Internal fruit rot (Fusarium spp.) of Greenhouse Bell Peppers

Abstract

Since 2003 the cultivation of bell peppers in Belgium has to deal with a new disease that leads to internal fruit rot and is caused by Fusarium species. Infection takes place in the flowering stage. The pathogen stays latent during the growth of the fruit after which fungal mycelium can develop during ripening, but mostly after harvest, causing internal and later external fruit rot. Around 75% of the isolates obtained from diseased fruits belonged to the Fusarium lactis species complex (FLASC). F. oxysporum and F. proliferatum were also isolated but less frequently, 14% and 9% respectively. The pathogenicity of these Fusarium species was studied in assays using fruit as well as flower inoculation on different cultivars. Differences in pathogenicity were most clearly observed after fruit inoculation. These results however were not consistent with the results of flower inoculation, which is considered more representative, that showed only very little difference between the Fusarium species. Furthermore there was also an impact of the cultivar on the development of internal fruit rot. To gain a better insight in the latent phase of the infection process and particularly to study the development of the frequency of latent infections during the growing period of the fruit an experiment was set up and repeated three times over the course of the growing season. The presence of Fusarium in the flowers and in the fruits was determined at several time points between flowering and harvest using traditional surface disinfection and plating techniques using either natural infection or artificially inoculated (FLASC) flowers. The frequency of latently infected fruits stayed at a similar level from flower to harvest, indicating only very limited opportunities to affect the disease after initial infection took place. Preventing initial infection will thus be an important factor in the control of internal fruit rot. One way to reduce the amount of initial infections may be the removal of withering tissues such as pistil and petals, as preliminary results have shown that these were frequently saprophytically colonized with FLASC isolates. Several experiments indicated however that such removal was not successful, suggesting that the infection process is quite fast and that the number of airborne spores is insufficiently lowered by the removal of withering flowering structures. As our study to gain more insights into this pathosystem goes on, opportunities for sustainable control of internal fruit rot, such as prevention of flower infection by biological control agents, and screening for disease resistance, are being explored.status: publishe