Mineral composition modulates Erwinia amylovora resistance in pear based on path analysis

The effects of mineral composition (N, P, K, Mg, Fe, Cu, and Zn) against fire blight caused by Erwinia amylovora, the most devastating disease of pome fruits, was investigated in pear. Due to the transport physiology of minerals, the leaf contained higher concentrations of every mineral analyzed, especially macro-minerals (N, P, K, and Mg) compared to the fruit. Minerals obtained from the leaves were not statistically correlated with resistance to fire blight, however all the minerals examined in the fruit, except for K, were found to be significant. Increased P and Mg concentrations were associated with disease resistance, while N, Zn, Fe, and Cu were associated with susceptibility. Nitrogen-causing susceptibility exerted 61% of this impact through itself directly and was sharply distinguished from other mineral compounds. Furthermore, the indirect effect of nitrogen on disease susceptibility through Cu (39%), Zn (33%), and Fe (30%) was even higher than the direct effect of these minerals (21%, 24%, and 29%, respectively). The direct effects of P (13%) and Mg (10%), which are associated with an increase in resistance, were lower than the indirect effects (19% and 29%, respectively) due to their negative correlation with nitrogen, showing that the main effect of these minerals was in suppressing the negative effects of nitrogen on susceptibility by maintaining mineral balance.