Arbuscular mycorrhizal fungi (AMF) can control soilborne diseases such as Fusarium oxysporum f.sp. lycopersici (Fol). Root exudates play an important role in plant-microbe interactions in the rhizosphere, especially, in the initial phase of these interactions. In this work, we focus on (i) elucidating dynamics in root exudation of Solanum lycopersicum L. in an intercropping system due to AMF and/or Fol; (ii) its effect on Fol development in vitro; and (iii) the testing of the root exudate compounds identified in the chromatographic analyses in terms of effects on fungal growth in in vitro assays. GC-MS analyses revealed an AMF-dependent increase in sugars and decrease in organic acids, mainly glucose and malate. In the HPLC analyses, an increase in chlorogenic acid was evident in the combined treatment of AMF and Fol, which is to our knowledge the first report about an increase in chlorogenic acid in root exudates of AM plants challenged with Fol compared with plants inoculated with AMF only, clearly indicating changes in root exudation due to AMF and Fol. Root exudates of AMF tomato plants stimulate the germination rate of Fol, whereas the co-inoculation of AMF and Fol leads to a reduction in spore germination. In the in vitro assays, citrate and chlorogenic acid could be identified as possible candidates for the reduction in Fol germination rate in the root exudates of the AMF+Fol treatment because they proved inhibition at concentrations naturally occurring in the rhizosphere.

In a series of laboratory experiments, acclimated pupae of Tuta absoluta were exposed to various constant low temperatures in order to estimate their maximum survival times (Kaplan–Meier, Lt99.99). A Weibull function was fitted to the data points, describing maximum survival time as a function of temperature. In another experiment at −6°C, the progress of mortality increasing with exposure time was identified. These values were fitted by a sigmoidal function converging asymptotically to 100% mortality for very long exposure times. Analysing mortality data from the maximum survival experiment by a generalized linear model showed a significant common slope parameter (p < .001) that reveals parallelism of the survival curves at each temperature if a log time axis is used. These curves appear stretched (time scaled) if plotted with a nonlogarithmic time axis. By combining these mathematical relations, it was possible to calculate a species‐specific ‘mortality surface’ which exhibits mortalities, depending on temperature and duration of exposure. In order to accumulate hourly mortalities for courses of varying temperatures, an algorithm was developed which yields mortality values from that surface taking into account the attained mortality level. In validation experiments, recorded mortalities were compared against modelled mortalities. Prediction of mortality was partially supported by the model, but pupae experiencing intensely fluctuating temperatures showed decreased mortality, probably caused by rapid cold hardening during exposure. Despite this observation, mortality data converged to distinct levels very close to 100% depending on the intensity of temperature fluctuations that were characteristic for different types of experiments. The highest mortality limit occurred at intensely fluctuating temperatures in laboratory experiments. This constituted a benchmark that was not reached under various field conditions. Thus, it was possible to identify temperature limits for the extinction of field populations of Tuta absoluta pupae.

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