Host plant cultivar, leaf positions and nutrition affect the expression of Marssonina blotch resistance in apple

Three experiments were conducted under polyhouse conditions during 2010–2011, using inoculated one year old grafted plants of apple, to determine the influence of host plant cultivars, leaf position and nutrition on the development of Marssonina blotch disease. none of the tested apple cultivars was resistant to Marssonina blotch, however, Granny Smith and Gibbson's Golden showed moderately resistant reaction. The commercial cultivars royal delicious, Golden delicious, Vance delicious and Scarlet Spur were found highly susceptible. The upper leaves were more resistant than the lower leaves when one year old plants of Starking delicious cultivar were tested. The progression of Marssonina blotch from the base of the plant upwards on apple plants could be due to difference in leaf resistance. in addition, macronutrient combinations with full dose of nitrogen, registered good growth of potted apple plants, consequently, reduced the severity of disease, which was increased by its half and double dosages.