2. Material and methods
2.1. Preparation of CZ powder and TMV suppression
P. fluorescens strain CZ was isolated from tobacco field soils at
Qingdao Experimental Farm and stored at 4 C. The stocked bacteria
culture was incubated in nutrient broth medium (10 g peptone, 3 g beef grease, 5 g NaCl, 1 g glucose) or in a mixture medium in a microbial fermentor at 28 C for 72 h to prepare CZ
sub-cultures. P. fluorescens CZ cultures in mixture medium were
mixed with silica white at a ratio of 6 ml:1 g and spray dried.
Silicone surfactant (ethoxy modified trisiloxane) 2& (v/v) was
added before use.
The number of colony forming units (cfu) of CZ culture in
nutrient broth medium, mixture medium and a 100-fold dilution of
CZ were determined by means of dilution plate count using an
automatic colony counter. The in vitro suppression of TMV was
determined by rub-inoculating N. tabacum cv. Samsun NN with a
mixture containing an 80-fold dilution of TMV (1 g TMV-infected
tobacco leaf tissue ground in 80 ml PBS) and the same amount of
CZ. The suppression effects of CZ powder at 10, 25, 50, 100 and 150-
fold dilutions were also determined. Each treatment was performed
with three replications, each consisting of six plants. The
first three leaves were inoculated and the number of necrotic spots
was examined. Water was applied as control.