Sweet Sorghum: Breeding and Bioproducts - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 12

dominance and overdominance inheritance, utilization of hybrid vigor by develop-
ing sweet sorghum hybrids is an attractive option. Also one of the parents with high
sucrose content will suffice in getting good hybrids with high sugar and juice
yield [ 44 ].
From these studies, it is quite evident that significant diversity exists in traits
important for biofuel production and this opens up excellent opportunities for sweet
sorghum improvement. Biofuel traits are governed by multiple genes and both
additive and dominant components of gene action have to be exploited while
breeding for high stalk sugar and juice-yielding genotypes. It was demonstrated
that the improved hybrids top ranking for grain and sugar yields in rainy season are
not top ranking in the post-rainy season and vice versa. It is important to breed for
rainy and post-rainy seasons separately [ 2 - 4 ]. The selections for post-rainy season
adaptation should be made in post-rainy season only, and for rainy season adapta-
tion, selections can be made in both rainy and post-rainy seasons.

Breeding Objectives

In general, the sweet sorghum breeding programs aim to develop parents and
hybrids which can address both first and second generation (lignocellulosic feed-
stock development) biofuel production issues. The breeding objectives are:

1. To develop sweet sorghum female parents with high stalk sugar and grain yield
2. To develop restorer lines/varieties with high sugar content and resistance to stem
borer and shoot fly
3. To develop and identify sorghum hybrids (amenable for mechanical harvesting)
with high biomass suitable for use in bioethanol and bioenergy production

Breeding Methods

The most commonly used programs in sweet sorghum improvement are short-term
programs (pedigree method and backcross) and long-term programs (population
improvement methods). The most common approach in sweet sorghum breeding
has been elite

elite crosses followed by pedigree selection. Breeding new female
lines, B and R lines have increasingly become dependent on crossing elite by elite
lines, B B and in some cases such as improving for resistance B R lines. In case

of male lines (R lines) improvement, it is R R crosses. This process progressively

narrows the genetic base of breeding programs and requires new traits, especially
resistances, to be brought in by pre-breeding and often backcrossing. The success of
a backcrossing program depends on the precision with which the desired trait can be
identified and thus introgressed into the recurrent parent through backcrossing.