Ethephon : A Versatile Growth Sugar Cane Industry

Vol. 5 (4) : 213-223 (2003) REVIEW ARTICLE Ethephon : A Versatile Growth Sugar Cane Industry Regulator for Yangrui Li I and S. Solomon 2 JGuangxi Academy of Agricultural Sciences, Nanning, P.R. China 21ndian Institute of Sugarcane Research, Lucknow - 226 002, India In many sugarcane growing areas of the world, sugar productivity per se is low due to physio-biochemical constraints and adverse climatic conditions during growth and ripening. The cane growth and sucrose accumulation are severely impeded due to many factors such as poor sprouting and low tillering, climatic impediments during cane maturation, poor sprouting of winter initiated ratoon, sub-optimal quality of stand-over crop and undesired flowering in commercial sugarcane plantation. Plant growth regulators have been found to mitigate the adverse affects of these constraints to some extent. Studies carried out at many places show that application of plant growth regulating chemical such as ethephon (ethrel or 2.chloroethyl phosphonic acid) leads to enhancement in seed cane sprouting under normal and late-planted conditions. The tiller number, millable canes, and biomass productivity per unit area increases following ethephon treatment. It's efficacy has been demonstrated in improving sprouting of winter initiated ratoon of early maturing varieties, with consequent increase in ratoon tillers at a later stage. Ethephon also hastens the cane maturation process which favours early milling and suppresses flowering as well as sustains quality during late-milling. Ethephon application on sugarcane could be an important agrotechnology from cane grower's and miller's point of view due to its multiple benefits. It is an eco- friendly chemical and has tremendous potential to augment cane yield and sugar productivity. KEYWORDS : Ethephon, sprouting, tillering, ratoon, stand-over, cane quality, sugar recovery Sustainable sugar productivity is the major concern for the global sugar industry due to increase in the cost of sugarcane cultivation and rise in sugar consumption in many developing countries of Asia, Africa and Latin America. To step up sugar production efficiency, most research work is focused on the bio-dynamics of cane growth and sugar accumulation process. Despite these new revelations, cane productivity could reach only 39% (85.6 t dm.ha -l.yr -1) of the theoretical maximum, calculated by Loomis and Williams (1963). The highest sugar productivity figure is cited from Hawaii (35.2t sucrose.ha-l.yr-1; Ham, 1970), followed by Australia, (32.8t sucrose.ha-l.yrt; Leffingwell, 1985). Recent studies show that on industry-wise basis, production of sugar per unit area is not increasing rapidly as might be expected, given past research achievements and improved management-technology. The upcoming gene technologies and new generation plant growth regulators (PGRs) have the desired potential to increase sugar content and improve crop Author for Correspondence : Yangrui Li e-mail : yangruili40@hotmail.com economics. Thus there is further scope of increasing sugar productivity if physiological and biochemical constraints are identified and modified through plant growth regulation(nickell, 1984). Moore et al. (1997) suggested that about 60% higher cane yield could be attained by removing yield limiting constraints. In many sub-tropical cane growing areas, initial growth (sprouting and tillering) of cane plant is restricted by high temperature and low humidity in the early phase and extremely low temperature at maturity phase. As such sugarcane plant get only 4 to 5 months for profuse growth and in this short span of time it is not possible to derive full benefits of its genetic potential, leading to low sugar productivity. In many countries sucrose plateau of most cane varieties is short and decline sets in quickly due to high ambient temperature. The poor sprouting and initial growth of ratoon crop during winter months also affect sugar productivity in many areas. Plant growth regulators have been found to circumvent some of the physiological constraints and in this direction impressive progress has been made to use ethephon (ethrel, CEPA or 2-chloroethyl phosphoric acid) in sugarcane culture and improve 213

crop economics. In sugarcane, many beneficial response of ethrel application have been reported depending upon the time and rate of application. This versatile growth regulator has been found to enhance sprouting of seed cane pieces under normal and lateplanted conditions, induces tiller development in many genotypes, helps in sprouting of underground stubble buds and can prevent flowering- a growth stage which is detrimental in commercial sugarcane plantatio, n. However, its most beneficial effect is recorded in increasing sucrose content of the juice during incline phase by inducing early maturity, nevertheless its effects on maintaining quality have also been reported during late-milling period. This review highlights the beneficial effect of ethephon on cane growth, yield attributes and sugar productivity. There are multitude of factors which limit sucrose productivity, however we have reviewed the work related to (a) sprouting and settling vigor of seed cane pieces, (b) tillers, millable canes and biomass production, (c) improving cane quality during early season, (d) quality sustenance during late crushing, (e) sprouting of winter initiated rations, (f) promoting sugarcane growth and morphophysiological attributes at low concentration, (g) inhibiting flowering in commercial plantation, and (h) quality sustenance in stand-over sugarcane. It is envisioned that commercial usage of ethephontechnology in problematic areas will enable the cane growers and processors to harvest more sugar per unit area. (a) Ethephon improves sprouting of seed cane pieces In many cane growing areas ( sub-tropical India) initial sprouting of cane sett is poor (35-40%) and therefore, a heavy input in the form of cane seed is a regular practice which is uneconomical. Beside soil moisture, which is a major constraint in cane germination, activation of bud was found to be equally important for normal sprouting process. Many desirable varieties tend to sprout poorly, resulting in uneven or irregular stand of crop. A number of setttreatment chemicals are now available, however, preharvest foliar spray of ethephon on seed cane has been found to be the most adoptable and economical method from farmers' point of view. Studies conducted in Louisiana, Hawaii, China, Colombia, Brazil and India have demonstrated that ethephon has tremendous potential to improve sprouting of seed cane pieces. A pre-harvest foliar ethephon treatment to seed cane three weeks prior to cutting and planting results in more uniform sprouting and a heavier stand of cane and number of required seed pieces may be reduced by up to 25 per cent. Studies carried out in India (Solomon et al., 1996.) have shown about 13-17 per cent enhancement in sett sprouting in ethephon treated seed cane pieces. The varietal reaction to ethephon application on seed cane varies considerably, ranging from 10-30 per cent, Which is due to differential response to ethephon treatment. In western part of Indian sub-tropics, where sugarcane is normally planted after the harvest of wheat crop (late-planting or summer planting in May), cane sprouting and tillering processes are impeded due to high ambient temperature, light intensity and low soil moisture. Yadav and Prasad (1987) reported beneficial effect of ethephon application on tillering in late-planted sugarcane. Solomon (unpublished) noticed positive effect of preharvest foliar application of ethephon on sprouting of cane sett under late-planted conditions.on an average, about 10-15 per cent enhancement in sett sprouting could be achieved through ethephon treatment. This is a substantial gain for those areas where poor sprouting of cane sett is a perpetual problem and a major yield constraint. Studies carried out in southern cane growing region of China by Wen et al. (1989) and Ye et al. (2003b) have shown that soaking seed canes pieces with 50 mg.l -1, 100 mg.l -l and 200 mg.l -1 ethephon solutions promoted the germination, tillering and early growth of sugarcane, but higher concentrations showed inhibitory effects. Ye et al. (2003b) reported that soaking seed canes with ethephon concentrations of 50 mg.l -1, 100 mg.l -l and 200 mg.l -l, respectively, markedly increased the germination and tillering rate, and improved the agronomic characters and cane quality. Studies of Zhang et al. (2001a, b) pointed out that the effects of ethephon soaking treatments on germination and plant growth might be variety-dependent although it promoted tillering and sugar accumulation so resulted in higher sucrose content in cane at the technical maturing stage in all cases. The work carried out by many researchers has conclusively demonstrated that ethephon can rather dramatically improve sprouting of seed cane pieces and also improve settling vigour due to vigrous formation of sett as well as shoot root system. However, it is important that these seed cane pieces should be planted as soon as possible after cutting. Improved sprouting of seed cane pieces, following ethephon treatment has been reported from countries such as Brazil, Colombia, Hawaii (USA), Taiwan, Louisiana (USA), China, India, etc. A judicious use of this technology could offer great economic benefits to the cane growers, especially in areas where sprouting per se is poor. Based on various experiments conducted in China, appropriate quantities of ethephon has been applied in about 50,000 hectares of sugarcane in Guangxi, and most of it was used at early growth stage or in soaking seed cane treatments 214

(b) Ethephon enhances tillering and biomass production Tillering in sugarcane is an important phase of growth and is greatly influenced by environmental factors like light, temperature as well as application of fertilizers and growth regulating chemicals. These tillers mature into stalks or sugar storage compartments and are of great economic value to the sugar industry. Under certain conditions, early and vigorous tillering is directly related to higher cane and sucrose yield. This is due to the fact that e.arlier formed stalks and primaries are invariably richer in sucrose content at maturity than the latter ones (McColl, 1976; Coleman, 1976; Shih and Gascho, 1980). Ethephon has been found to stimulate tiilering and stalk formation without producing corresponding yield increases in cereals (Van Andil, 1973). In sugarcane, stalk per se is yield component and therefore, varietal response to the applied ethephon could be at variance (Eastwood, 1979). It is observed that some cane varieties tiller poorly resulting in gappy stand and reduced cane tonnage at harvest. Field trials were therefore directed towards assessing the effect of ethephon on the degree of tillering in many cane varieties, under sub-tropical conditions. Studies carried out by Solomon et al (1998) showed that ethephon treatment, in genotypes Col 148 and Co 997 leads to increase in number of millable cane to the extent of 12-16%. Yadav and Prasad (1987) reported a significant improvement in tillering and yield of late-planted sugarcane with ethephon. Shetiya and Dendsay (1992) reported that varieties CoJ 64,Co 1148 and Coil12 tillered freely in response to post-emergence spray of ethephon and gave higher yields at final harvest than the unsprayed control. A series of experiments (Cheng and Chen, 1993; Li et al., 1997,2001, 2002; Liang et al., 1995b; Pan et al., 1997; Wen et al., 1990; Xing et al., 2002) on foliar spray of different concentrations of ethephon have been conducted at early growth stage of sugarcane. These studies have proved that low concentration of ethephon promoted the differentiation and stimulated the plant growth and finally resulted in higher cane yield and sugar output. Foliar spray of ethephon (at 50, 100, 200 300 and 400 mg.l -l) at late tillering stage indicated that (Liang et al., 1995b) the treatments with 50, 100 and 200 mg.l -t ethephon recorded higher cane yield while treatment with 300 and 400 mg.l 1 gave lower cane yield as compared with the control (0 mg.l -1 ethephon). The highest yield was recorded from 100 mg.l -j ethephon treatment. The growth retardation for some time after ethephon treatment was noticed, however, inhibitory effects were more serious with higher concentrations of ethephon although treatments promoted more tillers and so resulted in more millable stalks than the control at harvest. When the low concentration (5Oand 100 mg.l l ethephon) of ethephon was applied, the inhibition effect on the plants lasted for very short time (5 to 10 days). The inhibitory effect lasted for very long time for the treatment with 400 mg.l -t ethephon and it produced much shorter and smaller stalks and therefore recorded significantly lower cane yield than the control. This group working in China has recommended about 100 mg.l 1 of ethephon which seem to be appropriate for foliar spray at early growth stage of sugarcane. A post-emergence application of ethephon is characterized by profuse tillering but it results in an appreciable reduction of shoot and leaf length. Therefore, on an individual stalk basis, there seems to be reduction of stalk growth which is however, compensated by enhanced tillering and has a direct bearing on the ultimate biomass and cane productivity. Reports published from Hawaii, Brazil and Jamaica show that many cultivars tillers freely in response to ethephon treatment. Since some sugarcane varieties are more sensitive to ethephon treatment than others, it is imperative that small-scale test be conducted at different rates before testing the enhanced tillering effects of ethephon in large areas. (c) Ethephon promotes sprouting and re-growth of winter harvested ratoon The early sprouting and subsequent growth of winter harvested ratoon crop (especially early maturing cane genotypes) is one of the important aspect of ratoon production in many areas. This problem has been reported from countries and areas like India, Taiwan, south China, etc. It has been observed that under extremely low ambient-soil temperature, normal ratoon husbandry practices do not have much beneficial effects on sprouting of under ground subterranean buds. The poor stubble sprouting leads to a gappy stand with a substantial decline in yield and quality of succeeding ratoon crops. Many reports from Taiwan (Peng and Twu, 1978, Yang and Ho, 1980) and India (Kanwar and Kaur, 1977, 1981; Chauhan et al., 1984; Bendegiri, 1993) showed' that application of a few chemicals could alleviate this problem to a certain extent, however, selection of chemicals and its response depends on factors like, location, soil type, variety, etc. At Taiwan Sugar Institute, application of ethephon (1000mg/1) on cane stubble during winter months could induce ratoon shoots to the tune of 24 per cent over the check, two months after initial spray (Yang, 1986). In China, Wen et al. (1990) reported that spraying of ethephon on the stubbles promoted the sprouting and the growth of ratoon crops of sugarcane. Experiments carried out in sub-tropical India showed that pre-harvest foliar application of ethephon (December and January harvested plant crop), 7 to 10 days before harvest has a stimulatory effect on stubble bud sprouting and growth during winter 215

months (Solomon, 1996a; Solomon et al., 1998). A significant increase in stubble bud sprouting and tiller number was recorded following ethephon treatment. Enhancement in stubble bud sprouting under field condition was about 8-10 per cent after a fortnight of ratoon initiation as compared to untreated check. The number of ratoon tillers per unit area, as recorded after 120 days of ratoon initiation, was 15-17 per cent more in the treated plots. The results obtained from a series of field trials indicated that pre-harvest foliar application of ethephon during the cold season could induce ratoon sprouts and tillers at an early growth stage. Such beneficial effects may contribute a significant increase in cane yield at harvest. These studies suggested that use of ethephon could improve ratoon cane productivity of early varieties and will be of considerable help to cane growers as well as sugar factorieg, in increasing area under high sugar early maturing varieties. (d) Ethephon advances cane maturity and improves sucrose accumulation Sugarcane ripening is primarily a close interaction between weather-variety (crop age)-soil moisture and therefore, some increments in sugar content can be expected through improved agri-management practices. In many cane growing areas, early part of the milling season usually starts before the cane reaches a peak maturity i.e. juice quality and purity are typically poor. Advancement of cane maturity is considered as one of the most important achievements from the factory operational point of view due to improved sugar recovery and growth of subsequent ratoon crop. Many chemical ripeners are in vogue in the contemporary sugar industry with variable response and economic gains. A survey conducted by Eastwood and Davis in 1997 indicated that commercially there were three ripeners in use worldwide, today. In the northern hemisphere, glyphosate predominates. Fusilade Super and ethrel are ripeners of choice in the southern hemisphere. In Mauritius, Fusilade Super and Moddus have been tested successfully but the use of former had to be discontinued in certain areas due to its detrimental effect on ratoon growth and yield (Anon., 1996). The first commercial use of ethephon in sugarcane plantation to induce early maturity in incline phase was patronized by South African sugar industry and is widely used for this purpose today (Donaldson and Staden, 1989). About 37% of the irrigated crop and about 2% of the non-irrigated crop were ripened with chemicals in South Africa during 1997. In South Africa, early research indicated that ethrel increased sugar content and sugar yield in NCo376 and other varieties when soil moisture was adequate and response were more consistent (Rostron, 1974, 1977). Responsiveness to ethephon was linked to low juice purity (Rostron, 1975). Like the Australian 'experience, the relationship between juice purity at spraying did not account for the full variation of the responses to ethrel. Optimal rates of ethephon for different varieties and time of harvest after spraying were determined and recommend to growers after intensive research (Rostron, 1975). Multiple applications of ethephon were found to improve sucrose concentration over single applications (Rostron, 1985). Ethrel treated cane had lower extraneous matter at the mill compared to the control because of the reduced leaf material (Rostron, 1977), ethephon increased sucrose content only in the upper stalk sections (Rostron, 1977). Many studies have established that ethephon applied 10 to 12 weeks ahead of milling season, increases the sucrose content of the juice without affecting the growth of plant. This important property of ethephon gives the cane grower more flexibility in deciding on the time of harvest of crop. A similar finding was reported by Yang (1986) from Taiwan, indicating that aerial spray of ethephon (2 1/ha), 6-10 weeks prior to harvest consistently increase sucrose content in juice with no adverse effect on stalk density, height and cane yield of the succeeding ratoon crop. Studies were also initiated in Burdekin region of northern Queensland (Morgan et al., 2001) to examine the responsiveness of a number of sugarcane cultivars to ripener treatments: ethrel (ethephon) plus fusilade (ethrel/fusilade), fusilade (fluazifop) alone, verdict (haloxyfop) and glyphosate. Eight weeks after application, glyphosate and ethrel/fusilade(piggy backing) significantly increased mean CCS by 1.2 and 0.75 units respectively. There was no significant response to fusilade alone or verdict. There was significant variety by ripener interactions for both glyphosate and ethrel/fusilade treatments indicating that some cultivars responded better than others did to both treatments. This study has shown that glyphosate and ethrel/fusilade can increase the sucrose content of many cultivars that can now be studied further on the basis of their responsiveness. The ability of these chemicals to enhance sugar quality in immature crops with low CCS suggests that the profitability associated with early season harvesting can be significantly improved. In China, several researchers reported the ripening effect of ethephon on sugarcane in 1980s (Wu, 1983; Wen, 1985; Ye and Sheng, 1985). Experiments carried out by Lin et al. (1990) proved that foliar spray of 400 mg/l ethephon in early October resulted in significant increase in sucrose content in cane and improved the juice quality for three sugarcane varieties since about one month after the treatment. The cane yield was also increased when the crop was harvested in next February. Similar experiments were repeated for many times and the ripening effect was good in most of the cases with foliar spray of 400 mg.l ~ ethephon at the beginning of sugar accumulation stage of sugarcane (Liao et al., 1997, 2003; Nong et al., 1998; Yao et al., 2000a,b). According to these experiments (Yao et al., 2000), 216

ethephon was highly effective in promoting sugar accumulation and increasing sucrose content in the immature internodes but not in the mature internodes of sugarcane. After spraying high concentration (400 mg.l -r in most cases) of ethephon, a temporary retardation of the crown growth became evident and edges of the old leaves showed yellowing. But these symptoms were released and the growth of plant recovered after a certain period of chemical treatment (Lin et al., 1990). Physio-biochemical implications of ethephon treatment on sugarcane plants were investigated by Chinese sugarcane researchers. The laboratory analyses showed that, after foliar spray of 400 mg.lethephon, water content of the sugarcane plant leaves decreased by 1% ~3%, and the chlorophyll content and the respiratory rate also decreased (Lin et al., 1990), and the activities of NADP-malic enzyme (Lin etal., 1992), acid invertase (Lia0 et al., 1997, 2003), nitrate reductase and amylase (Liao et al., 1997) were inhibited while the activities of peroxidase (Lin et al., 1992), polyphenol oxidase (Liao et al., 2003), neutral invertase and acid phosphotase (Liao et al., 1997, 2003) increased in the plant leaves as compared with the control.. In some experiments, spraying high concentration of ethephon decreased the activities of Mg2 Ca2 in the leaves (Lin et al., 1992), but the opposite results were observed in other experiments (Liao et al., 2003). The treatment of 400 mg.l -~ ethephon also increased the activities of peroxidase (Yao and Li, 2002a) and IAA oxidase (Yao et al., 2000a) in the stalk internodes of sugarcane. The experimental results indicated that (Yao et al., 2002a), the first physiological response of sugarcane plant to ethephon treatment was to induce generation of large quantity of the inner ethylene, accompanied with lower level of IAA in the leaf tissues. Yao et al. (2002b) showed that application of 400 mg.l -1 ethephon increased activities of acid and neutral invertases in immature stalk internode (internode 2) over the control in two weeks, during the early phase of technical maturing stage, therefore enhancing the sugar accumulation in the stalks. The invertase activities decreased 4 weeks after ethephon treatment as compared with the control, inhibiting the inversion of stored sucrose which was probably responsible for higher sucrose content after ethephon treatment. The activities of amylase, acid invertase, peroxidase and foliar nitrate reductase (NRA) were assayed in late-planted sugarcane treated with 500mg/1 ethephon during tillering stage (Solomon et al., 1988). The foliar amylase activity showed manifold increase, whereas there was a marginal decline in invertase activity. The in vivo,foliar NRA and peroxidase activity showed upward trends. In Indian.sub-tropics, climatic conditions for ripening are favourable, but despite this natural boon sugar recovery per se is very poor during early part of the milliing season (8.5-9.0 % cane). However, limited efforts have been made in sub-tropics to apply cane maturants in commercial plantation. The field trials conducted (Solomon et al., 1998, 1993) so far have conclusively proved that ethephon could produce a fairly consistent response and improve cane quality during early season without any adverse effect on top feed quality and ratoon re-growth. Based on the extensive practical evidence and field exploration, it could be concluded that aerial application of ethephon has the potential to improve sugar recovery during early season. These studies indicate that ethephon could be successfully used in advancing cane maturity under sub-tropical climate, as well. However, it is imperative that a maturity survey of the crop should be undertaken before its application in commercial sugarcane plantation. Many studies have shown that when planning ethephon application in sugarcane commercial plantation, following crop conditions should be kept in mind for most consistent responses: (i) (ii) Crop is technically immature and growing vigorously when the chemical is applied. The juice purity can be used as an indication of the crop's maturity and it should be less than 75-78% for ethephon application. Have the potential to continue active growth for at least a further 3 to 4 weeks with at least 8 green leaves per stalk. (iii) Show no signs of nutrient deficiency and free of pest and disease problems. (iv) Exhibit less than 25% flower emergence. (e) Ethephon treatment improves drought resistance in sugarcane In southern cane growing belt of China, drought is a recurrent problem. Many experiments conducted in 1996 (Liao et al., 2003) confirm that the treatment of foliar spray o.f 4.00 mg.l -I ethephon in October to November improved the drought resistance of sugarcane plants under severe water deficit condition. The ethephon treated crop remained significantly more green than the control that recorded only 2.8 green leaves each plant in average after long duration of dry weather from late September to late December. In Guangxi province (China) severe drought happens very often since September, and ethephon treatment not only promotes the ripening but also improves the growth status of sugarcane plants. The ethephon treatment increased both cane yield and sucrose content in cane and finally resulted in higher sugar production. Further experiments on drought tolerance also proved that low concentration of ethephon~ treated at the early growth stage or 'soaking see d canes also improved the drought resistant ability of sugarcane plants (Li et al., 2002a; Liao et al., 2003; Yao, 2002; 217

Ye et al., 2003a,b). Yao et al. (2002b) found that spraying low concentration of ethephon on the leaves alleviated the injury of cell membrane caused by water deficiency stress, and maintained relatively lower osmotic rates of electrolytes and soluble sugar, and increased the proline content and water potential in the leaf tissues, and promoted the activities of cell protective enzymes such as peroxidase, catalase and polyphenol oxidase, and improved the gas exchange characteristics, increased the stomata conductance and intercellular CO 2 concentration, and increased the net photosynthetic rate. Zhou et al. (unpublished) found that spraying with 100 mg.l- Iof ethephon at early tillering stage remarkably increased the density of vascular bundles and enlarged the areas of epigenetic vessels and phloem in the leaves, and promoted the absorbability, which was good for improving the drought resistant ability of sugarcane plants. Liao et al. (2003) reported that foliar spray of 100 mg.l -I ethephon at the early growth stage promoted the stomatal differentiation, interlay of the lateral wall of the epidermis cells, morphological structure of the mesophyll cells and the stomatal apparatus in the leaves, which would be good for improving photosynthesis and protecting the leaf tissues from being injured under drought condition. Ye et al. (2003a) found that, under drought condition, the treatment of foliar spray 100 mg.l -1 ethephon at early growth stage of sugarcane retained relatively stable contents of chlorophyll and water in the leaves, and produced higher cane yield as compared with the control. Wu et al. (2003) reported that under the stress of soil moisture, spraying of ethephon at 100 mg L-Ion the leaves at early growth stage optimized the canopy architecture at the technical ripening stage. The treatment also resulted in an increase in the bound water content and the ratio of bound water to free water, increased the chlorophyll content and retained its relative stability, increased the proline content which perhaps imparted drought tolerance to two experimental sugarcane varieties as compared to untreated control. Ye etal. (2003b) reported that, under drought conditions, the seed cane soaking treatments with 50 mg.l -~, 100 mg.l -l and 200 mg.l 1 ethephon, respectively, recorded marked improvement in germination and tillering rates, and improved the agronomic characters and the cane quality as compared to control. Ethrel application reduced the loss of sucrose from severely drought stressed cane up to 20 weeks after spraying. This was thought to have been the result of reduced water use by sprayed cane, which allowed more efficient use of available water (Rostron, 1977). (f) Ethephon promotes sugarcane growth and morpho-physiological attributes at low concentration Extensive studies were carried out to ascertain the morphological, physiological and biochemical mechanism of ethephon at low concentration which promotes sugarcane growth. (i) Effects on morphological structure Spraying low concentration of ethephon on the leaves at early growth stage showed a short time of inhibition on growth of the above-ground part of sugarcane plants, resulting in shorter and narrower leaves accompanied with more tillers and newly born leaves. Luo et al. (1996, 1997) reported that foliar spray of 100 mg L -1 ethephon at the tillering stage reduced length and width of leaves but promoted differentiation of the vascular bundles in the leaves, increased the relative number of vascular bundles and ratio of total width of vascular bundles and total width of vascular bundle phloem in the leaves, thus provided better condition for substance transferring. Differentiation of the mesophyll cells was also promoted by the 100 mg L -l ethephon treatment which resulted in more tips on the cells, so broadened the exterior surface of the mesophyll cells, and allowed more chloroplasts arrangement. The granule of the chloroplasts and the layers of the granule were also increased. These changes brought to a significant increase in the total photosynthetic area in the mesophyll cells of sugarcane leaves. Li et al. (2002a,b) reported that ethephon treatments accelerated the differentiation of vascular bundles of sugarcane stalk, increasing density of the bundles, and changing the xylem vessels and phloem in the bundles in the stalks, and the treatment with 80 mg.li of ethephon increased area of the vascular bundles in the stalks, which could improved the ability of transport. The treatment with 80 mg.l -I ethephon inhibited the growth of stem and its epidermis cells for a short time, but restored quickly and turned to promote them later, increasing the radial wall area of the epidermis cells and promoting the transverse expansion of the stem, but the treatment with 300 mg.l -1 ethephon inhibited the growth all time found that low concentration of ethephon treatment could enhance remarkably the density of vascular bundles and enlarged the areas of epigenetic vessels and phloem in the leaves, and promoted the absorbability of sugarcane plants, and showing more content of silicon in the leaves. (ii) Effects on photosynthesis Low concentration of ethephon treatment promotes sugarcane photosynthesis and increases the net photosynthetic rate after short time (about a week) but high concentration of ethephon treatment inhibits the photosynthesis (Liang et al., 1994; Lin et al., 1992; Yao, 2002; Ye et al., 2003a,b; Xing et al., 2003; Zhu, 2002). According to a series of experiments, low concentration of ethephon treatment increased the chlorophyll content in the leaves (Liang et al., 1994; Pan et al., 1997b; Xing et al., 2003), and the activities of important enzymes related to 218

the photosynthesis, including PEP carboxylase (Xing et al., 2003), NADP-malic enzyme (Liang et al., 1994; Xing et al., 2003), carbonic anhydrase (Zhu, 2002), pyruvate phosphate dikinase (Zhu, 2002), amylase, Mg2+-ATPase and Ca2 (Liang et al., 1995a), and the stomata conductance, intercellular CO 2 and respiratory rate in the leaves, and the activities of the DCIP photoreduction and cyclic photophosphorylation (but not the noncyclic photophosphorylation), and the more formation of the chlopophyll-protein complex of thylakoid in the chloroplasts (Zhu, 2002). In general, the treatment with low concentration of ethephon comprehensively improves the photosynthetic ability of sugarcane. (iii) Effects on root activity and nutrient absorption Based on the experimental results of Huang (2002), foliar spray of 100 mg.l -t ethephon at early growth stage of sugarcane increased root length and root activity, and reduced the activity of peroxidase in the roots. The low concentration of ethephon treatment also increased the bleeding sap quantity and the cytokinnins and potassium in the bleeding sap, and increased the activity of nitrate reductase in the leaf +3 and the soluble sugar content in the leaf sheath. It also significantly increased the absorption of N, P and K by roots. Zhou et al. (unpublished) reported that foliar spray of low concentration of ethepbon promoted the absorption of Si and Mg by sugarcane plants. (iv) Effects on some important metabolic enzymes Peroxidase : Peroxidase is related to many important physiological processes such as cell differentiation, tissue maturation and adoptability of plant to environments. In sugarcane, the genotypes with smaller stalks and plants at slower growth stage such as early growth stage and sugar accumulation stage show relatively higher activity of peroxidase in the leaves (Li, 1990). The proxidase activity increased during the first week after foliar spray of ethephon, but it showed significantly lower activity at the low concentration of ethephon treatment than the control after one month of the treatment. This low activity was recorded until onset of sugar accumulation stage and gradually increased at later stages as compared with the control (Liang et al., 1995a,b; Pan et al., 1997a; Yao et al., 2002b; Yao and Li, 2002). The situation in the stem, however, is quite different. Li et al. (2002b) reported that proper concentration of ethephon promoted the activity of peroxidase in the cytoplasm and cell walls of the stems for whole growth stage. Invertase : Liang et al. (1995a) reported that foliar spray of 50 mg.l -K and 100 mg.l l ethephon at the tillering stage increased the acid invertase activity in leaves of sugarcane from early to middle growth stage, and both the treatments with low and high concentrations of ethephon could increase the neutral invertase activity in the leaves. The low concentration of ethephon treatment also promoted the activity of acid Invertase and neutral invertase in the stalk internodes at booming stage of sugarcane (Yao et al., 2002). ATPase : Studies by Liang et al. (1995a) showed that foliar spray of 50 mg.l -j and 100 mg.l l ethephon at the tillering stage increased the activity of Mg2+-ATPase and Ca2+-ATPase in the leaves of sugarcane. Li et al. (2002) reported that proper concentration of ethephon promoted the activity of Ca2+-ATPase in the cytoplasm and cell walls and that of Mg2+-ATPase in the cytoplasm of stems from early to middle growth stage. Yao et al. (2002) reported the low concentration of ethephon treatment increased the activity of Mg2+-ATPase and Ca 2 ATPase in the stalk internodes at booming stage of sugarcane. Besides, the treatment with low concentration of ethephon also increased the activities of polyphenol oxidase (Liang et al., 1995a; Pan et al., 1997a; Li et al., 2002), superoxidase dismutase (Pan et al., 1997a; Yao et al., 2002) and catalase (Yao et al., 2002) in the leaves of sugarcane. (g) Ethephon inhibits flowering in commercial sugarcane plantation Flowering of sugarcane in commercial plantation can be detrimental to sugar yields and causes a decreased economic benefits. This problem becomes quite severe in many cane growing countries depending upon the varieties grown, local cultural practices and fluctuation in weather conditions. The flowering process in sugarcane is extremely sensitive to the environment. In Hawaii, cane is maintained in the field for two years before being harvested and therefore, flowering during the first year causes significant losses in sugar production. Nickell (1984) reported that under the Hawaiian cropping conditions, flowering reduces sugar yield by 3.2 tons per hectare. Studies from India (Thulijaram Rao, 1968) showed that arrowing does not affect yield or quality if the cane crop is harvested within a period, of three months. These observations were supported by Garg et al. (1979), indicating that for initial period of two months after initiation of tassel, the deterioration in juice quality was less, however it declined rapidly with the rise in ambient temperature. The earlier approach of using paraquat or diquat in commercial plantation was discouraged due to their negative effect on cane yield. On the contrary, application of ethephon does not effect vegetative growth and therefore, is a preferred chemical for flowering control. Experiments conducted in Brazil (Coleti et al., 1986), Hawaii (Osgood et al., 1982), Sudan (Hardy and Dove, 1986) and India (Bendegiri 219

et al., 1991; Solomon et al., 1997) have shown that ethrel application 1 to 3 weeks before floral induction provides excellent control. Detailed studies were carried out in Mauna Kea sugar plantation (Hawaii) in late August 1981 on variety H70-0144 growing under non-irrigated conditions. Application of ethephon at 500 grams a.i/ha from August to September resulted in 98 percent tassel control when applied shortly before the traditional flower induction time frame. Similar results were noticed from Brazil where application of ethephon at 480 grams a.i./ha gave very consistent flowering control. The treated areas produced significant increases in both cane tonnage and sugar yields per hectare, compared to untreated areas of control fields. In Thailand, two field experiments were conducted at Suphan Buri and Rayong Field Crops Research Centers in 1995 to determine the optimum period and rate of ethephon application to inhibit the flowering of cane crop. The results of both experiments showed that ethephon application inhibited the flowering of the U-Thong 2 sugarcane cultivar. At Suphan Buri, an ethephon application rate of 960 g a.i./ha significantly lowered the number of flowering stalks when compared to an application rate of 480 g a.i./ha. In India (Solomon unpublished) carried out studies on control of flowering in commercial plantation at Hasanpur (Bihar) by spraying 500 mg/l ethephon. This resulted in nearly 75-80% inhibition of tassel formation in treated plots. Application of ethephon is therefore a most practical approach to control flowering in commercial sugarcane plantation. In majority of cases, the quality of treated cane improved with lower fiber and sometimes higher juice content. (h) Ethephon sustains quality of stand-over sugarcane crop The stand-over crop in sugarcane is a peculiar phenomenon often results due to lack of proper planning in planting-harvesting-milling schedules. The consequences in term of sugar production are usually detrimental to the farmers and processors as a large quantity of crop remains in the field, after attainment of peak maturity. In recent years some instances have been reported (Solomon et al., 1997) where mills were unable to crush the targeted amount of cane and a huge quantity of fully mature crop was left in the field which had to be processed during summer months resulting in low sugar recovery. This late-milling of sugarcane has deleterious impact on cane tonnage, sugar recovery and processing operations due to high amount of non-sugar compounds and bacterial metabolites, such as dextran. A foliar application of ethephon or ethephon + 2% sodium metasilicate on stand-over cane could minimize inversion and retained juice quality (Singh et al., 1982; Solomon, 1996b). The results showed that combined spray not only maintained the quality of left-over crop but also improved the sucrose content in a few cane varieties. CONCLUSION Sugarcane is an important commercial crop however, sugar productivity per se in many cane growing areas is low due to physio-biochemical and climatic constraints. In order to mitigate the impact of bio-productivity barriers such as sub-optimal cane germination, tillering, sucrose accumulation, ratoon sprouting, poor quality of stand-over crop and flowering in commercial plantation, semicommercial scale trials were carried out at different locales using ethephon. Applie'ation of ethephon has been found to promote seed cane sprouting (13-17%), improved tillering and millable cane formation (12-16%) and helped in initiation and formation of ratoon shoots/tillers of winter harvested cane (8-10%). It's beneficial response had been observed in the advancement of cane maturity with appreciable gain in CCS per cent, giving adequate flexibility to cane growers on the time of harvest. Additionally, its efficacy has been demonstrated in minimizing sucrose losses in stand-over crop at high temperature and control of flowering in large scale sugarcane plantation. Ethephon, therefore, seems to be the only chemical with wide-spectrum of beneficial activity on sugarcane and has the potential to augment sugar productivity under diverse agro-climatic conditions. REFERENCES Anonymous (1996). Annual Report. Mauritius Sugar Industry Research Institute, Mauritius. Bendegiri, A.V, (1993). Growth regulators in cane production. Proc. Seminar on Utility of Growth Regulators in Cane Production. Deccan Sugar Technologists Assoc. India, 24th July. Chauhan, R.S., Verma, R.S. and Pathak, K.C. (1984). Effect of cycocel application in improving stubble sprouting of winter harvested ratoon. Co-op. Sugar, 16 : 135-138. Chen, J.C.P. and Chou, C.C. (1993). Cane Sugar Hand Book. John Wiley and Sons Inc. New York. Coleman, R.E. (1976). Physiological responses induced by cane ripeners. Ann. 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Yao, R.L., Li, Y.R., Yang, L.T. and Zhang, G.R. (2002b). Effects of ethephon on ATPase and invertase activities in internodes of sugarcane at boom growth stage. Chinese J. Tropical Crops, 23(2) : 66-71. Ye, Y.P., Tang, J., Li, Y.R., Li, Y.J. and Yang, L.T. (2003a). Studies on some physiological indices for drought-resistance in two sugarcane varieties under drought and irrigation conditions. Sugarcane, (accepted). Ye, Y.P., Yang, L.T., Li, Y.R. and Li, Y.J. (2003b). Effects of seed-cane soaking with ethephon on the drought resistance in sugarcane. Sugar Crops of China, (accepted). Ye, Z.B. and Sheng, J.H. (1985). Experiments of the ripening effect of chemicals on sugarcane. Guangdong Agric. Sci., (6) : 23-24. Zhang, X.J., Li, Y.R. and Lin, Y.K. (2001a). Effects of different concentrations of ethephon soaking seed cane on agronomical characters and some physiological and biochemical characters in sugarcane stalk tissue. Sugarcane, 8(3) : 14-19. Zhang, X.J., LI, Y.R. and Lin, Y.K. (2001b). Effects of different concentrations of ethephon soaking seed cane on plant growth and some physiological and biochemical characters in sugarcane. Sugar Crops of China, (3) : 9-13. Zhu, J.J. (2002). Comprehensive effects of ethephon and ethephon plus gibberellin treatments on photosynthesis of sugarcane. M.S. thesis of Guangxi University, Nanning, China. Yang-Rui Li was born in Beiliu City, Guangxi, China on 5 April 1957. He graduated and earned B.A. degree in Department of Agronomy, Guangxi Agricultural University in January 1982, and M.S. and Ph.D. degrees in Department of Agronomy, Fujian Agricultural University in July 1985 and January 1988, respectively. He was employed as a lecturer in Department of Agronomy, Guangxi Agricultural College from January 1988 to December 1989, and visiting scientist in Department of Agricultural Biochemistry, University of Hawaii, USA from December 1989 to February 1991, and associate professor (from March 1991 to November 1992) and professor (since December 1992) in Department of Agronomy, Guangxi Agricultural College, and visiting scientist at University of Nebraska-Lincoln, USA from November 1994 to August 1996, and professor and deputy president of Guangxi University from April 1997 to April 1998, and president of Guangxi Academy of Agricultural Sciences since May 1998. His research interests include crop (especially sugarcane) physiology, biochemistry and molecular biology, sugarcane genetics and breeding and cultivation, chemical regulation of growth and development of sugarcane. He has more than 170 publications in these areas, and received 11 scientific research achievement awards from Chinese government up to the present. 222

Dr. S. Solomon is a Principal Scientist at the Indian Institute of Sugarcane Research, Lucknow (India). He has a long association with the sugarcane crop and specializes in the area of sugarcane quality, post-harvest management, mill sanitation, etc. and providing consoltancy services to many sugar mills in India. He has published over 40 research papers and many reviews and special reports on the management of post-harvest losses and sugar recovery. Dr. Solomon has published two books Cane Sugar : Production Management and Sugarcane : Agro-Industrial Imperatives (Vision 21 ~' Century). He is also author of five technical bulletins published from the institute. Dr. Solomon is appointed as one of the refrees of International Commission of Uniform Methods of Sugar Analysis (ICUMSA) and also a member on the national committee of this commission. SPECIAL DISCOUNTS for Subscribing "Sugar Tech" for 3, 5 and 10 years 3 YEARS Individuals Institutions/Universities/Factories India Abroad Rs US$ s Euro 750.00 60.00 40.00 60.00 2000.00 200.00 135.00 200.00 5 YEARS Individuals Institutions/Universities/Factories India Abroad Rs US$ s Euro 1000.00 100.00 60.00 100.00 3000.00 300.00 180.00 300.00 10 YEARS Individuals Institutions/Universities/Factories India Abroad Rs US$ s Euro 1500.00 200.00 120.00 200.00 6000.00 550.00 330.00 550.00 ~- 11 ~, v ~, -,, e- 2003 & 2004 Subscription from Institutions in India and Abroad would get free the volume 4 (4 numbers) Save money by subscribing Sugar Tech for 3, 5 and 10 years, respectively. 223