Breeding of Sugarcane - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 30

Keywords Sugarcane • Ethanol • Genetic resources • Molecular markers •
Saccharum complex

Introduction

More than 1 billion tons of sugarcane are harvested each year. This exceeds the
production level of the main food crops of the world, corn, wheat, and rice. Each of
these has an annual production of about 600 million tons per year of plant biomass.
Sugarcane is the world's biggest source of sugar surpassing sugar beet and is
without doubt the most important crop for the production of energy and
bio-products such as fibers (paper, cardboard, plastic) [ 1 , 2 ]. Sugarcane has an
average yield of 40-70 t per hectare depending on the country. Some specific
varieties are able to yield up to 150 t per hectare under experimental conditions.
The production of cane has been increasing and will likely continue to expand in
tropical and subtropical environments, if the use of cane as an energy source
continues to grow.
Crop improvement programs have been successful, because in the last 50 years,
the cane has had an increase of about 40 % in its productivity. Crop improvement
however takes about 8-12 years to achieve a new variety. Biotechnological
approaches can become crucial to overcome the limitations of classical breeding.
Besides the length of time needed to obtain new material, sugarcane is a complex
organism because of its high ploidy levels (aneuploidy and polyploidy). Sugar-
cane's genome structure creates challenges for the development of transgenic plants
that may foster the development for new market segments, such as with high
saccharose content (richness), drought tolerance, and high yield of ethanol and
biomass for biofuels. This chapter describes the genetic improvement of sugarcane
and general breeding objectives.

Taxonomy and Domestication

Sugarcane is a semiperennial plant belonging to the Poaceae family, Panicoideae
subfamily, Andropogoneae tribe, and genus Saccharum L. [ 3 ]. Actually the varie-
ties cultivated in Brazil and the world are hybrids from the genus Saccharum which
includes six species:

two wild species, S. spontaneum L. (2 n ¼ 40-128) and

S. robustum Brandes and Jeswit ex Grassl. (2 n ¼ 60-205), and four cultivated

forms, S. officinarum L. (2 n ¼ 80), S. barberi Jeswit (2 n ¼ 81-124), S. sinensis

Roxb. 60-80). The species

S. officinarum and S. spontaneum are the biggest contributors to the genome of
the modern varieties. The species S. officinarum or “noble cane” is able to accu-
mulate high saccharose levels in the stem but offer low resistance to diseases. It
originated from hybrids between S. spontaneum , S. miscanthus , and Erianthus

(2 n ¼ 111-120), and S. edule Hassk. (2 n ¼