It is well understood that the productivity and thus the final yield of a crop
are the result of several interacted factors, which have different effects on yield.
This requires the determination of all factors affecting yield or other traits, the
relationships among these factors, the value of correlation coefficient and the
degree to which yield is affected by each of these factors.
The relations between genes and their phenotypic effects do not always
ensure the presence of a particular effect, the causes that modify the effect of
particular genes can be traced to the large gap between the genetic material
and the phenotype
of an organism.
Thus, development must also depend upon environmental factors of which
interaction may occur between the environment and the genetype. The
appearance of an organism does not always reflect its genetic constitution and
various environments may affect the same genotype differently.
