Inhibitory effect of boron against Botrytis cinerea on table grapes and its possible mechanisms of action

Boron, an essential plant micronutrient, was effective in the form of potassium tetraborate for control of postharvest gray mold caused by Botrytis cinerea on table grapes stored at room temperature or at 0 °C. The inhibition of fruit decay was closely correlated with boron concentrations and partially influenced by pH value of the solution. Boron strongly inhibited spore germination, germ tube elongation, and mycelial spread of B. cinerea in the culture medium. Application of boron at 1% caused the appearance of abnormal spores (disrupted) in some cases. By using propidium iodide fluorescent staining, loss of membrane integrity in B. cinerea was observed after boron treatment. Furthermore, boron led to the leakage of cellular constituents (soluble proteins and carbohydrates) from hyphae of B. cinerea. These data suggest that the mechanisms by which boron decreased gray mold decay of table grapes may be directly related to the disruption effect of boron on cell membrane of the fungal pathogen that resulted in the breakdown of the cell membrane and loss of cytoplasmic materials from the hyphae.