Encyclopedia
Please note this is an old version of this entry, which may differ significantly from the current revision.
Subjects:
Agriculture, Dairy & Animal Science
Sugarcane is an important sugar crop and it can be subjected to ratooning for several years. The advantages of ratooning include quality improvement, efficiency enhancement, and reduced costs and energy use. The genotype, environment, cultivation management, and harvesting technology affect the productivity and longevity of ratoon cane, with the genetic basis being the most critical factor.
- sugarcane ratooning ability
- trait markers
- sugarcane breeding
- sugar production
- segregating population
- sugarcane stubble
1. Introduction
Sugarcane (Saccharum spp. hybrids) is an important sugar crop that can be subjected to ratooning over multiple years. Sucrose from sugarcane accounts for 86% of the world’s [1] and 90% of China’s total sugar output [2]. In China, approximately 60–70% of sugar production costs are spent on raw sugarcane stalks. Compared with newly planted sugarcane, i.e., plant cane, ratoon cane has multiple advantages including faster leaf spreading, more rapid plant growth, earlier strike maturity, and reduced production costs due to savings on fertilizers, seed cane, field preparation, planting and early field management.
Sugarcane stalks are a fresh agricultural product that must be processed as soon as possible after harvesting. The immediate processing is performed to minimize the conversion of sucrose into reducing sugars within the sugarcane stem to increase the sugar output. Sugarcane originated from the tropics and requires a warm climate, and only when the temperature is above 20 °C can the mean effective accumulated temperature meet the requirement for sugarcane normal growth and development. Previous data also suggest that the non-optimum germination or sprouting temperatures, too low or too high, may be a factor for yield decline in ratoon cane [3]. Compared with plant cane, ratoon plants have an established, and strong root system, representing the unique skeleton of carbon and energy source for the initial plant development [4]. The root system, which is essential for regrowth of sugarcane and the ratoon vigor of each cycle [4], can be used for water transport to leaves during the period of photosynthesis, in which photosynthetic products are accumulated and in turn promote a rapid leaf expansion and plant growth during the early growing stage. Therefore, ratoon plants have more effective accumulated temperature and longer effective growth period, resulting in more sugar accumulation and earlier technical maturity. In contrast, newly planted sugarcane plants firstly need to grow roots, especially permanent roots, which requires a relatively longer period and a higher effective accumulated temperature. As a result, the newly planted sugarcane does not use light and thermal sources efficiently at this stage. Therefore, from the perspective of energy utilization, ratoon sugarcane has a significant energy-saving characteristic. According to published reports, ratoon sugarcane requires only 89,040,000 calories per ton of sugarcane production, while newly planted sugarcane requires 204,550,000 calories per ton [5], suggesting that plant cane uses 2.3 times more calories than ratoon cane. This opinion is supported by Hunsigi and Krishna (1998) [6], who believed that an irrigated ratoon crop requires only 295 days for its maturity compared with 482 days in plant cane.
Ratoon cane is very important in sugarcane production. After the harvest of sugarcane, the underground portion of the strikes gives rise to a succeeding crop, which is known as ratoon crop. Sugarcane ratooning is a planting system that is generally adopted by each sugarcane-producing country. However, the number of ratoons varies from 1–8 [7] (Table 1). The proportion of the ratoon cane is generally around 50% of the cultivated area, and can even reach 75% in some regions (Table 1). The average proportion is 50–55% in tropical areas, while approximately 40–45% in subtropical areas [8].
The cost of sugarcane production is much higher in China than in other countries including Brazil. Except for the low cost of arable land, better ecological and soil conditions, and the complete mechanical operations in sugarcane production, sugarcane variety with a strong strike is one of the most important reasons for the low cost in Brazil. In the Brazil agricultural practice, a cycle of consecutive ratooning for 4–5 years after the harvest of plant cane is generally adopted due to the standard cycle of plant-cane followed by three years of ratooning not being profitable. In India, it has been reported that the cost of ratoon crop is 25–30% lower than that of plant cane [7]. However, due to low yields (40–50 t/ha), ratoon crop accounts for only 40% [8,9] or 40–45% [7] of the total cane area and sugarcane is only ratooned for one to two years in India [10], resulting in the relatively higher cost in sugarcane production. This is supported by another report, which suggests that ratoon cane contributes only 30% of the total cane production, though it accounts for over 50% of the acreage [11]. Another report [7] also pointed out the problem of low yields of ratoon crop, indicating only 30–35 t/ha as compared to 65–75 t/ha of plant cane in India. In Pakistan, ratoon crop can save 25–30% in past [12] and 30–40% in current production costs [13], indicating a widening gap in costs. In China, there is a high proportion of ratoon cane. In Guangxi and Yunnan, the two most important sugarcane-producing provinces accounting for more than 80% of the total areas in China, ratoon crop accounts for 50–60% and 70% of the sugarcane production, respectively. However, due to the poor ratooning ability of the varieties, a cropping system of plant cane followed by two ratoons is generally adopted except for Zhanjiang Guangdong, where only one ratoon is adopted mostly due to the serious pests and smut caused by Sporisorium scitamineum. Therefore, the short longevity of ratooning is considered to be the major cause of high sugarcane production costs in China.
Table 1. Comparison of ratoon status in major sugarcane planting countries.
| Country Name | Ratoon Percentage (%) | Ratoon Age (Year) | References |
|---|---|---|---|
| America | 80–85 | 2–3 | [14] |
| Brazil | 80–90 | 4–5 | [14,15] |
| Australia | 80–85 | 2–3 | [14] |
| South Africa | 80–90 | 4–5 | [14,15] |
| China | 50–70 | 2–3 | [15] |
| India | >50 | 1–2 | [7,8,9,10] |
| World | 75 | 4–7 | [8,14,15] |
2. Definition of Sugarcane Ratooning Ability
It is widely accepted that variations in ratooning ability exist in different genotypes and hybrid offspring [16]. The definitions of ratooning ability that have been provided by different authors are as follows: the yield of second ratoon as a percentage of the yield of newly planted sugarcane [17]; ratoon crop performance as a percentage of a reference yield, usually that of the plant cane, first ratoon or the mean of these two crops [18]; the ability to maintain yield with the increased ratooning years [19]; the yield of the ratooning year as a percentage of the yield for the reference variety of that year [20]; a joint evaluation based on the quantity, growth speed, strength, final stem formation rate, number of effective stems, and yield of ratoon cane in the last season [21]. Although there are differences in description of ratooning ability, the core is similar, that is, a good performance in ratoon cane yield or ratoon can produce several profitable crops. In other words, the longer the ratooning cycle and the smaller yield decline in ratoon crops, the stronger ratooning ability.
3. Phenotypes of Ratooning Ability in Sugarcane
Ratooning increases the income of sugarcane growers due to the saving cost in cultivation, and increases the income of industry because of mature earlier, better juice quality and thus improves sugar recovery at times of the crushing season compared with plant cane [7,13]. For example, in plant cane and the second ratoon, the average sucrose content was 14.84% and 16.54%, respectively [22]. Most studies on sugarcane ratooning ability have focused on analyzing the variation in ratooning ability based on phenotypic traits [5,17,19,20,23,24,25,26,27,28,29]. Generally, the most effective way for the improvement of sugarcane ratooning ability is to select lines directly based on the yield performance of ratoon crops. However, it is not conducive to shortening the selection cycle, and the huge segregated population in sugarcane hybrid F1 limits this measure due to considerable time and resources. For example, to identify one commercial quality variety from the original F1 population requires 11 years of sequentially planted selection from approximately 75,000 genotypes [17]. An alternative approach is to select lines based on the yields of plant cane because varieties with high plant cane yields normally produce high ratoon crop yields [24,30]. Indirectly selecting genotypes with strong resistance to diseases and insect pests may also increase the ratooning ability of the selected sugarcane breeding materials [17,31]. In some cases, the ratooning ability has been indirectly evaluated by assessing the biomass or light utilization efficiency of sugarcane [30], and assessing drought tolerance in those arid or semi-arid cultivated regions is also suggested [32].
Ratooning ability is a trait that a commercial quality variety must have. Indicative traits of a strong ratooning ability include both morphological indicators of sugarcane root residue/stubble and traits that directly contribute to cane yield and sugar output, such as a high number of stalks, high viability of buds, large number of viable buds, large number of viable roots, high cane yield, high sugar output [5,17,19,24,25,28,29,33], and high tillering rate in plant cane [34]. Milligan et al. found that stalk number was the only trait in the plant cane markedly correlated to the yield of the ratoon crop [17]. Qin et al. demonstrated in their research that sugarcane lines with strong ratooning ability displayed rapid germination, higher germination rate and tillering rate, and higher stalk number in plant cane [28,35,36]. Additionally, a higher stubble germination rate and the larger shoot number were observed in the ratoon crops, which result in high stalk number and higher cane yields than those in plant-cane. A similar observation was obtained by other reports [11,14,33]. It is also believed that the ratooning ability of sugarcane is mainly identified by four important factors, namely, root traits, the total number of strikes or shoot population, stalk number, and cane yield. Good performance on the four aspects above in its plant cane and the ratoon crops is necessary for the selection of varieties with a strong ratooning ability. In addition, a sugarcane variety is considered to have a poor ratooning ability if the cane yield in ratoon crop is lower than that of its plant cane. The morphological characteristics of sugarcane stubble are closely related to the ratooning ability of the sugarcane [29]. In addition, sugarcane varieties with strong ratooning ability have a low stubble mortality rate and a short internodal length of underground stems, together with the obviously larger total number of underground buds and the effective tillers [29]. Generally, if there is an increased number of effective tillers formed by the lower buds of the main stems, and there is an increased total number of effective tillers on the main stems, then the variety likely has strong ratooning ability [29].
There was a significant interaction effect between varieties and growing seasons for all yield and qualitative traits except for the purity of sugarcane juice [19]. In addition, in the second ratoon crop, both cane yield and total recoverable sugars (TRS) were significantly higher in the varieties with strong ratooning ability than in those with weak ratooning ability. Based on an investigation of later crop, Olaoye found that single stalk weight, cane yield, total soluble solids (Brix), and sucrose percentage, were highly heritable traits that displayed the potential to obtain high genetic gain [20]. Additionally, a study on the genetic relationships among sugarcane traits in a large population indicates that stalk number was the primary determinant of cane yield and thus became more important trait in determining cane yield in the ratoon crops (r = 0.77), much higher than those of stalk diameter (r = 0.52) and stalk length (r = 0.33) [33]. Research also indicated that, for varieties with poor ratooning ability, the ratoon crops had a much lower cane yield than the plant-cane [29,34] or a sharp decline in cane yield in the first ratoon compared with plant cane [18]. Meanwhile, the yield decrease was only observed in varieties with strong ratooning ability in the second ratoon crop [20]; however, it is desirable to perform ratooning in sugarcane production for as many years as possible. In addition, a significant correlation was found between the number of shoots and the genotype/cane yield/harvesting time in sugarcane [37]. In addition, the relationship between the ratooning ability and the changes in endogenous hormone contents during germination of underground buds in stubbles have also been studied [5]. Recent studies have also indicated that the experimental location is particularly important for evaluation of the ratooning ability [38].
In brief, for the selection of ratooning ability, direct indicators are the stubble morphology, stalk number, and the germination and tillering rates in the plant cane and the ratoon crops, while indirect indicators included disease resistance especially smut, pest resistance, biomass, light use efficiency, and hormone content during stubble bud germination. The number of indicators used in selection may vary, but researchers have the same or a similar opinion on those indicators. In addition, more attention should be paid to the selection of the experimental location, mostly due to the reason that the effect of the location on ratooning ability is visible.
4. Main Factors Influencing Longevity and Productivity of Ratoon Sugarcane
The ratooning ability or good ratooning potential is an essential pre-requisite or the most critical factor for good ratoon [11,38,39]. A series of investigations have been conducted on the factors that affect the longevity of ratoon cane. The genotype, cultivation management, and environment contribute to the ratoon crop in descending order [4,11]. The ratoon crop yields decline typically with age [39]. Studies have also shown that, in subtropical regions, a major bottleneck for improving ratoon productivity is the poor germination rate of buds in the stubble remaining after winter harvesting [8]. There is a report that the poor germination rate of the ratoon crop not only affects the number of seedlings per unit area, but also leads to a large number of ineffective tillers throughout the growing season, resulting in the lower stalk number at harvest [40]. The trait of stalk number has the greatest impact on sugarcane yield. Guangxi, the largest sugarcane producing area accounting for more than 60% of the total sugar in China, is located in the subtropical region, where germination is a severe challenge during ratooning due to the serious smut infection during growing process and the frequent rainfall during harvest. The breeding and promotion of sugarcane varieties with strong ratooning ability is a technical approach to effectively solve this problem. This is because the ratooning ability directly affects the germination rate of the ratoon crop, thereby directly influencing the establishment of the high-yielding seedling population, and ultimately cane yield. Therefore, the ratooning ability is one of the most important target traits in sugarcane breeding and has always been valued by breeders [8,19,23,26,27,36,41].
From both the perspective of reducing production costs and improving the productivity of the ratoon crops, breeding and growing varieties with a strong ratooning ability is the most important prerequisite for extending the number of ratooning years and increasing the yield of the ratoon crops. Furthermore, in sugarcane-producing areas with low temperatures, frost, drought, pests, diseases (especially smut), stem borers, or extensive management, the ratooning ability of sugarcane varieties is particularly important for extending the number of ratooning years and increasing the yield of ratoon crops.
This entry is adapted from the peer-reviewed paper 10.3390/biology10101052
This entry is offline, you can click here to edit this entry!
