Study of the variability for resistance to spot botch in spring wheat

Seeds of 365 divers bred wheat lines were sown in paired row plots of 2m length. The field was heavily fertilized and frequently irrigated to provide a congenial environment for the development of the spot blotch disease. Observations were recorded for disease severity (%) as well as using 0-9 scale. Disease was rated three times i.e. at growth stages 69, 77 and 83 (Zadoks et.al.1974) to calculate AUDPC. Plant height, days to maturity and test weight was also recorded for each genotype. A wide variability for resistance to spot blotch was observed in the wheat lines screened. In one year of testing, 15 lines were found to have resistant. The proportion of moderately resistant, moderately susceptible and susceptible lines were 47%, 43% and 6% respectively. The resistant as well as susceptible lines belonged to early, medium as well as late maturity groups. However the late maturity lines appeared to carry greater resistance than early ones. The useful resistant lines having dwarf stature and early days to maturity were 15. These lines can be exploited in crossing programme to developing spot blotch resistant early maturing lines suited to rice wheat cropping system of NEPZ. Most of the wheat lines showed susceptible reaction. However, differential reaction was also observed in same line. Thus, the differential reaction for spot blotch severely in some of the genotypes supported the idea of independent gene control.