Calculation of disease index (DI)
DI severity was classified into nine different levels according to the percentage of the leaf area affected by the disease in individual leaves (James, 1971). Levels 0 to 9 respectively were 0, 0~5, 6~10, 11~20, 21~30, 31~40, 41~60, 61~80, and 81~100 %, respectively. DI was calculated using the following formula:
\begin{equation} DI=\frac{\sum\left(x*t\right)}{s*\sum t}\times 100\nonumber \\ \end{equation}
where x is the degree of disease severity, t is the total number of leaves showing each degree of disease severity, and s is the highest degree of disease severity observed.
Statisticalanalysis
The plant DI, phytohormones concentration and colony diameter, were analyzed with the SPSS software (Version22.0, IBM, Chicago, USA). Statistically significant differences were determined by ANOVA followed by Duncan’s post hoc tests. A value of P < 0.05 was considered to be statistically significant.