Plant Physiology

PHYSIOLOGICAL BASIS OF YIELD VARIATION BETWEEN AND WITHIN SUGARCANE VARIETIES GROWN UNDER CONTRAST-

ING ENVIRONMENTS I. COMPONENTS OF SUCROSE YIELD AT HARVEST

G. C. Soopramanien and M. H. R. Julien

Mauritius Sugar Industry Research Institute, Reduit

ABSTRACT

Four commercial varieties of sugarcane were sown at different dates during the planting season under contrasting environments. All were harvested at a fixed age of 68 weeks. Sucrose yield variation at harvest was analyzed in terms of its components; tiller density, tiller dry weight and sucrose concentration (sucrose % dry weight). The variation in sucrose yield at harvest was due to wider variations in biological yield as compared to sucrose concentration. Tiller density was found to be a major yield determinant. The effect of site and planting date indicated that warm conditions favored dry matter accumulation while cool conditions increased sucrose accumulation. High sucrose yield at harvest among the varieties was associated with biological yield in a low tillering and high stalk dry weight variety.

Varietal differences in sucrose yield were affected by both site and planting date indicating possible varietal adaptation. However, sucrose concentration characteristic of varieties was not drastically affected by site or planting date. Varietal adaptation was attributed

I to both tiller density and stalk dry weight. The absence of large dif- ferences in stalk weight or sucrose concentration at harvest between tillers of different ages showed homogeneity of the population of surviving tillers and that the late tillers were able to compete with

I the early ones. Treatment effects on plant morphology as related to physiological attributes are discussed in relation to yield maximiza- tion.

INTRODUCTION

In a number of countries where sugarcane i s grown;the planting and har- vesting periods extend over several months. The sequences of climatic conditions during the year are such that the sugarcane is not always sown under optimal

1 conditions for germination and tillering. In Mauritius, the planting season ex- tends from March up to August while harvesting i s done between June and De- cember.

It i s accepted that a knowledge of the physiological basis of yield variation

504

I G. C. SOOPRAMANIEN AND M. H. R. JULIEN 505

in any crop is a pre-requisite for the formulation of strategies for increases in yield a t harvest (watson12). The achievement for different crops have been sum- marized recently ( ~ v a n s ~ ). Up to now very few studies have been carried out on growth and developmental aspects of the sugarcane plant under field conditions. Studies undertaken in South Africa, Guyana and the West $dies have already been reported ( ~ o s n e l l ~ , Mc Lean et a/', Mc coil7). These reports indicated a need for information on the behavior of sucrose yield components during the crop cycle so as to relate them to yield variation observed a t harvest.

In crops such as wheat or rice, similar economic yields at harvest may be achieved through different combinations of two or more components. In the above crops, such components are: number of productive tillers per unit area, grain number and grain weight ( ~ v a n s ~ ) . In sugarcane, the components of sucrose yield are the number of stalks (tillers or shoots) per unit area, their average weight and sucrose concentration (sucrose % dry weight).

Studies on the physiological basis of yield variation in sugarcane were initiated in Mauritius in 1973. Growth and developmental aspects of four com- mercial varieties grown under contrasting environments were studied in a plant cane and ratoon crops. The results on sucrose yield a t harvest in the plant cane

I crop are dealt with in this paper and those on the tillering aspect are presented

1 i n the subsequent one. i

I MATERIALS AND METHODS

A 4 x 4 factorial design with three replicates was used in this study. Four commercial varieties (M 13/56, M 351157, S 17 and M 93/48) were planted a t four different dates a t equal intervals. The same design was used in all three sites (Pamplemousses, Trianon and Alma). Variety M 13/56 is high tillering with thin stalks and narrow leaves; M 93/48 i s low tillering but has thick stalks and broad leaves. Variety M 351 (57 is similar to the latter but has a poor sucrose concentration. Variety S 17 i s intermediate in plant habit but has a high sucrose concentration a t harvest.

Some characteristics of the three sites are given in Table 1.

TABLE 1. Characteristics of the three sites

Mean Annual rainfall

Site (mm) Altitude (based on

(m) 30 years) Soil type

Pamplemousses 79 1494 Low Humic Latosol Trianon 305 1589 Low Humic Latosol Alma 442 33 26 Humic Ferruginous Latosol

506 PLANT PHYSIOLOGY

The first sowing was done in, March ,1973 and the three subsequent ones at eight weeks interval (referred to as April, June and August planting date treat- ments, respectively). Each plot consisted of 10 rows a t 1.6 meters wide and 8 meters long. All three sites were rainfed.

The primary shoots which emerged after planting in each treatment were tagged with paint in four border rows on each side. These shoots were referred to as 'early' tillers. Tiller emerging within the following 7 or 8 weeks were also tagged with a different paint mark and referred to as medium or mid-season tillers. All other tillers emerging later were not marked and referred to as 'late' tillers. 3,

Each planting date treatment was harvested at 68 weeks at the three sites. At harvest, the number of stalks in each group was recorded in each row (tiller group density was derived from the records). A random sample (12 stalks) of each group of stalks was taken to the laboratory to determine stalk height and internode number, leaf fresh weight, stalk fresh weight, pol %'cane (sucrose % fresh weight) of stalk sample (de Saint ~ntoine"), fibre % cane (de Saint An- toine and de ~roberville' ' ) and Brix % cane.

Samples of leaf and leaf sheath were dried to constant weight (48 hours at 80°C in a ventilated oven) to determine dry weight. A separate sample of one meter row length including a l l three groups of tillers were analyzed separately for average stalk dry weight and sucrose concentration. Using above data, the fol- lowing variables were calculated: stem dry matter content (fiber % cane + Brix % cane); Sucrose per stalk; total stalk dry weight (stem + leaves + leaf sheaths); sucrose concentration (sucrose % stalk dry weight). filler density, total crop dry weight, sucrose yield per unit area and per average stalk were also calculated as well as the sucrose concentration, dry weight, length and internode number for each group of tillers.

R ESU LTS

Planting date, site and variety were responsible for the significant variation in sucrose yield a t harvest. The variation observed for site and planting date could be explained by more pronounced differences in crop dry weight as com- pared to sucrose concentration which was also responsible for the varietal dif- f erences.

Treatments main effects on sucrose yield and i t s components are illustrated in Fig. 1. Among the three sites, a higher sucrose and crop dry weight yields were observed a t the warmer site, Pamplemousses, than at Alma where the climate was cooler. The difference in crop dry weight between these two sites was more pro- nounced than for sucrose yield due to a lower sucrose concentration at Pample- mousses as compared to that of Alma. The pronounced crop dry weight dif- ference i s explained by tiller density differences (Fig. 1) and also by a lower stalk dry weight at Alma only.

Sugar yields were similar and significantly higher in the first two plantings

G. C. SOOPRAMANIEN A N D M. H. R. JU LIEN 5w- ,

Site Planting Date Variety N-

FIGURE 1,'Effect of site and planting date on sucrose yield over i t s components in four sugarcane varieties.

dates as compared to the later ones. Once again, the differences were due to higher crop dry weights but not to higher sucrose concentration in the earlier planting5 and tiller density was solely responsible for crop dry weight differences (Fig. 1).

The thick stalk varieties (M 93/48, M 351157) reached harvest with the highest sucrose and dry weight yields but with the lowest sucrose concentration.

508 PLANT PHYSIOLOGY

In contrast with planting date effect, dry weight yields variation for varietal ef- fect was due more to stalk dry weight component than to tiller density (Fig. 1).

A significant interaction between site and planting date was observed for sucrose yield as could be explained by the high dry weight yield obtained from April sowing a t Pamplemousses and which could be attributed to higher tiller density. (Table 21.

TABLE 2. Mean* sucrose, dry weight, pol % DM, tiller density and average stalk weight of four planting dates at three sites.

Tiller Stalk Sit& Planting Sucro e Dry t. Pol % DM no. dry wt.

date gm-' gm-' + * m -2 g

Mar. 5 Apr. 30

Pamplemousses J~~~ 25

Aug. 20

Mar. 5 Apr. 30

Trianon June 25

Aug. 20

Mar. 5 Apr. 30

Alma June 25 Aug. 20

LSD P 0.05 228 488 2.4 6 52

Different letters denote significant difference between planting dates at P 0.05 * Mean of four varieties

* * Sucrose concentration

The performance of the varieties was not similar at all sites and resulted in a significant interaction.Varieties M 13/56 and M 93/48 haventhus, similar and high- est yields a t Pamplemousses while the former was the lowest at the other two sites (Table 3). It should be noted that the high tillering characteristic of variety M 131 56 was compensated for i t s low stalk dry weight only at Pamplemousses. The good performance of variety S 17 a t Trianon could be ascribed to both i t s crop dry weight and sucrose concentration. Although crop dry weight of S 17 and M 13/56 were similar at Alma, the sucrose yield of the former was better on account of i t s high sucrose concentration (Table 3).

Interactions between varieties and planting date were generally low for al l characters measured except for the overall poor performance of S 17 when plant-

G. C. SOOPRAMANIEN AND M. H. R. JULIEN 509

TABLE 3. Mean* sucrose, dry weight, pal % DM, tiller density anb average stalk weight of four varieties at three sites

T

Tiller Stalk Variety Sucrose Dry wt. Pol %DM -' no. dry wt.

gm-2 gm-2 ** g

M 13/56 1682 a 3926 a 43.0 a 105a 375b M 351157 1318 b 3705 a 35.1 c 89b 421b

Pamplemousses 17 1269 b 2925 b 43.1 a 73 c 402 b

M 93/48 1633 a 4041 a 40.5 b 75c 539 a

MI3156 1173c 2915b 40.6b 88 a 328 c M 351157 1355 bc 3694 a 3 7 . 0 ~ 86a 427 b

1401 ab 3147 b 44.6 a 74 b 428 b 72 b 534 a

M 13/56 1058 c 2470 b 42.9 b 80 b 306c M 351157 1324 ab 3352 a 40.2 c 88 a 378 b

11 20 bc 2457 b 48.4 a 69 c 356 b M 93/48 1434 a 3304a 43.5 b 69 c 505 a

LSD P 0.05 228 488 2.4 6 52 - Different letters denote significant difference between planting date treatments at P0.05

* Mean of four planting dates ** Sucrose concentration

TABLE 4. Tiller group density (10 mW2) a t the three sites

Tiller type Planting

date Early Middle Late

Mar. 25 a 20 b 50 b Apr.

Pamplemousses 16 c 32 a 64 a

June 21 b 23 b 31 d July 10 d 15 c 37 c

Apr. 9 a 9 a 69 a 62 b

July 7 a 6 a 50 c

Apr. 12 a 13 a 58 a June 9 b 13 a 43 c July 7 c 10 a 50 b

" ~ & e ) e n t letters denote significance b e m e n planting dates at P0.05

TABLE 5. Mean internode number, height and stalk dry weight of tiller groups a t three sites.

Site planting Internode no. per stalk Height (ern)

Stalk dry weight ( 9 )

date Early Medium Late Early Medium Late Early Medium Late

Mar. 5 23.3 a 24.7 a 18.3 b 192c 212a 163c Apr. 30 23.7 a 23.3 a 19.3 ab 205 b 186 c 181 b

Pamplemousses June 25 24.1 a 21.6 b 19.8 a 223 a 200 b 201 a Aug.20 23.8a 20.1b18.7ab 192c 176d 158c

Ap:. 30 22.5 a 20.3 b 20.1 a 217a 207a 210a Trianon June 25 20.2 b 20.6 b 18.9 a 173b 186b 173b

Aug. 20 23.2 a 24.2 a 20.7 a 180b 190b 174b

Apr. 30 24.3 a 22.4 b 20.7 b 249 a 249 a 235 a Alma June 25 21.5 b 20.8 c 20.7 b 209 b 209 b 203 b

Aug. 20 22.9 24.2 a 23.1 a 192c 194c 187c

Different letters denote significance between planting dates at P0.05.

I G, C. SOOPRAMANIEN AND M. H. R. JULIEN 51 1

I

I ed in August which could be due to a low tiller density.

As indicated already, tiller density at harvest seems to be a more dominaint crop dry weight determinant than average stalk dryweight. The data collected on tiller density and stalk dry weight for the three groups of tillers are presented in Tables 4 and 5. The late season group of tillers which included those emerging 12 to 13 weeks after sowing represented a larger fraction of the whole population at harvest. Variation in total tiller density particularly between planting date treatments was due mainly to variation in late tillers. The proportion of each tiller group was nearly similar within each site, except a t Pamplemousses where the late group represented a lower proportion (Table 4). The same trend was observed for either the high tillering variety M 13/56 or the low tillering M 93/48.

TABLE 6. Sucrose concentration of tiller groups a t the three sites

Site Planting Early Medium Late date

Mar. 5 45.2 ab 46.4 a 43.3 b Apr. 30 51.2 a 51.2 a 50.4 a

Pamplemousses June 25 51.1 a 48.2 b 49.4 b Aug. 20 49.9 a 48.8 a 49.5 a

Apr. 30 48.7 a 48.6 a 48.5 a Trianon June 25 48.8 a 47.2 a 47.5 a

Aug. 20 50.6 a 48.5 b 50.0 a

Alma Apr. 30 50.0 b June 25 51.4 a Aug. 20 50.5 a

Different letters denote significance between tiller types at PO.05

I n spite of differences in number of tillers a t harvest, in each group both the sucrose concentration and stalk dry weight for the tiller groups did not large- ly differ except for Pamplemousses where a consistently higher stalk dry weight was recorded for the early as compared to the late season group. At Pamplemous- ses, the late tillers of all varieties were lighter a t harvest, this being more pro- nounced in variety M 93/48. At the same site, the early tillers for the June and August planting dates were significantly heavier than those obtained from the earlier plantings. This was also true for the medium and late tillers but the dif- ferences were less marked. Variations in stalk dry weight were generally not al- ways proportionately related to stalk length particularly at Alma and Pample- mousses. In a similar way, differences in stalk length were not always reflected by their respective internode number.

I DISCUSSION

The two main components of sucrose yield in sugarcane as well as in sugar beet are total biological yield and sucrose concentration. These two crops differ from graminaceous ones like rice, wheat or maize because their economic pro-

duct, i.e. sucrose, is a direct product of photosynthesis and is stored in their vegetative structures.

In the present studies, total biological yield for sugarcane has been con- sidered as the product of the number of millable stalks (or tillers) and their average weight a t harvest. Variation in sucrose yield a t harvest was found to be due to wider variation in biological yield which was not always offset by the sucrose concentration component. In Australia, 6arrie2 found out that variation in weight of cane a t harvest was five times greater than that of percentage extract- ible sucrose component.

Sucrose yield variation under the conditions of the present trials could be attributed to the differing climatic conditions among the three sites and within sites to the differences in climatic sequences that prevailed between sowing and harvesting of the different planting date treatments. Both site and planting date treatments affected tiller density to a larger extent than average tiller dry weight. Hence, a t least in this study tiller density could be considered as the most im- portant yield determinant. Pathway coefficient analysis applied elsewhere to yield components in random and selected sugarcane populations have also shown that stalk number was the most important component of cane yield (James5).

Stalk dry weight at harvest in sugarcane may be regarded as an integral of growth under the sequences of climatic conditions during the crop cycle. Within site, only a small variation in stalk dry weight was present. Hence, it seems that under local conditions, further increases in sucrose yield might be possible through an increase of sucrose concentration particularly for the early part of the harvest season and for the latter part of the season through an in- crease in number of millable stalks.

Among the four varieties used it was observed that high sucrose and dry matter yields were obtained, irrespective of site or planting date, from variety M 93/48 which has broader leaves and thicker stalk as compared to the others. In the results presented by Mc col17, varieties with higher fresh weight per stalk at harvest also ranked among the higher sucrose yielding ones. However, in the present studies irrespective of site or planting date, variety M 93/48 had always a lower sucrose concentration than variety S 17 but a higher sucrose yield and was ranked as a low tillering variety. Therefore, further increases in sucrose yield would be possible by combining the crop dry of M 93/48 with sucrose concentra- tion characteristic of S 17 or alternatively the high tillering habit and survival rate of variety M 13/56 with the high stalk dry weight of variety M 93/48.

The above suggestions do not represent an easy task for the breeder due to the negative relationships that exist between crop yield and sucrose concentra- tion. Furthermore, as the sugarcane i s replanted locally after a t least seven years, the ratoon crop results will confirm whether the desirable characteristics in the above varieties will be maintained.

As in other countries with defined cool and warm seasons, the present results have confirmed the beneficial effect of the cool season on sucrose concent-

ration (Aughtryl). However, as cooler conditions do not favor dry matter accu- mulation or tillering, a lower crop dry weight with a higher sucros~mncentration was observed a t Alma (cool site) as compared to the other two sites, The results have also confirmed that irrespective of site, sucrqse concentration ,was the limiting factor for the early part of the cropping season. Heqce, the breeder's aim should be somewhat biased towards early ripening varieties such as S 17. It would be of interest to find out whether the relationship between storage tissue anatomy and sugar uptake as found by Owuru and Mc avid' holds for such a variety. On a short-term basis the problem of low sucrose concentration a t harvest may be resolved to some extent by the use of a chemical ripener (Julien etaI6). '

The lack of relationship between plant morphology and dry matter yield observed for the various treatments particularly when considering results for different tiller groups indicate that environment do not affect in a similar way the two above attributes. The present study has highlighted this I;henomenon which requires further investigations because of i t s importance for varietal se- lection.

Differences in sucrose concentration between tiller groups were small or absent and suggest that aye has l i t t l e influence on dry matter partitioning and sucrose accumulation. In some instances, particularly for the mid-season plant- ings, the populations were also homogenous for stalk dry weight. This suggests that the late. tillers are able to compete with earlier ones and must have had a higher growth rate as they reached harvest within a shorter time. Further studies are necessary to determine whether the above i s due to an age effect per se or is related to difference in leaf area ratio. However, in some treatment combina- tions where there were differences in stalk dry weight between tiller groups, stalk age appears to have played a more dominant role. The relationship of the above variations to the ratelduration of tillering will be presented in a subsequent paper.

REFERENCES ,

1. Aughtry, J.D. (1958). T& response of ratoon cane to nitrogen as influenced by climate and age of cane. J. Jamaican Assoc. Sug. Technol. 21 :8-15.

2. Barrie, A.G. (1960). Variations in the yield of farms with equal potential in the Mulgrave area. Proc. 27th Conf. Qd. Soc. Sugarcane Technol. 159-1 65.

3. Evans, L.T. (1975). Crop physiology - some Case Histories. Camb. Univ. Press, London, 374 p.

4. Gosnell, J.M. (1969). Some effects of increasing age .on sugarcane growth. Proc. ISSCT 13:499-513.

/ 5. James, N.I. (1971). Yield components in random and selected sugarcane

populations. Crop Science 11 :906-908.

6. Julien, M.H.R., G.C. Soopramanien, J.F. Martine and H. Medan (1978).

514 PLANT PHYSIOLOGY

I Growth and sucrose content and regrowth in sugarcane treated with ripener Polaris. Rev. agric. sucr. Ile Maurice 57:172-187.

7. Mc Coll, D. (1976). Growth and sugar accumulation of sugarcane. I, Per- centage of sugar in relation to pattern of growth. Expl. Agric. 12: 369- 377.

8. Mc Lean, F.C., C.R. Mc David and Y. Singh (1969). Preliminary results on net assimilation rate studies in sugarcane. Proc. ISSCT 13:849-858.

9. Owuru, 0.0. and C.R. Mc David (1977). The anatomy of the storage tissue of sugarcane in relation to sugar uptake. Ann. Bot. 41 :401-404.

10. de Saint Antoine, J.D. de R. (1969). A simplified method of calculating pol of cane harvested in experimental plots. Rep. Maur. Sug. Ind, Res. Inst. 17: 120-1 21,

11. ,and de Frobewille, R. (1964). The direct determination of fibre in cane. Rep. Maur. Sug. Ind. Res. Inst. 11 :142.

12. Watson, D.J. (1 971). Size, structure and activity of the productive system of crops. In "Potential Crop Production", Ed. Wareing, P.F. and J.P. Cooper. Heineman Educational Books Limited, London, 387 p.

BASES HSIOLOGICAS DE LA VARIACION DE RENDIMIENTO ENTRE Y DENTRO DE VAKIEDADE$ DE CANA

1. Componentes de Rendimiento de Sucrosa a la Hora de Cosechar.

G.C. Sooprananien y M.H.R. Juiien

RESUMEN

Cuatro variedades comerciales plantadas en diferentes tiempos durante la temporada de plantar cana bajo ambientes contrastados se cosecharon a un tiempo fijo de 68 smanas. La variacion de sucrosa a1 tiempo de cosecl~ar fue analizado en sus componentes: densidad de retoiios; peso seco y concentracion de sucrosa (sucrosa % peso seco) del retofio. La variacion del rendimiento de sucrosa a1 (cosechar) fue debido a variaciones mas amplias en rendimiento biologics opuesto a la concentracion de sucrosa. La densidad de retofio se descubrio como el inayor determinante de rendimiento. Tratamiento del sitio asi coino

I de la fecha de plantar ha indicado que condiciones calidas favorecieron la _a_cumulacion de materia seca mientras que condiciones frias o frescas

G. C. SOOPRAMANIEN AND M. H. R. JULlEN 515

fomentaron la acumulacion Be sucrosa. El alto rendimiento de sucrosa a la hora de cosechar en tre las variedades fue asociado con ren- dirnientos biologicos en la variedad de bajo rebiio y peso seco de 10s troncos. Diferencias entre variedades en el rendimiento d e sucrosa fue ron modificadas juntamente por el sitio y la fecha de plantar indicando adaptacion posible de variedades.

La caracteristica de concentracion de sucrosa de las variedades no se modificaron drasticamente por el sitio o por tratamientos de la fecha de plantar. Adaptacion de variedades fue atribuido juntamente con la densidad de retofio como a1 peso seco del tronco. La ausencia de grandes diferencias en el peso seco del tronco o de la concentracion de sucrosa a la horamde cosechar entre re tofi os de dif eren tes edades mostro homogenidad de la populacion de los'retofios que supervivieron y que 10s que se formaron mas tarde pudieron competir con 10s primeros. Se discuten 10s efectos de tratamiento en plantas morfologicas relaciona- das a atributos fisiologicos en relacion a la maximinacion de rendi- miento.