In order to utilize these genetic resources efficiently in breeding programs, morphological traits necessary for classification and identification, agronomic traits responsible for the resistance against diseases and pests, and commercial traits related to productivity and quality, are investigated. The information on these traits is very useful for achieving breeding targets. Breeding targets should be set with a long-term view. So far, breeding targets have been such as high yield, high nutritional value and resistance against diseases and pests. But nowadays, new targets have been added to cope with changes in the sericultural system such as large numbers of silkworm reared and adaptability to densely planted fields suitable for mechanical harvesting.
Crossing is the major breeding method adopted for the development of new mulberry varieties.
In this method, the choice of parent selection plays a vital role of in achieving the objective. They have desirable traits, and crossing is easy and simple. Since the 1960 s, polyploidy breeding has been produced artificially by colchicine, which is capable of doubling chromosome number. However, these varieties were not popularized very much, despite their high leaf productivity, because they were rather sensitive to dwarf disease, which causes the most serious growth damage, and of slightly poor quality. In 1971, a dwarf disease resistance test was added to the program.