Sustainable control of internal fruit rot in bell peppers (Capsicum annuum L.)

Since 2003, Belgian bell pepper growers are confronted with a new disease called internal fruit rot, which is caused by Fusarium species. The pathogen infects the fruit via the flowers and stays latent until ripening or even post harvest, after which fungal mycelium can develop and cause an internal and later external fruit rot.
About 75% of the isolates obtained from diseased peppers belong to the Fusarium lactis species complex (FLASC) while F. oxysporum and F. proliferatum were less frequently isolated, 14% and 9%, respectively. The pathogenicity of these three Fusarium species was compared on two to four cultivars using assays involving fruit as well as flower inoculation. Differences in pathogenicity between the Fusarium species were most clearly observed after fruit inoculation, but these were not consistent with the results of flower inoculation, which is considered more representative.
To better understand the latent phase of the infection process, and especially to investigate if there is a decline in the number of latent infections during the growing period, we determined the presence of Fusarium in the flowers and fruit at 10 time points between flowering and harvest using traditional surface disinfection and plating techniques using either natural infection or artificially inoculated (FLASC) flowers. This experiment was repeated at least three times during the growing season. To our surprise, the frequency of latently infected fruit stayed at a similar level during the entire growing process, indicating that there may be only limited opportunities to affect the amount of disease after the initial infection took place.
One method to reduce the number of initial infections may be to remove the withering tissue such as the pistil and petals, as preliminary research showed these were saprophytically colonized with FLASC isolates. Such removal proved not successful in several experiments, indicating the infection process is quite fast and the number of airborne spores is insufficiently lowered by removal of these structures.
Our study provided more insights into this pathosystem, which may result in opportunities for the sustainable control of internal fruit rot via prevention of flower infection and screening for disease resistance.