Botrytis cinerea, a fungal pathogen that causes gray mold, displays a high degree of phenotypic diversity. Light emitting diodes (LEDs) with specific light spectrum are increasingly used as lighting resource for plant greenhouse production. The chosen light spectrum can also have an effect on the pathogens in this production system. In this study, we investigated the phenological diversity in 15 B. cinerea isolates upon different light treatments. Daylight, darkness, and LED lights with different wavelengths (white, blue, red, blue+red) were chosen as treatments. The 15 Botrytis isolates differed in their mycelial growth rate, conidia production, and sclerotia formation. Light quality had a limited effect on growth rate. All isolates sporulated under daylight treatment, red light resulted in lower sporulation, while white, blue, and blue+red light inhibited sclerotia formation in all isolates, and sporulation in most, but not all isolates. Pathogenicity of the Botrytis isolates was studied on 2-week-old strawberry (Fragaria × ananassa 'Elsanta') leaves grown under white, blue, and red LED lights. The isolates differed in virulence on strawberry leaves, and this was positively correlated to oxalic acid production by B. cinerea in vitro. Red LED light improved leaf basal resistance to all the tested Botrytis isolates. Blue light pretreatment resulted in decreased leaf resistance to some isolates. Furthermore, we used image analysis to quantify the virulence of the different Botrytis isolates based on changes in photosynthetic performance of the strawberry leaves: chlorophyll fluorescence (F v /F m), chlorophyll index (ChlIdx) and anthocyanin content (modified anthocyanin reflection index, mAriIdx). F v /F m showed a strong negative correlation with disease severity and can be an indicator for the early detection of gray mold on strawberry leaves.

Fusarium oxysporum f. sp. lactucae race 4 causes vascular necrosis and wilting of lettuce. First observed in Belgium in 2015, the lack of disease resistance in commercial cultivars allowed this pathogen to spread to nearly the entire Belgian production area within 4 years. Different levels of disease development were observed in different commercial greenhouses. To help explain this variation, we collected 78 Fusarium isolates and characterized them both physiologically and genetically. Molecular race identification indicated that 91% of the isolates belonged to race 4, while 6% of the isolates belonged to race 1, which was not previously reported in Belgium. Pathogenicity assays using differential cultivars confirmed the molecular race assignment of selected isolates. Cultivar Patriot was identified as a suitable new differential cultivar to race 4. Race 4 isolates were more aggressive than race 1 isolates at 24°C, but only when using chlamydospore inoculum instead of a root dip assay containing microconidia. Variation in pathogenicity and aggressiveness of the races may explain differences in disease development in commercial greenhouses. Based on genotyping‐by‐sequencing (GBS), race 1 and race 4 isolates were highly similar to reference isolates. Fusarium curvatum, F. oxysporum f. sp. tulipae and F. oxysporum f. sp. rhois were phylogenetically separated from F. oxysporum f. sp. lactucae races 1 and 4 based on the GBS data, but not when using multilocus sequence data. Within F. oxysporum f. sp. lactucae race 4, the GBS data differentiated two rather homogeneous groups, suggesting at least two introductions. However, the two groups did not differ in aggressiveness.