Biochemical and histochemical parameters associated with slow blighting of spot blotch (Bipolaris sorokiniana (Sacc.) Shoem.) in wheat (Triticum spp.)

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat (Triticum spp.) in warm and humid wheat growing regions of the world. Area under the disease progress curve (AUDPC) in field experiment was used to find out the role of total phenol content (TPC), phenylalanine ammonia-lyase (PAL) activity and lignin deposition in the development of slow blight. Ten recombinant inbred lines (RILs) of spring wheat obtained from the cross between the susceptible parent 'Sonalika' and the resistant parent 'Yangmai 6' along with their parental genotypes were scored for disease severity (DS), AUDPC and lesion size in a field experiment on spot blotch. These lines were also evaluated for TPC, PAL and lignin deposition. The minimum DS, AUDPC and lesion size were recorded in the resistant parent 'Yangmai 6' (13%, 116.04 and 0.23 cm(2), respectively) and RILs (18%, 113.3 and 0.27 cm(2), respectively in RIL83 and RIL89) which associated with an elevated level of phenol content (395 mg g(-1) fresh weight (wt) at 48 hours after inoculation (hai), PAL (928.41 mu moles cinnamic acid (cna) mg(-1) fresh wt) and higher quantity of lignin (84%). While DS, AUDPC and lesion size were comparatively higher in the susceptible parent 'Sonalika' as well as susceptible RILs (100%, 938.27 and 3.43 cm(2), respectively). Mean TPC (133.5 mg g(-1) fresh wt 24 hai, respectively), PAL (248.8 mu moles cna mg(-1) fresh wt) and lignin (10%) were significantly lower in the susceptible genotype 'Sonalika' and suscptible RILs. The study indicated that enhanced level of TPC, PAL and higher lignin deposition led to the development of slow blighting of spot blotch in terms of lower AUDPC and smaller lesion size in resistant RILs of wheat.