Development of Marssonina blotch (Marssonina coronaria) in different genotypes of apple

Development of Marssonina leaf blotch (Marssonina coronaria) of apple was studied in 70 genotypes under natural epiphytotic conditions during 2005 and 2006 cropping seasons. No disease was developed on five cultivars (Democrat, Maharaja Chunth, Mutsu, Golden Spur and Granny Smith) whereas 14 cvs were rated as resistant, nine as moderately resistant, seven as moderately susceptible, 15 as susceptible and 20 as highly susceptible. Rate of disease development varied among the cultivars, rate of disease spread decreased with the progress in time and AUDPC ranged from 0.75 to 23.25. All the commercial cultivars were found highly susceptible.