Some say that "strain" is incorrect.
Strains of bacteria, varieties of cannabis...
strain 2 (strn) ---http://www.thefreedictionary.com/strain
n.
1. The collective descendants of a common ancestor; a race, stock, line, or breed.
2. Any of the various lines of ancestry united in an individual or a family; ancestry or lineage.
3. Biology A group of organisms of the same species, having distinctive characteristics but not usually considered a separate breed or variety: a superior strain of wheat; a smooth strain of bacteria.
4. An artificial variety of a domestic animal or cultivated plant.
5. A kind or sort: imaginings of a morbid strain.
6.
a. An inborn or inherited tendency or character.
b. An inherent quality; a streak. See Synonyms at streak.
7.
a. The tone, tenor, or substance of a verbal utterance or of a particular action or behavior: spoke in a passionate strain.
b. A prevailing quality, as of attitude or behavior.
8. Music A passage of expression; a tune or an air. Often use in the plural: melodic strains of the violin.
9.
a. A passage of poetic and especially lyrical expression.
b. An outburst or a flow of eloquent or impassioned language.
---varieties doesn't sound as good as "strains"