Plant materials: One hundred F2 individuals derived from a cross
between CO39 (susceptible) and Tadukan (resistant) lines of rice,
Oryza sativa L., were investigated for blast reaction, using the isolate
B157 (Andra Pradesh, India). This isolate is highly pathogenic and
dominant in the southern parts of India. It has also been studied in
various laboratories (Kachroo et al. 1995, Soundararajan et al. 2004).
The F2 generation rice population was also used for molecular
mapping of the blast resistance gene. Three-week-old F2 plants were
inoculated with the spores of blast fungal isolate at a concentration of
2 · 105/ml in 0.02% Tween 20, and incubated in a humid chamber for
24 h. The disease reactions were scored, 7 days post-inoculation,
following the standard protocol (Bonman and Mackill 1988). A recombinant
inbred line, RIL29, derived from CO39 · Moroborekan
(Wang et al. 1994) was tested against B157 and found to be resistant
(score 1) against it. In order to carry out the allelism test, the F2
population (75 plants) of Tadukan (Pi38, present study) · RIL29
(Pi1 and Pi7, Wang et al. 1994, Campbell et al. 2004) were evaluated
against the blast isolate B157.