), 'CP89-2143' is phased out from the EAA due to susceptibility to orange rust and high orange rust pressure in Florida, but it is expanding as major cultivar in Texas and some areas of Louisiana. 'CP88-1762' and 'CP72-2086' also had high ranks ranging from 2 to 5 in SPT, TCA, and TSA. 'CP88-1762' is among the principal cultivars in Florida with 1.1% of total acreage planted in EAA; however, 'CP72-2086' dropped down to < 1% acreage. In contrast, 'CP85-1382' and 'CP88-1508' fared poorly in all three ranking categories (rank = 8) when compared to other CP clones. It is not surprising that growers have lost interest in these two clones, which are absent from the latest census. 'CP80-1743' reflects average rankings of either 5 or 6 for SPT, TCA, and TSA, and ranked tenth for acreage (1.6% of total acreage) in EAA. However, it is difficult to obtain accurate yield data from small plots using 'CP 80-1743', because it is extremely susceptible to rodent damage in small plots, whereas rodent damage is not nearly as severe in commercial fields.
Some clones are characterized by high sucrose concentrations (SPT) and low cane tonnage (TCA), or vice versa. Growers prefer to plant clones with high SPT as transport and milling costs are reduced. Cultivars like 'CP78-1628' with high SPT (rank = 2) and low TCA (rank = 8) are more profitable and favored by growers than low sucrose concentration, high cane tonnage clones like 'CP88-1834' (SPT rank = 13; TCA rank = 4) or 'CP89-2377 '(SPT rank = 12; TCA rank = 2).
Performance at Different Locations
Table 2 presents performance ranks for sucrose concentration (SPT), cane tonnage (TCA), and sucrose yields (TSA) for each genotype at each of the five sites included in this study. 'CP70-1133' tended to have higher relative SPT (rank = 7) and TSA (rank = 7) at UF/IFAS EREC than other sites, whereas 'CP72-1210' recorded poor TSA yields (rank > 8) at all locations. 'CP72-2086' recorded higher relative TSA yields at the EREC (rank = 5) and Sundance (rank = 4) sites compared to the Hillsboro (rank = 11) site. 'CP78-1628' recorded relatively high performance (ranks < 6) for all yield traits at all locations, whereas 'CP80-1743' was notable for good relative sucrose yield performance at EREC (TSA rank = 2), but poor performance at Lakeview (TSA rank = 11). 'CP80-1827' had low sucrose yields (TSA rank > 4 at all locations, and 'CP84-1198' recorded high relative sucrose yields at the Hundley site (TSA rank = 3), as did 'CP85-1382' (TSA rank = 5). 'CP88-1508' recorded poor relative sucrose yields (TSA rank > 8) across all locations, whereas 'CP88-1762' demonstrated high relative yields (TSA ranks ranging from 1 to 6) across the five locations. 'CP88-1834' was notable for poor sucrose concentration (SPT rank > 10) at all locations, but high TCA (rank = 1) and TSA (rank = 2) at the Lakeview site. CP89-2143' was a clear standout, with superior SPT and TSA (rank =1) at four of five sites, and very high SPT and TSA performance (rank = 2) at one of the five farm sites. Finally, 'CP89-2377' tended to have lower sucrose concentration performance (SPT rank > 6) but higher cane tonnage performance (TCA rank < 7).
Our results highlight the influence of environment on sugarcane yields in a visually homogenous region. The EAA sugarcane production area is characterized by flat basin topography, well-drained organic soils with high N mineralization rates, and high to very high organic matter contents (Bottcher and Izuno 1994). Unlike other sugarcane production areas in the world, rainfall is not normally considered a limiting factor to sugarcane production in the EAA due to the excellent water-holding capacity of the organic soils and generally abundant water supply from Lake Okeechobee (Alvarez et al. 1982). Sucrose yields averaged over the same cultivars, growing season, crop age, and time of harvest varied greatly from 2% to 46% among locations. In contrast to the results of Julien and Delaveau (1977) in Mauritius, this study supports arguments for multi-locational evaluation of sugarcane germplasm in Florida both during the breeding program and following cultivar release. South Africa has had a released variety trial program in place since 1966 (Redshaw 2000) to recommend cultivars to growers in different agroclimatic zones. Released variety trials make inherent sense in South Africa where 23 bioresource regions have been identified in Kwa-Zulu Natal province, where sugarcane production areas range from loamy sandy soils in warm coastal areas to clay-rich soils in cooler highlands. Our study in the EAA of south Florida indicates that a similar approach to released variety trials may also be useful in more homogenous regions.
Sugarcane germplasm is released after numerous years of replicated on-farm trials, yet considerable variation in cultivar-relative performance may occur following cultivar release. Many breeding programs do not have the resources available to assess cultivar performance following release. Relative performance of new cultivars compared to industry standards is often obtained ad hoc from mill managers and industry professionals without replicated tests. Ellis et al. (2004) compared variety trials to commercial production in Australia, and reported that differences in cultivar ranking between data sets were due to uneven deployment of cultivars in commercial fields. They concluded that variety trials could not be enhanced to evaluate uneven deployment effects. However, in South Africa, post-release variety trials have been used to recommend varieties to growers (Redshaw 2000). Our study indicates that a systematic agronomic evaluation of released sugarcane cultivars is valuable in determining relative cultivar performance and identifying recommendation domains most suited for different cultivars.
When the rankings of genotypes at different sites were compared, the cultivar rankings at the Lakeview site did not correlate well with the other locations in this study. Significant G x E interactions indicated that the Lakeview site was located in a different agroecological zone than the other sites. Differences in soil depth, mineral content, and air temperature may contribute to G x E interactions in the EAA. Lakeview is < 1 km from Lake Okeechobee in a "warmland" area, with soils containing appreciably greater mineral content than the other sites included in this study. Early breeding strategies in the EAA recognized the importance of selection for both "warmland" sites and "coldland" sites farther from Lake Okeechobee (Bourne 1972). Cultivars 'F31-962', 'F31-436', and 'CL41-223' occupied over 50% of the EAA acreage in the 1940s–1960s, but faded from prominence as sugarcane acreage spread farther from the lake. Rates of leaf appearance vs. thermal time differ among sugarcane cultivars (Bonnett 1998; Sinclair et al. 2004). Differing cultivar growth rates at different cumulative thermal time may be part of the mechanism involved in the G x E interaction of warmland vs. coldland sites. Although the CP program breeds new cultivars in a warmland environment adjacent to Lake Okeechobee, all cultivars are tested in multiple coldland areas and one warmland environment before cultivar release.
This data set indicates that a significant G x E interaction still exists in many recently released cultivars, with the recommendation domain of 'CP88-1508' and 'CP88-1834' closer to Lake Okeechobee than 'CP72-2086' or 'CP80-1743'. 'CP89-2143' had a remarkably high, stable sucrose concentration and sucrose yield across all locations. Growers in the EAA interested in improving sucrose concentration of their sugarcane crop may plant 'CP89-2143'; however, its susceptibility to orange rust reduced its tonnage in recent years.
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Sugarcane sucrose concentration (SPT), cane yield (TCA), sucrose yield (TSA), and cultivar performance ranksa for combined data from all experimental sites in Florida. The census rankb indicates cultivar popularity (in terms of total plant cane and ratoon crop acreage) as documented in the 2010 Florida sugarcane variety census (Rice et al. 2011).
Cultivar rankings within each site for sucrose concentration (SPT), cane yield (TCA) and sucrose yield (TSA). Sites (see Figure 1) are UF/IFAS Everglades Research and Education Center (EREC), Hillsboro Farm (HB), Hundley Farm (HU), Lakeview Farm (LV), and Sundance Farm (SU).