Histopathology of internal fruit rot of sweet pepper caused by Fusarium lactis

Abstract

The etiology of internal fruit rot of greenhouse-grown sweet pepper, caused by the fungus Fusarium lactis, was investigated during anthesis and fruit development using stereo, fluorescence and scanning electron microscopy. Proliferation of fungal mycelium was observed on the surface of the stigma one day after inoculation (DAI). Mycelial growth was also visible in the transmitting tissues of the style and inside the ovary at 5 and 6 DAI. When externally symptomless sweet pepper fruits were sectioned 45 DAI, typical internal fruit rot symptoms were observed. Culturing of hyphal-like strands and ovules from inoculated flowers on potato dextrose agar (PDA) confirmed the presence of F. lactis. Similarly, symptomless seeds from infected fruit also yielded colonies of the fungus on PDA. These findings support the hypothesis that internal fruit rot of greenhouse sweet pepper caused by F. lactis is initiated through the infection of the stigma and style during anthesis. Moreover, symptomless seed infection may contribute to disease spread between greenhouses, although further work is needed to understand how F. lactis becomes established and spreads from infected seeds to flowers.