ABSTRACT
The genus Saccharum (family: Poaceae, tribe: Andropogoneae, subtribe: Saccharinae), collectively known as sugarcane, is comprised of six polyploid, outcrossing species namely S. officinarum Linnaeus (2n = 80), S. barberi Jeswiet (2n = 81-124), S. sinense Roxb. (2n = 111-120), S. spontaneum Linnaeus (2n = 40-128), S. robustum Brandes and Jeswiet ex Grassl (2n = 60-80), and S. edule Hassk. (2n = T60, 70, 80) (Brandes 1958, Sreenivasan et al. 1987). Modern sugarcane cultivars (Saccharum spp. hybrids; 2n = 100-130) are the descendants of interspecific hybridization, that occurred in the early 1900s, between the domesticated species S. officinarum, and its wild relative S. spontaneum. The initial interspecific hybrids were repeatedly backcrossed to S. officinarum via a process termed “nobilization” mainly to recover the high sugar-producing ability of S. officinarum and to minimize the negative effects of S. spontaneum (Roach 1972; Sreenivasan et al. 1987). The nobilization process also resulted in improved cane yields, ratooning ability and increased resistance to biotic and abiotic stresses. During nobilization the progeny inherited 2n gametes from the S. officinarum parent (Bremer 1961; Bhat and Gill 1985). Modern sugarcane represents the extreme example of polyploidy, with a double genome structure in which the number of homologous and homoeologous chromosomes can vary among genotypes from the same cross. The genome composition of modern sugarcane is about 70-80% S. officinarum, 10-20% S. spontaneum and 5-17% of recombinant chromosomes (D’Hont et al. 1996; Piperidis and D’Hont 2001). Readers may refer to Chapter 3 for a detailed description of origin and history of cultivated sugarcane.
