The samples derived from plant tissues, i.e.,
lettuces, green oak, red oak, cos, and butter head,
were collected from the commercially available
vegetables grown in hydroponic farms located in
several provinces in Eastern Thailand, i.e., Chon
Buri, Chachoengsao, and Prachin Buri. The sample
was performed in nutrient film technique system
(NFT) and dynamics root floating technique system
(DRFT). Five individual lettuces were randomly
sampled from both vegetables that showed symptomatic
infection and non-symptomatic infection of the
root. A 50 ml of nutrient solution and water used
in the preparation of nutrient solution were also
collected and kept in sterilized glass bottles. The
lettuces were collected from both of the conventional
farms used for commercial and the organic farm
(Lung Gai Farm), which were located in Nakhon
Ratchasima, Northeastern Thailand. Five individual
lettuce plants were randomly sampled from
non-symptomatic infection of the root. Nutrient
solution, water, and plant samples were collected
and separately placed in plastic bags and then kept
in iceboxes until used.
Isolation of rhizobacteria from lettuce roots
An isolation of rhizobacteria was performed
by spread-plate technique modified from the
technique described by Rangjaroen et al. (2008) and
Hussen (2003). In brief, a five g of lettuce roots
were washed by sterilized water subsequently mixed
with 95 ml sterilized water, and mashed with a
stomacher. A series of serial ten-fold dilutions were
prepared from the root suspension to make 10-2 to
10-8 dilution. A one ml sample from serial dilutions
was spread on nutrient agar (NA) and incubated
at 28 ํC for 24 to 48 h. Each colony with different
morphological appearances was counted and
subsequently re-streaked onto a new plate using
the same media until pure colonies were obtained.
The organism from the pure colony was transferred
into a nutrient agar slant tube, incubated until full
colonies were observed and then kept at 4 ํC. In
the case of nutrient solution and water, a one ml
sample was added to a test tube containing nine
ml sterilized water. The sample in the tube was
vigorously mixed using vortex for one min. Then,