Inheritance of resistance to blast (Magnaporthe grisea, T.T. Hebert) in some rice (Oryza sativa L.) cultivars

Abstract

The research work was undertaken at Raipur, Ambikapur and Jagdalpur district of Chhattisgarh,
India, with the objectives of identifying functional resistance conferring genes in Chhattisgarh
state, monitoring resistance in some genotypes/breeding lines and detecting variability in the
blast population over the years, understanding the mode of inheritance of resistance to blast in
some selected resistant donors. The experimental materials consisted of (a) a set of thirty one
blast monogenic / differential lines along with seventy nine other genotypes including breeding
lines, resistant and susceptible checks, were tested at blast 'hot spots' Ambikapur for three years
(2007-2009), (b) F1, F2, and F3 populations of the 28 crosses attempted for the inheritance study
were screened against the blast population at Ambikapur to ascertain the genetic ratios. The
inheritance investigation uncovered that blast resistance in R 1013-2307-1-1, R 1124-91-2-73,
R 1518-762-3-564-1, R 1558-2423-3-1445-1 and R 1559-2425-2-1449-1 was controlled by a single
dominant gene, while two independent dominant genes governed resistance in R 1519-781-5-598-
1 and R 1540-1888-1278-1. The blast population in the Northern Hilly Region proved highly
unpredictable and comprised of more than two highly virulent races. Breakdown of many resistant
strains and genes occurred during the study, which could be attributed to changes in the frequency
of pathogenic races prevailing over the years. Among the blast differential genes (monogenic
lines) tested, only 'Pi-z5' gene consistently imparted complete resistance against the blast population
in the Northern Hilly Region of Chhattisgarh, Pi-z, Pi-9 and Pi-kh provided variable level of
resistance. Eight strains viz., R 1518-762-3-564-1, R 1519-781-5-598-1, R 1540-1888-1278-1, R 1558-
2423-3-1445-1, B 6441-FMR-6-0-0, F 7-10, IR42221-145-2-3-2 and 5173 showed consistently stable
resistant reaction over the years.