Screening for Plant Growth-Promoting Traits
Cytokinin Production
To check cytokinin production by the select axenic bacterial
isolates, a modified cucumber cotyledon greening
bioassay was used. Bacterial cultures were streaked on half
sides of the M9 medium containing 20% glucose, 0.2%
casamino acid, 2 pg/l biotin, and 0.7% agar for 72 h, and
then the etiolated cotyledons from five-day-old cucumber
seedlings were placed on the other half by avoiding direct
contact [21]. After 24 h of incubation at 25ºC in the dark,
the plates were exposed to light (55 µmol·m-2·s-1) for three h
at room temperature. Chlorophyll content of the cotyledons
1774 Raza F. A., et al.
relative to negative control (bacterial culture’s lack of ability
to produce cytokinin) was measured by a UV 4000 spectrophotometer,
O.R.I. (Germany). Benzyl amino purine
(BAP) of 10 µM concentration was taken as positive control.
Increased chlorophyll content provides evidence for
positive cytokinin activity. The experiment was done thrice
with each bacterial culture.