Glossary Plant Breeding

proper environment is present; conversely, no amount of manipulation of an
environment will produce a character if necessary gene(s) is absent. It is the interplay
of these two agents that determine the development of the character. Geneticists use
this term as a synonym for characteristic or trait.
Character Difference. A contrasting difference between two organisms (or two pure
lines) with respect to one particular character. For example, plant height is a
character, and the two lines, one with tall and other with dwarf statures represent
character difference.
CHAs. Chemical Hybridising Agents. These are chemical agents used to selectively kill
pollens of a genotype likely to be used as female parent in a hybrid-breeding
programme (ethrel, DPX 3378, MG1 & MG2, for example). Ethrel causes female
sterility in Indian mustard when applied at the rate of 2000-3000 ppm. MG1 & MG2
are carcinogenic and have residual effect too. Oxanilates @ 1500 ppm can also be
applied for the same purpose during stamen-pistil primordia stage. However, no
chemicals are perfectly selective. In wheat, chemicals such as CH 9701, CH 9702, CH
9708, CH 9831, and CH 9832 have exhibited acceptable levels of male-sterility. The
most suitable stage for the spray of CHAs has been found as 10-15 mm of spike
length.
Chasmogamy. One of the outbreeding devices as in rice. In this case, opening of flower
buds follows after bursting of the anther. Thus, some extent of outcrossing (4-5%) is
almost always ensured.
Check Cross. The crossing of an unknown genotype with a phenotypically similar
individual of known genotype. The F 2 segregation serves to establish whether the
same phenotypes stem from the action of identical or dissimilar alleles of the same
locus or from the action of non-allelic genes.
Chi-Square ( 2 )Test. A statistical test used to determine the probability of obtaining
observed proportions by chance, under a specific hypothesis.
Chiasma. A cross-shaped structure formed following crossing over between any two
non-sister chromatids of a pair of homologous chromosomes during meiosis. It is
visible manifestation of crossing over.
38