In order to assess the disease severity, the length of
the xylem vessel with brownish discoloration was estimated.
The plants were assigned to a category on a scale
of 1–5 (c1 = 1–5 %, c2 = 5–15 %, c3 = 15–35 %,
c4 = 35–67.5 %, c5 = 67.5–100 %) according to the
length of xylem vessel discoloration. Disease severity
was calculated for a batch of five plants in each treatment
by the following formula: