Relationships between the incidence of fire blight in apple orchards and plant nutritional imbalance indices

Fire blight disease is a major threat to the apple orchards in various regions of the world. The multivariate compositional nutrient diagnosis (CND) was considered to evaluate the effect of plant nutrient imbalance in development of fire blight in 'golden delicious' apple orchards in Fars province, Iran. To establish CND norms and the ?re blight severity index, 81 commercial orchards were used. The CND reference norms (V*(x)) for a low ?re blight severity subpopulation were calculated as V*(N) = 2.813 +/- 0.186, V*(P) = 0.297 +/- 0.147, V*(K) = 2.660 +/- 0.149, V*(Ca) = 2.442 +/- 0.218, V*(Mg) = 1.188 +/- 0.061, V*(S) = 0.595 +/- 0.399, V*(Fe) = -0.952 +/- 0.212, V*(Mn) = -3.132 +/- 0.195, V*(Zn) = -4.040 +/- 0.366, V*(Cu) = -5.032 +/- 0.177, V*(B) = -3.361 +/- 0.120, V*(Rd) = 6.521 +/- 0.128. According to the calculated leaf nutrient indices based on the CND reference norms and principal component analysis (PCA), leaf Ca, S, B and Zn deficiency and leaf K and P excess significantly correlated with the enhancement of fire blight severity index (FBSI). The reduction of global nutrient imbalance index (CND-r(2)) to below 20.38 decreases the severity of ?re blight in 'golden delicious' apple orchards.