Introduction
Sugarcane productivity and how it is affected by stress
Sugarcane productivity
Stress and its impact on sugarcane productivity
Impact of abiotic stress on sugarcane productivity
Impact of biotic stress on sugarcane productivity
Development of stress-tolerant plants through in vitro selection and mutation breeding
Marker-assisted selection for stress-tolerant varieties of sugarcane
Genetic engineering for developing biotic- and abiotic-resistant transgenic lines of sugarcane
Genomics for stress tolerance in sugarcane
Genomics for biotic stress tolerance
Genomics for abiotic stress tolerance
Involvement of sugarcane microRNA in stress responses
Concluding remarks
References
Introduction
Sugarcane is the highest yielding crop worldwide and accounts for ~80% of the sugar (sucrose) production in the world (Nayak et al., 2014; Zhou et al., 2016). The genus falls in the tribe Andropogoneae in the grass family Poaceae. The tribe includes other tropical grasses such as Sorghum and Zea (maize). Very closely related to Saccharum are another four genera (Erianthus section Ripidium, Miscanthus section Diandra, Narenga and Sclerostachya) that readily interbreed, forming what is now commonly referred to as the Saccharum complex (Daniels and Roach, 1987). The polyploid-aneuploid (unbalanced number of chromosomes) nature of these genera creates a challenge for the taxonomist (Daniels and Roach, 1987; Sreenivasan et al., 1987). The genus Saccharum comprises six species: S. barberi, S. edule, S. officinarum, S. robustum, S. sinense and S. spontaneum (Daniels and Roach, 1987). Of these, S. officinarum (the domesticated sugar-producing species) and S. spontaneum (a vigorous wild species with many aneuploidy forms) are thought to be the ancestors of cultivated sugarcane. S. officinarum originally derived from S. robustum, while S. barberi and S. sinense are thought to have been derived by crossing S. officinarum and S. spontaneum (Asano et al., 2004; Sandhu et al., 2012). However, Irvine (1999) suggested that there are only two true species – S. officinarum and S. spontaneum – and therefore, current sugarcane commercial cultivars are thought to be hybrids with 80% to 90% of the genome from S. officinarum and 10% to 20% of the genome from S. spontaneum (Grivet et al., 1996; Hoarau et al., 2002). The chromosome number of these species ranges from 40 to 200 (Asano et al., 2004). Genetic improvement of sugarcane through conventional breeding programmes is difficult because of the polyploid and aneuploid nature of the genus Saccharum.
As a relatively recently domesticated species, sugarcane exhibits little of the available genetic diversity having been incorporated or actively analysed for introgression into domesticated varieties (Dillon et al., 2007; Sreenivasan et al., 1987), and breeding programs in the early 1900s focused on hybridization of S. officinarum clones, but quickly progressed to interspecific crosses incorporating S. spontaneum. This resulted in improved agronomic traits, such as tilling, stand and trashiness abilities, ratooning and disease resistance, but required a backcrossing program to S. officinarum, called ‘nobilization,’ to elevate the sucrose content (Dillon et al., 2007; Edmé et al., 2005). Since then, the majority of breeding programs have focused on intercrossing between the hybrids, though in recent decades the larger increases in genetic gains have been made by incorporating more diverse ge...
