Assessment of gummosis symptom
To analyze disease incidence and intensity, a 10 m wide transect was laid along a river in the study site and nine 100 x10 m rectangular plots were marked to record observations. Each plot contained 6-10 trees and the total number of trees measured was 79. The first plot was 10 m away from the boundary of the restoration plot and distance between each plot was a minimum of 20 m. The symptoms of gummosis were evaluated on each tree by marking three segments on the stem viz., 1) lower stem (L) which includes the base of the stem up to 137 cm in height (height at which dbh is measured); 2) upper stem (U) - area between 137.1 cm to the base of the first branch and 3) stem covered by the crown (S) (Fig.2)
The number of wounds with new or old gummosis in each stem segment was recorded. Disease severity was calculated based on the number of wounds with gummosis occurring on each tree. The progress of gummosis along the stem was made by observing occurrence of gummosis on each segment on individual stems. Number of wounds with gummosis in each tree segment (L, U, and S), and distance between asymptomatic and symptomatic trees were recorded bimonthly between February and August 2015. Tree positions were recorded using GPS (Global Positioning System) and computed by ArcGIS 10.1.
Mean disease severity (%) on individual tree was calculated using the following formula (Cooke (1998).
Mean of Disease Severity (%) on individual tree (Eq.1)
\begin{equation} \frac{\left(\mathrm{z1+z2+z3}\right)}{\mathrm{3}}\mathrm{\times\ 100\%}\ \nonumber \\ \end{equation}
Disease incidence was calculated based on the number of trees showing gummosis out of total number of trees observed.
Disease incidence (DI) (Eq.2)
\begin{equation} \frac{\mathrm{n}}{\mathrm{N}}\mathrm{\times 100\%}\nonumber \\ \end{equation}
Where
n = Number of trees with new (oozing at the time of observation) or old gummosis
N = Total number of trees assessed
z1 = Number of gummosis on the lower stem
z2 = Number of gummosis on the upper stem
z3 = Number of gummosis on the stem covered by crown
‘3’ represents 3 segments of the stem observed for gummosis
The horizontal pattern of distribution was arrived at by measuring the shortest distance between trees with gummosis symptoms which was then grouped for each measurement occasion.