a) Primary Introduction:

• When the introduced variety is well suited to the new environment, it is released for commercial cultivation without any alteration in the original genotype, this constitutes primary introduction.
• Primary introduction is less common, particularly in countries having well organized crop improvement programmes.
• Introduction of semi dwarf wheat varieties Sonora 64, Lerma Roja and of semi dwarf rice varieties Taichung Native 1 (TN-1), IR-8 and IR-36 are some examples of primary introductions.

b) Secondary Introduction:

• The introduced variety may be subjected to selection to isolate a superior variety.
• Alternatively, it may be hybridized with local varieties to transfer one or few characters from this variety to the local ones these processes are known as secondary introduction.
• Examples of secondary introduction are Kalyan Sona and sonalika wheat varieties selected from material introduced from CIMMYT, Mexico.