Collection and maintenance of isolates.
Isolates of P. grisea were collected
from trap nurseries planted at five sites and
farmer fields in Thailand (Fig. 1) from
1993 to 1994. The trap nurseries consisted
of lines and cultivars known to differ in
resistance to the pathogen and a range of
local cultivars (Table 1), and were managed
using standard protocol (18). The
cultivars were grouped based on their field
reactions at five sites (Table 1). Sites were
located in the principal rice growing regions
of Thailand that are separated by
mountain ranges. Ubon Rice Research
Center (UBN) is the principal breeding
center for the Northeast, and field plots of
segregating and advanced lines are managed
to maximize disease severity and