Training Manual Development Of Cultivars And Seed ... - icrisat

Sorghum
An Overview of Sorghum Cultivar Development
J W Stenhouse
Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal crop in the world after wheat,
rice, maize, and barley. It is cultivated annually over approximately 45 million ha, producing approximately
60 million t of grain. Sorghum grain is a major food in much of Africa, South Asia, and Central America,
and an important animal feed in the USA, Australia, and South America. In addition to these uses of the
grain, sorghum crop residues and green plants also provide sources of animal feed, building materials,
and fuel, particularly in the semi-arid tropics (SAT).
Sorghum is adapted to tropical and subtropical climates but the greater part of the area of the
crop falls in drought-prone, semi-arid tropical regions of the world. In these areas, it is usually grown with
limited inputs in conditions of sparse rainfall and low soil fertility, and exposed to a range of diseases and
pests. As a result, the yields are poor.
In fact, the yield potential of sorghum is quite high; grain yields can exceed 10 t ha -1 under
favorable conditions. However, a majority of the subsistence farmers who typically cultivate this crop are
unable to take advantage of this potential because they have limited options for improving their
management practices. Hence, improvements in sorghum production in the SAT are more readily
achieved through seed-based technologies such as cultivars with improved tolerance to drought and low
soil fertility, and resistance to pests and diseases.
Breeding Behavior of Sorghum and Types of Cultivars
The breeding behavior of a crop influences the methods used by plant breeders to produce improved
cultivars and the types of cultivars that can be developed.
Sorghum is a predominantly self-pollinating crop which shows little inbreeding depression.
However, significant levels of natural outcrossing also occur. The level of outcrossing varies according
to the panicle type of the cultivar. It can be as much as 30-60% in loose-panicled grassy sorghum, but
a more typical figure would be < 1 0 % in compact-panicled types (House 1985). As a result of this
combination of self-pollination and outcrossing, most of the landraces of sorghum that are normally grown
by subsistence farmers are mixtures of inbred and partially inbred lines. Improvement can be achieved
by purification of the more productive lines in the mixture by selfing to develop pure-line varieties.
However, because of the tendency for further outcrossing to occur, these pure-line varieties require
deliberate maintenance by selfing to keep them pure.
Several male sterility systems are found in sorghum which can be used by plant breeders to
widen the range of possibilities for improving the crop and to develop different cultivar types. Genetic
male sterility, which is controlled by recessive genes at any one of several loci (Doggett 1988), can be
used to promote outcrossing and generate random-mating populations for improvement by various
recurrent selection methods. In particular, male sterility caused by ms 3 , ms 7 , and a/genes has been used
for this purpose (Murty et al. 1994). These random-mating populations of sorghum, unlike other crops,
are rarely suitable for direct use by the farmer because of their ragged appearance (House 1985).
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