Foliar spray time affects the efficacy of applied manganese on enhancing cucumber resistance to Podosphaera fuliginea

摘要

Foliar application of manganese (Mn) is an effective factor in enhancing of plant resistance to fungal diseases, but the efficiency of this method strongly depends on the application time. The present study was aimed to investigate the effect of application time of Mn on cucumber resistance against powdery mildew, caused by Podosphaera fuliginea. For this purpose, high levels of Mn in cucumber leaves were provided by foliar spray of MnSO4, and Mn-amino acid complexes (Mn-Lysine and Mn-Methionine) at 14, 10, 7, and 4 days before inoculation (dbi) by P. fuliginea. The excess levels of Mn led to a significant reduction in fungal disease. The highest reduction in disease severity was observed when Mn solutions were applied 4 dbi. The cucumber plants treated by Mn at 4 dbi accumulated the higher level of Mn in their leaves than those treated at 14, 10 and 7 dbi. The concentration of Mn in leaf was more important factor than the changes of shoot and root dry masses, PO and PPO activities and leaf cell wall lignin content in effectiveness of applied Mn. The Mn-amino acid complexes were more effective than MnSO4 in increase of dry mass and leaf lignin content. Mn-Lys was the most effective source of Mn in decrease of disease severity. Based on the results, application time is a significant factor determining the efficiency of foliar Mn application on increase of crop resistance to P. fuliginea.