Identification of volatiles generated by potato tubers (Solanum tuberosum CV-Maris Piper) infected by Erwinia carotovora, Bacillus polymyxa and Arthrobacter sp.

Bacteria were isolated from internal tissues of surface sterilized healthy tubers of Solanum tuberosum cv. Maris Piper (8 different isolates) and from tubers inoculated with Erwinia carotovora ssp. carotovora showing soft-rot symptoms (3 different isolates), and identified by fatty acid profiling. B acillus polymyxa and an Arthrobacter sp. were isolated from both sources, E , carotovora only from the soft-rotted tubers. The volatile organic compoun ds (VOCs) generated by tubers inoculated with E. carotovora, B. polymyxa an d the Arthrobacter sp. were identified. Inoculated tubers of cv. Maris Pipe r were incubated under controlled humidity (95% relative humidity) and temp erature (10 degrees C) to simulate typical storage conditions. B. polymyxa and Arthrobacter sp. did not cause symptoms, whilst E. carotovora caused li mited soft-rot infections after 4 weeks at the low temperatures typically a ssociated with potatoes in storage. The VOCs released to the headspace arou nd these tubers were collected using an adsorbent system and analysed by Ga s Chromatography-Mass Spectrometry (GC-MS). Twenty-two volatiles unique to E, carotovora infection of potato tubers were found, including 10 alkanes, four alkenes, two aldehydes, one sulphide, one ketone, one alcohol, one aro matic, one acid and one heterocyclic compound. B. polymyxa generated three unique volatiles: N,N-dimethylformamide, 1-pentadecene and 1-hexadecane. On ly one volatile, 2,3-dihydrofuran, was unique to the Arthrobacter infection . Production of volatile nitrogen species from E, carotovora-infected tuber s increased with time, whereas none were detected in the headspace above un infected tubers. Further analysis using a modified GC-MS method established that ammonia, trimethylamine and several volatile sulphides were evolved f rom tubers infected by E. carotovora. No specific volatile was useful as a marker associated with any of the three bacterial species but in the case o f E, cavotovora-infected potato tubers a significant increase in the volume of compounds evolved was clearly observed. The results are discussed in re lation to the use of sensors to detect VOCs evolved from infected tubers in order to provide an early warning system for the control of soft rot in po tato stores.