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. When a selected strain is officially recognized to have excellent characteristics, it is commercially released as a new variety. Such a system is believed to be indispensable to allow the Japan s breeding network to release a new mulberry variety to farmers. Mulberry varieties Generally speaking, varieties belonging to M. bombysis , have lobed and shallow bottom leaves.
Branches are brown or gray, and the winter buds are oval and sharp-pointed.
New shoot development is a stage in which new shoots develop using reserves stored in stump or root the previous year. Growth stage is when carbohydrates and other substances are produced for vegetative growth by means of photosynthesis in leaves. Storage stage is when most photosynthetic substances are stored for next year's growth. The exploited mulberry plants resume growth using the remaining storage substances. Nutritive value of mulberry leaves The silkworm eats only mulberry leaves to make its cocoon, producing the silk.