(R = 0, 1, 2 and 3) and susceptible (S = 4, 5 and 6).
A modified resistance index (RI) formula was used
to assess the resistance index (Sirithunya et al.,
2001). The RI was expressed as RI = S/T, where
S is the number of isolates showing a resistance
reaction and T is the total number of isolates used
for screening. Thus, the RI value can range from
0 (susceptible) to 1 (resistant)