Agriculture Reference
In-Depth Information
Figure 9.14. Sodium hydroxide (NaOH) test for wheat: Red wheat (left), white wheat (right).
CyToLoGICAL TESTS
Earlier, it was implied that with increasing use of biotechnology in varietal development, methods of incor-
porating special cytological markers could make varietal identiication both easier and more deinitive.
However, the only test used to distinguish among varieties on the basis of cytological observations is the
chromosome count test.
Chromosome Count Test
During the 1960s, many new tetraploid grass and legume varieties were released in the United States. The
double chromosome complement of these (tetraploid) varieties compared to their diploid counterparts has
provided seed analysts with a built-in genetic purity test by merely counting the number of chromosomes
in the cells of the seedling root tips (Will et al., 1967). Like many other genetic purity tests, chromo-
some counts cannot be used to distinguish between different varieties with the same chromosome number.
However, they are useful in detecting contamination, especially diploid contamination of tetraploid variet-
ies (Fig. 9.15). The tests are a valuable aid in monitoring the genetic purity of certain varieties of certiied
tetraploid grasses and legumes, especially ryegrass and red clover.
The use of chromosome count tests is more limited for higher polyploid species, such as wheat and
bluegrasses, because of the dificulty associated with counting the chromosomes and the complexity of
their polyploidy.
