Some sugarcane facts…………

K K Vinod

Sugarcane (Saccharum officinarum) falls under the family Graminae, is known to be under cultivation in India from the Vedic times. India is considered to be one of the centres of diversity for Saccharum and allied genera. Sugarcane is one of the important agro-industrial crops in the country. Sugarcane is grown in India in 3.8 million hectares, producing 300 million tonnes of cane at approximately 71 tonne/ha of cane yield. The country produces about 20 million tonnes of sugar through 470 sugar mills spread all over the country giving employment to around 20 million people directly or indirectly. Of the total sugarcane production, about 60 per cent is utilised by the white sugar industry and the rest for gur, khandsari, seed, chewing etc. India is the highest producer of sugar in the world at present, however, the demand for sugar for internal consumption is growing due to the increased per capita consumption and the increase in population size. The increased requirement of sugar has to be met mostly through increased production per hectare since there is no possibility of further increase in the area under sugarcane due to competition from other crops, urbanisation etc.

The theoretical maximum yield of cane has been estimated to be 339.42 tonnes per hectare on the basis of the efficiency (3.6%) of use of total incident solar radiation. The world’s highest recorded yield is reported to be 255 tonnes per hectare. Recently, farmers in Gujarat are reported to have achieved yields as high as 340 tonnes per hectare. Compared to these yield levels, the national average is around 71 tonnes with the yields in various states ranging from 46 tonnes in Bihar to 113 tonnes in Tamil Nadu. Thus there is ample scope for improvement of cane and sugar productivity in the country.

The Genus Saccharum and the ‘Saccharum Complex’

Sugarcane belongs to the family Graminae in the genus Saccharum, a member of the tribe Andropogoneae abundant in tropical and subtropical regions. The term ‘Saccharum complex’ was used by Mukherjee (1957) to denote that the genera Saccharum, Erianthus (sect. Ripidium), Sclerostachya and Narenga constituted a closely related interbreeding group involved in the origin of sugarcane, to which Daniels et al. (1975) added the genus Miscanthus sect Diandra Keng (Table). The taxonomy, evolution, distribution and characteristics of genera in the Saccharum complex and the species of the genus Saccharum have been reviewed by Daniels and Roach (1987). Salient features of the Saccharum species and of the allied genera relevant to their use in pre-breeding are outlined.

Species of Saccharum complex

Species	Chromosome numbers (2n)
Saccharum spontaneum	40, 48, 56, 64, 80, 128
S. officinarum	80
S. barberi	81-124
S. sinense	111 - 120
S. robustum	60, 80
S. edule	60, 80
Narenga phorphyrocoma	30
Sclerostachya fusca	30
Erianthus spp.	20, 30, 40, 60
Miscanthus spp.	30, 40

S. officinarum L., an octaploid, 2n = 80, indigenous to New Guinea, has provided the genetic background and the sucrose genes of modern sugarcane hybrids. Clones of S. officinarum have thick stalks, high juice purity, low fibre and starch content, low vigour and adaptability to environmental stresses, and they are susceptible to diseases.

S. spontaneum L., 2n = 40-128, is distributed widely from New Guinea, the Mediterranean to Africa. Clones of S. spontaneum are highly polymorphic from bushy types to tall stalks with low sucrose and high fibre content. They played an important role in providing disease resistance and vigour to modern hybrids.

Saccharum robustum Brandes and Jesweit ex Grassl., indigenous to New Guinea, has stalks of up to 10 m high which are hard, woody and pithy with little juice. Five groups are recognized with two cytotypes 2n = 60 and 2n = 80 (Price, 1965). This species contributed towards the evolution of some Hawaiian varieties.

Saccharum barberi Jesw. and Saccharum sinense Roxb., 2n = 81-124, presumably evolved in Northern India and China, are characterized by thin to medium stalks, low sucrose, high fibre and tolerance to stress conditions. They are of limited fertility and their use in breeding is restricted. Molecular studies have confirmed that both S. barberi and S. sinense possess S. officinarum and S. spontaneum genomes.

The genus Erianthus Michx Sect. Ripidium Henrard, 2n = 20-60, is distributed in India, South­east Asia to Japan, Indonesia and New Guinea. Seven species are described. Clones of Erianthus are highly vigorous, tall with slender stalks of good diameter and display disease resistance, excellent ratooning ability and drought tolerance.

The genus Miscanthus Anderss., 2n = 38-114, is distributed from Tahiti through Eastern Indonesia, Indo­China to northern China, Siberia and Japan. The species vary from small wiry­leafed types to taller ones, occurring from sea level in Indonesia to 3300m in Taiwan. Four sections have been described with prominent species.

Saccharum has also been successfully crossed with Sorghum and Zea mays. Several earlier reports of hybridisation during the 1930s with bamboo, Sorghum etc. could not be substantiated.

Nobilisation of cane

Sugarcane (Saccharum spp.) is one of the crops for which interspecific hybridization has provided a major breakthrough in its improvement. Modern commercial sugarcane varieties (Saccharum hybrids, 2n=100-130) are derived from interspecific hybridization. Nobilisation refers to the crossing of the wild cane, S. spontaneum, to the noble cane S. officinarum, and further backcrossing of progenies to the latter, and includes the planned introgression of the other Saccharum species and related genera into the noble cane. Initial work on hybridisation and selection were restricted to intercrossing the S. officinarum clones (both typical and atypical) and limited success was obtained through intervarietal crosses, but improved vigour and resistance to many diseases became possible only after inter specific crosses were attempted. Kobus in 1897 crossed a S. barberi clone ‘Chunnee’ with S. officinarum and by backcrossing the progeny to the S. officinarum for dilution of the traits from the barberi clone obtained ‘sereh’ disease resistant varieties. This led to increased interest in interspecific hybrids were renewed.

In India, Barber in 1912 crossed ‘Vellai’ a S. officinarum clone with a S. spontaneum clone (2n = 64 ) found locally and obtained several promising clones starting with Co 205 which became the first interspecific hybrid to become a commercial success in India. Co 205 replaced the officinarum and the barberi varieties in cultivation in North India, on account of its hardiness and ability to withstand abiotic stresses better. In addition to introducing disease resistance in the noble background, nobilisation produced unexpected gains in general vigour, increased cane and sugar yields, adaptability to stress conditions and ratooning ability. The early success of interspecific hybridization led to the intercrossing of other species to produce tri­species hybrids that proved very successful in subtropical areas in India. Subsequently clones of S. barberi were nobilised to produce clones which were intercrossed to S. spontaneum clones. Some of these early trispecific hybrids became commercially successful in subtropics and in several other countries as well. Though earlier attempt for sugarcane breeding was to improve the yield, however, the quality of the cane was also given equal importance owing to industrial relevance of the cane produced.

References

Daniels, J. and Roach, T. (1987) Taxonomy and evolution. In: Sugarcane Improvement Through Breeding. Heinz, D.J. (ed.) Elsevier, Amsterdam, pp. 7-84.

Daniels, J., Smith, P., Paton, N. and Williams, C.A. (1975) The origin of the genus Saccharum. Sugarcane Breeders Newsletter 36, 24-39.

Mukherjee, S.K. (1957) Origin and distribution of Saccharum. Botanical Gazette 119, 55-61.