Can volatiles emitted by compost during spawn run be used to detect green mould infection early?

Abstract

In recent years green mould (Trichoderma aggressivum) has presented big problems to the Dutch mushroom industry. T. aggressivum infects compost at a very early stage and in the Dutch situation infection most likely takes place at the compost yard. Even though compost producers in the Netherlands are very keen to prevent green mould problems, occasionally still a number of crops get infected. Therefore there is a need for a reliable method that allows early detection of Trichoderma green mould. Although qPCR methods have been developed for quantitation of T. aggressivum, these cannot be used for detection in compost. In the Netherlands spawn run is performed in bulk at the compost yards and is referred to as phase 3 composting. During this process, spawned compost is incubated in tunnels and ventilated with large volumes of air to control compost temperature. During this process the compost is inaccessible for sampling. Literature data showed that Agaricus bisporus and T. aggressivum use volatiles to affect each other’s growth rate. We tested the possibility to detect Trichoderma green mould using the volatiles that are emitted during spawn run. This eventually could lead to a sophisticated non-invasive detection method of T. aggressivum in the process air of the tunnels, without the need to sample inside the tunnel during spawn run. For this we compared volatiles that are produced in non-infected compost with volatiles that are produced in infected compost. In our experimental model, 300 g of phase 2 compost, is spawned and inserted in aerated glass vessels. Compost is colonised at an air temperature of 24°C. After 7, 10 and 14 days of spawn run, process air is sampled both in infected and non-infected cultures and analysed by coupled gas chromatography mass spectrometry (GC-MS). During this 14-day period white mushroom mycelium develops in the non-infected compost. In the infected compost the compost turns black with occasional tufts of white mycelium and green spores. Volatile blends that are produced during normal compost colonisation (when Agaricus bisporus interacts with Scytalidium thermophilum and other micro flora present in compost) differ from those produced during colonisation of T. aggressivum infected compost. Some of the volatiles appear to be specific for T. aggressivum infected compost. Next to this also consistent differences in the overall pattern of volatile production are seen. Infections with T. harzianum, T. atroviride, an Aspergillus species, or Smokey mould (Penicillium citreonigrum) produce different volatile patterns. Significant differences between the volatile blends of infected and non-infected compost are visible after 7 days of compost colonisation. In commercial practice of phase 3 composting, tunnels are likely to be partially infected. On-going research is directed at studying larger amounts of compost that is only partially infected