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

used to establish replicated trials to compare individual selections more critically. Replicated testing of
yield or other traits can begin at any stage after progenies are reasonably uniform.
The criteria used to select plants vary from location to location. Some generally desirable traits
include large panicle, good panicle exertion, appropriate time of maturity, plant height, bold grains, good
seed-set, high seed number, and attractive plant type. Specific criteria, which may differ from location
to location, include resistances to insects and diseases and grain quality for different end-users.
Testing Restoration Ability
Inbred lines with appropriate traits for use as restorer lines must be tested to determine their fertilityrestoration
reaction. Pollen from the test lines is used to pollinate one or more heads of a cytoplasmicgenetic
male-sterile line. The seed produced is harvested and sown to produce a hybrid crop. One or
more heads of the hybrid are bagged prior to flowering to determine whether or not the hybrid is selffertile.
Only lines which give fully fertile hybrids under bagging will be retained as restorers for wide
testing in combination with different male-sterile lines to generate experimental hybrids for agronomic and
yield testing. The fertility of hybrids should be tested during the season in which they will be grown, as
fertility restoration can be influenced by temperature and humidity, and can differ dramatically from
season to season.
Desirable Traits of Good Restorers and Pure-Line Varieties
Restorer lines are normally not intended for direct use as cultivars. Therefore, they do not necessarily
combine all the traits that are favored by farmers. They combine traits that make them suitable for use
as parents of hybrids. These include fertility-restoration reaction, good pollen-shedding capacity,
appropriate height (usually shorter than the varieties), and good grain yield.
The ability of a line to produce good hybrids in combination with male-sterile lines is known as
its combining ability. A line with good general combining ability will tend to give high-yielding hybrids with
many male-sterile parents. Clearly, this is an advantageous trait in a restorer parent. It can be quantified
in comparison with other restorer lines in specially designed testing schemes. In sorghum, combining
ability is closely associated with per se performance of the line. Yield testing of the restorer lines,
therefore, often substitutes for formal combining-ability tests.
Pure-line varieties are intended for use directly by farmers. They must, therefore, combine the
traits desired by the farmers in the target location or area. These normally include high grain yield,
stability of yield over a range of conditions, appropriate duration to maturity, plant height, resistances to
endemic pests and diseases, and suitable grain and stover quality. Typically, pure-line varieties are taller
than restorer lines with higher grain and stover yields.
Maintenance of Restorer Parents and Pure-Line Varieties
The procedures for maintenance of restorer lines and pure-line varieties of sorghum are essentially the
same. In both cases, the process begins with planning seed requirements and projecting backwards.
Using conservative estimates of yields likely to be achieved, the size of the maintenance exercise
required at each stage and its timing to ensure prompt delivery of the final product is planned.
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