No abstract

Internal fruit rot in bell pepper is an important fungal disease which results in mycelium growth and/or necrosis on the ovarium and fruit flesh. It is mainly caused by members of the Fusarium lactis species complex (FLASC) and emerged as a major threat for bell pepper production worldwide. Infection already starts during anthesis but the symptoms are only visible later on in the production chain. An accurate prediction of the disease incidence in the greenhouse based on environmental parameters is an important step towards a sustainable disease control. Based on a large dataset (2011-2016) a binomial, logistic regression model was developed. This model enables an accurate prediction of internal fruit rot occurrence based on simple and robust input parameters such as temperature and relative humidity during anthesis. Spore density was included as a simplified, practical parameter describing the presence or absence of internal fruit rot one week earlier. The obtained model was validated with an independent dataset of five different commercial bell pepper greenhouses. The chance of internal fruit rot infection increased with temperature and relative humidity. Once a greenhouse is infected, only lower temperatures can reduce future risks. However, the chance of the disease to occur remains very high. This prediction model offers a strong instrument for growers to optimize greenhouse climate conditions to restrain internal fruit rot incidence. In addition, the model can be used to apply accurate biological or chemical treatments to achieve a more sustainable greenhouse control. A guideline table for climate adjustment is presented.

The Cucurbitaceae is a genetically diverse group of plants containing several important commodity crops in many parts of the world such as cucumber, pumpkin and melon. In the last decades, fruit rot caused by Stagonosporopsis spp. became a major disease in both field grown and greenhouse grown cucurbits. Yield losses due to Stagonosporopsis can show seasonal peaks up to 30%. Despite its economic importance, only limited information is available about growth characteristics of Stagonosporopsis cucurbitacearum. Our in vitro studies with different media indicated an optimal growth rate of the fungus within the range of pH 5 to pH 6. Independent of the carbon source (sucrose, glucose, dextrose, fructose) alkalization of 1-3,5 pH units was noticed under both carbon deprivation and excess. The observed pH modulation could not always be related with a more favourable growth environment. The key factor influencing both pH modulating capacity and growth showed to be the nitrogen source. Supplying nitrate, ammonium or a combination of both, the environmental pH respectively increased, decreased or remained stable. In addition to a pH elevating effect nitrate supply did also stimulate growth whilst growth on ammonium containing media was seriously affected. This research highlights the importance of the nitrogen source in the growth and regulation of environmental pH by fungi and adds in our understanding of S. cucurbitacearum pathogenicity.