4. Field experiments
Field experiments were performed in 2010 and 2011 at Qingdao
Experimental Farm. N. tabacum cv. NC89 plants were sprayed with
100-fold dilution CZ three times at 7-day intervals after transplanting.
Three replicates were arranged per treatment in a randomized
block design, each consisting of forty plants in single-row
plots. 200-fold Ningnanmycin dilution or water was applied to
plants as controls. The tobacco field was drip-irrigated. All plants
were examined for disease severity before flowering. TMV symptoms
were rated according to the standard of GB/T23222-2008 (Ren
et al., 2008).
2.5. Statistics
All data were calculated using the following formulas and
analyzed with Duncan’s new multiple range test using the DPS data
processing system.
Disease severity ¼ Xðdisease grade
number of plants in each gradeÞ
100=ðtotal number of plants
highest disease gradeÞ
Disease ratio ¼ ðinfected plants=total plantsÞ 100%